![8 Robot Spacecraft
a tube to a particular joint, it triggers or actuates movement. Pneumatic
actuators are inexpensive and simple, but their movement is not precise.
Therefore, this kind of actuator usually is found in nonservo, or pick-and-
place, robots. Hydraulic actuators are quite common and are capable of
producing a large amount of power. The main disadvantages of hydraulic
actuators are their accompanying apparatuses (pumps and storage tanks)
and problems with fluid leaks. Electrical actuators provide smoother
movements, can be controlled very accurately, and are very reliable; how-
ever, these actuators cannot deliver as much power as hydraulic actuators
of comparable mass. Nevertheless, for modest power actuator functions,
electrical actuators often are preferred.
Many industrial robots are fixed in place or move along rails and guide-
ways. Some terrestrial robots are built into wheeled carts, while others use
their end effectors to grasp handholds and pull themselves along. Advanced
robots use articulated manipulators as legs to achieve a walking motion.
A robot’s end effector (hand or gripping device) generally is attached
to the end of the manipulator arm. Typical functions of this end effector
include grasping, pushing and pulling, twisting, using tools, performing
insertions, and various types of assembly activities. End effectors can be
mechanical, vacuum or magnetically operated; can use a snare device; or
can have some other unusual design feature. The shapes of the objects
that the robot must grasp determine the final design of the end effector.
Usually most end effectors are some type of gripping or clamping device.
Robots can be controlled in a wide variety of ways, from simple limit
switches tripped by the manipulator arm to sophisticated computerized
remote-sensing systems that provide machine vision, touch, and hearing.
In the case of a computer-controlled robot, the motions of its manipula-
tor and end effector are programmed: that is, the robot memorizes what
it is supposed to do. Sensor devices on the manipulator help to establish
the proximity of the end effector to the object to be manipulated and then
feed information back to the computer controller concerning any modifi-
cations needed in the manipulator’s trajectory.
Another interesting type of terrestrial robot system, the field robot,
has become practical recently. A field robot is a robot that operates in
unpredictable, unstructured environments, typically outdoors (on Earth)
and often operates autonomously or by teleoperation over a large work-
space (typically a square mile [square kilometer] or more). For example,
in surveying a potentially dangerous site, the human operator will stay
at a safe distance away in a protected work environment and control (by
cable or radio frequency link) the field robot, which then actually oper-
ates in the hazardous environment. The United States Air Force’s Predator
aerial surveillance robot and various bomb-sniffing, explosive-ordnance
disposal (EOD) robots are examples of some of the most advanced field](https://image.slidesharecdn.com/90762-250507233629-f0b052df/85/Robot-Spacecraft-Frontiers-in-Space-1st-Edition-Joseph-A-Angelo-26-320.jpg)
![20 Robot Spacecraft
vehicle’s steering was very erratic and the Mariner 1 spacecraft was going
to crash somewhere on Earth, possibly in the North Atlantic shipping
lanes or in an inhabited area. Undaunted by the heartbreaking loss of the
Mariner 1 spacecraft, which was never given a chance to demonstrate its
capabilities, the NASA/JPL engineering team quickly prepared its identical
twin, named Mariner 2, to pinch-hit and perform the world’s first inter-
planetary flyby mission.
This photograph, taken during the Apollo 12 lunar landing mission (November 1969), shows astronaut Charles
Conrad, Jr., examining the Surveyor 3 robot spacecraft. Between 1967 and 1968, NASA used several Surveyor
lander spacecraft to carefully examine the lunar surface before sending humans to the Moon. Surveyor 3 was
launched from Cape Canaveral on April 17, 1967, and successfully soft-landed on the side of a small crater in the
Ocean of Storms region on April 19, 1967. (The lunar module [Intrepid] used by the Moon-walking astronauts
Conrad and Alan L. Bean appears in the background.) (NASA)](https://image.slidesharecdn.com/90762-250507233629-f0b052df/85/Robot-Spacecraft-Frontiers-in-Space-1st-Edition-Joseph-A-Angelo-38-320.jpg)
![The soft Napæan race will soon repent[26]
Their anger, and remit the punishment.
The secret in an easy method lies;
Select four brawny bulls for sacrifice,
Which on Lycæus graze without a guide;
Add four fair heifers yet in yoke untried.
For these, four altars in their temple rear,
And then adore the woodland powers with
prayer.
From the slain victims pour the streaming
blood,
And leave their bodies in the shady wood:
Nine mornings thence, Lethæan poppy
bring,
To appease the manes of the poet's[27]
king:
And, to propitiate his offended bride,
A fatted calf and a black ewe provide:
This finished, to the former woods repair." }
His mother's precepts he performs with
care; }
The temple visits, and adores with prayer; }
Four altars raises; from his herd he culls,
For slaughter, four the fairest of his bulls:
Four heifers from his female store he took,
All fair, and all unknowing of the yoke.
Nine mornings thence, with sacrifice and
prayers,
The powers atoned, he to the grove repairs.
Behold a prodigy! for, from within
The broken bowels, and the bloated skin,
A buzzing noise of bees his ears alarms:
Straight issue through the sides assembling
swarms.](https://image.slidesharecdn.com/90762-250507233629-f0b052df/85/Robot-Spacecraft-Frontiers-in-Space-1st-Edition-Joseph-A-Angelo-53-320.jpg)
![Dark as a cloud, they make a wheeling
flight,
Then on a neighbouring tree, descending,
light:
Like a large cluster of black grapes they
show,
And make a large dependance from the
bough.
Thus have I sung of fields, and flocks,
and trees,
And of the waxen work of labouring bees;
While mighty Cæsar, thundering from afar,
Seeks on Euphrates' banks the spoils of
war;
With conquering arts asserts his country's
cause,
With arts of peace the willing people draws;
On the glad earth the golden age renews,
And his great father's path to heaven
pursues;
While I at Naples pass my peaceful days,
Affecting studies of less noisy praise;
And, bold through youth, beneath the
beechen shade,
The lays of shepherds, and their loves, have
played.
FOOTNOTES:
[18] Note I.
[19] Dr Carey reads, "through the race of life they quickly run,"
and has altered the punctuation to the sense thus conveyed; but
I retain the reading of the first edition—though—which is clearly
the meaning of Virgil. The original is as follows:
Ergo ipsas quamvis angusti terminus ævi](https://image.slidesharecdn.com/90762-250507233629-f0b052df/85/Robot-Spacecraft-Frontiers-in-Space-1st-Edition-Joseph-A-Angelo-54-320.jpg)
![Excipiat, neque enim plus septima ducitur æstas,
At genus immortale manet, &c.
[20] The first edition has grandsons.
[21] By the list of errata to the first edition, we are directed to
read, "lizards shunning light;" but as lizards had been mentioned
in the preceding couplet, the correction itself seems erroneous. I
follow Dr Carey in rejecting it.
[22] Note II.
[23] Dr Carey proposes to read will seem, according to the
second edition, and to adapt the whole sentence to that
construction; but the present tense seems more poetical, as
placing the manœuvres of Proteus more vividly before Aristæus.
If Dryden thought of adopting the future, he did not complete his
purpose. I have therefore followed the original edition.
[24] Note III.
[25] This whole line is taken from the Marquis of Normanby's
translation.—Dryden.
[26] Dr Carey reads relent; but repent is here used in a well
known scriptural sense; not as expressing remorse, but simple
pity.
[27] Poet-king, in Dr Carey's edition: but the original edition reads
as above.](https://image.slidesharecdn.com/90762-250507233629-f0b052df/85/Robot-Spacecraft-Frontiers-in-Space-1st-Edition-Joseph-A-Angelo-55-320.jpg)
![TO
THE MOST HONOURABLE
JOHN,
LORD MARQUIS OF NORMANBY,
EARL OF MULGRAVE,[28] &c.
AND
KNIGHT OF THE MOST NOBLE ORDER OF THE
GARTER.
A heroic poem, truly such, is undoubtedly the greatest work which
the soul of man is capable to perform. The design of it is to form the
mind to heroic virtue by example. It is conveyed in verse, that it may
delight, while it instructs: the action of it is always one, entire, and
great. The least and most trivial episodes, or under-actions, which
are interwoven in it, are parts either necessary or convenient to](https://image.slidesharecdn.com/90762-250507233629-f0b052df/85/Robot-Spacecraft-Frontiers-in-Space-1st-Edition-Joseph-A-Angelo-60-320.jpg)
![carry on the main design; either so necessary, that, without them,
the poem must be imperfect, or so convenient, that no others can
be imagined more suitable to the place in which they are. There is
nothing to be left void in a firm building; even the cavities ought not
to be filled with rubbish, (which is of a perishable kind, destructive
to the strength,) but with brick or stone, though of less pieces, yet
of the same nature, and fitted to the crannies. Even the least
portions of them must be of the epic kind: all things must be grave,
majestical, and sublime; nothing of a foreign nature, like the trifling
novels, which Ariosto,[29] and others, have inserted in their poems;
by which the reader is misled into another sort of pleasure, opposite
to that which is designed in an epic poem. One raises the soul, and
hardens it to virtue; the other softens it again, and unbends it into
vice.
One conduces to the poet's aim, the completing of his work, which
he is driving on, labouring and hastening in every line; the other
slackens his pace, diverts him from his way, and locks him up, like a
knight-errant, in an enchanted castle, when he should be pursuing
his first adventure. Statius, as Bossu has well observed, was
ambitious of trying his strength with his master Virgil, as Virgil had
before tried his with Homer. The Grecian gave the two Romans an
example, in the games which were celebrated at the funerals of
Patroclus. Virgil imitated the invention of Homer, but changed the
sports. But both the Greek and Latin poet took their occasions from
the subject; though, to confess the truth, they were both
ornamental, or, at best, convenient parts of it, rather than of
necessity arising from it. Statius, who, through his whole poem, is
noted for want of conduct and judgment, instead of staying, as he
might have done, for the death of Capaneus, Hippomedon, Tydeus,
or some other of his seven champions, (who are heroes all alike,) or
more properly for the tragical end of the two brothers, whose
exequies the next successor had leisure to perform when the siege
was raised, and in the interval betwixt the poet's first action and his
second—went out of his way, as it were on prepense malice, to
commit a fault. For he took his opportunity to kill a royal infant by](https://image.slidesharecdn.com/90762-250507233629-f0b052df/85/Robot-Spacecraft-Frontiers-in-Space-1st-Edition-Joseph-A-Angelo-61-320.jpg)
![the means of a serpent, (that author of all evil,) to make way for
those funeral honours which he intended for him. Now, if this
innocent had been of any relation to his Thebaïs—if he had either
furthered or hindered the taking of the town—the poet might have
found some sorry excuse at least, for detaining the reader from the
promised siege. On these terms, this Capaneus of a poet engaged
his two immortal predecessors; and his success was answerable to
his enterprise.[30]
If this œconomy must be observed in the minutest parts of an epic
poem, which, to a common reader, seem to be detached from the
body, and almost independent of it; what soul, though sent into the
world with great advantages of nature, cultivated with the liberal
arts and sciences, conversant with histories of the dead, and
enriched with observations on the living, can be sufficient to inform
the whole body of so great a work? I touch here but transiently,
without any strict method, on some few of those many rules of
imitating nature, which Aristotle drew from Homer's Iliads and
Odysseys, and which he fitted to the drama; furnishing himself also
with observations from the practice of the theatre, when it flourished
under Æschylus, Euripides, and Sophocles: for the original of the
stage was from the epic poem. Narration, doubtless, preceded
acting, and gave laws to it: what at first was told artfully, was, in
process of time, represented gracefully to the sight and hearing.
Those episodes of Homer, which were proper for the stage, the
poets amplified each into an action; out of his limbs they formed
their bodies; what he had contracted, they enlarged; out of one
Hercules, were made infinity of pygmies, yet all endued with human
souls; for from him, their great creator, they have each of them the
divinæ particulam auræ. They flowed from him at first, and are at
last resolved into him. Nor were they only animated by him, but their
measure and symmetry was owing to him. His one, entire, and great
action, was copied by them according to the proportions of the
drama. If he finished his orb within the year, it sufficed to teach
them, that their action being less, and being also less diversified
with incidents, their orb, of consequence, must be circumscribed in a](https://image.slidesharecdn.com/90762-250507233629-f0b052df/85/Robot-Spacecraft-Frontiers-in-Space-1st-Edition-Joseph-A-Angelo-62-320.jpg)
![less compass, which they reduced within the limits either of a
natural or an artificial day; so that, as he taught them to amplify
what he had shortened, by the same rule, applied the contrary way,
he taught them to shorten what he had amplified. Tragedy is the
miniature of human life; an epic poem is the draught at length.[31]
Here, my lord, I must contract also; for, before I was aware, I was
almost running into a long digression, to prove, that there is no such
absolute necessity that the time of a stage action should so strictly
be confined to twenty-four hours, as never to exceed them, for
which Aristotle contends, and the Grecian stage has practised. Some
longer space, on some occasions, I think, may be allowed, especially
for the English theatre, which requires more variety of incidents than
the French. Corneille himself, after long practice, was inclined to
think, that the time allotted by the ancients was too short to raise
and finish a great action: and better a mechanic rule were stretched
or broken, than a great beauty were omitted. To raise, and
afterwards to calm the passions—to purge the soul from pride, by
the examples of human miseries, which befal the greatest—in few
words, to expel arrogance, and introduce compassion, are the great
effects of tragedy; great, I must confess, if they were altogether as
true as they are pompous. But are habits to be introduced at three
hours' warning? are radical diseases so suddenly removed? A
mountebank may promise such a cure, but a skilful physician will not
undertake it. An epic poem is not in so much haste: it works
leisurely; the changes which it makes are slow; but the cure is likely
to be more perfect. The effects of tragedy, as I said, are too violent
to be lasting. If it be answered, that, for this reason, tragedies are
often to be seen, and the dose to be repeated, this is tacitly to
confess, that there is more virtue in one heroic poem, than in many
tragedies. A man is humbled one day, and his pride returns the next.
Chemical medicines are observed to relieve oftener than to cure: for
it is the nature of spirits to make swift impressions, but not deep.
Galenical decoctions, to which I may properly compare an epic
poem, have more of body in them; they work by their substance and
their weight. It is one reason of Aristotle's to prove, that tragedy is](https://image.slidesharecdn.com/90762-250507233629-f0b052df/85/Robot-Spacecraft-Frontiers-in-Space-1st-Edition-Joseph-A-Angelo-63-320.jpg)
![the more noble, because it turns in a shorter compass; the whole
action being circumscribed within the space of four-and-twenty
hours. He might prove as well, that a mushroom is to be preferred
before a peach, because it shoots up in the compass of a night. A
chariot may be driven round the pillar in less space than a large
machine, because the bulk is not so great. Is the Moon a more noble
planet than Saturn, because she makes her revolution in less than
thirty days, and he in little less than thirty years? Both their orbs are
in proportion to their several magnitudes; and, consequently, the
quickness or slowness of their motion, and the time of their
circumvolutions, is no argument of the greater or less perfection.
And, besides, what virtue is there in a tragedy, which is not
contained in an epic poem, where pride is humbled, virtue rewarded,
and vice punished; and those more amply treated, than the
narrowness of the drama can admit? The shining quality of an epic
hero, his magnanimity, his constancy, his patience, his piety, or
whatever characteristical virtue his poet gives him, raises first our
admiration. We are naturally prone to imitate what we admire; and
frequent acts produce a habit. If the hero's chief quality be vicious,
as, for example, the choler and obstinate desire of vengeance in
Achilles, yet the moral is instructive: and, besides, we are informed
in the very proposition of the Iliads, that this anger was pernicious;
that it brought a thousand ills on the Grecian camp. The courage of
Achilles is proposed to imitation, not his pride and disobedience to
his general, nor his brutal cruelty to his dead enemy, nor the selling
his body to his father.[32] We abhor these actions while we read
them; and what we abhor, we never imitate. The poet only shews
them, like rocks or quicksands, to be shunned.
By this example, the critics have concluded, that it is not necessary
the manners of the hero should be virtuous. They are poetically
good, if they are of a piece; though, where a character of perfect
virtue is set before us, it is more lovely; for there the whole hero is
to be imitated. This is the Æneas of our author; this is that idea of
perfection in an epic poem, which painters and statuaries have only
in their minds, and which no hands are able to express. These are](https://image.slidesharecdn.com/90762-250507233629-f0b052df/85/Robot-Spacecraft-Frontiers-in-Space-1st-Edition-Joseph-A-Angelo-64-320.jpg)
![the beauties of a god in a human body. When the picture of Achilles
is drawn in tragedy, he is taken with those warts, and moles, and
hard features, by those who represent him on the stage, or he is no
more Achilles; for his creator, Homer, has so described him. Yet even
thus he appears a perfect hero, though an imperfect character of
virtue. Horace paints him after Homer, and delivers him to be copied
on the stage with all those imperfections.[33] Therefore they are
either not faults in a heroic poem, or faults common to the drama.
After all, on the whole merits of the cause, it must be acknowledged,
that the epic poem is more for the manners, and tragedy for the
passions. The passions, as I have said, are violent; and acute
distempers require medicines of a strong and speedy operation. Ill
habits of the mind are like chronical diseases, to be corrected by
degrees, and cured by alteratives; wherein, though purges are
sometimes necessary, yet diet, good air, and moderate exercise,
have the greatest part. The matter being thus stated, it will appear,
that both sorts of poetry are of use for their proper ends. The stage
is more active; the epic poem works at greater leisure, yet is active
too, when need requires; for dialogue is imitated by the drama, from
the more active parts of it. One puts off a fit, like the quinquina, and
relieves us only for a time; the other roots out the distemper, and
gives a healthful habit. The sun enlightens and cheers us, dispels
fogs, and warms the ground with his daily beams; but the corn is
sowed, increases, is ripened, and is reaped for use in process of
time, and in its proper season. I proceed, from the greatness of the
action, to the dignity of the actors; I mean to the persons employed
in both poems. There likewise tragedy will be seen to borrow from
the epopee; and that which borrows is always of less dignity,
because it has not of its own. A subject, it is true, may lend to his
sovereign; but the act of borrowing makes the king inferior, because
he wants, and the subject supplies. And suppose the persons of the
drama wholly fabulous, or of the poet's invention, yet heroic poetry
gave him the examples of that invention, because it was first, and
Homer the common father of the stage. I know not of any one
advantage which tragedy can boast above heroic poetry, but that it](https://image.slidesharecdn.com/90762-250507233629-f0b052df/85/Robot-Spacecraft-Frontiers-in-Space-1st-Edition-Joseph-A-Angelo-65-320.jpg)
![is represented to the view, as well as read, and instructs in the
closet, as well as on the theatre. This is an uncontended excellence,
and a chief branch of its prerogative; yet I may be allowed to say,
without partiality, that herein the actors share the poet's praise. Your
lordship knows some modern tragedies which are beautiful on the
stage, and yet I am confident you would not read them. "Tryphon
the stationer"[34] complains, they are seldom asked for in his shop.
The poet who flourished in the scene, is damned in the ruelle;[35]
nay more, he is not esteemed a good poet by those, who see and
hear his extravagancies with delight. They are a sort of stately
fustian, and lofty childishness. Nothing but nature can give a sincere
pleasure; where that is not imitated, it is grotesque painting; "the
fine woman ends in a fishes tail."
I might also add, that many things, which not only please, but are
real beauties in the reading, would appear absurd upon the stage;
and those not only the speciosa miracula, as Horace calls them, of
transformations, of Scylla, Antiphates, and the Læstrygons, which
cannot be represented even in operas; but the prowess of Achilles or
Æneas would appear ridiculous in our dwarf-heroes of the theatre.
We can believe they routed armies, in Homer or in Virgil; but ne
Hercules contra duos in the drama. I forbear to instance in many
things, which the stage cannot, or ought not to represent; for I have
said already more than I intended on this subject, and should fear it
might be turned against me, that I plead for the pre-eminence of
epic poetry, because I have taken some pains in translating Virgil, if
this were the first time that I had delivered my opinion in this
dispute. But I have more than once already maintained the rights of
my two masters against their rivals of the scene,[36] even while I
wrote tragedies myself, and had no thoughts of this present
undertaking. I submit my opinion to your judgement, who are better
qualified than any man I know, to decide this controversy. You come,
my lord, instructed in the cause, and needed not that I should open
it. Your "Essay of Poetry,"[37] which was published without a name,
and of which I was not honoured with the confidence, I read over](https://image.slidesharecdn.com/90762-250507233629-f0b052df/85/Robot-Spacecraft-Frontiers-in-Space-1st-Edition-Joseph-A-Angelo-66-320.jpg)
![merit, not your titles. Thus, like Apelles, you stood unseen behind
your own Venus, and received the praises of the passing multitude;
the work was commended, not the author; and I doubt not, this was
one of the most pleasing adventures of your life.[38]
I have detained your lordship longer than I intended in this dispute
of preference betwixt the epic poem and the drama, and yet have
not formally answered any of the arguments which are brought by
Aristotle on the other side, and set in the fairest light by Dacier. But I
suppose, without looking on the book, I may have touched on some
of the objections; for, in this address to your lordship, I design not a
treatise of heroic poetry, but write in a loose epistolary way,
somewhat tending to that subject, after the example of Horace, in
his First Epistle of the Second Book to Augustus Cæsar, and in that
to the Piso's, which we call his "Art of Poetry;" in both of which he
observes no method that I can trace, whatever Scaliger the father,
or Heinsius, may have seen, or rather think they had seen. I have
taken up, laid down, and resumed as often as I pleased, the same
subject; and this loose proceeding I shall use through all this
prefatory dedication. Yet all this while I have been sailing with some
side-wind or other toward the point I proposed in the beginning,—
the greatness and excellency of a heroic poem, with some of the
difficulties which attend that work. The comparison, therefore, which
I made betwixt the epopee and the tragedy, was not altogether a
digression; for it is concluded on all hands, that they are both the
master-pieces of human wit.
In the mean time, I may be bold to draw this corollary from what
has been already said, that the file of heroic poets is very short; all
are not such who have assumed that lofty title in ancient or modern
ages, or have been so esteemed by their partial and ignorant
admirers.
There have been but one great Ilias, and one Æneïs, in so many
ages. The next, but the next with a long interval betwixt, was the
Jerusalem;[39]](https://image.slidesharecdn.com/90762-250507233629-f0b052df/85/Robot-Spacecraft-Frontiers-in-Space-1st-Edition-Joseph-A-Angelo-68-320.jpg)
![Fortunam Priami cantabo, et nobile bellum—
mere fustian, as Horace would tell you from behind, without pressing
forward, and more smoke than fire. Pulci, Boiardo, and Ariosto,[40]
would cry out, "make room for the Italian poets, the descendants of
Virgil in a right line:" father Le Moine, with his saint Louis; and
Scudery with his Alaric, for a godly king and a Gothic conqueror; and
Chapelain would take it ill that his Maid should be refused a place
with Helen and Lavinia.[41] Spencer[42] has a better plea for his
"Fairy Queen," had his action been finished, or had been one; and
Milton, if the devil had not been his hero, instead of Adam; if the
giant had not foiled the knight, and driven him out of his strong-
hold, to wander through the world with his lady errant; and if there
had not been more machining persons than human in his poem.
After these, the rest of our English poets shall not be mentioned. I
have that honour for them which I ought to have; but, if they are
worthies, they are not to be ranked amongst the three whom I have
named, and who are established in their reputation.
Before I quitted the comparison betwixt epic poetry and tragedy, I
should have acquainted my judge with one advantage of the former
over the latter, which I now casually remember out of the preface of
Ségrais before his translation of the Æneïs, or out of Bossu, no
matter which: "The style of the heroic poem is, and ought to be,
more lofty than that of the drama." The critic is certainly in the right,
for the reason already urged; the work of tragedy is on the passions,
and in a dialogue; both of them abhor strong metaphors, in which
the epopee delights. A poet cannot speak too plainly on the stage:
for volat irrevocabile verbum; the sense is lost, if it be not taken
flying. But what we read alone, we have leisure to digest; there an
author may beautify his sense by the boldness of his expression,
which if we understand not fully at the first, we may dwell upon it,
till we find the secret force and excellence. That which cures the
manners by alterative physic, as I said before, must proceed by
insensible degrees; but that which purges the passions, must do its](https://image.slidesharecdn.com/90762-250507233629-f0b052df/85/Robot-Spacecraft-Frontiers-in-Space-1st-Edition-Joseph-A-Angelo-70-320.jpg)
![business all at once, or wholly fail of its effect, at least in the present
operation, and without repeated doses. We must beat the iron while
it is hot, but we may polish it at leisure. Thus, my lord, you pay the
fine of my forgetfulness; and yet the merits of both causes are
where they were, and undecided, till you declare whether it be more
for the benefit of mankind to have their manners in general
corrected, or their pride and hard-heartedness removed.
I must now come closer to my present business, and not think of
making more invasive wars abroad, when, like Hannibal, I am called
back to the defence of my own country. Virgil is attacked by many
enemies; he has a whole confederacy against him; and I must
endeavour to defend him as well as I am able. But their principal
objections being against his moral, the duration or length of time
taken up in the action of the poem, and what they have to urge
against the manners of his hero; I shall omit the rest as mere cavils
of grammarians; at the worst, but casual slips of a great man's pen,
or inconsiderable faults of an admirable poem, which the author had
not leisure to review before his death. Macrobius has answered what
the ancients could urge against him; and some things I have lately
read in Tanneguy le Fèvre, Valois, and another whom I name not,
which are scarce worth answering. They begin with the moral of his
poem, which I have elsewhere confessed, and still must own, not to
be so noble as that of Homer.[43] But let both be fairly stated; and,
without contradicting my first opinion, I can shew, that Virgil's was
as useful to the Romans of his age, as Homer's was to the Grecians
of his, in what time soever he may be supposed to have lived and
flourished. Homer's moral was to urge the necessity of union, and of
a good understanding betwixt confederate states and princes
engaged in a war with a mighty monarch; as also of discipline in an
army, and obedience in the several chiefs to the supreme
commander of the joint forces. To inculcate this, he sets forth the
ruinous effects of discord in the camp of those allies, occasioned by
the quarrel betwixt the general and one of the next in office under
him. Agamemnon gives the provocation, and Achilles resents the
injury. Both parties are faulty in the quarrel; and accordingly they](https://image.slidesharecdn.com/90762-250507233629-f0b052df/85/Robot-Spacecraft-Frontiers-in-Space-1st-Edition-Joseph-A-Angelo-71-320.jpg)
Robot Spacecraft Frontiers in Space 1st Edition Joseph A. Angelo
- 1. Robot Spacecraft Frontiers in Space 1st Edition Joseph A. Angelo download https://ebookgate.com/product/robot-spacecraft-frontiers-in- space-1st-edition-joseph-a-angelo/ Get Instant Ebook Downloads – Browse at https://ebookgate.com
- 2. Get Your Digital Files Instantly: PDF, ePub, MOBI and More Quick Digital Downloads: PDF, ePub, MOBI and Other Formats Robotics A Reference Guide to the New Technology 1st edition Edition Joseph A. Angelo Jr. https://ebookgate.com/product/robotics-a-reference-guide-to-the- new-technology-1st-edition-edition-joseph-a-angelo-jr/ The Facts On File Space and Astronomy Handbook Joseph A. https://ebookgate.com/product/the-facts-on-file-space-and- astronomy-handbook-joseph-a/ DIY Instruments for Amateur Space Inventing Utility for Your Spacecraft Once It Achieves Orbit 1st Edition Sandy Antunes https://ebookgate.com/product/diy-instruments-for-amateur-space- inventing-utility-for-your-spacecraft-once-it-achieves-orbit-1st- edition-sandy-antunes/ Robot Grippers 1st Edition Gareth J. Monkman https://ebookgate.com/product/robot-grippers-1st-edition-gareth- j-monkman/
- 3. How Does a Spacecraft Reach the Moon Science in the Real World 1st Edition Barbara J. Davis https://ebookgate.com/product/how-does-a-spacecraft-reach-the- moon-science-in-the-real-world-1st-edition-barbara-j-davis/ Make an Arduino Controlled Robot 1st Edition Margolis https://ebookgate.com/product/make-an-arduino-controlled- robot-1st-edition-margolis/ Spacecraft Systems Engineering 4th Edition Peter Fortescue https://ebookgate.com/product/spacecraft-systems-engineering-4th- edition-peter-fortescue/ Spacecraft Systems Engineering Third Edition Peter Fortescue https://ebookgate.com/product/spacecraft-systems-engineering- third-edition-peter-fortescue/ Fundamental Spacecraft Dynamics and Control 1st Edition Weiduo Hu https://ebookgate.com/product/fundamental-spacecraft-dynamics- and-control-1st-edition-weiduo-hu/
- 5. Robot Spacecraft JOSEPH A. ANGELO, JR. Frontiers in Space Frontiers in Space Frontiers in Space
- 6. To the memory of my paternal (Italian) grandparents, Antonio and Nina, who had the great personal courage to leave Europe early in the 20th century and embrace the United States as their new home. Through good fortune they met, married, and raised a family. Their simple, hardworking lives taught me what is most important in life. This book also carries a special dedication to Mugsy-the-Pug (February 23, 1999, to January 2, 2006)—my faithful canine companion—who provided so much joy and relaxation during the preparation of this book and many other works. ROBOT SPACECRAFT Copyright © 2007 by Joseph A. Angelo, Jr. All rights reserved. No part of this book may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying, recording, or by any information storage or retrieval systems, without permission in writing from the publisher. For information contact: Facts On File, Inc. An imprint of Infobase Publishing 132 West 31st Street New York NY 10001 Library of Congress Cataloging-in-Publication Data Angelo, Joseph A. Robot spacecraft / Joseph A. Angelo, Jr. p. cm.— (Frontiers in space) Includes bibliographical references and index. ISBN 0-8160-5773-7 1. Space robotics—Juvenile literature. 2. Space probes—Juvenile literature. 3. Roving vehicles (Astronautics)—Juvenile literature. I. Title. II. Series. TL1097.A54 2007 629.47—dc22 2006001118 Facts On File books are available at special discounts when purchased in bulk quantities for businesses, associations, institutions, or sales promotions. Please call our Special Sales Department in New York at (212) 967-8800 or (800) 322-8755. You can find Facts On File on the World Wide Web at http://www.factsonfile.com Text design by Erika K. Arroyo Cover design by Salvatore Luongo Illustrations by Sholto Ainslie Printed in the United States of America VB FOF 10 9 8 7 6 5 4 3 2 1 This book is printed on acid-free paper.
- 7. Preface vii Acknowledgments x Introduction xi ✧ 1 From Pioneer Lunar Probes to Interstellar Messengers 1 ARTIFICIAL INTELLIGENCE 2 The Basic Principles of Robotics 6 Pioneer to the Moon and Beyond 9 EARLY SOVIET LUNA MISSIONS 14 Jet Propulsion Laboratory (JPL)—America’s Premier Space Robot Factory 17 MESSENGER MISSION 26 Robot Spacecraft in Service to Astronomy 30 ✧ 2 How Robot Spacecraft Work 34 Space Robots in Service to Science 35 General Classes of Scientific Spacecraft 37 Functional Subsystems 50 SOLAR PHOTOVOLTAIC CONVERSION 51 ELECTRO-OPTICAL IMAGING INSTRUMENTS 52 Spacecraft Clock and Data Handling Subsystem 56 SINGLE-EVENT UPSET 57 Navigation of a Robot Spacecraft 58 Telecommunications 59 Deep Space Network 61 Contents
- 8. ✧ 3 Robot Spacecraft Come in All Shapes and Sizes 67 Pioneer 3 Spacecraft 68 Ranger Project 70 Lunar Prospector Spacecraft 75 LUNAR PROSPECTOR’S NEUTRON SPECTROMETER 76 Magellan Spacecraft 78 Galileo Spacecraft 80 NASA’s Soccer-Ball Space Robot 85 USING ROBOTS OR HUMANS IN SPACE EXPLORATION 88 ✧ 4 Flyby Spacecraft 91 Mariner 10—First Spacecraft to Mercury 92 Pioneer 11—First Space Robot to Saturn 94 The Grand Tour of Voyager 2 98 NEPTUNE AND TRITON 100 ✧ 5 Orbiters, Probes, and Penetrators 103 Mariner 9 Spacecraft 105 Viking 1 and 2 Orbiter Spacecraft 107 Mars Global Surveyor (MGS) Spacecraft 109 Mars Climate Orbiter (MCO)—Lost in Space Due to Human Error 110 MARS OBSERVER (MO) MISSION 111 Mars Odyssey 2001 Spacecraft 112 Cassini Spacecraft 113 Huygens Spacecraft 120 Pioneer Venus Mission 122 Ulysses Spacecraft 122 ✧ 6 Lander and Rover Spacecraft 126 Surveyor Project 126 Lunokhod 1 and 2 Robot Rovers 128 Viking 1 and 2 Lander Spacecraft 130 Mars Pathfinder Mission 132 MARS POLAR LANDER (MPL)—ANOTHER MARTIAN MYSTERY 134 Mars Exploration Rover (MER) 2003 Mission 135
- 9. ✧ 7 Sample Return Missions 139 Genesis Solar-Wind Sample Return Mission 141 Stardust Mission 143 Mars Sample Return Mission 146 EXTRATERRESTRIAL CONTAMINATION 148 ✧ 8 Mobile Robots as Scientific Laboratories 150 Prospecting for Lunar Water with Smart Robots 151 Smarter Robots to the Red Planet 153 ✧ 9 Robot Spacecraft Visiting Small Bodies in the Solar System 159 Giotto Spacecraft 162 Deep Space 1 (DS1) Spacecraft 164 Deep Impact Spacecraft 167 Rosetta Spacecraft 170 Near Earth Asteroid Rendezvous (NEAR) Spacecraft 171 Dawn Spacecraft 174 ✧10 Future Generations of Robot Explorers 177 New Horizons Pluto–Kuiper Belt Flyby Mission 178 KUIPER BELT 180 Telepresence, Virtual Reality, and Robots with Human Traits 181 ANDROIDS AND CYBORGS 184 Mars Airplane 185 Robots Exploring Icy Regions 187 EUROPA 190 Star Probe Mission 193 Space Nuclear Power 195 The Need for High Levels of Machine Intelligence 197 ✧ 11 Self-Replicating Systems 202 The Theory and Operation of Self-Replicating Systems 203 Extraterrestrial Impact of Self-Replicating Systems 208 Control of Self-Replicating Systems 212
- 10. ✧12 Interstellar Probes 218 Interstellar Journeys of the Pioneer 10 and 11 Spacecraft 220 Voyager Interstellar Mission 224 Thousand Astronomical Unit (TAU) Probe Mission 227 Designing an Interstellar Probe 229 Project Daedalus 232 ✧ 13 Conclusion 236 Chronology 237 Glossary 259 Further Reading 291 Index 297
- 11. It is difficult to say what is impossible, for the dream of yesterday is the hope of today and the reality of tomorrow. —Robert Hutchings Goddard Frontiers in Space is a comprehensive multivolume set that explores the scientific principles, technical applications, and impacts of space technology on modern society. Space technology is a multidisciplinary endeavor, which involves the launch vehicles that harness the principles of rocket propulsion and provide access to outer space, the spacecraft that operate in space or on a variety of interesting new worlds, and many dif- ferent types of payloads (including human crews) that perform various functions and objectives in support of a wide variety of missions. This set presents the people, events, discoveries, collaborations, and important experiments that made the rocket the enabling technology of the space age. The set also describes how rocket propulsion systems support a variety of fascinating space exploration and application missions—mis- sions that have changed and continue to change the trajectory of human civilization. The story of space technology is interwoven with the history of astron- omy and humankind’s interest in flight and space travel. Many ancient peoples developed enduring myths about the curious lights in the night sky. The ancient Greek legend of Icarus and Daedalus, for example, por- trays the age-old human desire to fly and to be free from the gravitational bonds of Earth. Since the dawn of civilization, early peoples, including the Babylonians, Mayans, Chinese, and Egyptians, have studied the sky and recorded the motions of the Sun, the Moon, the observable planets, and the so-called fixed stars. Transient celestial phenomena, such as a passing comet, a solar eclipse, or a supernova explosion, would often cause a great deal of social commotion—if not out right panic and fear—because these events were unpredictable, unexplainable, and appeared threatening. vii Preface
- 12. It was the ancient Greeks and their geocentric (Earth-centered) cos- mology that had the largest impact on early astronomy and the emer- gence of Western Civilization. Beginning in about the fourth century B.C.E., Greek philosophers, mathematicians, and astronomers articulated a geocentric model of the universe that placed Earth at its center with everything else revolving about it. This model of cosmology, polished and refined in about 150 C.E. by Ptolemy (the last of the great early Greek astronomers), shaped and molded Western thinking for hundreds of years until displaced in the 16th century by Nicholas Copernicus and a helio- centric (sun-centered) model of the solar system. In the early 17th century, Galileo Galilei and Johannes Kepler used astronomical observations to validate heliocentric cosmology and, in the process, laid the foundations of the Scientific Revolution. Later that century, the incomparable Sir Isaac Newton completed this revolution when he codified the fundamental principles that explained how objects moved in the “mechanical” universe in his great work Principia Mathematica. The continued growth of science over the 18th and 19th centuries set the stage for the arrival of space technology in the middle of the 20th cen- tury. As discussed in this multivolume set, the advent of space technology dramatically altered the course of human history. On the one hand, mod- ern military rockets with their nuclear warheads redefined the nature of strategic warfare. For the first time in history, the human race developed a weapon system with which it could actually commit suicide. On the other hand, modern rockets and space technology allowed scientists to send smart robot exploring machines to all the major planets in the solar sys- tem (including tiny Pluto), making those previously distant and unknown worlds almost as familiar as the surface of the Moon. Space technology also supported the greatest technical accomplishment of the human race, the Apollo Project lunar landing missions. Early in the 20th century, the Russian space travel visionary Konstantin E. Tsiolkovsky boldly predicted that humankind would not remain tied to Earth forever. When astronauts Neil Armstrong and Edwin (Buzz) Aldrin stepped on the Moon’s surface on July 20, 1969, they left human footprints on another world. After mil- lions of years of patient evolution, intelligent life was able to migrate from one world to another. Was this the first time such an event has happened in the history of the 14-billion-year-old universe? Or, as some exobiolo- gists now suggest, perhaps the spread of intelligent life from one world to another is a rather common occurrence within the galaxy. At present, most scientists are simply not sure. But, space technology is now helping them search for life beyond Earth. Most exciting of all, space technology offers the universe as both a destination and a destiny to the human race. Each volume within the Frontiers in Space set includes an index, a chronology of notable events, a glossary of significant terms and concepts, viii Robot Spacecraft
- 13. a helpful list of Internet resources, and an array of historical and current print sources for further research. Based upon the current principles and standards in teaching mathematics and science, the Frontiers in Space set is essential for young readers who require information on relevant topics in space technology, modern astronomy, and space exploration. Preface ix
- 14. x Iwish to thank the public information specialists at the National Aero- nautics and Space Administration (NASA), the National Oceanic and Atmospheric Administration (NOAA), the United States Air Force (USAF), the Department of Defense (DOD), the Department of Energy (DOE), the National Reconnaissance Office (NRO), the European Space Agency (ESA), and the Japanese Aerospace Exploration Agency (JAXA), who generously provided much of the technical material used in the preparation of this series. Acknowledgment is made here for the efforts of Frank Darmstadt and other members of the editorial staff at Facts On File, whose diligent attention to detail helped transform an interesting concept into a series of publishable works. The support of two other special people merits public recognition here. The first individual is my physician, Dr. Charles S. Stewart III, M.D., whose medical skills allowed me to success- fully complete the series. The second individual is my wife, Joan, who, as she has for the past 40 years, provided the loving spiritual and emotional environment so essential in the successful completion of any undertaking in life, including the production of this series. Acknowledgments
- 15. Modern space robots are sophisticated machines that have visited all the major worlds of the solar system, including (soon) tiny Pluto. Robot Spacecraft examines the evolution of these fascinating, far-traveling spacecraft—from the relatively unsophisticated planetary probes flown at the dawn of the Space Age to the incredibly powerful exploring machines that now allow scientists to conduct detailed, firsthand investigations of alien worlds within this solar system. Emerging out of the space race of the cold war, modern robot spacecraft have dramatically changed what we know about the solar system. In this century, an armada of ever more sophisticated machine explor- ers will continue this legacy of exploration as they travel to the farthest reaches of the solar system and beyond. Robot spacecraft have formed a special intellectual partnership with their human creators by allowing us to explore more “new worlds” in one human lifetime than in the entire history of the human race. This unprecedented wave of discovery and the continued acquisition of vast quantities of new scientific knowledge—per- haps even the first definitive evidence of whether alien life exists—will transform how human beings view themselves and their role in the uni- verse. Robot Spacecraft describes the historic events, scientific principles, and technical breakthroughs that now allow complex exploring machines to orbit around, or even land upon, mysterious worlds in our solar system. The book’s special collection of illustrations presents historic, contem- porary, and future robot spacecraft—allowing readers to appreciate the tremendous aerospace engineering progress that has occurred since the dawn of the space age. A generous number of sidebars are strategically positioned throughout the book to provide expanded discussions of fun- damental scientific concepts and robot-spacecraft engineering techniques. There are also capsule biographies of several space exploration visionaries and scientists, to allow the reader to appreciate the human dimension in the development and operation of robot spacecraft. xi Introduction
- 16. It is especially important to recognize that, throughout the 20th and 21st centuries and beyond, sophisticated robot spacecraft represent the enabling technology for many exciting scientific discoveries for the human race. Awareness of these technical pathways should prove career-inspiring to those students now in high school and college who will become the scientists, aerospace engineers, and robot designers of tomorrow. Why are such career choices important? Future advances in robot spacecraft for space exploration no longer represent a simple societal option that can be pursued or not, depending upon political circumstances. Rather, contin- ued advances in the exploration of the solar system and beyond form a technical, social, and psychological imperative for the human race. We can decide to use our mechanical partners and become a spacefaring species as part of our overall sense of being and purpose; or we can ignore the challenge and opportunity before us and turn our collective backs on the universe. The latter choice would confine future generations to life on just one planet around an average star in the outer regions of the Milky Way Galaxy. The former choice makes the human race a spacefaring species with all the exciting social and technical impacts that decision includes. Robot Spacecraft examines the role the modern space robot has played in human development since the middle of the 20th century and then projects the expanded role space robots will play throughout the remain- der of this century and beyond. Who can now predict the incredible societal impact of very smart machines capable of visiting alien worlds around other suns? One very exciting option on the space-robot technol- ogy horizon is that of the self-replicating system—a robot system so smart it can make copies of itself out of the raw materials found on other worlds. Later in this century, as a wave of such smart robots start to travel through interstellar space, people here on Earth might be able to answer the age- old philosophical question: Are we alone in this vast universe? Robot Spacecraft also shows that the development of modern space robots did not occur without problems, issues, and major financial com- mitments. Selected sidebars within the book address some of the most pressing contemporary issues associated with the application of modern robot technology in space exploration—including the long-standing space- program debate concerning the role of human explorers (i.e., astronauts and cosmonauts) versus machine explorers. For some managers within the American space program, this debate takes on an “either/or” conflict; for others, the debate suggests the need for a more readily embraced human- machine partnership. Robot Spacecraft also describes how future advances in robot technology will exert interesting social, political, and technical influences upon our global civilization. The technology inherent in very smart space robots will exert a tremendous influence upon the trajectory of human civilization that extends well beyond this century. xii Robot Spacecraft
- 17. Some interesting impacts of smart space robots include their use in the development of permanent human settlements on the Moon and Mars, in exploration of the outermost regions of the solar system, as interstellar emissaries of the human race, and in operation of a robot-spacecraft- enabled planetary defense system against killer asteroids or rogue comets. Sophisticated space robots also have a major role to play in the discovery of life (extinct or existing) beyond Earth and in the emergence of a suc- cessfully functioning solar-system civilization. Advanced space-robot systems, endowed with high levels of machine intelligence by their human creators, are unquestionably the underlying and enabling technology for many interesting future developments. Robot Spacecraft has been carefully designed to help any student or teacher who has an interest in robots discover what space robots are, where they came from, how they work, and why they are so important. The back matter contains a chronology, glossary, and an array of historical and cur- rent sources for further research. These should prove especially helpful for readers who need additional information on specific terms, topics, and events in space-robot technology. Introduction xiii
- 19. 1 Robot spacecraft have opened up the universe to exploration. Modern space robots are sophisticated exploring machines that have, or will have, visited all the major worlds of the solar system, including tiny Pluto. Emerging out of the politically charged space race of the cold war, a progressively more capable family of robot spacecraft have dramati- cally changed what scientists know about the alien worlds that journey together with Earth around a star called the Sun. In a little more than four decades, scientists have learned a greater amount about these wandering lights, called πλαυετες (planets) by the ancient Greek astronomers, than in the previous history of astronomy. Thanks to space robots, every major planetary body—and (where appropriate) its collection of companion moons—has now become a much more familiar world. Similarly, sophis- ticated robot astronomical observatories placed on strategically located platforms in space have allowed astronomers and astrophysicists to meet the universe face-to-face, across all portions of the electromagnetic spec- trum. No longer is the human view of the universe limited to a few narrow bands of radiation that trickle down to Earth’s surface through an inter- vening atmosphere that is often murky and turbulent. This chapter introduces the basic principles of robotics. Space robots share certain common features with their terrestrial counterparts. They also involve, however, a blending of aerospace and computer technologies that is far more demanding, unusual, and sophisticated than that generally needed for robots operating here on Earth. Space robots have to work in the harsh environment of outer space and sometimes up on strange alien worlds about which little is previously known. Under certain circumstances, telepresence and virtual reality technol- ogies will allow a human being to form a real-time, interactive partnership with an advanced space robot, which serves as a dextrous mechanical sur- rogate capable of operating in a hazardous, alien world environment. For 1 From Pioneer Lunar Probes to Interstellar Messengers 1
- 20. example, an advanced future space robot might explore remote regions of the Moon, while its human controller, working inside a permanent lunar surface base or even back on Earth, uses virtual reality-technologies to make important new discoveries. As a space robot operates farther away, the round-trip communi- cations distance with human controllers back on Earth must soon be measured not in thousands of miles (or kilometers), but rather in light The term artificial intelligence (AI) is commonly taken to mean the study of thinking and per- ceiving as general information-processing func- tions—or the science of machine intelligence (MI). In the past few decades, computer systems have been programmed to diagnose diseases; prove theorems; analyze electronic circuits; play complex games such as chess, poker and backgammon; solve differential equations; assemble mechani- cal equipment using robotic manipulator arms and end effectors (the “hands” at the end of the manipulator arms); pilot uncrewed vehicles across complex terrestrial terrain, as well as through the vast reaches of interplanetary space; analyze the structure of complex organic molecules; under- stand human speech patterns; and even write other computer programs. All of these computer-accomplished func- tions require a degree of intelligence similar to mental activities performed by the human brain. Someday, a general theory of intelligence may emerge from the current efforts of scientists and engineers who are now engaged in the field of artificial intelligence. This general theory would help guide the design and development of even smarter robot spacecraft and exploratory probes. Artificial intelligence generally includes a number of elements or subdisciplines. Some of the more significant of these elements or subdisci- plines are: planning and problem solving, percep- tion, natural language, expert systems, automation, teleoperation and robotics, distributed data man- agement, and cognition and learning. All artificial intelligence involves elements of planning and problem solving. The problem- solving function implies a wide range of tasks, including decision making, optimization, dynamic- resource allocation, and many other calculations or logical operations. Perception is the process of obtaining data from one or more sensors and processing or ana- lyzing these data to assist in making some subse- quent decision or taking some subsequent action. The basic problem in perception is to extract from a large amount of (remotely) sensed data some feature or characteristic that then permits object identification. One of the most challenging problems in the evolution of the digital computer has been the communications that must occur between the human operator and the machine. The human operator would like to use an everyday, or natural, language to gain access to the computer system. The process of communication between machines and people is very complex and frequently requires sophisticated computer hardware and software. An expert system permits the scientific or technical expertise of a particular human being to be stored in a computer for subsequent use by other human beings who have not had the ARTIFICIAL INTELLIGENCE m m 2 Robot Spacecraft
- 21. minutes. The great distances associated with deep-space exploration make the real-time control of a robot spacecraft by human managers imprac- tical, if not altogether impossible. So, in order to survive and function around or on distant worlds, space robots need to be smart—that is, they need to contain various levels of machine intelligence, or artificial intel- ligence (AI). As levels of machine intelligence continue to improve in this century, truly autonomous space robots will become a reality. Someday, equivalent professional or technical experience. Expert systems have been developed for use in such diverse fields as medical diagnosis, mineral exploration, and mathematical problem solving. To create such an expert system, a team of soft- ware specialists will collaborate with a scientific expert to construct a computer-based interactive dialogue system that is capable, at least to some extent, of making the expert’s professional knowl- edge and experience available to other individuals. In this case, the computer, or thinking machine, not only stores the scientific (or professional) expertise of one human being, but also uses its artificial intelligence to permit ready access to this valuable knowledge base by other human users. Automatic devices are those that operate without direct human control. NASA has used many such automated smart machines to explore alien worlds. For example, the Viking 1 and 2 lander spacecraft placed on the Martian surface in 1976 represent one of the great early triumphs of robotic space exploration. After separation from the Viking orbiter spacecraft, the lander (pro- tected by an aeroshell) descended into the thin Martian atmosphere at speeds of approximately 9,940 miles per hour (16,000 km per hour). The descending lander was slowed down by aero- dynamic drag until its aeroshell was discarded. Each robot lander spacecraft slowed down further by releasing a parachute and then achieved a gentle landing by automatically firing retrorockets. Both Viking landers successfully accomplished the entire soft landing sequence automatically, with- out any direct human intervention or guidance. Teleoperation implies that a human operator is in remote control of a mechanical system. Con- trol signals can be sent by means of hardwire (if the device under control is nearby) or in a wireless mode via transmitted electromagnetic signals—for example, laser or radio frequency—(if the robot system is some distance away and operates within line-of-sight of the transmitter). NASA’s Pathfinder mission to the surface of Mars in 1997 success- fully demonstrated teleoperation of a mini-robot rover at interplanetary distances. The highly suc- cessful Mars Pathfinder mission consisted of a stationary lander spacecraft and a small surface rover. NASA named the lander spacecraft the Carl Sagan Memorial Station in honor of the American astronomer Carl Sagan (1934–96), who popular- ized astronomy and the search for extraterrestrial life. The mini-rover was called Sojourner, after the American civil rights crusader Sojourner Truth. The six-wheeled mini-robot rover vehicle was actually controlled (or teleoperated) by the Earth- based flight team at the Jet Propulsion Laboratory (JPL) in Pasadena, California. The human opera- tors used images of the Martian surface obtained by both the rover and the lander systems. These interplanetary teleoperations required that the rover be capable of some semi-autonomous oper- ation, since there was a time delay of signals that averaged between 10 and 15 minutes in duration— (continues) m m From Pioneer Lunar Probes to Interstellar Messengers 3
- 22. depending upon the relative positions of Earth and Mars over the course of the mission. This rover had a hazard avoidance system and surface movement was performed very slowly. Starting in 2004, NASA’s Mars Exploration Rovers, Spirit and Opportunity, provided even more sophisticated and rewarding teleopera- tion experiences at interplanetary distances, as they rolled across different portions of the Red Planet. Of course, in dealing with the great dis- tances in interplanetary exploration, a situa- tion eventually arises in which electromagnetic wave transmission cannot accommodate any type of effective “real-time control.” When the device to be controlled on an alien world is many light-minutes or even light-hours away, and when actions or discoveries require split- second decisions, teleoperation must yield to increasing levels of autonomous, machine- intelligence-dependent robotic operation. Robot devices are computer-controlled mechanical systems that are capable of manip- ulating or controlling other machine devices, such as end effectors. Robots may be mobile or fixed in place and either fully automatic or teleoperated. The more AI a robot has, the less dependent it is upon human supervision. Large quantities of data are frequently involved in the operation of automatic robotic devices. The field of distributed data manage- ment is concerned with ways of organizing cooperation among independent, but mutually interacting, databases. Instead of transmitting enormous quantities of data back to Earth, an advanced robot explorer will use AI to selec- tively sort and send only the most interesting data. In AI, the concept of cognition and learn- ing refers to the development of a level of machine intelligence that can deal with new facts, unexpected events, and even contra- dictory information. Today’s smart machines handle new data by means of preprogrammed methods or logical steps. Tomorrow’s smarter machines will need the ability to learn, possibly even to understand, as they encounter new situations and are forced to change their mode of operation. Perhaps late in this century, as the field of artificial intelligence sufficiently matures, sci- entists can send fully automatic robot probes on interstellar voyages. Each interstellar probe must be capable of independently searching a candidate star system for suitable extrasolar planets that might support extraterrestrial life. 4 Robot Spacecraft (continued) m m human engineers will construct an especially intelligent robot that exhib- its a cognitive “machine mind” of its own. Artificial intelligence experts suggest that smart exploring machines of the future will have (machine) intelligence capabilities sufficient to repair themselves, to avoid hazard- ous circumstances on alien worlds, and to recognize and report all of the interesting objects or phenomena they encounter. Starting in the late 1950s—at about the same time that the space race of the cold war began—robots (terrestrial and extraterrestrial) became more practical and versatile. One of the reasons for this important
- 23. transformation was the vast improvement in computer technology and electronics (especially the invention of the transistor) that took place during this same period. The information-processing-and-storage revolution continues. As tomorrow’s com- puter chips and microprocessors pack more information-technology punch, future space robots will enjoy far more sophisticated levels of artificial intelli- gence than those existing today. Over the next four decades, robotic spacecraft will accomplish ever more exciting explora- tion missions throughout the solar system and beyond. Several of these very exciting missions are discussed in the latter por- tions of this book. At this point, it is important simply to recognize that sophisticated robot space- craft represent the enabling technology for many of the most important scientific discoveries that await the human race in the remainder of this century. Space robots are the mechanical partners that enable the human race to fulfill its destiny as an intel- ligent, spacefaring species. Failure to fully appreciate or to capitalize upon the oppor- tunity offered by the space robot will con- fine future generations of human beings to life on just one planet around an aver- age star in the outer regions of the Milky Way Galaxy. By recognizing the value of and vigorously using the space robot, the human race will, however, emerge within the galaxy as an active, spacefaring species. By initially reaching for the stars with very smart machines, future generations of human beings will experi- ence all of the exciting social and technical impacts involved in becoming an interstellar spacefaring species. There is an interesting correlation between progress in space explora- tion by robots and parallel progress in computer technology and aerospace technology. To emphasize the connection, this chapter provides a brief look at some of the most interesting American space robots, as found in the Pioneer, Ranger, Mariner, Viking, and Voyager programs. Subsequent From Pioneer Lunar Probes to Interstellar Messengers 5 Robot spacecraft have revolutionized knowledge about the solar system and visited all the major planets. This is a montage of planetary images taken by NASA spacecraft. Included are (from top to bottom) Mercury, Venus, Earth (and Moon), Mars, Jupiter, Saturn, Uranus, and Neptune. The inner planetary bodies (Mercury, Venus, Earth, Moon, and Mars) are roughly to scale with each other; the outer planets (Jupiter, Saturn, Uranus, and Neptune) are roughly to scale with each other. (NASA/JPL)
- 24. 6 Robot Spacecraft chapters provide more detailed insights into the technical features of these marvelous machines and many of the important scientific discoveries that they brought about. The main objective in this chapter is to provide a his- toric snapshot of how space robots emerged from simple, often unreliable, electromechanical exploring devices into sophisticated scientific platforms that now extend human consciousness and intelligent inquiry to the edges of the solar system and beyond. ✧ The Basic Principles of Robotics Robotics is the science and technology of designing, building, and pro- gramming robots. Robotic devices, or robots as they are usually called, are primarily smart machines with manipulators that can be programmed to do a variety of manual or human labor tasks automatically, and with sensors that explore the surrounding environment, including the land- scape of interesting alien worlds. A robot, therefore, is simply a machine that does mechanical, routine tasks on human command. The expression robot is attributed to Czech writer Karel Capek, who wrote the play R.U.R. (Rossum’s Universal Robots). This play first appeared in English in 1923 and is a satire on the mechanization of civilization. The word robot is derived from robata, a Czech word meaning compulsory labor or servitude. Here on Earth, a typical robot normally consists of one or more manipulators (arms), end effectors (hands), a controller, a power supply, and possibly an array of sensors to provide information about the envi- ronment in which the robot must operate. Because most modern robots are used in industrial applications, their classification is traditionally based on these industrial functions. So terrestrial robots frequently are divided into the following classes: nonservo (that is, pick-and-place), servo, pro- grammable, computerized, sensory, and assembly robots. The nonservo robot is the simplest type. It picks up an object and places it at another location. The robot’s freedom of movement usually is limited to two or three directions. The servo robot represents several categories of industrial robots. This type of robot has servomechanisms for the manipulator and end effector, enabling the device to change direction in midair (or midstroke) without having to trip or trigger a mechanical limit switch. Five to seven direc- tions of motion are common, depending on the number of joints in the manipulator. The programmable robot is essentially a servo robot that is driven by a programmable controller.This controller memorizes (stores) a sequence of movements and then repeats these movements and actions continuously. Often, engineers program this type of robot by “walking” the manipulator and end effector through the desired movement.
- 25. From Pioneer Lunar Probes to Interstellar Messengers 7 The computerized robot is simply a servo robot run by computer. This kind of robot is programmed by instructions fed into the controller elec- tronically. These smart robots may even have the ability to improve upon their basic work instructions. The sensory robot is a computerized robot with one or more artificial senses to observe and record its environment and to feed information back to the controller. The artificial senses most frequently employed are sight (robot or computer vision) and touch. Finally, the assembly robot is a computerized robot, generally with sensors, that is designed for assembly line and manufacturing tasks, both on Earth and eventually in space. In industry, robots are designed mainly for manipulation purposes. The actions that can be produced by the end effector or hand include: (1) motion (from point to point, along a desired trajectory or along a con- toured surface); (2) a change in orientation; and (3) rotation. Nonservo robots are capable of point-to-point motions. For each desired motion, the manipulator moves at full speed until the limits of its travel are reached. As a result, nonservo robots often are called limit- sequence, bang-bang, or pick-and-place robots. When nonservo robots reach the end of a particular motion, a mechanical stop or limit switch is tripped, stopping the particular movement. Servo robots are also capable of point-to-point motions; but their manipulators move with controlled variable velocities and trajectories. Servo robot motions are controlled without the use of stop or limit switches. Four different types of manipulator arms have been developed to accomplish robot motions. These are the rectangular, cylindrical, spherical, and anthropomorphic (articulated or jointed) arms.Each of these manipu- lator arm designs features two or more degrees of freedom (DOF)—a term that refers to the direction a robot’s manipulator arm is able to move. For example, simple straight-line or linear movement represents one DOF. If the manipulator arm is to follow a two-dimensional curved path, it needs two degrees of freedom: up and down and right and left. Of course, more complicated motions will require many degrees of freedom. To locate an end effector at any point and to orient this effector to a particular work volume requires six DOF. If the manipulator arm needs to avoid obstacles or other equipment, even more degrees of freedom are required. For each DOF, one linear or rotary joint is needed. Robot designers sometimes combine two or more of these four basic manipulator arm configurations to increase the versatility of a particular robot’s manipulator. Actuators are used to move a robot’s manipulator joints. Three basic types of actuators are currently used in contemporary robots: pneumatic, hydraulic, and electrical. Pneumatic actuators employ a pressurized gas to move the manipulator joint. When the gas is propelled by a pump through
- 26. 8 Robot Spacecraft a tube to a particular joint, it triggers or actuates movement. Pneumatic actuators are inexpensive and simple, but their movement is not precise. Therefore, this kind of actuator usually is found in nonservo, or pick-and- place, robots. Hydraulic actuators are quite common and are capable of producing a large amount of power. The main disadvantages of hydraulic actuators are their accompanying apparatuses (pumps and storage tanks) and problems with fluid leaks. Electrical actuators provide smoother movements, can be controlled very accurately, and are very reliable; how- ever, these actuators cannot deliver as much power as hydraulic actuators of comparable mass. Nevertheless, for modest power actuator functions, electrical actuators often are preferred. Many industrial robots are fixed in place or move along rails and guide- ways. Some terrestrial robots are built into wheeled carts, while others use their end effectors to grasp handholds and pull themselves along. Advanced robots use articulated manipulators as legs to achieve a walking motion. A robot’s end effector (hand or gripping device) generally is attached to the end of the manipulator arm. Typical functions of this end effector include grasping, pushing and pulling, twisting, using tools, performing insertions, and various types of assembly activities. End effectors can be mechanical, vacuum or magnetically operated; can use a snare device; or can have some other unusual design feature. The shapes of the objects that the robot must grasp determine the final design of the end effector. Usually most end effectors are some type of gripping or clamping device. Robots can be controlled in a wide variety of ways, from simple limit switches tripped by the manipulator arm to sophisticated computerized remote-sensing systems that provide machine vision, touch, and hearing. In the case of a computer-controlled robot, the motions of its manipula- tor and end effector are programmed: that is, the robot memorizes what it is supposed to do. Sensor devices on the manipulator help to establish the proximity of the end effector to the object to be manipulated and then feed information back to the computer controller concerning any modifi- cations needed in the manipulator’s trajectory. Another interesting type of terrestrial robot system, the field robot, has become practical recently. A field robot is a robot that operates in unpredictable, unstructured environments, typically outdoors (on Earth) and often operates autonomously or by teleoperation over a large work- space (typically a square mile [square kilometer] or more). For example, in surveying a potentially dangerous site, the human operator will stay at a safe distance away in a protected work environment and control (by cable or radio frequency link) the field robot, which then actually oper- ates in the hazardous environment. The United States Air Force’s Predator aerial surveillance robot and various bomb-sniffing, explosive-ordnance disposal (EOD) robots are examples of some of the most advanced field
- 27. From Pioneer Lunar Probes to Interstellar Messengers 9 robots. These terrestrial field robots are technical first cousins to the more sophisticated, teleoperated robot planetary rovers that have roamed on the Moon and Mars. Most of the space robots mentioned in this book draw a portion of their design heritage from terrestrial robots. The need to survive in outer space or on an unknown alien world has imposed much more stringent design requirements upon even the sim- plest of the space robots. When a factory robot has a part fail or a terres- trial field robot loses a wheel, human technicians are normally available to fix the problem quickly and efficiently. When a space robot that is millions of miles from Earth has a malfunction, it is on its own, and the difficulty can lead to catastrophic failure of an entire exploration mission. A simple example will illustrate this important point. When a mobile rover on Earth gets some dust or soil on the lenses of its machine vision system, a human technician is available to gently remove the troublesome material. When a sudden wind gust coats a surface rover with Martian soil, there is no person available to “dust it off.” The rover either has to be able to clean itself or else function with reduced machine vision and possibly reduced electric power, if the troublesome red-colored dust has also coated its solar cells. Because of this and similar mission-threatening “simple problems,” some aerospace engineers have suggested operating smart planetary rov- ers in teams. A team of advanced mechanical critters could be designed to help each other, whenever one runs into difficulty. In the dust-coating example, a second rover might come by, scan its dust-coated companion, and then use a special brush tool (grasped by its manipulator arm) to remedy the situation. The operative concept here is to design future space robots that are robust with in-depth design redundancy. In that way, the smart machine, perhaps with a little coaxing from human controllers on Earth, can fix itself or at least implement appropriate“workarounds,”and thus keep the explo- ration mission going. Another important design strategy is to engineer space robots so that they can work in teams. That way, one or more func- tional robots can assist and/or repair their companion robot in distress. ✧ Pioneer to the Moon and Beyond The dictionary defines a pioneer as a person who ventures into the unknown. That definition proved very appropriate for the first family of American deep space robots, which were given the name Pioneer. The initial spacecraft to be launched and the first space missions to actually be carried out by the United States Air Force were the Pioneer lunar probes of 1958. Now just a frequently overlooked page in aerospace history, these early Pioneer lunar probes were the world’s first attempted deep-space missions.
- 28. 10 Robot Spacecraft The first series of Pioneer spacecraft was flown between 1958 and 1960. Pioneer 1, 2, and 5 were developed by Space Technology Laboratories, Inc. and were launched for NASA by the Air Force Ballistic Missile Division (AFBMD). Pioneer 3 and 4 were developed by the Jet Propulsion Laboratory (JPL) and launched for NASA by the U.S. Army Ballistic Missile Agency (ABMA) at Redstone Arsenal, Alabama—the tech- nical team also responsible for the launch of Explorer 1, the first American satellite, on January 31, 1958. In January 1958, the Air Force Ballistic Missile Division (AFBMD) and its technical advisory contractor, Space Technology Laboratories (STL) proposed using the newly developed Thor missile with the second stage of the Vanguard rocket to launch the first missions to the Moon. The new launch vehicle configuration was named the Thor Able. The stated purpose of these early lunar-probe missions were to gather scientific data from space and to gain international prestige for the United States by doing so before the former Soviet Union. During the cold war, both superpowers were bitter political rivals, and space exploration provided each country with a convenient showcase in which to display national superiority on a global basis. After President Dwight Eisenhower’s administration activated the Advanced Research Projects Agency (ARPA) on February 7, 1958, the new agency’s first directives to the military services dealt with lunar probes. AFBMD was to launch three lunar probes using the Thor Able configura- tion; ABMA was to launch two lunar probes using its Juno II vehicle; and the Naval Ordnance Test Station (NOTS) at China Lake was to provide a miniature imaging system to be carried on the lunar probes. Space Technology Laboratories (STL) designed and assembled the lunar probes known as Pioneer 0, Pioneer 1, and Pioneer 2. Pioneer 0 was the first United States attempt at a lunar mission and the first attempt by any country to send a space probe beyond Earth orbit. The Pioneer 0 robot probe was designed to go into orbit around the Moon and carried a televi- sion (TV) camera and other instruments as part of the first International Geophysical Year (IGY) science payload. Unfortunately, the 84-pound (38-kg) robot probe was lost when the Thor rocket vehicle exploded 77 seconds after launch from Cape Canaveral. The Thor rocket blew up at an altitude of 10 miles (16 km), when the launch vehicle and its payload were about 10 miles downrange over the Atlantic Ocean. Erratic telemetry sig- nals were received from the Pioneer 0 payload and upper rocket stages for 123 seconds after the explosion. Range safety officials tracked the upper stages and payload until they impacted in the Atlantic Ocean. The original plan was for the Pioneer 0 spacecraft to travel for 62 hours to the Moon, at which time a solid propellant rocket motor would fire to put the spacecraft into a 18,000-mile (28,960-km) lunar orbit that would
- 29. From Pioneer Lunar Probes to Interstellar Messengers 11 last for about two weeks. Pioneer 0’s scientific instrument package had a mass of 25 pounds (11.3 kg). The package consisted of an image-scanning infrared television system to study the Moon’s surface, a micrometeorite detector, a magnetometer, and temperature-variable resistors to record internal thermal conditions of the spacecraft. Batteries provided electric power. Finally, Pioneer 0 was to be spin-stabilized at a rate of 1.8 revolu- tions per second. Pioneer 1 was the second and most successful of the early American space-probe efforts, as well as the first spacecraft launched by the newly created civilian space agency, NASA. Similar in design to Pioneer 0, the 75-pound (34.2-kg) mass Pioneer 1 was launched from Cape Canaveral on October 11, 1958, by a Thor Able rocket vehicle. Due to a launch vehicle malfunction, Pioneer 1 only attained a ballistic trajectory and never reached the Moon as planned. The spacecraft’s ballistic trajectory had a peak altitude of 70,730 miles (113,800 km). On October 13, after about 43 hours of flight, the spacecraft ended data transmission when it reentered Earth’s atmosphere over the South Pacific Ocean. Despite the spacecraft’s failure to reach the Moon because its launch vehicle did not provide suf- ficient velocity to escape Earth’s gravity, Pioneer 1’s instruments did return some useful scientific data about the extent of Earth’s trapped radiation belts. Pioneer 1’s scientific instrument package had a mass of 39 pounds (17.8 kg), making it slightly heavier than the scientific payload carried by Pioneer 0. Pioneer 1 contained an image-scanning infrared television system to study the Moon’s surface, an ionization chamber to measure radiation levels in space, a micrometeorite detector, a magnetometer, and temperature-variable sensors to record thermal conditions in the interior of the spacecraft. Pioneer 1 was spin-stabilized at 1.8 revolutions per sec- ond and received its electric power from limited lifetime batteries. Pioneer 2 was the last of the Thor Able space probes, which were designed to orbit the Moon and make measurements in interplanetary space between Earth and the Moon—a region called cislunar space. This spacecraft was nearly identical to Pioneer 1. Launched from Cape Canaveral on November 8, 1958, the space probe never achieved its intended lunar orbit. Instead, shortly after launch the third stage of the Thor Able rocket separated but failed to ignite. Given an inadequate velocity, Pioneer 2 only attained an altitude of 963 miles (1,550 km) before reentering Earth’s atmosphere over northwest Africa. Due to its short flight, Pioneer 2 col- lected only a small amount of useful scientific data about near-Earth space. Following the unsuccessful U.S. Air Force/NASA Pioneer 0, 1, and 2 lunar probe missions in 1958, the U.S. Army and NASA collaborated in launching two additional probe missions. Smaller than the previous Pioneer spacecraft, Pioneer 3 and 4 each carried only a single experiment
- 30. 12 Robot Spacecraft to detect cosmic radiation. It was the intention of the mission planners in both the U.S. Army and NASA that the two space probes would perform a flyby of the Moon and return data about the radiation environment in cislunar space. The Jet Propulsion Laboratory (JPL) constructed the Pioneer 3 and 4 spacecraft, which were nearly identical in mass, shape, size, and functions. Pioneer 3—a 12.9-pound (5.9-kg), spin-stabilized, cone-shaped space- craft—was launched on December 6, 1958, from Cape Canaveral by the U.S. Army Ballistic Missile Agency (ABMA), using a Juno II rocket. Developed in conjunction with NASA, Pioneer 3 was designed to pass close to the Moon some 34 hours after launch and then go into orbit around the Sun. Propellant depletion, however, caused the first-stage rocket engine to shut down 3.7 seconds early. This premature termination of thrust prevented Pioneer 3 from reach- ing escape velocity. Instead, the spacecraft always remained a captive of Earth’s gravity field and traveled on an enormously high ballistic trajectory, reaching a maximum altitude of 63,615 miles (102,360 km) before falling back to Earth. On December 7, Pioneer 3 reentered Earth’s atmosphere and burned up over Africa. This planned lunar probe returned telemetry for about 25 hours of its approximately 38-hour journey. The other 13 hours (of missing telemetry) corre- sponded to communications-blackout periods owing to the location of the two tracking stations. Mercury batteries pro- vided Pioneer 3 with its electric power. The spacecraft’s scientific payload included Geiger-Mueller tube radiation detectors, which provided data indicating the exis- tence of two distinct trapped radiation belt regions around Earth. Pioneer 4, launched on March 3, 1959, by a Juno II rocket, was the first U.S. spacecraft to escape Earth’s gravity and also the first to go into orbit around the Sun. Like Pioneer 3, its technical sibling, The Pioneer 4 spacecraft being installed on top of its Juno II launch vehicle at Cape Canaveral in February 1959. Pioneer 4 was the first United States spacecraft to orbit the Sun. (NASA/MSFC)
- 31. From Pioneer Lunar Probes to Interstellar Messengers 13 Pioneer 4 was a cone-shaped, spin-stabilized spacecraft built by the Jet Propulsion Laboratory and launched by the U.S. Army Ballistic Missile Agency in conjunction with NASA. The main scientific payloads of this 13.4-pound (6.1-kg) mass spacecraft were a lunar radiation environment experiment (using a Geiger-Mueller tube detector) and a lunar photogra- phy experiment. The cone-shaped Pioneer 4 probe was 20 inches (51 cm) high and 9.1 inches (23 cm) in diameter at its base. The cone itself was made of a thin fiberglass shell coated with a gold wash to make it an electrical con- ductor and painted with white stripes to assist in thermal control of the spacecraft’s interior. A ring of mercury batteries at the base of the cone provided electric power. After a successful launch, Pioneer 4 achieved its primary objective (an Earth-Moon trajectory), returned radiation data, and served as a valuable space-probe-tracking exercise. The robot probe passed within 37,290 miles (60,000 km) of the Moon’s surface on March 4, 1959, at a speed of 4,490 miles per hour (7,230 km/h). The lunar encounter distance was about twice the planned flyby altitude, so the spacecraft’s photoelectric sensor for the lunar photography experiment did not trigger. Although Pioneer 4 did indeed fly past the Moon, the Soviet Union’s Luna 1 spacecraft had passed by the Moon several weeks earlier (on January 4, 1959) and laid claim to the distinction of being the first human-made object to escape Earth’s gravity and to fly past another celestial body. A Russian space robot, not an American robot, had won the first lap in the cold war’s hotly contested, but officially undeclared, race to the Moon. This politically uncomfortable “second-place” trend would continue for much of the 1960s, until that fateful day at the end of the decade (July 20, 1969), when American astronauts Neil Armstrong and Edwin “Buzz” Aldrin claimed the victory lap by leaving human footprints on the Moon’s surface for the first time. The glare of this magnificent human spaceflight accomplishment often obscures the fact that the pathway to the Moon was paved by a family of American space robots named Ranger, Surveyor, and Lunar Orbiter. After several early attempts to reach the Moon, the U.S. Air Force and NASA sent the spin-stabilized Pioneer 5 spacecraft on a mission to investigate interplanetary space between Earth and Venus. The 95-pound (43-kg) robot space probe was successfully launched from Cape Canaveral on March 11, 1960, by a Thor Able rocket vehicle. Instrumentation onboard Pioneer 5 measured magnetic field phenomena, solar flare par- ticles, and ionization. On June 26, 1960, which was the spacecraft’s last day of transmission, Pioneer 5 established a communications link with Earth from a record distance of 22.5 million miles (36.2 million km). Among its scientific contributions, Pioneer 5 confirmed the existence of interplanetary
- 32. The name Luna was given to a series of robot spacecraft successfully sent to the Moon in the 1960s and 1970s by the former Soviet Union. Between 1958 and 1959, there were also several “unannounced” Luna launch failures, as the Soviet Union attempted to reach the Moon with a robot probe before the United States. Aerospace mis- sion failures were not officially acknowledged by the Soviet Union during the cold war. However, post–cold war cooperation in space exploration has allowed Western analysts to assemble and reconstruct some details about these unsuccessful early lunar probe missions. Tentatively identified failed Luna launches include Luna 1958A (Sep- tember 23, 1958), Luna 1958B (October 12, 1958), Luna 1958C (December 4, 1958), and Luna 1959A (June 18, 1959). Luna 1 was the first robot spacecraft of any country to reach the Moon and the first in a series of Soviet automatic interplanetary stations suc- cessfully launched in the direction of the Moon. The 794-pound (361-kg) sphere-shaped Luna 1 was also called Mechta (Dream). The robot probe was launched by a modified intercontinental bal- listic missile from the Baikonur Cosmodrome (Tyuratam) on January 2, 1959. The Soviets sent Luna 1 directly toward the Moon from the launch site, using a trajectory that suggested the space- craft was most likely intended to crash-land on the Moon. After 34 hours of flight, however, Luna 1 missed the Moon, passing within 3,725 miles (6,000 km) of the lunar surface on January 4. Fol- lowing its close encounter with the Moon, Luna 1 went into orbit around the Sun between the orbits of Earth and Mars. So Luna 1 also became the first human-made object to escape from Earth’s gravi- tational field and go into orbit around the Sun. Luna 1 was a sphere-shaped spacecraft with five antennae extending from one hemisphere. The robot probe had no onboard propulsion system and relatively short-lived batteries provided all its electric power. The spacecraft contained radio equipment, a tracking transmitter, a telemetry system, and scientific instruments for examin- ing interplanetary space. Measurements made by Luna 1 provided scientists with new data about Earth’s trapped radiation belts, as well as the important discovery that the Moon has no mea- surable magnetic field. Instruments on Luna 1 also indicated the presence of the solar wind (ionized plasma emanating from the Sun), which streams through interplanetary space. Data transmissions from Luna 1 ceased about three days after launch, when the spacecraft’s batteries ran down. Because of its high velocity and its prominent package of various metallic emblems with the Soviet coat of arms, Western aerospace analysts concluded that Luna 1 was primarily intended to crash on the Moon and (in a manner of speaking) to “plant the Soviet flag.” Luna 2 was the second of a series of early Soviet spacecraft launched in the direction of the Moon. Luna 2 had the distinction of being the first human-made object to land on the Moon. The Soviet space probe made impact on the lunar sur- face east of Mare Serenitatis near the Archimedes, Aristides, and Autolycus craters. The 858-pound (390-kg) spacecraft was similar in design to Luna 1. This means that Luna 2 was shaped like a sphere with protruding antennae and instrument ports. The science payload included radiation detectors, a magnetometer, and micrometeorite detectors. The spacecraft also carried a political payload, namely Soviet emblems and pennants. EARLY SOVIET LUNA MISSIONS m m 14 Robot Spacecraft
- 33. The Luna 2 space probe was launched on September 12, 1959, from the Baikonur Cosmo- drome. On September 14, after almost 34 hours of spaceflight, radio signals from spacecraft abruptly ceased, indicating that Luna 2 had made impact (crash landed) on the Moon. The robot space probe confirmed that the Moon has no apprecia- ble magnetic field and also discovered no evidence that the Moon has trapped radiation belts. Luna 3 was the third robot spacecraft success- fully launched to the Moon by the former Soviet Union and the first spacecraft of any country to return photographic images of the lunar farside. The spacecraft’s relatively coarse images showed that the Moon’s farside was mountainous and quite different from the nearside, which always faces Earth. Luna 3’s images caused excitement among astronomers around the world, because these pictures (no matter how crude by today’s space mission standards) allowed them to make the first tentative atlas of the lunar farside. Luna 3 was spin-stabilized and radio-controlled from Earth. The 613-pound (279-kg) spacecraft was a cylindrically shaped canister with hemispherical ends and a wide flange near the top end. The Luna 3 robot spacecraft (sometimes called an automatic interplanetary station in the Russian aerospace literature) was 51 inches (130 cm) long and 47 inches (120 cm) wide at its maximum diameter (that is, at the flange). Soviet engineers mounted solar cells along the outside of the cylinder in order to recharge the chemical batteries within the spacecraft. The interior also contained a dual-lens camera, an automatic film processing system, a scanner, radio equipment, and gyroscopes for attitude control. When the film was processed, commands from Earth activated a sequence of automated actions that moved the film from the processor to the scanner. Each photograph was scanned and converted into electrical signals, which were then transmitted back to Earth. The mission profile for Luna 3 involved a loop around the Moon that allowed the robot space- craft to automatically photograph the unknown farside. After launch from the Baikonur Cos- modrome on October 4, 1959, Luna 3 departed Earth on an interplanetary trajectory to the Moon. About 40,400 miles (65,000 km) from the Moon, the attitude control system was activated and the spacecraft stopped spinning. The lower end of the spacecraft was oriented toward the Sun, which was shining on the lunar farside. On October 6, Luna 3 passed within 3,850 miles (6,200 km) (at closest approach) of the Moon near its south pole and then continued on to the farside. On October 7, the photocell on the upper end of the spacecraft detected the sunlit farside and started the pho- tography sequence. The first image was taken at a distance of 39,500 miles (63,500 km). Luna 3 took its last photograph about 40 minutes later, when the spacecraft was at a distance of 41,500 miles (66,700 km) from the surface of the Moon. During this trail-blazing mission, a total of 29 photographs were taken, covering approximately 70 percent of the previously unseen and unknown farside. After the photography portion of its mission was com- pleted, Luna 3 resumed spinning, passed over the north pole of the Moon, and returned toward Earth. As Luna 3 approached Earth, a total of 17 resolvable (but noisy and grainy) photographs were transmitted by October 18 to Soviet space- craft controllers. Then, on October 22, they lost contact with the probe. Western analysts believe Luna 3 remained in orbit until about April, 1960, at which point it reentered Earth’s atmosphere and burned up. m m From Pioneer Lunar Probes to Interstellar Messengers 15
- 34. 16 Robot Spacecraft magnetic fields and helped explain how solar flares trigger magnetic storms and the northern and southern lights (auroras) on Earth. With the launch of Pioneer 6 (also called Pioneer A in the new series of robot spacecraft) in December 1965, NASA resumed using these space probes to complement interplanetary data acquired by the Mariner spacecraft. Over the years, NASA’s solar-orbiting Pioneer spacecraft have contributed an enormous amount of data concerning the solar wind, solar magnetic field, cosmic radiation, micrometeoroids, and other phenomena of interplanetary space. Pioneers 7, 8, and 9 (second-generation robot spacecraft) were launched between August 1966 and November 1968 and continued NASA’s investigation of the interplanetary medium. These spacecraft pro- vided large quantities of valuable data concerning the solar wind, magnetic and electrical fields, and cosmic rays in interplanetary space. Data from second-generation Pioneer spacecraft helped space scientists draw a new picture of the Sun as the dominant phenomenon of interplanetary space. The Pioneer 10 and 11 spacecraft were designed as true deep-space robot explorers—the first human-made objects to navigate the main asteroid belt, the first spacecraft to encounter Jupiter and its fierce radia- tion belts, the first to encounter Saturn, and the first spacecraft to leave the solar system. This far-traveling pair of robot spacecraft also investigated magnetic fields, cosmic rays, the solar wind, and the interplanetary dust concentrations as they flew through interplanetary space. The Pioneer Venus mission consisted of two separate spacecraft launched by the United States to the planet Venus in 1978. The Pioneer Venus Orbiter (also called Pioneer 12) was a 1,173-pound (553-kg) space- craft that contained a 100-pound (45-kg) payload of scientific instruments. Pioneer 12 was launched on May 20, 1978, and placed into a highly eccen- tric orbit around Venus on December 4, 1978. For 14 years (from 1978 to 1992) the Pioneer Venus Orbiter gathered a wealth of scientific data about the atmosphere and ionosphere of Venus and their interactions with the solar wind, as well as details about the planet’s surface. Then, in October 1992, this spacecraft made an intended final entry into the Venusian atmo- sphere, collecting data up to its final fiery plunge and dramatically ending the operations portion of the Pioneer Venus mission. Data analysis and scientific discovery would continue for years afterward. The Pioneer Venus Multiprobe (also called Pioneer 13) consisted of a basic bus spacecraft, a large probe, and three identical small probes. The Pioneer Venus Multiprobe was launched on August 8, 1978, and separated about three weeks before entry into the Venusian atmosphere. The four (now-separated) probes and their (spacecraft) bus successfully entered the Venusian atmosphere at widely dispersed locations on December 9, 1978, and returned important scientific data as they plunged toward the planet’s
- 35. From Pioneer Lunar Probes to Interstellar Messengers 17 surface. Although the probes were not designed to survive landing, one hardy probe did and transmitted data for about an hour after impact. ✧ Jet Propulsion Laboratory (JPL)— America’s Premier Space Robot Factory The American space age began on January 31, 1958, with the launch of the first U.S. satellite, Explorer 1—an Earth-orbiting spacecraft built and controlled by the Jet Propulsion Laboratory (JPL). For almost five decades, JPL has led the world in exploring the solar system with robot spacecraft. The Jet Propulsion Laboratory (JPL) is a federally funded research and development facility managed by the California Institute of Technology for the National Aeronautics and Space Administration (NASA). The Laboratory is located in Pasadena, California approximately 20 miles (32 km) northeast of Los Angeles. In addition to the Pasadena site, JPL oper- ates the worldwide Deep Space Network (DSN), including a DSN station, at Goldstone, California. JPL’s origin dates back to the 1930s, when Caltech professor Theodor von Kármán (1881–1963) supervised pioneering work in rocket propul- sion for the U.S. Army—including the use of strap-on rockets for “jet- assisted take-off” of aircraft with extra heavy cargoes. At the time, von Kármán was head of Caltech’s Guggenheim Aeronautical Laboratory. On December 3, 1958, two months after the U.S. Congress created NASA, JPL was transferred from the U.S. Army’s jurisdiction to that of the new civil- ian space agency. The Laboratory now covers 177 acres (72 hectares) adja- cent to the site of von Kármán’s early rocket experiments in a dry riverbed wilderness area of Arroyo Seco. In the 1960s, JPL began to conceive, design, and operate robot space- craft to explore other worlds. This effort initially focused on NASA’s Ranger and Surveyor missions to the Moon—robot spacecraft that paved the way for successful human landings by the Apollo Project astronauts. The Ranger spacecraft were the first U.S. robot spacecraft sent toward the Moon in the early 1960s to prepare the way for the Apollo Project’s human landings at the end of that decade. The Rangers were a series of fully attitude-controlled robot spacecraft designed to photograph the lunar surface at close range before making impact. Ranger 1 was launched on August 23, 1961, from Cape Canaveral Air Force Station and set the stage for the rest of the Ranger missions by testing spacecraft navigational performance. The Ranger 2 through 9 spacecraft were launched from November 1961 through March 1965. All of the early Ranger missions (namely, Ranger 1 through 6) suffered setbacks of one type or another. Finally, Ranger 7, 8, and 9 succeeded, with flights that returned many
- 36. 18 Robot Spacecraft NASA’s Ranger spacecraft were sent to the Moon in the early to mid-1960s to pave the way for the Apollo Project’s human landings at the end of that decade. These attitude-controlled robot spacecraft were designed to photograph the lunar surface at close range before impacting. (NASA/JPL) Minutes before impact on March 24, 1965, NASA’s Ranger 9 robot spacecraft took this close-up television picture of the lunar surface. (NASA)
- 37. From Pioneer Lunar Probes to Interstellar Messengers 19 thousands of lunar surface images (before impact) and greatly advanced scientific knowledge about the Moon. NASA’s highly successful Surveyor Project began in 1960. It consisted of seven robot lander spacecraft that were launched between May 1966 and January 1968, as an immediate precursor to the human expeditions to the lunar surface in the Apollo Project. These versatile space robots were used to develop soft-landing techniques, to survey potential Apollo mis- sion landing sites, and to improve scientific understanding of the Moon. The Surveyor 1 spacecraft was launched on May 30, 1966, and soft- landed in the Ocean of Storms region of the Moon. The space robot dis- covered that the bearing strength of the lunar soil was more than adequate to support the Apollo Project’s human-crewed lander spacecraft (called the lunar module, or LM). This finding contradicted the then-prevalent hypothesis that a heavy spacecraft like the LM might sink out of sight in the anticipated talcum-powder-like, ultra-fine lunar dust particles. The Surveyor 1 spacecraft also telecast many images from the lunar surface. Surveyor 2 was the second in this series of soft-landing robots. Successfully launched on September 20, 1966, by an Atlas-Centaur rocket from Cape Canaveral, this robot lander experienced a vernier engine fail- ure during a midcourse maneuver while en route to the Moon. The failure of one vernier engine to fire resulted in an unbalanced thrust that caused Surveyor 2 to tumble. Attempts by NASA engineers to salvage this mission failed. Things went much better for NASA’s next robot lander mission to the Moon. The Surveyor 3 spacecraft was launched on April 17, 1967, and soft-landed on the side of a small crater in another region of the Ocean of Storms. The perky space robot used the shovel attached to its mechani- cal arm to dig a trench and thus it was discovered that the load-bearing strength of the lunar soil increased with depth. Surveyor 3 also transmitted many images from the lunar surface. At the same time that JPL engineers were busy with the Ranger and Surveyor missions, they also conducted Mariner spacecraft missions to Mercury, Venus, and Mars. The Mariner missions were true trail-blazing efforts that continued through the early 1970s and greatly revised scien- tific understanding of the terrestrial planets and the inner solar system. The first Mariner mission, called Mariner 1, was intended to perform a Venus flyby. (Chapter 3 presents the different types of robot spacecraft and their characteristic missions.) NASA and JPL engineers based the design of this spacecraft on the Ranger lunar spacecraft. A successful liftoff of Mariner 1’s Atlas-Agena B launch vehicle on July 22, 1962, soon turned tragic. When the rocket vehicle veered off course, the range safety officer at Cape Canaveral Air Force Station was forced to destroy it some 293 seconds after launch. Because of faulty guidance commands, the rocket
- 38. 20 Robot Spacecraft vehicle’s steering was very erratic and the Mariner 1 spacecraft was going to crash somewhere on Earth, possibly in the North Atlantic shipping lanes or in an inhabited area. Undaunted by the heartbreaking loss of the Mariner 1 spacecraft, which was never given a chance to demonstrate its capabilities, the NASA/JPL engineering team quickly prepared its identical twin, named Mariner 2, to pinch-hit and perform the world’s first inter- planetary flyby mission. This photograph, taken during the Apollo 12 lunar landing mission (November 1969), shows astronaut Charles Conrad, Jr., examining the Surveyor 3 robot spacecraft. Between 1967 and 1968, NASA used several Surveyor lander spacecraft to carefully examine the lunar surface before sending humans to the Moon. Surveyor 3 was launched from Cape Canaveral on April 17, 1967, and successfully soft-landed on the side of a small crater in the Ocean of Storms region on April 19, 1967. (The lunar module [Intrepid] used by the Moon-walking astronauts Conrad and Alan L. Bean appears in the background.) (NASA)
- 39. From Pioneer Lunar Probes to Interstellar Messengers 21 Following a successful launch from Cape Canaveral on August 27, 1962, Mariner 2 cruised through interplanetary space, and then became the first robot spacecraft to fly past another planet (in this case, Venus). Mariner 2 encountered Venus at a distance of about 25,500 miles (41,000 km) on December 14, 1962. Following the flyby of Venus, Mariner 2 went into orbit around the Sun. The scientific discoveries made by Mariner 2 included a slow retrograde rotation rate for Venus, hot surface tempera- tures and high surface pressures, a predominantly carbon-dioxide atmo- sphere, continuous cloud cover with highest altitude of about 37 miles (60 km), and no detectable magnetic field. Data collected by Mariner 2 during its interplanetary journey to Venus showed that the solar wind streams continuously in interplanetary space and that the cosmic dust density is much lower than in the region of space near Earth. The Mariner 2 encounter helped scientists dispel many pre-space age romantic fantasies about Venus, including the widely held speculation Following its launch on August 27, 1962, NASA’s Mariner 2 became the first robot spacecraft to successfully fly past another planet (Venus). Its technical twin, Mariner 1, was lost on July 22, 1962, when range safety destroyed an errant launch vehicle. This picture shows the spacecraft’s solar panels and high- gain antenna extended, as displayed during the interplanetary cruise phase of the planetary flyby mission. (NASA)
- 40. 22 Robot Spacecraft (which appeared in both science and science-fiction literature) that the cloud-shrouded planet was a prehistoric world, mirroring a younger Earth. Except for a few physical similarities like size and surface gravity level, robot spacecraft visits in the 1960s and 1970s continued to show that Earth and Venus were very different worlds. For example, the surface temperature on Venus reaches almost 932°F (500°C), its atmospheric pressure is more than 90 times that of Earth, it has no surface water, and its dense atmosphere, with sulfuric acid clouds and an overabundance of carbon dioxide (about 96 percent), represents a runaway greenhouse of disastrous proportions. The next Mariner project undertaken by NASA and JPL targeted the planet Mars. Two spacecraft were prepared, Mariner 3 and its backup Mariner 4 (an identical twin). Mariner 3 was launched from Cape Canaveral on November 5, 1964, but the shroud encasing the spacecraft atop its rocket failed to open properly and Mariner 3 did not get to Mars. Three weeks later Mariner 4 was launched successfully and sent on an eight-month voyage to the Red Planet. Why was such a quick recovery and new launch possible in so short a time? In the early days of space exploration, launch vehicle failures were quite common, so aerospace engineers and managers considered it pru- dent to build two (or more) identical spacecraft for each important mis- sion. Should one spacecraft experience a fatal launch accident, the other spacecraft could quickly be readied to take advantage of a particular interplanetary launch window. If both spacecraft proved successful, the scientific return for that particular mission usually more than doubled. In this fortunate case, scientists could use the preliminary findings of the first space robot to guide the data collection efforts of the second robot as it approached the target planet several weeks later. NASA’s three most suc- cessful “robot twin missions” of the 1970s were Pioneer 10 and 11 (flybys), Viking 1 and 2 (landers and orbiters), and Voyager 1 and 2 (flybys). Starting in 2004, fortune smiled again when NASA’s twin Mars Exploration Rovers (MERs), named Spirit and Opportunity, arrived safely on the Red Planet and began moving across the surface to inaugurate highly productive sci- entific investigations. A launch window is the time interval during which a spacecraft can be sent to its destination. An interplanetary launch window is generally con- fined to a few weeks each year (or less) by the location of Earth in its orbit around the Sun. Proper timing allows the launch vehicle to use Earth’s orbital motion in its overall trajectory. Earth-departure timing is also criti- cal, if the spacecraft is to arrive at a particular point in interplanetary space simultaneously with the target planet. By carefully choosing the launch window, interplanetary spacecraft can employ a minimum energy path called the Hohmann transfer trajectory, after the German engineer Walter
- 41. From Pioneer Lunar Probes to Interstellar Messengers 23 Hohmann (1880–1945), who described this orbital transfer technique in 1925. Orbital mechanics, payload mass, and rocket-vehicle thrust all influ- ence interplanetary travel. The most energy-efficient launch windows from Earth to Mars occur about every two years. Determining launch windows for missions to the giant outer planets is a bit more complicated. For example, only once every 176 years do the four giant planets (Jupiter, Saturn, Uranus, and Neptune) align themselves in such a pattern that a spacecraft launched from Earth to Jupiter at just the right time might be able to visit the three other giant planets on the same mission, using a technique called gravity assist. (Gravity assist is discussed in chapter 2) This unique opportunity occurred in 1977, and NASA scientists took advantage of a special celestial alignment by launching two sophisticated robot spacecraft, called Voyager 1 and 2, on multiple giant planet encounter missions. As described shortly, Voyager 1 visited Jupiter and Saturn, while Voyager 2 took the so-called “grand tour” and visited all four giant planets on the same mission. In the cold war environment of the early 1960s, a great deal of political emphasis and global attention was given to achievements in space explo- ration. The superpower that accomplished this or that space exploration “first” earned a central position on the world political stage. So, NASA managers soon recognized that building identical-twin spacecraft (just in case one did not complete the mission) proved to be a relatively inexpen- sive approach to pursuing major scientific objectives while earning political capital. Superpower competition during the cold war fueled an explosion in space exploration and produced an age of discovery, unprecedented in history. Primarily because of robot spacecraft, more scientific information about the solar system and the universe was collected in between 1960 and 2000 than in all previous human history. This exciting wave of discovery continues in the post–cold war era, as more sophisticated space robots, such as Cassini/Huygens, explore the unknown. Before discussing the spectacular results of the Viking mission or the great journeys of Voyager spacecraft,this chapter returns to the very impor- tant Mariner 4 mission to Mars. Mariner 4 was successfully launched from Cape Canaveral on November 28, 1964, traveled for almost eight months through interplanetary space, and then zipped past Mars on July 14, 1965. At its closest approach, Mariner 4 was just 6,120 miles (9,845 km) from the surface of Mars during the flyby. As this space robot encountered Mars, it collected the first close-up images of another planet. These images, played back from a small video recorder over a long period, showed lunar-type impact craters, some of them touched with frost in the chill of the Martian evening. Mariner 4’s 21 complete pictures, in addition to 21 lines of a 22nd picture, might be regarded as quite crude when compared to the high- resolution imagery of Mars provided by contemporary robot spacecraft.
- 42. 24 Robot Spacecraft These first images of another world started a revolution that overturned many long-cherished views about the Red Planet, however. Throughout human history the Red Planet, Mars, has been at the center of astronomical thought. The ancient Babylonians followed the motions of this wandering red light across the night sky and named it after Nergal, their god of war. Later, the Romans, also honoring their own god of war, gave the planet its present name. The presence of an atmo- sphere, polar caps, and changing patterns of light and dark on the surface caused many pre–space age astronomers and scientists to consider Mars an “Earthlike planet”—the possible abode of extraterrestrial life. The American astronomer Percival Lowell (1855–1916) was one of the most outspoken proponents of the canal theory. In several popular publications, NASA’s Mariner 4 snapped this photograph of Mars at a slant range of 7,800 miles (12,550 km), as the robot spacecraft flew past the Red Planet on July 14, 1965. (NASA)
- 43. From Pioneer Lunar Probes to Interstellar Messengers 25 he insisted that Mars was a dying planet whose intelligent inhabitants con- structed huge canals to distribute a scarce supply of water around the alien world. Invasions from Mars was one of the popular themes in science- fiction literature and in the entertainment industry. For example, when actor Orson Welles broadcast a radio drama in 1938 based on H. G. Wells’s science-fiction classic The War of the Worlds, enough people believed the report of invading Martians to create a near panic in some areas of the northeastern United States. With Mariner 4 leading the scientific parade, however, a wave of sophisticated robot spacecraft—flybys, orbiters, landers, and rovers—have shattered the canal theory—the persistent romantic myth of a race of ancient Martians struggling to bring water from the polar caps to the more productive regions of a dying world. Spacecraft-derived data have shown that the Red Planet is actually a “halfway” world. Part of the Martian sur- face is ancient, like the surfaces of the Moon and Mercury, while part is more evolved and Earthlike. Mars remains at the center of intense inves- tigation by a new wave of sophisticated robot spacecraft. The continued search for microbial life (existent or extinct) and the resolution of the intriguing mystery about the fate of liquid water, which appears to have flowed on ancient Mars in large quantities, top the current exploration agenda. Other successful Mariner missions included Mariner 5, launched in 1967 to Venus; Mariner 6, launched in 1969 to Mars; Mariner 7, launched in 1969 to Mars; and Mariner 9, launched in 1971 to Mars. In November 1971, Mariner 9 became the first artificial satellite of Mars and the first spacecraft of any country to orbit another planet. The robot spacecraft waited patiently for a giant planet-wide dust storm to abate and then com- piled a collection of high-quality images of the surface of Mars that pro- vided scientists with their first global mosaic of the Red Planet. Mariner 9 also took the first close-up images of the two small (natural) Martian satellites, Phobos and Deimos. Mariner 10 became the first spacecraft to use a gravity-assist boost from one planet to send it to another planet—a key innovation in space- flight, which enabled exploration of the outer planets by robot spacecraft. Mariner 10’s launch from Cape Canaveral in November 1973 delivered the spacecraft to Venus in February 1974, where a gravity-assist flyby allowed it to encounter the planet Mercury in March and September of that year. Mariner 10 was the first and, thus far, the only spacecraft of any country to explore the innermost planet in the solar system. On August 3, 2004, NASA launched MESSENGER from Cape Canaveral and sent the orbiter spacecraft on a long-interplanetary journey to Mercury. In March 2011, MESSENGER is set to become the first robot spacecraft to achieve orbit around Mercury.
- 44. MESSENGER is a NASA acronym that stands for the MErcury Surface, Space ENvironment, GEochemistry and Ranging mission. The space robot will orbit Mercury following three flybys of that planet. The orbital phase will use data collected during the flybys as an initial guide to conducting its focused scientific investigation of this mysterious world, which remains the least explored of the terrestrial (or inner) planets of the solar system. On August 3, 2004, the 1,070-pound (485- kg) MESSENGER was successfully launched from Cape Canaveral Air Force Station by a Boe- ing Delta II rocket. During a planned 4.9-billion- mile (7.9-billion-km) interplanetary journey that includes 15 trips around the Sun, MESSENGER has flown past Earth once (in August 2005), will fly past Venus twice (in October 2006 and June 2007), and then past Mercury three times (in January 2008, October 2008, and September 2009) before easing into orbit around Mercury. The Earth and Venus flybys use the gravity- assist maneuver to guide MESSENGER toward Mercury’s orbit. The three Mercury flybys will help MESSENGER match the planet’s speed and location for an orbit insertion maneuver in March 2011. The flybys of Mercury also allow MESSENGER to gather important data, which scientists will then use to plan the yearlong orbital phase of the mission. The MESSENGER spacecraft, designed and built for NASA by the Johns Hopkins University Applied Physics Laboratory (JHUAPL) is only the second robot spacecraft sent to Mercury. Mariner 10 flew past Mercury three times in 1974–75, but, because of orbital mechanics limitations, could only gather detailed data on less than half of the planet’s surface. The MESSENGER mission has an ambitious science plan. The space robot’s complement of seven science instruments will determine Mercury’s composition; produce color images of the planet’s surface on a global basis; map Mercury’s magnetic field and measure the prop- erties of the planet’s core; examine Mercury’s intriguing poles to determine the extent of any water ice or other frozen volatile material deposits in permanently shadowed regions; and characterize Mercury’s tenuous atmosphere and Earthlike magnetosphere. m MESSENGER MISSION m m m The first intense search for life on Mars was begun in 1975, when NASA launched the agency’s Viking missions, consisting of two orbiter and two lander spacecraft. Development of the elaborate robotic mission was divided between several NASA centers and private U.S. aerospace firms. JPL built the Viking orbiter spacecraft, conducted mission communications, and eventually assumed management of the mission. The Viking mission and the search for life on Mars are discussed in subsequent chapters. Credit for the single space-robot mission that has visited the great- est number of giant planets goes to JPL’s Voyager project. Launched in 1977, the twin Voyager 1 and Voyager 2 flew by the planets Jupiter (1979) and Saturn (1980–81). Voyager 2 then went on to have an encounter with 26 Robot Spacecraft
- 45. From Pioneer Lunar Probes to Interstellar Messengers 27 Artist’s concept of NASA’s Viking mission spacecraft (orbiter and lander combined) approaching Mars in 1976. (NASA) Artist’s concept of NASA’s far-traveling Voyager 2 robot spacecraft, as it looks back upon Neptune and its moon Triton, seven hours after its closest approach to the distant planet on August 25, 1989. Artist Don Davis created this painting based on a computer- assembled simulation of the spacecraft’s trajectory through the Neptune system. (NASA/JPL)
- 46. 28 Robot Spacecraft Uranus (1986) and with Neptune (1989). Both Voyager 1 and Voyager 2 are now traveling on different trajectories into interstellar space. In February 1998, Voyager 1 passed the Pioneer 10 spacecraft to become the most dis- tant human-made object in space. The Voyager Interstellar Mission (VIM) (described in Chapter 12) should continue well into the next decade. Millions of years from now—most likely when human civilization has completely disappeared from the surface of Earth—four robot spacecraft (Pioneer 10 and 11, Voyager 1 and 2) will continue to drift through the interstellar void. Each spacecraft will serve as a legacy of human ingenu- ity and inquisitiveness. By carrying a special message from Earth, each far-traveling robot spacecraft also bears permanent testimony that at least one moment in the history of the human species a few people raised their foreheads to the sky and reached for the stars. Though primarily designed for scientific inquiry within the solar system, these four relatively simple robotic exploring machines are now a more enduring artifact of human civilization than any cave painting, great monument, giant palace, or high- rise city created here on Earth. A new generation of more sophisticated spacecraft appeared in the late 1980s and early 1990s. These vehicles allowed NASA to conduct much more detailed scientific investigation of the planets and of the Sun. The robot spacecraft used in the Galileo mission to Jupiter and the Cassini mis- sion to Saturn are representative of significant advances in sensor technol- ogy, computer technology, and aerospace engineering. The Galileo mission began on October 18, 1989, when the sophis- ticated spacecraft was carried into low Earth orbit by the space shuttle Atlantis and then launched on its interplanetary journey by means of an inertial upper stage (IUS) rocket. Relying on gravity-assist flybys to reach Jupiter, the Galileo spacecraft flew past Venus once and Earth twice. As it traveled through interplanetary space beyond Mars on its way to Jupiter, Galileo encountered the asteroids Gaspra (October 1991) and Ida (August 1993). Galileo’s flyby of Gaspra on October 29, 1991, provided scientists their first-ever close-up look at a minor planet. On its final approach to Jupiter, Galileo observed the giant planet’s bombardment by fragments of Comet Shoemaker-Levy-9, which had broken apart. On July 12, 1995, the Galileo mother spacecraft separated from its hitchhiking companion (an atmospheric probe) and the two robot spacecraft flew in formation to their final destination. On December 7, 1995, Galileo fired its main engine to enter orbit around Jupiter and gathered data transmitted from the atmospheric probe during that small robot’s parachute-assisted descent into the Jovian atmosphere. During its two-year prime mission, the Galileo spacecraft performed 10 targeted flybys of Jupiter’s major moons. In December 1997, the sophisticated robot spacecraft began an extended scientific mission
- 47. From Pioneer Lunar Probes to Interstellar Messengers 29 that featured eight flybys of Jupiter’s smooth, ice-covered moon Europa and two flybys of the pizza-colored, volcanic Jovian moon, Io. Galileo started a second extended scientific mission in early 2000. This second extended mission included flybys of the Galilean moons Io, Ganymede, and Callisto, plus coordinated observations of Jupiter with the Cassini spacecraft. In December 2000, Cassini flew past the giant planet to receive a much-needed gravity assist that enabled the large spacecraft to eventually reach Saturn. Galileo conducted its final flyby of a Jovian moon in November 2002, when it zipped past the tiny inner moon, Amalthea. The encounter with Amalthea left Galileo on a course that would lead to an intentional impact with Jupiter in September 2003. NASA mission controllers deliberately crashed the Galileo mother spacecraft into Jupiter at the end of the space robot’s very productive scientific mission, to avoid any possibility of contaminating Europa with terrestrial microorganisms. As an uncontrolled derelict, the Galileo might have eventually crashed This artist’s concept shows NASA’s Galileo spacecraft as it performed a very close flyby of Jupiter’s tiny inner moon Amalthea in November 2002. (NASA)
- 48. 30 Robot Spacecraft into Europa sometime within the next few decades. Many exobiologists suspect that Europa has a life-bearing, liquid-water ocean underneath its icy surface. Since the Galileo spacecraft was probably harboring a variety of hitchhiking terrestrial microorganisms, scientists thought it prudent to completely avoid any possibility of contamination of Europa. The easiest way to resolve the potential problem was to simply dispose of the retired Galileo in the frigid, swirling clouds of Jupiter. So, NASA and the JPL mis- sion controllers accomplished this task while still maintaining sufficient control over Galileo’s behavior and trajectory. Today, JPL remains heavily engaged in activities associated with deep- space automated scientific missions. Efforts at the Laboratory in Pasadena include subsystem engineering, instrument development, and more automated levels of data reduction and analysis to support deep space missions. The sophisticated Cassini, which is now exploring the Saturn system, and the robust Spirit and Opportunity Mars Exploration Rovers, which are now rolling across the surface of the Red Planet, are examples of successful contemporary JPL missions involving sophisticated robot spacecraft. On the horizon are such exciting space robot missions as Dawn—the first spacecraft ever planned to orbit two different celestial bodies after leaving Earth. Dawn will launch in 2007, orbit the large main belt aster- oid, Vesta, starting in 2011, and then begin orbiting the largest main belt asteroid, Ceres, in 2015. ✧ Robot Spacecraft in Service to Astronomy Each portion of the electromagnetic spectrum (that is, radio waves, infra- red radiation, visible light, ultraviolet radiation, X-rays, and gamma rays) brings astronomers and astrophysicists unique information about the universe and the objects within it. For example, certain radio frequency (RF) signals help scientists characterize cold molecular clouds. The cosmic microwave background (CMB) represents the fossil radiation from the big bang, the enormous ancient explosion considered by most scientists to have started the present universe about 15 billion years ago. The infrared (IR) portion of the spectrum provides signals that let astronomers observe non-visible objects such as near-stars (brown dwarfs) and relatively cool stars. Infrared radiation also helps scientists peek inside dust-shrouded stellar nurseries (where new stars are forming) and unveil optically opaque regions at the core of the Milky Way Galaxy. Ultraviolet (UV) radiation provides astrophysicists special information about very hot stars and quasars, while visible light helps observational astronomers characterize
- 49. Another Random Scribd Document with Unrelated Content
- 50. Forgetful of the law, nor master of his mind. Straight all his hopes exhaled in empty smoke, And his long toils were forfeit for a look. Three flashes of blue lightning gave the sign Of covenants broke; three peals of thunder join. Then thus the bride:—'What fury seized on thee, Unhappy man! to lose thyself and me? Dragged back again by cruel destinies, An iron slumber shuts my swimming eyes. And now, farewell! Involved in shades of night, For ever I am ravished from thy sight. In vain I reach my feeble hands, to join In sweet embraces—ah! no longer thine!' She said; and from his eyes the fleeting fair } Retired like subtile smoke dissolved in air, } And left her hopeless lover in despair. } In vain, with folding arms, the youth essayed To stop her flight, and strain the flying shade: He prays, he raves, all means in vain he tries, } With rage inflamed, astonished with surprise; } But she returned no more, to bless his longing eyes. } Nor would the infernal ferry-man once more Be bribed to waft him to the farther shore What should he do, who twice had lost his love?
- 51. What notes invent? what new petitions move? Her soul already was consigned to Fate, And shivering in the leaky sculler sate. For seven continued months, if Fame say true, The wretched swain his sorrows did renew: By Strymon's freezing streams he sate alone: The rocks were moved to pity with his moan: Trees bent their heads to hear him sing his wrongs: Fierce tigers couched around, and lolled their fawning tongues. So, close in poplar shades, her children gone, The mother nightingale laments alone, Whose nest some prying churl had found, and thence, By stealth, conveyed the unfeathered innocence But she supplies the night with mournful strains; And melancholy music fills the plains. Sad Orpheus thus his tedious hours employs, Averse from Venus, and from nuptial joys. Alone he tempts the frozen floods, alone The unhappy climes, where spring was never known: He mourned his wretched wife, in vain restored, And Pluto's unavailing boon deplored. The Thracian matrons—who the youth accused
- 52. Of love disdained, and marriage rites refused— With furies and nocturnal orgies fired, At length against his sacred life conspired. Whom even the savage beasts had spared, they killed, And strewed his mangled limbs about the field. Then, when his head, from his fair shoulders torn, Washed by the waters, was on Hebrus borne, Even then his trembling tongue invoked his bride; } With his last voice, 'Eurydice,' he cried. } 'Eurydice,' the rocks and river-banks replied." } This answer Proteus gave; nor more he said } But in the billows plunged his hoary head; } And, where he leaped, the waves in circles widely spread. } The nymph returned, her drooping son to cheer, And bade him banish his superfluous fear: "For now," said she, "the cause is known, from whence Thy woe succeeded, and for what offence. The nymphs, companions of the unhappy maid, This punishment upon thy crimes have laid; And sent a plague among thy thriving bees. — With vows and suppliant prayers their powers appease:
- 53. The soft Napæan race will soon repent[26] Their anger, and remit the punishment. The secret in an easy method lies; Select four brawny bulls for sacrifice, Which on Lycæus graze without a guide; Add four fair heifers yet in yoke untried. For these, four altars in their temple rear, And then adore the woodland powers with prayer. From the slain victims pour the streaming blood, And leave their bodies in the shady wood: Nine mornings thence, Lethæan poppy bring, To appease the manes of the poet's[27] king: And, to propitiate his offended bride, A fatted calf and a black ewe provide: This finished, to the former woods repair." } His mother's precepts he performs with care; } The temple visits, and adores with prayer; } Four altars raises; from his herd he culls, For slaughter, four the fairest of his bulls: Four heifers from his female store he took, All fair, and all unknowing of the yoke. Nine mornings thence, with sacrifice and prayers, The powers atoned, he to the grove repairs. Behold a prodigy! for, from within The broken bowels, and the bloated skin, A buzzing noise of bees his ears alarms: Straight issue through the sides assembling swarms.
- 54. Dark as a cloud, they make a wheeling flight, Then on a neighbouring tree, descending, light: Like a large cluster of black grapes they show, And make a large dependance from the bough. Thus have I sung of fields, and flocks, and trees, And of the waxen work of labouring bees; While mighty Cæsar, thundering from afar, Seeks on Euphrates' banks the spoils of war; With conquering arts asserts his country's cause, With arts of peace the willing people draws; On the glad earth the golden age renews, And his great father's path to heaven pursues; While I at Naples pass my peaceful days, Affecting studies of less noisy praise; And, bold through youth, beneath the beechen shade, The lays of shepherds, and their loves, have played. FOOTNOTES: [18] Note I. [19] Dr Carey reads, "through the race of life they quickly run," and has altered the punctuation to the sense thus conveyed; but I retain the reading of the first edition—though—which is clearly the meaning of Virgil. The original is as follows: Ergo ipsas quamvis angusti terminus ævi
- 55. Excipiat, neque enim plus septima ducitur æstas, At genus immortale manet, &c. [20] The first edition has grandsons. [21] By the list of errata to the first edition, we are directed to read, "lizards shunning light;" but as lizards had been mentioned in the preceding couplet, the correction itself seems erroneous. I follow Dr Carey in rejecting it. [22] Note II. [23] Dr Carey proposes to read will seem, according to the second edition, and to adapt the whole sentence to that construction; but the present tense seems more poetical, as placing the manœuvres of Proteus more vividly before Aristæus. If Dryden thought of adopting the future, he did not complete his purpose. I have therefore followed the original edition. [24] Note III. [25] This whole line is taken from the Marquis of Normanby's translation.—Dryden. [26] Dr Carey reads relent; but repent is here used in a well known scriptural sense; not as expressing remorse, but simple pity. [27] Poet-king, in Dr Carey's edition: but the original edition reads as above.
- 56. NOTES ON GEORGICS, IV. Note I. That, when the youthful prince—P. 99. My most ingenious friend, Sir Henry Shere, has observed, through a glass-hive, that the young prince of the bees, or heir presumptive of the crown, approaches the king's apartment with great reverence; and, for three successive mornings, demands permission to lead forth a colony of that year's bees. If his petition be granted, (which he seems to make by humble hummings,) the swarm arises under his conduct. If the answer be, le roi s'avisera,—that is, if the old monarch think it not convenient for the public good to part with so
- 57. many of his subjects, the next morning the prince is found dead before the threshold of the palace. Note II. Encompassed with her sea-green sisters round.—P. 112. The poet here records the names of fifteen river-nymphs; and for once I have translated them all; but, in the Æneïs, I thought not myself obliged to be so exact; for, in naming many men, who were killed by heroes, I have omitted some, which would not sound in English verse. Note III. ——Orpheus' dying prayers at length are heard.—P. 117. The Episode of Orpheus and Eurydice begins here, and contains the only machine which Virgil uses in the "Georgics." I have observed, in the epistle before the Æneïs, that our author seldom employs machines but to adorn his poem, and that the action which they seemingly perform, is really produced without them. Of this nature is the legend of the bees restored by miracle; when the receipt, which the poet gives, would do the work without one. The only beautiful machine which I remember in the modern poets, is in Ariosto, where God commands St Michael to take care, that Paris, then besieged by
- 58. the Saracens, should be succoured by Rinaldo. In order to do this, he enjoins the archangel to find Silence and Discord; the first to conduct the Christian army to relieve the town, with so much secrecy, that their march should not be discovered; the latter to enter the camp of the infidels, and there to sow dissention among the principal commanders. The heavenly messenger takes his way to an ancient monastery; not doubting there to find Silence in her primitive abode; but, instead of Silence finds Discord: the monks, being divided into factions about the choice of some new officer, were at snic and snee with their drawn knives. The satire needs no explanation. And here it may be also observed, that ambition, jealousy, and worldly interest, and point of honour, had made variance both in the cloister and the camp; and strict discipline had done the work of Silence, in conducting the Christian army to surprise the Turks.
- 59. ÆNEIS.
- 60. TO THE MOST HONOURABLE JOHN, LORD MARQUIS OF NORMANBY, EARL OF MULGRAVE,[28] &c. AND KNIGHT OF THE MOST NOBLE ORDER OF THE GARTER. A heroic poem, truly such, is undoubtedly the greatest work which the soul of man is capable to perform. The design of it is to form the mind to heroic virtue by example. It is conveyed in verse, that it may delight, while it instructs: the action of it is always one, entire, and great. The least and most trivial episodes, or under-actions, which are interwoven in it, are parts either necessary or convenient to
- 61. carry on the main design; either so necessary, that, without them, the poem must be imperfect, or so convenient, that no others can be imagined more suitable to the place in which they are. There is nothing to be left void in a firm building; even the cavities ought not to be filled with rubbish, (which is of a perishable kind, destructive to the strength,) but with brick or stone, though of less pieces, yet of the same nature, and fitted to the crannies. Even the least portions of them must be of the epic kind: all things must be grave, majestical, and sublime; nothing of a foreign nature, like the trifling novels, which Ariosto,[29] and others, have inserted in their poems; by which the reader is misled into another sort of pleasure, opposite to that which is designed in an epic poem. One raises the soul, and hardens it to virtue; the other softens it again, and unbends it into vice. One conduces to the poet's aim, the completing of his work, which he is driving on, labouring and hastening in every line; the other slackens his pace, diverts him from his way, and locks him up, like a knight-errant, in an enchanted castle, when he should be pursuing his first adventure. Statius, as Bossu has well observed, was ambitious of trying his strength with his master Virgil, as Virgil had before tried his with Homer. The Grecian gave the two Romans an example, in the games which were celebrated at the funerals of Patroclus. Virgil imitated the invention of Homer, but changed the sports. But both the Greek and Latin poet took their occasions from the subject; though, to confess the truth, they were both ornamental, or, at best, convenient parts of it, rather than of necessity arising from it. Statius, who, through his whole poem, is noted for want of conduct and judgment, instead of staying, as he might have done, for the death of Capaneus, Hippomedon, Tydeus, or some other of his seven champions, (who are heroes all alike,) or more properly for the tragical end of the two brothers, whose exequies the next successor had leisure to perform when the siege was raised, and in the interval betwixt the poet's first action and his second—went out of his way, as it were on prepense malice, to commit a fault. For he took his opportunity to kill a royal infant by
- 62. the means of a serpent, (that author of all evil,) to make way for those funeral honours which he intended for him. Now, if this innocent had been of any relation to his Thebaïs—if he had either furthered or hindered the taking of the town—the poet might have found some sorry excuse at least, for detaining the reader from the promised siege. On these terms, this Capaneus of a poet engaged his two immortal predecessors; and his success was answerable to his enterprise.[30] If this œconomy must be observed in the minutest parts of an epic poem, which, to a common reader, seem to be detached from the body, and almost independent of it; what soul, though sent into the world with great advantages of nature, cultivated with the liberal arts and sciences, conversant with histories of the dead, and enriched with observations on the living, can be sufficient to inform the whole body of so great a work? I touch here but transiently, without any strict method, on some few of those many rules of imitating nature, which Aristotle drew from Homer's Iliads and Odysseys, and which he fitted to the drama; furnishing himself also with observations from the practice of the theatre, when it flourished under Æschylus, Euripides, and Sophocles: for the original of the stage was from the epic poem. Narration, doubtless, preceded acting, and gave laws to it: what at first was told artfully, was, in process of time, represented gracefully to the sight and hearing. Those episodes of Homer, which were proper for the stage, the poets amplified each into an action; out of his limbs they formed their bodies; what he had contracted, they enlarged; out of one Hercules, were made infinity of pygmies, yet all endued with human souls; for from him, their great creator, they have each of them the divinæ particulam auræ. They flowed from him at first, and are at last resolved into him. Nor were they only animated by him, but their measure and symmetry was owing to him. His one, entire, and great action, was copied by them according to the proportions of the drama. If he finished his orb within the year, it sufficed to teach them, that their action being less, and being also less diversified with incidents, their orb, of consequence, must be circumscribed in a
- 63. less compass, which they reduced within the limits either of a natural or an artificial day; so that, as he taught them to amplify what he had shortened, by the same rule, applied the contrary way, he taught them to shorten what he had amplified. Tragedy is the miniature of human life; an epic poem is the draught at length.[31] Here, my lord, I must contract also; for, before I was aware, I was almost running into a long digression, to prove, that there is no such absolute necessity that the time of a stage action should so strictly be confined to twenty-four hours, as never to exceed them, for which Aristotle contends, and the Grecian stage has practised. Some longer space, on some occasions, I think, may be allowed, especially for the English theatre, which requires more variety of incidents than the French. Corneille himself, after long practice, was inclined to think, that the time allotted by the ancients was too short to raise and finish a great action: and better a mechanic rule were stretched or broken, than a great beauty were omitted. To raise, and afterwards to calm the passions—to purge the soul from pride, by the examples of human miseries, which befal the greatest—in few words, to expel arrogance, and introduce compassion, are the great effects of tragedy; great, I must confess, if they were altogether as true as they are pompous. But are habits to be introduced at three hours' warning? are radical diseases so suddenly removed? A mountebank may promise such a cure, but a skilful physician will not undertake it. An epic poem is not in so much haste: it works leisurely; the changes which it makes are slow; but the cure is likely to be more perfect. The effects of tragedy, as I said, are too violent to be lasting. If it be answered, that, for this reason, tragedies are often to be seen, and the dose to be repeated, this is tacitly to confess, that there is more virtue in one heroic poem, than in many tragedies. A man is humbled one day, and his pride returns the next. Chemical medicines are observed to relieve oftener than to cure: for it is the nature of spirits to make swift impressions, but not deep. Galenical decoctions, to which I may properly compare an epic poem, have more of body in them; they work by their substance and their weight. It is one reason of Aristotle's to prove, that tragedy is
- 64. the more noble, because it turns in a shorter compass; the whole action being circumscribed within the space of four-and-twenty hours. He might prove as well, that a mushroom is to be preferred before a peach, because it shoots up in the compass of a night. A chariot may be driven round the pillar in less space than a large machine, because the bulk is not so great. Is the Moon a more noble planet than Saturn, because she makes her revolution in less than thirty days, and he in little less than thirty years? Both their orbs are in proportion to their several magnitudes; and, consequently, the quickness or slowness of their motion, and the time of their circumvolutions, is no argument of the greater or less perfection. And, besides, what virtue is there in a tragedy, which is not contained in an epic poem, where pride is humbled, virtue rewarded, and vice punished; and those more amply treated, than the narrowness of the drama can admit? The shining quality of an epic hero, his magnanimity, his constancy, his patience, his piety, or whatever characteristical virtue his poet gives him, raises first our admiration. We are naturally prone to imitate what we admire; and frequent acts produce a habit. If the hero's chief quality be vicious, as, for example, the choler and obstinate desire of vengeance in Achilles, yet the moral is instructive: and, besides, we are informed in the very proposition of the Iliads, that this anger was pernicious; that it brought a thousand ills on the Grecian camp. The courage of Achilles is proposed to imitation, not his pride and disobedience to his general, nor his brutal cruelty to his dead enemy, nor the selling his body to his father.[32] We abhor these actions while we read them; and what we abhor, we never imitate. The poet only shews them, like rocks or quicksands, to be shunned. By this example, the critics have concluded, that it is not necessary the manners of the hero should be virtuous. They are poetically good, if they are of a piece; though, where a character of perfect virtue is set before us, it is more lovely; for there the whole hero is to be imitated. This is the Æneas of our author; this is that idea of perfection in an epic poem, which painters and statuaries have only in their minds, and which no hands are able to express. These are
- 65. the beauties of a god in a human body. When the picture of Achilles is drawn in tragedy, he is taken with those warts, and moles, and hard features, by those who represent him on the stage, or he is no more Achilles; for his creator, Homer, has so described him. Yet even thus he appears a perfect hero, though an imperfect character of virtue. Horace paints him after Homer, and delivers him to be copied on the stage with all those imperfections.[33] Therefore they are either not faults in a heroic poem, or faults common to the drama. After all, on the whole merits of the cause, it must be acknowledged, that the epic poem is more for the manners, and tragedy for the passions. The passions, as I have said, are violent; and acute distempers require medicines of a strong and speedy operation. Ill habits of the mind are like chronical diseases, to be corrected by degrees, and cured by alteratives; wherein, though purges are sometimes necessary, yet diet, good air, and moderate exercise, have the greatest part. The matter being thus stated, it will appear, that both sorts of poetry are of use for their proper ends. The stage is more active; the epic poem works at greater leisure, yet is active too, when need requires; for dialogue is imitated by the drama, from the more active parts of it. One puts off a fit, like the quinquina, and relieves us only for a time; the other roots out the distemper, and gives a healthful habit. The sun enlightens and cheers us, dispels fogs, and warms the ground with his daily beams; but the corn is sowed, increases, is ripened, and is reaped for use in process of time, and in its proper season. I proceed, from the greatness of the action, to the dignity of the actors; I mean to the persons employed in both poems. There likewise tragedy will be seen to borrow from the epopee; and that which borrows is always of less dignity, because it has not of its own. A subject, it is true, may lend to his sovereign; but the act of borrowing makes the king inferior, because he wants, and the subject supplies. And suppose the persons of the drama wholly fabulous, or of the poet's invention, yet heroic poetry gave him the examples of that invention, because it was first, and Homer the common father of the stage. I know not of any one advantage which tragedy can boast above heroic poetry, but that it
- 66. is represented to the view, as well as read, and instructs in the closet, as well as on the theatre. This is an uncontended excellence, and a chief branch of its prerogative; yet I may be allowed to say, without partiality, that herein the actors share the poet's praise. Your lordship knows some modern tragedies which are beautiful on the stage, and yet I am confident you would not read them. "Tryphon the stationer"[34] complains, they are seldom asked for in his shop. The poet who flourished in the scene, is damned in the ruelle;[35] nay more, he is not esteemed a good poet by those, who see and hear his extravagancies with delight. They are a sort of stately fustian, and lofty childishness. Nothing but nature can give a sincere pleasure; where that is not imitated, it is grotesque painting; "the fine woman ends in a fishes tail." I might also add, that many things, which not only please, but are real beauties in the reading, would appear absurd upon the stage; and those not only the speciosa miracula, as Horace calls them, of transformations, of Scylla, Antiphates, and the Læstrygons, which cannot be represented even in operas; but the prowess of Achilles or Æneas would appear ridiculous in our dwarf-heroes of the theatre. We can believe they routed armies, in Homer or in Virgil; but ne Hercules contra duos in the drama. I forbear to instance in many things, which the stage cannot, or ought not to represent; for I have said already more than I intended on this subject, and should fear it might be turned against me, that I plead for the pre-eminence of epic poetry, because I have taken some pains in translating Virgil, if this were the first time that I had delivered my opinion in this dispute. But I have more than once already maintained the rights of my two masters against their rivals of the scene,[36] even while I wrote tragedies myself, and had no thoughts of this present undertaking. I submit my opinion to your judgement, who are better qualified than any man I know, to decide this controversy. You come, my lord, instructed in the cause, and needed not that I should open it. Your "Essay of Poetry,"[37] which was published without a name, and of which I was not honoured with the confidence, I read over
- 67. and over with much delight, and as much instruction, and, without flattering you, or making myself more moral than I am—not without some envy. I was loth to be informed how an epic poem should be written, or how a tragedy should be contrived and managed, in better verse, and with more judgment, than I could teach others. A native of Parnassus, and bred up in the studies of its fundamental laws, may receive new lights from his contemporaries; but it is a grudging kind of praise which he gives his benefactors. He is more obliged, than he is willing to acknowledge; there is a tincture of malice in his commendations; for where I own I am taught, I confess my want of knowledge. A judge upon the bench may, out of good nature, or at least interest, encourage the pleadings of a puny counsellor; but he does not willingly commend his brother serjeant at the bar, especially when he controuls his law, and exposes that ignorance which is made sacred by his place. I gave the unknown author his due commendation, I must confess; but who can answer for me, and for the rest of the poets who heard me read the poem, whether we should not have been better pleased to have seen our own names at the bottom of the title-page? Perhaps we commended it the more, that we might seem to be above the censure. We are naturally displeased with an unknown critic, as the ladies are with a lampooner, because we are bitten in the dark, and know not where to fasten our revenge. But great excellencies will work their way through all sorts of opposition. I applauded rather out of decency, than affection; and was ambitious, as some yet can witness, to be acquainted with a man, with whom I had the honour to converse, and that almost daily, for so many years together. Heaven knows, if I have heartily forgiven you this deceit. You extorted a praise, which I should willingly have given, had I known you. Nothing had been more easy, than to commend a patron of a long standing. The world would join with me, if the encomiums were just; and, if unjust, would excuse a grateful flatterer. But to come anonymous upon me, and force me to commend you against my interest, was not altogether so fair, give me leave to say, as it was politic; for, by concealing your quality, you might clearly understand how your work succeeded, and that the general approbation was given to your
- 68. merit, not your titles. Thus, like Apelles, you stood unseen behind your own Venus, and received the praises of the passing multitude; the work was commended, not the author; and I doubt not, this was one of the most pleasing adventures of your life.[38] I have detained your lordship longer than I intended in this dispute of preference betwixt the epic poem and the drama, and yet have not formally answered any of the arguments which are brought by Aristotle on the other side, and set in the fairest light by Dacier. But I suppose, without looking on the book, I may have touched on some of the objections; for, in this address to your lordship, I design not a treatise of heroic poetry, but write in a loose epistolary way, somewhat tending to that subject, after the example of Horace, in his First Epistle of the Second Book to Augustus Cæsar, and in that to the Piso's, which we call his "Art of Poetry;" in both of which he observes no method that I can trace, whatever Scaliger the father, or Heinsius, may have seen, or rather think they had seen. I have taken up, laid down, and resumed as often as I pleased, the same subject; and this loose proceeding I shall use through all this prefatory dedication. Yet all this while I have been sailing with some side-wind or other toward the point I proposed in the beginning,— the greatness and excellency of a heroic poem, with some of the difficulties which attend that work. The comparison, therefore, which I made betwixt the epopee and the tragedy, was not altogether a digression; for it is concluded on all hands, that they are both the master-pieces of human wit. In the mean time, I may be bold to draw this corollary from what has been already said, that the file of heroic poets is very short; all are not such who have assumed that lofty title in ancient or modern ages, or have been so esteemed by their partial and ignorant admirers. There have been but one great Ilias, and one Æneïs, in so many ages. The next, but the next with a long interval betwixt, was the Jerusalem;[39]
- 69. I mean not so much in distance of time, as in excellency. After these three are entered, some lord-chamberlain should be appointed, some critic of authority should be set before the door, to keep out a crowd of little poets, who press for admission, and are not of quality. Mævius would be deafening your lordship's ears with his
- 70. Fortunam Priami cantabo, et nobile bellum— mere fustian, as Horace would tell you from behind, without pressing forward, and more smoke than fire. Pulci, Boiardo, and Ariosto,[40] would cry out, "make room for the Italian poets, the descendants of Virgil in a right line:" father Le Moine, with his saint Louis; and Scudery with his Alaric, for a godly king and a Gothic conqueror; and Chapelain would take it ill that his Maid should be refused a place with Helen and Lavinia.[41] Spencer[42] has a better plea for his "Fairy Queen," had his action been finished, or had been one; and Milton, if the devil had not been his hero, instead of Adam; if the giant had not foiled the knight, and driven him out of his strong- hold, to wander through the world with his lady errant; and if there had not been more machining persons than human in his poem. After these, the rest of our English poets shall not be mentioned. I have that honour for them which I ought to have; but, if they are worthies, they are not to be ranked amongst the three whom I have named, and who are established in their reputation. Before I quitted the comparison betwixt epic poetry and tragedy, I should have acquainted my judge with one advantage of the former over the latter, which I now casually remember out of the preface of Ségrais before his translation of the Æneïs, or out of Bossu, no matter which: "The style of the heroic poem is, and ought to be, more lofty than that of the drama." The critic is certainly in the right, for the reason already urged; the work of tragedy is on the passions, and in a dialogue; both of them abhor strong metaphors, in which the epopee delights. A poet cannot speak too plainly on the stage: for volat irrevocabile verbum; the sense is lost, if it be not taken flying. But what we read alone, we have leisure to digest; there an author may beautify his sense by the boldness of his expression, which if we understand not fully at the first, we may dwell upon it, till we find the secret force and excellence. That which cures the manners by alterative physic, as I said before, must proceed by insensible degrees; but that which purges the passions, must do its
- 71. business all at once, or wholly fail of its effect, at least in the present operation, and without repeated doses. We must beat the iron while it is hot, but we may polish it at leisure. Thus, my lord, you pay the fine of my forgetfulness; and yet the merits of both causes are where they were, and undecided, till you declare whether it be more for the benefit of mankind to have their manners in general corrected, or their pride and hard-heartedness removed. I must now come closer to my present business, and not think of making more invasive wars abroad, when, like Hannibal, I am called back to the defence of my own country. Virgil is attacked by many enemies; he has a whole confederacy against him; and I must endeavour to defend him as well as I am able. But their principal objections being against his moral, the duration or length of time taken up in the action of the poem, and what they have to urge against the manners of his hero; I shall omit the rest as mere cavils of grammarians; at the worst, but casual slips of a great man's pen, or inconsiderable faults of an admirable poem, which the author had not leisure to review before his death. Macrobius has answered what the ancients could urge against him; and some things I have lately read in Tanneguy le Fèvre, Valois, and another whom I name not, which are scarce worth answering. They begin with the moral of his poem, which I have elsewhere confessed, and still must own, not to be so noble as that of Homer.[43] But let both be fairly stated; and, without contradicting my first opinion, I can shew, that Virgil's was as useful to the Romans of his age, as Homer's was to the Grecians of his, in what time soever he may be supposed to have lived and flourished. Homer's moral was to urge the necessity of union, and of a good understanding betwixt confederate states and princes engaged in a war with a mighty monarch; as also of discipline in an army, and obedience in the several chiefs to the supreme commander of the joint forces. To inculcate this, he sets forth the ruinous effects of discord in the camp of those allies, occasioned by the quarrel betwixt the general and one of the next in office under him. Agamemnon gives the provocation, and Achilles resents the injury. Both parties are faulty in the quarrel; and accordingly they
- 72. Welcome to Our Bookstore - The Ultimate Destination for Book Lovers Are you passionate about books and eager to explore new worlds of knowledge? At our website, we offer a vast collection of books that cater to every interest and age group. From classic literature to specialized publications, self-help books, and children’s stories, we have it all! Each book is a gateway to new adventures, helping you expand your knowledge and nourish your soul Experience Convenient and Enjoyable Book Shopping Our website is more than just an online bookstore—it’s a bridge connecting readers to the timeless values of culture and wisdom. With a sleek and user-friendly interface and a smart search system, you can find your favorite books quickly and easily. Enjoy special promotions, fast home delivery, and a seamless shopping experience that saves you time and enhances your love for reading. Let us accompany you on the journey of exploring knowledge and personal growth! ebookgate.com