Where do we go from here?

by guest blogger Ken.

Howdy all! I hope everyone is hard at work in the new year, bringing space ever closer to Earth. Keep up the good work at Politico!

The last couple of weeks have certainly been eventful. Not just in the financial markets, where I'm getting a front row view of the action, but also in things space, where things also seem to be heating up. I've been piecing together the following for a few days, so please excuse any lapses in continuity.

Re: the financial markets, all I can really tell you is that all of the kabuki dance going on in D.C. and on Wall Street is not for your benefit, you little person of insignificant wealth, but rather to appease and placate the gods of Credit Default Swaps (CDS), whose corporate affect in the world is far, far greater than the mere corporeal existence of you or I. That was the Faustian bargain in granting companies "corp"-orate status - they have equal "status" with you in the courts, but they can exercise far more economic clout than the vast majority of individuals can ("classes" of individuals at least have a fighting chance) - they can afford far, far more lawyering than you or I. When companies have difficulty servicing their debt, that raises the odds of a default, which angers the gods of CDS, and they induce volatility in the market and require that more capital pay attention to them. By lowering rates, companies whose debt is little more than a promise can at least keep that promise for a little while longer. I saw an interesting chart recently that tracked the decline in LIBOR with the decline in Fed Funds, quite a parallel, given that LIBOR is supposed to be driven by petrodollars cached in Europe, and effectively decoupled from U.S. events. Everyone borrows variable rate based off LIBOR these days, then swaps into fixed rate. The risk there, as with CDS, is the ability of the counterparty to make good on their part of the deal. That's what has everyone spooked. Well, that and the ability of companies to keep servicing their debts. The problem with making so much money so freely available is that it's going to make it easier for folks who didn't engorge the first time around to figure "What the heck? Am I going to be the only one left to clean up this mess? Forget that! Party time!"

Good ol' Moral Hazard. Don't get me started on Fannie Mae and Freddie Mac. Of course, we've been pumping money into the economy pretty freely since about 1993. This is not a recent problem, but dates back to the early days of the Baby Boomers really taking the reins of control in this country. These problems date back to the cultural yuppie and fern bar days of the 1980s, with roots going even further back. There needs to be some fundamental shift in the way this nation conducts its affairs [though not to fundamentalism, good heavens no! Just a greater portrayal of, and admiration for, honesty and moral values]. And there's only one group of folks in this country that have the demographic heft to make that happen. I'll leave the rest of that logic puzzle to the reader.

Don't get me wrong. I'm a capitalist and firm believer in the benefits of trade, and a rather conservative one at that. An old country banker who's a bit worldly wise, perhaps too much so. I started in finance in 1989 with an internship at Shearson Lehman Brothers (not in NYC) while at college. My undergrad degree's in International Business & Economics. I started in banking in January 1993, in NYC in December of that year, and I've seen a lot since then. I worked the Wall Street Desk at BNP during the last four years of that decade. I am a globalist and dedicated to trade. Because free nations that trade freely with one another tend not to get into wars. That's a good thing, as war is bad for business (unless you can make it happen elsewhere and are supplying the armaments). My analytical skills are a global commodity, and I'm one of those rare folks who can actually understand the entirety of most derivative trades, and since I am an American citizen by birth it is my birthright that I may pursue my career anywhere an the world I can do so. That's an option that far more folks on this globe don't have, which is a shame. Because that stifles the free interchange of cultures and ideas, thereby limiting the pool of 'best practices' that one can be exposed to and thereby adopt in one's life.

Very little of which I've seen over the last several years. During the mortgage underwriting project I would often throw my hands up in the air and proclaim that we're becoming Nigeria. I saw the current rot in a pool of mortgages dating back to 2000/01. The best part is the prepayment penalty, which IIRC was about three years in tenor. Many of the ARMs had a reset after two years. This provided an incentive to refinance before the rate ratcheted up , but golly that happened to lie within the prepayment period, whereby if more than 20% of the loan was paid off in any one year, then a penalty of X% of the mortgage went to the lender to offset the future flow of interest payments which they used to expect before everything was packed up and shipped off to the warehouse for repackaging as collateralized debt obligations. Most of those penalties were rolled into the refi-ed mortgage, so most folks didn't get as much out of the cash-out refis as they thought they would, especially after all of the non-current and nearly non-current credit card and installment debt were rolled in as well. I saw it time and again. I also saw things like faked signatures, one app had 5 different SSNs in it, goofy appraisals, suspicious fax traffic, doctored paystubs and W-2s, defaults after <3 months, money laundering, the works. The game is that the financiers saw an endless stream of fee income from the prepayment penalties, which would be automatically triggered in most refis. Read the mortgage contract. I was amazed when it was pointed out to me that defaulting on a mortgage within the prepayment penalty period automatically triggers the fee, to be added to (actually given priority in payment streams) any amounts already due and owing under the default.

Believe you me, when I do buy a house (and I am not in any hurry. I have no intention of overpaying for crap), I am going to go over those documents with a fine-toothed comb. I'm not terribly fond of the modern culture of contracts of "I win and here's how you're going to make it happen for me", which is why, for example, I've been using a prepaid cell phone for years, pre-paid tolltag, I don't do automatic bill pay of anything other than my month-to-month wireless access, and my car is paid off (with about a third of the extended warranty to go), and for my birthday this week I paid off the last bit of debt. I don't owe anyone anything (except rent), and that's a pretty sweet feeling.

So I'm not terribly worried, but there sure are a lot of folks who should be, because they ain't been livin' right like proper Americans and all the rest of us are going to have to pay the price for it. So that's work. Hopefully now you've got a better idea of why I don't often talk about it.

On the space side, there has been a lot of interesting commentary going around, from Dr. Weinberg's and Dr. Griffin's comments in the space astronomy field, to the Planetary Society and Dr. Griffin's comments regarding Constellation and VSE, and even Jon's comments on it being about the journey, not the destination (amen), as well as comments from the STA meeting. I think it's great that space is getting more play in the press, even if it still has a ways to go quality-wise. An example is the Popular Mechanics article "Dissent Grows as Scientists Oppose NASA's New Moon Mission", which describes the circumstances of the announcement by the Planetary Society of a mid-February conference to discuss just how exactly it is that we're going to get to Mars. Rather than via the Moon, which can act as a springboard to leverage commercial and peaceful military involvement and develop cislunar space, perhaps we should be visiting asteroids, because they're really similar to Phobos and Deimos, the 'moons' of Mars. Of course, these are the same folks who think that the Lagrange points start at the Sun-Earth L-1 and L-2, rather than the much closer and easier to practice at Earth-Moon L-1, which isn't even as far away as the Moon!

Dr.Friedman's comments regarding the mentioning of 'humans' and 'Mars' together at NASA getting a slap is laughable given that mentioning 'humans' and 'Moon' together would have been grounds for dismissal (okay, figuratively). The Mars network got firmly established during the late-90s with Mars as THE and ONLY goal of consequence, and the Moon was last on pretty much everyone's list of objectives - though there did remain a few die-hard Moonatics carrying the torch in the sad and lonely back offices of NASA.

Then again, it is a bit of hubris for Dr. Griffin to state that the debate about the VSE was had in 2003, 2004, and 2005, and it was fulsome. I seem to recall the debate tapering off quite sharply after the May 2005 address to Congress, when NASA's mission was changed from designing a Crew Exploration Vehicle (CEV) to designing a National Launch System. Of course that's going to eat your lunch, budget-wise.

I noted that some folks had stopped by an old post here at Selenian Boondocks, entitled 'We're on a Road to Nowhere' and dating to mid-December 2005. So I stopped by and re-read it for the first time in ages (and discovered that sometimes I scare myself). It also notes the decrease in public debate that accompanied Dr. Griffin's ascension to Administratorship the end of 2004.

Dr. Friedman notes two basic criticisms of the Moon:
1) 'the lack of public resonance that the lunar base has', and
2) 'a lunar base might not be practical', indicating it would 'require' a lunar supply of water ice and is 'too close' to Earth for a practice Mars mission.

Weak. Really, really weak.
1) The lack of resonance is with NASA repeating an accomplishment of over 40 years ago slower, costlier and almost as good. There was no upswell of support in the space community for the NASA base at Shackleton crater because everone figured it was going to be around there anyway, and no one really believes that the Constellation throw-away-the-pieces architecture is a sustainable way to do a Moon base. And why is the incoming flight path over the ever-dark crater? [NB: Dr. Spudis tells me that's a notional flight path {a stupid one if you ask me. K}, and the flight path can be high up and then straight down to the pad] It's probably okay to do so -after- the crater has been thoroughly investigated, but it kind of seems counterintuitive to spew rocket exhaust into your field of examination. Plus, NASA's choice also showed that it was not going to be commercial in any way (other than 'We'll buy your fastner for our spacecraft, but you can't come along'). YOu need energy for operations to run a business, and for that you want to go to the high ground at the Lunar South Pole, the Leibnitz Plateau/Mont Malapert. You're not going to get as much of the moderate ambient lighting/temperature effect as lower down at Shackleton, but you will have your solar arrays in the Sun most of the time on the high ground, and you can always hop down to lower terrain (selenain?) as the need arises, such as to investigate the ever-dark properties of parts of Shackleton. The high ground is also where you want to emplace any Solar Power Towers that will peek over the foreshortened Lunar horizon and get constant sunlight to power the LOX works, SWIEXtract (whoa, I'm claiming copyright on that one!), Lunar base functions, and so on. Power towers also could provide for emplacement of lightpipes, solar mirrors, and bulk power transmitters. You need energy to do anything; it's a great business! So is building them.

2) Lunar bases could be supplied by asteroidal water, and that's the beauty of an EML-1 station - it's up out of the gravity wells of the Earth and Moon, making it a convenient staging point for asteroid expeditions, using Bigelow balloons and other components, as well as trips to and from the Moon, GEO, Sun-Mars L-1 (a great! staging point for all kinds of Mars and Phobos and Deimos missions), Ceres, and points beyond. The science community's beloved James Webb Space Telescope, stationed at Sun-Earth L-2, could be brought in to EML-1 for servicing and sent back out to SEL-2 on a low-energy trajectory, meaning maximum science payload and minimum fuel.

I personally find Dr. Friedman's last contention, that the Moon's too close, to be plain silly. I'm not buying that one, nor am I buying any possible business case for Mars. The supply line is too long for anything but the most hyper-precious goods. Water doesn't make sense, as that can come from asteroids and I'd much rather be mining them out of existence than poking around on Mars hoping to find a fossil. I'd much rather do that on a comet in hopes of finding evidence of pre-Solar life. Now that would be cool.

All of which is academic, if we can't lick the transport problem. My bet's on an EELV-derived architecture, though I'm not wedded to the concept. I do regret that more wasn't done with the industry studies conducted under O'Keefe, as there were a lot of really good ideas that came out of them. I'm not entirely sold on the Direct architecture, but I think I'm just biased against anything shuttle-derived because I'm so disappointed in all of the external tanks we've thrown away instead of putting to good use on orbit. I still don't see ESAS as sustainable over the near or long term, as there is zero commercial application for it, I can't really see a military application for it (but I don't ponder such things), and it's a sledgehammer solution for an instruction that asked for the use of a hammer. At least the initial instruction, the VSE Really, go read it.

The intial outline merely states:

"C. Space Transportation Capabilities Supporting Exploration
-Develop a new crew exploration vehicle to provide crew transportation for missions beyond low Earth orbit
-Separate to the maximum practical extent crew from cargo transportation to the ISS and for launching exploration missions beyond low Earth orbit"

Looking to the relevant section of the document, 'Exploration Building Blocks' we see that:

"NASA will initiate Project Constellation to develop a new Crew Exploration Vehicle for future crew transport. This vehicle will be developed in stages, with the first automated test flight in 2008 [snicker], more advanced test flights soon thereafter, and a fully operational capability no later than 2014. The design of the CEV will be driven by the needs of future human exploration missions described in this document...NASA does not plan to develop new launch vehicle capabilities except where critical NASA needs - such as heavy lift - are not met by commercial or military systems... [emphasis added] Such a vehicle could be derived from elements of the Space Shuttle, existing commercial launch vehicles, or new designs....NASA plans to invest in a number of new approaches to exploration, such as robotic networks, modular systems, pre-positioned propellants, advanced power and propulsion, and in-space assembly, that could enable these kinds of vehicles..."

Seriously, anyone who actually sits down and reads the Vision for Space Exploration will be amazed at how great a strategy framework it is. It would be nice if reporters would take the time to read the document before commenting on it or its intent.

We were given a great opportunity. The folks who crafted the VSE did a great job and I like it, even if it does have Mars in it. ;-)

Which leaves me with little doubt that something's a little stinky with this whole ESAS thing. Not that I'm a paranoid conspiracy freak, I've just looked at the details and that's what I've read from the available data, which I'll admit is insufficient to draw any conclusions. Which is why there still is doubt.

Part of that thinking comes from how far NASA has drifted from the spirit of VSE in focusing in on designing the NEW US Transportation system. That label comes from the Lunar Architecture Team presentation in December 2006 (slide 3). Even though the VSE says NASA does not plan to develop new launch vehicle capabilities. By making transportation of humans to space a "critical NASA need", you get to sidestep that little roadbock. By not doing anything about that little end run, Congress and the White House are implicitly endorsing the little change in plans, from focusing on exploration beyond LEO to building the US Transportation system.

Which is odd, given that Americans in general don't think of NASA as a launch vehicle agency. The numbers were in the study NASA commissioned in Feb/Mar of, IIRC, 2007 to help lay the groundwork for an update in NASA's communication strategy, at which Keith Cowing over at NASAWatch took a few swipes, and I did a couple of posts on it (NASA's New Plan for Talking At Us, Pts I & II). As I noted there, only about 14% of folks that took part in the various sessions saw it as NASA's job to launch things into space. The VSE said you can look at heavy lift, but otherwise look to the private sector or the military for your launch needs for the CEV. If NASA has wandered astray, it's because those with the authority to make that not happen have not exercised their authority, or have desired the current state of affairs.

My personal feelings are also that NASA should not be in the launch vehicle business. I don't think it's the right job for NASA, and their best bet is to buy American for the ride to orbit. Beyond Low Earth Orbit is NASA's job for the moment. First back to the Moon, not only to answer a lot of questions that the planetary scientists have, but (hopefully) also to establish a permanent means of travelling in the space between the Earth and Moon as a result. (Which is why I still think my Caplet architecture is the best bet, and modularity in design is called for in the VSE) An EML-1 station is a pretty good intermediate step that can be reached quickly, and really shouldn't be considered any less ridiculous than a Sun-Earth L-2 station that this workgroup is going to look at. I still don't see why the fact that the JWST is going to be at SEL-2 makes it a smart decision to put our next space station there.

The argument is driven mainly by the fact that SEL-2 is in fact the lowest delta-V launch point in near-Earth space to points beyond, without question. Mars, the Asteroid Belt, the Moons of Jupiter (now that's going to be a great adventure!), and beyond to the Kuiper Belt and Oort Cloud, maybe even skimming inflatable Murphy Bags through the atmospheres of Nepture and Uranus for their treasures. You want He3 in abundance? That's where you need to look.

But it's not all about trans-Terran space. We Absolutely Must begin looking Solward for objects because I for one am sick and tired of the crazy hype that surrounds every blindsider that passes near us (such 2007 TU24 or whatever) as it pops out beyond Earth's orbit for a bit. The problem is that looking in towards the Sun is a bit...problematic for most terrestrial scopes. The atmosphere washes out any resolution you might hope to achieve. Radar's different, but let's not go there right now. Beyond the atmosphere you still have to deal with all the stuff we're cluttering up space with out to GEO and the graveyard orbits.

The solution is to go a bit further out to EML-1, the top of the gravitational hill between the Earth and our Moon. Instruments will get sunward view a fair amount of the time, and on a regular basis. I'm not up to the math of calculating the view solutions, I'm just trying to picture a cone from EML-1 to the rim of the Moon, and to what extent the 5.1 degree inclination of the Moon's orbit to the plane of the ecliptic allows visibility Solward during the New Moon. (No, I'm not going to give you the distance to EML-1, you have to look it up, and remember that while the average distance to the Moon is 384,404km, that can vary between 356,410km and 406,697km between perigee and apogee, and the distance will vary proportionally)

So a really good dry run mission for a future CEV is to go put a set of instruments in a halo orbit around EML-1. The next CEV test can upgrade the suite of instruments. You're looking out for big rocks from space, and you're putting your new CEV through its paces. Eventually you throw some fuel tanks into a loop around EML-1 and the next CEV that passes through is going to the Moon. And thanks to the ability to top off the tanks at the top of the energy hill, they've been able to squeeze in a great new mobile rock lab. Personally I'd name mine Selenological Survey for Exploration and Xploitation of the Moon for mining, or SSEX Mm, but don't let the kids see that one. Maybe Selenological Investigation for New kNowledge, or SINN. The use of the domain extension .sin has proposed for servers set up on the Moon to relay-mails. It probably helps to know that the Sumerians had a great temple in Ur dedicated to the Moon god Nanna, or Suen...later contracted to Sin, still the name for the Moon today among Syrians and Kurds (from 'The Moon: Myth and Image'). Though my copy of The Moon Book says that Peruvian Indians and Ethiopians use Sin, while the Kurds use meh or hiv.

So the first NASA folks aren't just dropping off a Moon lab (and maybe returning it to L-1 as well for a sortie to a different location), but they're helping to put in place an architecture that others can use. L-1 can be a staging point to not only the Moon, but also GEO, L-4 & L-5, the asteroids, Mars, and beyond. Besides which, JWST could be brought back to EML-1 from SEL-1 on a low energy trajectory along the warp between SEL-2 and EML-1, which is the on-ramp to the InterPlanetary Superhighways (IPS), serviced by the guys at EML-1, and then sent back out on station at SEL-2 all shiny and pretty.

The marginal delta-V advantage of SEL-2 for launches does not offset the fact that it is a lousy place from which to launch missions to the Moon and GEO and HEO and MEO and LEO. These are places where we have billions of dollars worth of valuable assets. That makes them rich in economic opportunity. Too many in the space community don't think like business folks. Every time some academic or scientist goes in the media and says that going to the Moon is going to cost something like hundreds of billions of dollars, it's because they can only imagine such things occuring within the framework of what NASA can provide (and naturally would be competing with their projects...). Thankfully that's changing, but there's still an awful lot of blowhards out there unchallenged in their decrying of things about which they know little. Which is the fault of everyone, as we really haven't been paying much attention to the Moon over the last nearly forty years, and haven't needed much of a human knowledge base to carry on the NASA mission. That's about two generations, which means that we're woefully deficient in people, especially young people, who are really knowledgeable about the Moon.


So while all of that Sturm und Drang is going on I'm just quietly puttering away on the Lunar Library. I've got a few non-fiction reviews up over at the Out of the Cradle homepage, as well as the Bicentilune, which links to reviews of over 200 stories of adventure on our Moon. I'm anxiously awaiting a few new things, like the anime Freedom 3, the manga Earthlight 3, and a new old Choose-Your-Own-Adventure book: "Moonquest". Supposedly that last one was published on January 1st, and I popped down to the local B&N to grab a copy on the 2nd, which I had to prepay for before they would even move it from the warehouse to the store. Still waiting...

I'm probably going to head down to the Lunar and Planetary Conference in Houston in March. I'm especially curious about the outreach and education session on Sunday, as well as the Previews of Upcoming Publications exhibit. Maybe I can talk my way into a few review copies for the Lunar Library. I did submit an abstract to give a ten minute overview of the Lunar Library, with five minutes for questions while the next guy sets up, but after the ISU experience I'm not holding my breath.

I also just got a mailer about an upcoming Lunar science conference, the Lunar Science Conference. July 22-24 at NASA Ames Research Center at Moffett Field, Cali. According to the e-flyer, "The conference will review the state of knowledge of, and opportunities for, science:

-Of the Moon...
-On the Moon...
-From the Moon...

No doubt the recent NRC report on the Scientific Context for the Exploration of the Moon will be required reading. If not it should be as it is a good report that's worth a read through, and is structured along the three elements noted above. I think I talked about it back in the day.

This week is a somber one, and like Rand I share a birthday in this darkest part of the year for the U.S. Space Program. We should honor those brave Americans who took one of the most dangerous jobs around, flying in machines built of the cheapest materials by the lowest bidder. Actually, that's a bit unfair since the performance requirements of the space flight field are such that many of the materials developed (or capitalized) for use in the space field have found broad application elsewhere. Nevertheless, astronaut is one of the more dangerous jobs around, and these men and women face that danger with courage. It has been said that exploring new frontiers is another name for finding new and gruesome ways to die. This fact will not change with a thousand new launch vehicles and five 9s of performance reliability, and there are many particularly gruesome ways to die in space.

The question is not "should people run the risk of dying to go out into space?", but rather "how many people will have to die to advance civilization into the next frontier?" Whether we should penetrate into that frontier can only be answered in the affirmative; it is what human civilization has always done, and will always do. As to how many shall die, the question is unanswerable, as we're still evolving our civilizations here on Earth and untold millions die in misery while we do so. People die every day building the highways, bridges and tunnels of our American civilization. Examples abound.

Four hundred years ago, these men and women would have been out in the vast wilderness of North America, charting the best path for those to follow. Many would have been killed and/or eaten by bears or cougars or wolverines, someting horrific to those of the old continent [Yes, I am writing from a Eurocentric Classical Western Civ perspective]. Yet we did not stop our advance. We learned and accelerated. This can be no less for our next frontier. The space frontier. A place of wealth and abundance yet awaiting the application of the human spirit.

Let's get cislunar space licked so we can start sending out the professionals along well known paths. There's good reason to service GEO assets, and there's good reason to put solar power satellite assets in GEO. There's good reason to return to the Moon and much industry possible there. We can deploy a Solar system wide network of scientific probes along the IPS and bring them home for servicing & refueling. No more disposable billion dollar spacecraft pitched into the void to work for a short time before being lost to the aether. Orbital instruments that are looking Solward for asteroids and out-of-the-ecliptic for comets, not Starward for planets around other stars. Fuel depots, service stations, freeflyers, comm centers, electrical utilities, metals foundries, broadcast platforms, PV factories, robot garages. (all of which the tourists would be delighted to see, I'm sure)

From these will develop tomorrow's technologies, the products of which we'll be more than happy to sell to everyone. This is why I am interested in the Moon. There is business to be done in cislunar space if we can get over the transport hurdle. Business that can make this nation stronger in the face of the challenge of this century - energy supply that doesn't foul the biosphere. We can expand our economic sphere of influence from GEO out to EML1 and the Moon. Doing so will provide a platform for not only going further, but also providing a support role for Earth, the two most oft quoted being PV cells and structural elements for space-base Solar power in GEO (or on the Moon {or both}) and Helium-3, which has fusion and medical applications.

If we start at SEL-1 we forego all of that to go to...Mars. To look for water/life. I'm hoping that someone from the Mars side is going to start talking about the potential medical benefits of understanding alien DNA, because I really don't see a whole lot of export possibilities that are worth the six month supply line back to cislunar space. I've heard Deuterium mentioned, but I'm thinking we're not really hurting for deuterium back here on Earth. Maybe we could use Martian resources to build massive Solar arrays at SML4 and SML5 and beam the power back to Earth? (I shudder when I think of the focusing units on those puppies) Or ship the elements back to GEO?

I'm just not seeing it, and so with all due respect to the learned gentlemen and gentlewomen who will meet in February to discuss an SEL1 approach for the push to Mars, I would contend that they are pursuing the wrong goals.

It is not all about Mars. Mars is only one destination amongst many, and not even necessarily the best (moons of Jupiter gets that one in my book) or most important. Everyone knows where I stand on that last one.

Ken
[feeling a little uppity 'cause it's my birthday this week. I pay my taxes, I got a right to state my mind. And Jon lets me post my thoughts from time to time]

Giuliani and Space

While I am glad that it's looking less and less likely that he'll ever sit behind the desk in the Oval Office, I do have to commend Mr Giuliani for specifically bringing up COTS and commercial space transportation today in his op-ed article on FloridaToday.com:

We will maintain America's technological advantage in space. We will send Americans back to the moon and onto the next great frontier in human space exploration: Mars.

We will support the Commercial Orbital Transportation Systems Program to stimulate important private entrepreneurial efforts in spaceflight.

We will expand private-sector access to Cape Canaveral launch pads. To help prepare astronauts for longer stays in space, we will fund the Space Life Sciences Lab.

While a decent chunk of his article amounts to little more than your typical political pandering, his statement about COTS isn't your typical pandering--it isn't really likely going to get him anywhere near as many votes in Florida as promising a couple billion to expedite Ares-I.

I just wish a candidate that I could stand voting for would say something like that...

Discussion of Dr. Griffin's STA Comments on ESAS

I've had several people in several places ask me if I was going to do a point-by-point rebuttal of Mike Griffin's comments to the STA this week (for reference the text of his comments is available here). While I don't have the time to go into every single disagreement I have with what he said, I think there are a couple of key points I would like to point out. In other words, I've come to discuss Griffin, not to Fisk him.

Missing the Vision

Dr Griffin starts his defense of the chosen Constellation architecture by framing it "in the
context of policy and law that dictate NASA’s missions." As he said on page 2:

Any system architecture must be evaluated first against the tasks which it is
supposed to accomplish. Only afterwards can we consider whether it accomplishes
them efficiently, or presents other advantages which distinguish it from competing
choices.

He then went on to discuss President Bush's original announcement of the Vision for Space Exploration, and the NASA Authorization Act of 2005. I agree that it is important to make sure you know up-front what yardstick your program is going to be measured by. However, I think one thing becomes quickly obvious as you read Dr Griffin's quotes from those documents--he entirely focuses on the technical implementation details, and never once mentions the actual policy goals!

Quoting from "A Renewed Spirit of Discovery: The President’s Vision for U.S. Space Exploration":

Goal and Objectives
The fundamental goal of this vision is to advance U.S. scientific, security, and economic interests through a robust space exploration program.

These goals are the yardstick by which any VSE implementation needs to be judged. The rest of the technical details of how the space exploration program is carried out needs to be viewed in the light of these three areas of US interests. It doesn't matter if a proposed implementation hits all of the other technical details, if it doesn't really further US scientific, security, and economic interests, it isn't really compliant with the goals of the president's Vision.

Going into a little more detail on these goals, the Renewed Spirit of Discovery document continues (emphasis mine):

In support of this goal, the United States will:
• Implement a sustained and affordable human and robotic program to explore the solar system and beyond;
• Extend human presence across the solar system, starting with a human return to the Moon by the year 2020, in preparation for human exploration of Mars and other destinations;
• Develop the innovative technologies, knowledge, and infrastructures both to explore and to support decisions about the destinations for human exploration; and
• Promote international and commercial participation in exploration to further U.S. scientific, security, and economic interests.

Once again, all of the specific technical details like the CEV, retiring Shuttle in 2010, etc. are all pursuant to these goals.

Lastly, the NASA Authorization Act of 2005 (available here) states, once again with my emphasis:

The Administrator shall establish a program to develop a sustained human presence on the Moon, including a robust precursor program, to promote exploration, science, commerce, and United States preeminence in space, and as a stepping-stone to future exploration of Mars and other destinations.

Once again, you will notice that the key goals of this Vision, elucidated by both the President and Congress include not only science, but commerce, and in the president's case security.

I could go on about how Dr Griffin's focus on the parts of the Authorization Act that talk about heavy lift and shuttle derived ignored other sections in the act that talk about "encouraging the commercial use and development of space to the greatest extent practicable" (see Section 101.a.2. parts B-C). But I think the fundamental issue is that by focusing exclusively on just the technical side of the requirements, and not on the underlying goals, Griffin is missing the Vision.

Growth Potential

On page 7, Dr. Griffin starts making his case for the Constellation architecture with this somewhat ironic statement about the Space Shuttle:

Once before, an earlier generation of U.S. policymakers approved a spaceflight architecture intended to optimize access to LEO. It was expected – or maybe “hoped” is the better word – that, with this capability in hand, the tools to resume deep space exploration would follow. It didn’t happen, and with the funding which has been allocated to the U.S. civil space program since the late 1960s, it cannot happen. Even though from an engineering perspective it would be highly desirable to have transportation systems separately optimized for LEO and deep space, NASA’s budget will not support it. We get one system; it must be capable of serving in multiple roles, and it must be designed for the more difficult of those roles from the outset.

And then Dr Griffin goes on to try and justify an architecture based on building a duplicative LEO capable only launch vehicle first, and hoping that when that vehicle is finally done, that there will be funding for developing "the tools to resume deep space exploration"...

After that auspicious start, Dr. Griffin then reminds us that "the new system will and should be in use for many decades." Of course some of the historical analogies he draws could lead one to different solutions than it led him. For instance, he mentions that "In space, derivatives of Atlas and Delta and Soyuz are flying a half-century and more after their initial development." An interesting thing to note about Atlas and Delta is that the only reason why vehicles with the name Atlas and Delta are "still flying" a half-century after their initial development, is precisely because they are only derivatives of the original. In fact, the current EELVs have very little in common with the vehicles that originally bore their names.

On pages 8 and 9, Dr. Griffin concludes that (emphasis mine):

The implications of this are profound. We are designing today the systems that our grandchildren will use as building blocks, not just for lunar return, but for missions to Mars, to the near-Earth asteroids, to service great observatories at Sun-Earth L1, and for other purposes we have not yet even considered. We need a system with inherent capability for growth.

While I disagree with the direction Dr. Griffin is going, I do agree with his point in that last sentence. We do need a transportation architecture that has inherent capability for growth. I just don't think that the Constellation architecture really fits that bill.

The Promise of Commercial Space

Now, lest you think I'm going to spend yet another post hammering on Dr. Griffin, I'd like to quote a part of his speech that I really agreed with:

Further application of common sense also requires us to acknowledge that now is the time, this is the juncture, and we are the people to make provisions for the contributions of the commercial space sector to our nation’s overall space enterprise. The development and exploitation of space has, so far, been accomplished in a fashion that can be described as “all government, all the time”. That’s not the way the American frontier was developed, it’s not the way this nation developed aviation, it’s not the way the rest of our economy works, and it ought not to be good enough for space, either. So, proactively and as a matter of deliberate policy, we need to make provisions for the first step on the stairway to space to be occupied by commercial entrepreneurs – whether they reside in big companies or small ones.

I have to say that for all my disagreements with Griffin, he at least talks a good talk when it comes to commercial space. I full-heartedly agree with his point in this paragraph. When you think about it, even assuming everything works out according to his plan, Constellation is never going to be capable of supporting more than a dozen people off-planet at any time. While that may be a lot more than we have now, Ed Wright has a point when he says that that is a round-off error, not an exploration program. Basically, the only way we're going to see large numbers of people off planet, and the only way we're going to see the large-scale manned exploration and settlement of our solar system in our life times, is if the private sector can eventually play a much more expansive role in space transportation. As it is right now, so long as the commercial industry continues to play second fiddle to parochial interests and NASA-centricism, we're not really going to go much of anywhere.

So, the fact that NASA is at least doing something to help promote that day is a sign that they at least partially get it. A successful and thriving entrepreneurial space transportation industry is going to help them actually achieve their goal of extending human life throughout the solar system in a robust program of space exploration.

Griffin continues with more good comments in his next paragraph:

If designed for the Moon, the use of the CEV in LEO will inevitably be more expensive than a system designed for the much easier requirement of LEO access and no more. This lesser requirement is one that, in my judgment, can be met today by a bold commercial developer, operating without the close oversight of the U.S. government, with the goal of offering transportation for cargo and crew to LEO on a fee-for-service basis.

But here is where the conversation takes a dangerous turn:

Now again, common sense dictates that we cannot hold the ISS hostage to fortune; we cannot gamble the fate of a multi-tens-of-billions-of-dollar facility on the success of a commercial operation, so the CEV must be able to operate efficiently in LEO if necessary. But we can create a clear financial incentive for commercial success, based on the financial disincentive of using government transportation to LEO at what will be an inherently higher price.

To this end, as I have noted many times, we must be willing to defer the use of government systems in favor of commercial services, as and when they reach maturity. When commercial capability comes on line, we will reduce the level of our own LEO operations with Ares/Orion to that which is minimally necessary to preserve capability, and to qualify the system for lunar flight.

While I agree that the government not only is the government being "willing to defer in favor of commercial services" is a really good idea, I think that this approach (of hedging their bets by coming up with a competing in-house launcher) is fraught with risk. Also, while on first blush, it may appear to be common sense to not "hold the ISS hostage to fortune", it is my contention that this line of reasoning not only doesn't hold as much water as it seems.

First off, as has been pointed out on numerous occasions, including in Griffin's statements above, a commercial solution to ISS crew/cargo is going to be a lot more affordable than the in-house Ares-1/Orion solution. It has been mentioned before by people high up at NASA, that they really need COTS to succeed, because if they have to fly all the ISS missions themselves (especially if ISS doesn't get retired in 2016, which Dr. Griffin mentioned in this speech as a possibility), there really won't be anywhere near enough money to develop the lunar portions of the proposed Constellation architecture in time for the 2020 lunar return goal. You could say in a way that the existing Constellation architecture holds the rest of the Vision hostage to the fortune of COTS. If COTS doesn't succeed, there's no way NASA is going to be able to afford executing on the rest of the vision. If the supposed "backup plan" for ISS resupply won't produce acceptable results anyway if COTS doesn't turn out, NASA shouldn't be trying to make it a backup plan at all--they should invest more heavily in making sure that there are multiple COTS competitors and that they have enough resources to succeed. One of the single biggest execution risks for any COTS company is financing risks. And having a NASA "backup plan" that could potentially compete with them is one of the single biggest obstacles to be overcome in raising money for a COTS team.

Which brings me to my other concern. The danger of having NASA in-house launch vehicles and space access capabilities that can serve as a backup to COTS also allows them to directly compete with COTS if the budgetary situation goes sour. Think about it. If Ares-1 finally gets built and working, but Ares-V doesn't get funded, there's nothing for Ares-1 to do but service ISS. With how hard the esteemed congressmen from Florida, Utah, and Alabama are fighting to maintain the Shuttle workforce and infrastructure (even to the point of suggesting continuing to fly the Shuttle!), does anyone really think that they would just "stand down" at that point, even if there was a clearly superior commercial alternative? Not very likely. I'm sure they would come up with some technical reason why Ares-I was superior (after all, our probabilistic risk assessment says that Ares-I has a 1:2106.5923 chance of killing a crew, while our numbers show that they have a 1:500 chance--who do you want flying our brave astronauts?) and find a way to not actually stand down. The frustrating thing is that by setting things up the way NASA is doing, the NASA people don't even have to be malicious for such a result to happen--it's a natural and likely consequence of the perverse incentives that NASA and Congress are setting up.

So, while I personally think that Dr. Griffin really and emphatically believes in and supports commercial space development, I'm afraid that there's a high chance that some of his well-intended choices could end up coming back to haunt us.

Moon, MARS!!!! and Beyond

The last item I'd like to point out in Dr. Griffin's speech is one of the justifications he used for the "1.5 launch" architecture they selected. Dr. Griffin made the point that while he feels that Constellation needs to be backward compatible with ISS as a backup plan, it also needs to be forward compatible with Mars, because sometime in the 2030s, we're going to be going there. Now, I'm of the opinion that trying to guess what the best technical approach will be for a problem 30 years from now is somewhat of a fools errand. But that's just me I guess.

So, starting on page 16 he begins to layout his case:

On the other end of the scale, we must judge any proposed architecture against the requirements for Mars. We aren’t going there now, but one day we will, and it will be within the expected operating lifetime of the system we are designing today. We know already that, when we go, we are going to need a Mars ship with a LEO mass equivalent of about a million pounds, give or take a bit. I’m trying for one-significant-digit accuracy here, but think “Space Station”, in terms of mass.

Now, I'm not going to go into the fact that there are probably plenty of other approaches to Mars exploration that can change the equation entirely. That's a post for another day. For now, let's just run with that premise.

He then repeats the "everyone knows that ISS taught us that using 20 ton vehicles to build something big is a bad idea" catechism, but that's not what I'd like to discuss. The real gem is in this paragraph on page 17 (emphasis mine):

But if we split the EOR lunar architecture into two equal but smaller vehicles, we will need ten or more launches to obtain the same Mars-bound payload in LEO, and that is without assuming any loss of packaging efficiency for the launch of smaller payloads. When we consider that maybe half the Mars mission mass in LEO is liquid hydrogen, and if we understand that the control of hydrogen boiloff in space is one of the key limiting technologies for deep space exploration, the need to conduct fewer rather than more launches to LEO for early Mars missions becomes glaringly apparent.

It is true that one can draw that inference--that hydrogen boiloff means you should build as big of an HLV as possible. However, the conclusion I would draw is that if cryogenic propellant storage technologies are "key limiting technologies for deep space explortion", then the right answer is to stop trying to kludge around the problem--develop them! Don't use the existing state of the art in propellant handling and problems that are still 20 years down the road drive multi-billion dollar development projects today.

There are current technologies under development that could yield very low to zero boiloff of cryogenic propellants. There are multiple groups (ULA, Boeing, groups working with Glenn Research Center, etc.) pursuing multiple approaches to solving these problems. There are passive cooling and active cooling techniques. This isn't some high-risk technology like nuclear fusion. The technologies needed for cryogenic fluid management in space are mostly low-risk extensions of 40 years worth of research and development. More to the point, many if not all of these technologies need to be developed to make Constellation work for lunar trips anyway, and would still be needed for Mars trips.

Is 2030 really so close that we can't afford to do this right and actually develop the technologies we need instead of trying to kludge by with existing technologies?

Once you have the boiloff issue reduced or solved, that ~500klb of hydrogen ceases to be a headache, and begins to be an opportunity. That's a lot of demand for propellant in orbit, and it can be supplied commercially. You're already going to need propellant transfer technologies anyway if you have to launch the hydrogen in multiple launches, so what's to stop launching it in even smaller launches?

I guess my point is that if one of the key arguments for the 1.5 launch architecture over a more commercial one, or a less expensive shuttle derived one like DIRECT is hydrogen boiloff, I think their kludge around the issue isn't the right approach, and that they'd be better off just doing it the right way. Also, part of the reason why we have a federally funded aerospace program is to help prove out the technologies necessary for enabling the commercial exploitation of space, and actually solving problems like these would be much a much more responsible use of public funds than developing a kludge around point design like Ares V that doesn't advance the state of the art for the commercial benefit of the country.

Conclusions

I guess overall while there were some good points, there was also a lot of issues with Dr. Griffin's latest defense of Constellation. As discussed, I think that an a myopic focus on the technical details while ignoring the overall goals of the VSE has led to an architecture that isn't responsive to the key policy goals laid out by the president and reiterated by Congress (particularly with respect to promoting the commercial and security interests of the United States). I think that in spite of Griffin recognizing the need for growth and flexibility in any architecture, that he chose a rather brittle and inflexible one. I also think that while he showed that he does recognize the potential of commercial space, and the importance of NASA trying to promote it, I think that the way he's running COTS and Constellation will likely end up being highly counterproductive. Lastly, I think that in many cases, when confronted with a solvable engineering problem, Constellation has instead decided to kludge around the problem instead of properly solving it.

There are plenty of other issues I could've raised, but I figured these were some of the more obvious ones that I felt needed discussion.

Mass Confusion and White Knight 2 Kremlinology

For those of you who have been following my Orbital Access Methodologies series, you'll remember that I talked about the potential of using White Knight Two as the carrier plane for a small "assisted SSTO", or a "TSTO with glideforward first stage landing" (to coin a phrase for the good idea John Hare mentioned in comments to my last post). The key question was what the lift capacity of the plane was. Now, I work across the street from Scaled here in Mojave, and I know some people on the propulsion team, but knowing Scaled's usual desire for secrecy (and not wanting to get my friends in trouble), I had studiously been avoiding asking them for some time now.

So this morning I decided to do some googling, and I came across some numbers on Wikipedia that claimed the lift capacity was 30,500kg. Now, normally I wouldn't trust numbers from Wikipedia that I couldn't verify elsewhere, but the numbers jibed with some back-of-the-envelope Scaled "Kremlinology" I had been doing, so I decided to run some basic numbers on using it for an orbital launcher.

And the numbers looked good. Depending on assumptions, a 1000lb payload wasn't completely out of the question for the assisted SSTO design (enough for probably 2 people, or a pilot and a microsat, or a bigger microsat, or some propellant). And the TSTO design was showing on the order of 2000-4000lb depending on assumptions (based on LOX/Kero for the first stage and LOX/LH2 with a stock RL-10 for the upper stage).

Rob Coppinger over on his Flight Global blog, Hyperbola, put up a blog post along the same lines (talking about using White Knight 2 for launching orbital payloads), but something in the article caught my eye:

Flight learnt that WK2 has a 13,600kg (30,000lb) payload capacity sometime back.

So, now I was confused. Which was it, 30 metric tonnes like Wikipedia claimed, or 30,000lb like Rob was reporting. I brought this up, and Rob commented that the 30,000lb number came from a one-on-one interview they did today with Will Whitehorn of Virgin Galactic.

To me, that sounded pretty authoritative.

Out of curiosity, I decided to go back to Wikipedia and try to figure out where they had gotten their number from. I figured they must have misheard something--maybe they read the earlier Flight report and accidentally mistook 30,000lb for 30,000kg or something like that. Anyhow, the source for the data was given as a Pratt&Whittney press release and a video from a presentation at Oshkosh this year. The first release didn't have too much information (just that the four PW308 engines each produce ~6900lb of takeoff thrust, for a total takeoff thrust of just under 28klbf). The second link was for an hour long presentation given by Alex Tai and Will Whitehorn. Being a nerd, I decided to listen through to try and figure out where that darned number came from. And sure enough, right around 32:45-33:00 into the video, Will Whitehorn says that they were building White Knight Two with extra range and lifting capacity, and that it could lift "30 tons" (or possibly tonnes) to about 60,000ft.

So, now I'm just confused.

As a comparison, WK1/SS1 combined had a takeoff weight of around 17000lb, with its two engines producing somewhere around 3850lbf each (if I'm reading the right engine), for a T/W ratio of about 0.45 at takeoff. If a similar T/W ratio is used for the WK2/SS2 combo, it would predict a takeoff weight of about 61,000lb. That would put the WK2/SS2 combo at a similar weight ratio (of WK2 to SS2 weight) as the WK1/SS1 combo. So at least that jibes.

So I guess what I'm wondering is, if anyone can shed any light on this? The most likely explanation is that when giving his presentation, Will meant to say 30,000lb and said 30 tons instead, and that in his interview with Rob, he stated the correct value. However, it's also possible that he either mispoke in his interview with Rob, or both numbers could be right--30 tons may be the maximum payload, but 30klb is roughly the weight of SS2?

The big reason why this matters is that it effects my air-launch ideas substantially. If the later numbers Rob is quoting are accurate, then it's highly unlikely that you could make a reusable orbital vehicle that could use WK2 for air launch. You might, if you make enough compromises get something, but it would be a rather marginal design. Which would mean that while WK2 could still provide an interesting carrier platform for TSTO ELV microsat launchers and for manned suborbital missions; real air-launch RLVs would need to either wait for WK3 or would have to find some other way of getting airborne--and that may very well break the case for them at least for the foreseeable future.

I hate it when an inconvenient fact kills a perfectly beautiful theory, especially when its my theory.

Orbital Access Methodologies Part II: The Key Challenge of TSTO RLVs

Before I go into detail on any of the two stage to orbit (TSTO for the uninitiated) approaches that I mentioned in my post last week, I'd like to briefly discuss what I think is the key issue that drives the design and development tradeoffs for reusable TSTO launch vehicles. That issue is: how do you get the first stage back after a mission, and ready to fly again?

This article will focus on the key tradeoff that stems from this question: whether to try and recover the first stage downrange, or whether to try and perform some sort of return to launch site maneuver. The answer to this question is probably the number one driver of what approach one takes for developing a TSTO vehicle.

RTLS vs. Downrange Recovery
As I pointed out in my brief discussion about SSTO vs. TSTO approaches in Part I of this series, attaining orbit is mostly about building up a lot of horizontal velocity, and only a little bit about gaining vertical altitude. For performance optimized TSTO ELVs, the first stage often imparts a significant portion of the overall delta-V (especially for ELVs delivering satellites to GTO or GSO). This means that it ends up coming in hot, fast, and a long way downrange from the original launch site. Now, there are several different approaches to deal with this problem (or avoid it altogether).

One option is to just let the stage come down where it wants to, and recover it downrange. Downrange recovery can take several forms including recovering a stage out of the ocean after a splashdown, landing the stage at a downrange site and ferrying it back (either by rocket flight, a carrier plane, or by truck, train, or barge), or it could involve mid-air recovery of part or all of the first stage. While downrange recovery may is the general approach that probably imposes the smallest performance penalty, each of the actual approaches to down-range recovery have some pluses and minuses.

Splashdown Recovery
Let's take splashdown recovery first. Falcon-1 is an example of the splashdown recovery. The stage separates where a typical ELV would want to have a staging event, and then (hopefully) it's fished out of the ocean and refurbished for reuse. Some of the benefits of splashdown recovery:

1. Splashdown recovery is probably one of the easiest and best understood methods for recovering a traditional ELV-like first stage.
2. There's a large experience base to use as a foundation for carrying out such a design.
3. Even if your flight rate is low enough that it isn't saving you much money, you're still able to learn a lot from being able to perform post-flight inspection on the propulsion hardware. Thus, even if you aren't flying enough to save a lot of money via recovery, it will help your reliability.
4. Ocean splashdowns don't require anywhere near as heavy of recovery equipment as land parachute landings.
   

But they also have several drawbacks:

1. Trying to make a complicated rocket engine sea-water compatible, especially a turbopump-fed rocket engine, is not a trivial task. Material selection, and getting the stage out of the salt water (and cleaned out) as quick as possible are all required.
2. There's a lot of time and labor involved in hauling the stage back, cleaning it out, making sure nothing got damaged on reentry or splashdown, testing everything to make sure it's still in working order, etc. This fundamentally limits how frequently you can refly a given stage. It also translates into a lot of extra personnel and labor-hours required above and beyond what you would normally need to just build, test, and fly an expendable vehicle.
3. The wear and tear from ocean recovery, splash down, etc. are likely going to limit the number of reflights you can get on a stage or engine before major overhaul or outright replacement.
4. Your potential launch sites are limited, since you need a large body of water on which you can drop big heavy hardware. Most likely (for US entities) that means flying out of one of the existing ranges like Wallops, Vandenberg, or Canaveral. These locations, while excellent for flying missiles, and while also improving their commercial friendliness over time, are still a long way from the environment you want to be operating a reusable launch vehicle out of.
5. While it's possible to design a launch vehicle splashdown recovery first stage in such a way that a first stage failure doesn't necessarily imply the loss of your cargo, it is much harder to design such systems for graceful abort modes. Unless the upper stage is also designed for splashdown recovery (with the payload designed for it as well), a stage failure probably will result in loss of payload. This loses you one of the big potential advantages of reusability--graceful and intact aborts.

Mid-Air Recovery
The idea behind mid-air recovery is that instead of allowing the stage to crash down into the water, you instead snatch it (or a high-value part of it) out of the air using a helicopter or other sort of aircraft aircraft. This is similar to how Genesis was supposed to be recovered, and was the method used for recovering a lot of the film capsules from early spysats. There are actual serious players looking at this idea, but I don't know if it's supposed to be public knowledge yet, so that will have to be a post for another day. There was also a paper floating around by a company that does mid-air recovery work, including work for the SpaceHab ARCTUS project. If I can dig it up again, I'll probably post about that as well.

Anyhow, here are some of the benefits of mid-air recovery:

1. No salt water contamination in the rocket hardware! This greatly cuts down on the amount of work that needs to be done to turn a stage around. No need for decontamination. No need for stripping down hardware. Probably eliminates the need to "requalify" the propulsion system before reflight.
   
2. Gentle, low-shock recovery is much less likely to damage stage or propulsion hardware, also making it more likely that the hardware can just be reused after some inspection.
3. There are companies that specialize in this sort of thing, and you can just rent their services instead of trying to do this in-house. They aren't cheap, but they're a lot cheaper than building a new stage every time.
4. Your propulsion system is going to be in about as close to the same condition as it was when the engine shut down as you'll get for any recovery technique--this makes it a lot easier to get good reliable data on wear-and-tear on the engine, so you can improve the quality over time.
   

But here are some of the challenges:

1. Complex recovery technique. Sure, you can practice it a whole lot for not too much money, but there is some increased risk of failing with the rendezvous or recovery operations, which could occasionally cost you a stage.
2. Weight limits. Even with the latest techniques, which can recover payloads up to 80% of the maximum cargo capacity of the helicopters, you're still limited to around 22klb or less. Depending on the size of your stage, this may mean that you can only recover part of the stage (like say the engines). That'll still likely save at least some money, but it's not as big of a win as getting the whole stage back intact.
3. There may also be issues with trying to recover a big, but fluffy stage. Depending on the weight distribution, there could be some real oscillation issues (like what happened when they tried to move the Roton ATV under helicopter).
   
4. Range issues. Depending on how far downrange your stage comes back, you might need to also rent not just a helicopter, but some sort of barge to operate the helicopter off of. This will increase the amount of time it takes to turn a stage compared to if you could just fly it back.
   
5. Like with splashdown recovery, this method of recovery still doesn't give you graceful and intact recovery methods in the case of a first-stage failure. With dump valves and two helicopters, and a mid-air recoverable upper stage, you might be able to recover the payload over part of the trajectory, but you'll still have zones where a failure means sure loss of the payload (or a launch escape abort if you're flying people). It isn't a showstopper, but it does reduce the upside somewhat.
6. Due to challenges #1 and #5, you probably still need to launch out over the ocean, which means that once again you're still going to face the issue of launching out of an existing missile range. Basically, since there's a chance you could biff the in-air recovery, you have to do this over an unpopulated area. And since your vehicle doesn't likely have graceful failure modes, it's more like an existing ELV than a more traditional RLV, and will probably be treated as such by the FAA and the ranges. Not a showstopper either, and it might just be possible to pull this off with an over-land launch if you can find a sufficiently deserted area, but definitely a challenge.

Mid-air recovery is probably too weight constrained for something like a complete (but dry) Falcon IX first stage, but might be an interesting option for recovering the Falcon IX upper stage or the Falcon I first stage. It'd also probably be just the right size for recovering the first stage if they hadn't canceled the Falcon V. Other than the weight limit, there's some real benefits of this approach over the traditional splashdown technique.

Downrange On-Land Recovery
This type of recovery can take several forms. It could be a powered VTVL landing at a downrange pad. It could be a powered or glide landing for a HTHL. It could be a parachute and airbags landing (like Kistler, just downrange). But basically you have the thing land, on the land, downrange, and then fly the thing back, or ship it back.

Here are some of the benefits:

1. Much more efficient, performance-wise, than any of the RTLS approaches. You can still stage at the most optimal staging velocity, therefore making your upper stage design a lot easier. You also get a lot more payload per given takeoff (and dry) mass.
2. At least some of the RTLS approaches can also sometimes use this as a performance enhancing option--in case you need to launch a bigger payload than you can handle with a normal RTLS trajectory.
3. Unlike mid-air recovery, this recovery approach can scale up to fairly large sizes.
4. In emergency cases for RTLS approaches, you may want to be able to land your vehicle at alternative downrange sites anyway.
5. Unlike the other two downrange recovery options, this option is a lot more compatible with intact and graceful aborts.

And here are some of the challenges:

1. A given launch site will typically have its launch azimuths (directions in which you can launch) restricted a lot more for downrange land recovery than it will for an RTLS vehicle. This is because you need to have a suitable place downrange where you can actually land. This makes downrange recovery vehicles less flexible than RTLS capable vehicles.
2. You need facilities at both ends, especially if you intend to fly the stage back after landing.
   This may entail having almost as many launch support people at the downrange site as at the initial site, which greatly increases the fixed costs of such a system. Probably not quite double (since you don't have payload processing facilities there), but it's a non-trivial expense.
   
3. If you do a rocket powered return, you've now effectively halved both your flight rate (as you have to do two launches, two landings, two ground preps, etc. per a single paying flight), and halved the number of revenue generating flights you can get out of a given airframe. Both of these directly affect the bottom line.
   
4. If the return flight is a rocket-powered suborbital flight (as per AST's definitions), I think that each of your downrange sites will need to be an FAA licensed launch site, and you will need launch licenses for all of the return flights. Now, once you have one launch license to base things off of, getting additional ones should be easier, but its still extra paperwork. Also, your Ec and MPL calculations are going to be different for the return flight, because your IIP will move at different rates over different areas under your groundtrack for the two trajectories (not to mention mission-critical operations will occur with your IIP over a different location). All of this stuff has to be taken into account.
5. If you have a jet powered return (either using a carrier aircraft, or if the stage has built-in jet engines), you now need to deal with the aircraft side of FAA, which may entail getting the vehicle type-certified. I'm not certain, but having a vehicle that operates under both regimes is likely going to make things a lot harder, not easier. Being unusual is not a virtue when dealing with regulators. If you're using an existing carrier craft, that'll make things easier however, as it is purely a subsonic aircraft, and thus a lot closer to what FAA is used to dealing with.
   
6. If you try to return the stage via trucking or train, now the stage has to be "roadable". Which means making it skinny enough to fit on existing transports. While this may be feasible for some smaller, dense-propellant RLV stages (after all I think that Falcon IX is roadable), it is a constraint on the size of stage. And the aspect ratio roadability forces you into is not as ideal for VTVL stages. VTVL stages want to be shorter and squater than typical rocket stages.
   
7. If you return the stage via trucking or train, you now need heavy moving equipment at any downrange sites, experienced heavy equipment personnel there, and it's going to cost you a lot of extra time. All of these things add cost, and slow down your turn time.
   

Conclusions: The Case for RTLS
Now, I probably ought to clarify something. I don't think any of these downrange recovery ideas are stupid. If done right, they can save a lot of money compared to a purely expendable system, while also increasing reliability by allowing for post-flight inspections and the like. Especially with the downrange land-landing techniques, you can get all of the benefits of traditional RLVs.

In other words, while there are some challenges with downrange recovery, there are often some real benefits. There are some cases where using these downrange recovery approaches really is the best choice. SpaceX and the others looking at these approaches aren't being foolish by pursuing them. I just think that the inherent limitations of this sort of reuse (especially the first two options--splashdown and mid-air recovery) will probably prevent it from being a revolutionary as opposed to a modest, evolutionary improvement over a purely ELV approach. Now, in the near to medium term, even when RLVs first start flying, they'll likely be relatively quite small compared to the EELVs (for reasons I'll go into in a later post). Which means that approaches that allow existing ELVs to become somewhat more reusable, and improve their economics somewhat are actually useful. I think that while small RLVs will bump ELVs out of the people, light cargo, and propellant markets very quickly after they enter the field, there'll still be payloads that are too big for RLVs that are small enough to be economically viable in the near-to-medium term. The ULA's, SpaceX's, and Sea Launch's of the world will still have a useful role to play for some time yet. Particularly for launching bigger payloads like Bigelow stations, transfer stages, etc. So, having ways to improve them is good, even if they aren't necessarily going to change the world all by themselves.

As for the last options--land recovery downrange, it actually does have the potential to be revolutionary. But the approach still has some serious economic and regulatory drawbacks that are sufficient to make one start looking at RTLS approaches, even though they may be less optimal from a purely performance-based standpoint. There are four primary (and one somewhat oddball) RTLS techniques/trajectories: pop-up, glideback, boostback, flyback, and once around return. Of these five approaches, the most well known (until recently) and thus most thoroughly studied is the flyback approach. However, the first three are the ones (pop-up, glideback, and boostback) that I think are the most promising and relevant to near-term orbital RLV endeavors, and thus will get the bulk of my focus for the remainder of this series (Parts III-V). But I'll probably spill a few electrons discussing the last two as well. They are interesting after all.

It's The Journey That Matters, Not The Destination

The story broke yesterday that a group of scientists, astronauts, and other space enthusiasts is going to be meeting at Stanford next month to discuss an alternative to the Vision for Space Exploration. Clark and several others have already commented, but I figured I ought to throw in my two cents.

Basically, I'm skeptical.

While there are some good things in the plan, such as supposedly more commercial involvement, and destinations that tap better into some of the supposedly more pressing space-related concerns of the US populace (ie planetary defense against near-earth objects), there's still a lot to be concerned about.

Are we going to see a repeat of what happened with the VSE, where there were all sorts of wonderful platitudes about commercial involvement at the start, that end up being effectively nothing in the end? I mean, COTS is great and all, but NASA spending $10B on its own in-house solution (that's going to end up competing with COTS for ISS cargo/crew delivery when Ares V never gets built), while giving only $500M for more commercial approaches is not what we were led to believe back in the early days of the VSE. Once NASA gets its hands on this new plan, how much commercial content will really survive? If the only commercial involvement ends up being renting an extra Bigelow module or two, it won't be a complete waste, but that's not saying much.

At least from what I've seen, they still are talking about "giving America the Shaft", and wasting countless billions on Ares V, and EDS. If they do that, they're still going to have all the extremely expensive shuttle infrastructure that will have to get paid for every year. Sure, they'll save a little on the edges by not having an LSAM line running, and possibly save a tiny bit by cutting back on the mission tempo (only one manned mission per year or every other year maybe)--though with how much of the money will be going to fixed infrastructure, the savings won't really be that great.

What this new approach probably won't do (any more than what we're getting with the ESAS implementation of the VSE) is actually be relevant to the commercial development of space, or helping our civilization become a truly spacefaring one.

I guess people just get way too hung up on the destinations. Quite frankly, where NASA goes over the next 20 years is of almost trivial importance compared to how it goes there. For all I care, they could set their sites on performing manned exploration of Europa, just so long as they do it in a way that actually helps promote the development of the infrastructure we need to become a truly spacefaring society.

I know I keep hitting on these concepts over and over again, but that's because while the meme is spreading, it still hasn't really sunk in among those in power. There's nowhere in the solar system that's of such pressing importance as to justify a NASA designed and operated transportation system.

On the flip side, almost anywhere in the solar system is a good enough destination if NASA were to go with a truly commercial transportation system. One using commercial propellant depots in orbit that buy propellants from whoever can launch it cheapest, and sell it to whoever wants to move something around in space (both NASA, commercial entities, and other governments). One where NASA "astronauts" are passengers flying on commercial vehicles alongside cosmonauts, taikonauts, UKnauts, Koreanauts, ESAnauts, private (or government) customers going to Bigelow stations or on CSI or Space Adventure operated trips around the moon. One where NASA only builds and operates the actual spacecraft, not the launch vehicles. Because if NASA helps build up a commercial industry like that, we'll end up getting not just whatever the destination de jour is, but everywhere else as well. Maybe NASA ends up spending most of its resources focused on putting boots on Mars, but with a propellant depot on orbit, and NASA acting as an anchor tenant with enough demand to help close the business cases for future RLVs, you're going to see space travel cheap enough that a lot more people can get in the game, and a lot more destinations may be visited. While NASA's off planting flags on Mars, some groups will be exploring NEOs, others will be offering tourist trips to and around the Moon, and others might even be building cloud colonies on Venus.

Anyhow, I think you get my point. We'll see what this new group comes up with. They might surprise us, but for now I remain skeptical.

An Insane, But Interesting Idea: Fleet Launched Orbital Craft

Ok, before I go into this latest blog post, I want to put a disclaimer up front:

• This idea is crazy.
  
• I'm not posting this because I think it's the greatest idea since sliced bread.
• I don't think that this the one and true way to get to space.
• Don't try this at home.
• I don't necessarily thing this is better than .
• Oh, and did I mention I thought this idea was a bit crazy?

But even if it's crazy, it is interesting. And it was developed by a guy with the same last name as me, Allen Goff of Novatia Labs (Sacramento, CA), so while it's a bit crazy, it's definitely clever.

The idea is what Allen called Fleet Launched Orbital Craft, or which another author calls "Separated Ascent Stage Launch Vehicles" (I'll call it by Allen's term "FLOC" from here on out). The idea is somewhat related to bimese and trimese launch vehicles. In a bimese launch vehicle, you have a TSTO vehicle where both stages are identical to each other. Both stages ignite for a vertical takeoff, and the ideas typically use propellant crossfeed to guarantee that one stage is still full when the other one's propellants are almost depleted. At that point the empty stage separates and returns home while the other one proceeds on to orbit. Trimese approaches are similar, but use three identical stages. The theory being that by designing just one stage and using it several times, you can get a lower development cost, even if both stages are somewhat suboptimal.

FLOC is just the logical extension (or maybe reductio ad absurdum) of the Bimese/Trimese concept. You could technically call it an n-mese concept, where instead of only 2 or 3 similar stages you instead have "n" similar stages. John Carmack's looking at one version of the n-mese concept (like OTRAG did in the past), but this one is different from John's modular concept. The big difference between FLOC and a more traditional n-mese approach like John's is that for FLOC, not all of the stages are attached when the vehicles are on the ground. An illustration from Chris Taylor's AIAA article on the economics of the approach (AIAA 2006-4783) might clarify things a bit:


Basically, you have 2^n stages at takeoff, each of them paired together into a bimese configuration. They all takeoff together, all from right near each other (ie they probably all launch within 1-2 seconds of each other, and within 1-2km of each other). They fly as close together as is physically safe. They use propellant crossfeed to guarantee that one stage on each of the bimese pairs is still full when the other one runs dry. When those stages run dry, each bimese pair stages. The "empty" stages all return to the launch site (possibly using an airbreathing engine once back down to subsonic speed to cruise back). The full stages then perform a...wait for it...exoatmospheric rendezvous with each other, mechanically hook-up so they can operate as a new bimese pair, reestablish propellant crossfeed, and then continue on their way. You then lather, rinse, and repeat until your final stage ends up in orbit.

I mean, what could possibly go wrong?

Seriously though, as Chris points out in his AIAA paper (linked above), while the idea is totally crazy, it does have some interesting ramifications. Chris points out that using a fleet of 8-32 launch vehicles, you can place extremely large payloads into orbit using stages that have a propellant fraction similar to a 747 without having to use cryogenic propellants. Also, you can "tune" your payload to orbit (or your suborbital performance) by adding more or less bimese pairs. Using a 747 sized launch vehicle, they were predicting up to 200 metric tonnes (!!) of payload to orbit in a single launch campaign using 32 vehicles. That's about twice as much as a Saturn V, with a stage design that's so low performance it's more like a commercial airplane than a rocketship. As I said previously, smaller payloads could be done as well using smaller numbers of stages.

How hard can doing a dozen exoatmospheric rendezvous be? I mean, you have about a 2 minute window for each rendezvous operation. That's plenty of time....

Needless to say, there would need to be a lot of operations development and practice before such a system could become practical. The rendezvous happen outside of the atmosphere, which definitely helps a lot. And the launch vehicles can all launch from the same area at the same time, which also helps a lot. It's a lot easier to do a rendezvous when you're already flying along an almost identical trajectory at the same time. You'd probably need some sort of automated hold-down mechanism for the bimese pairs, or some way of starting up all the rockets in idle and automatically checking to make sure things are working on each vehicle before you commit to launch. You'd probably also want to do things like building in more thrust than the vehicles actually need (so that underperformance on one engine, or a premature engine shut down doesn't risk the mission). Having a redundant bimese pair or two (depending on the number of stages you're launching already) could also help. Another point that should be made is that in the 2 minute rendezvous window, you only have to get the vehicle pairs mated back together--you can actually hook up the propellant crossfeed after the engines have lit, so long as it happens before you burn about say 1/3 of the propellant of the combined vehicles. This allows you to take the process in two steps instead of having to do both all at once.

More importantly, I'd also like to see the rapid rendezvous and mating demonstrated a lot of times on a subscale basis before trying this for real. You could demonstrate at least some of the basics using cold-gas thrusters on armed robots on something like a Zero-G flight. That would at least allow you to get some of the basics of grappling and mating down in an environment where you could easily get 50-100+ attempts for only a few tens of thousands of dollars. The next step would be demonstrating with two subscale suborbital vehicles that you could consistently do the full rendezvous and mating operation exoatmospherically. With suborbital vehicles, you could start out with a more relaxed rendezvous window of say 5 minutes, and work your way down as you get the bugs worked out.

The good news is that a single one of these stages (or a single bimese pair) should have enough performance to perform a suborbital flight with a decent sized payload. You can then slowly work your way up from there. With a 4 stage configuration, you should be able to at least get to orbit with some payload (something light, probably in the 1-2 tonnes range) once you've demonstrated and debugged doing a single exoatmospheric rendezvous mission. After that, it's mostly operations from there, working your way up to the point where you have enough reliability to reliably pull off larger missions.

Anyhow, for more details, read the paper. I just thought that while this idea was crazy, it was a very fun and interesting form of crazy, and does actually get you thinking.

Anyway, enjoy!

Patience

I'm glad to see that my first "orbital access methodologies" post has received as much attention as it has already. As I mentioned in my original post last month, I intend to talk about a few other promising approaches that I discussed for that guest lecture at UND in November. The rest of these approaches are TSTO approaches, including the "pop-up" VTVL approach favored by Armadillo (and discussed in the excellent book, "The Rocket Company"), the "glideback" approach that I think is the most likely approach someone like XCOR would take, and the "boostback" approach, which is similar to what Kistler ended up pursuing in the end.

I've ended up fleshing these out to a lot more detail than what I went over in my presentation at UND (going from two 3x5 cards worth of notes to 12 pages worth of text), so it's been taking me a lot more time to write these than I had originally intended. I thought at first that I'd be able to bang these out, one per evening, when in reality it's a lot closer to a full week worth of evenings.

In addition, I have at least one Jonny/Jimmy blogging post, one politics post, one family update, a follow-on to the Thrust Augmented Nozzles post, and a post about reusable lunar landers in the queue....

I wanted to give you all a heads up on what I'm working on, but also to ask for patience. This stuff takes me a while. Thank you all though for the kind words and support!

Orbital Access Methodologies Part I: Air Launched SSTO

As I mentioned last month, I would like to briefly discuss in a series of blog posts some of the more promising potential approaches for reusable orbital transportation. There is often a tendency among engineers to completely dismiss any idea other than ones own preferred approach as being unrealistic, naive, flawed, impossible, inefficient, etc. However, the more I've studied the problem, the more I've come to the conclusion that there are probably several technical approaches that can be made to work for providing reliable, low-cost access to orbit. Each of them has its own set of strengths, challenges, unresolved questions, and operating characteristics. By their nature, this means that different approaches may lend themselves better to different potential market niches and different development paths.

The first such approach I would like to introduce for discussion is epitomized by a proposed design (illustrated below, credit: Teledyne Brown) that was brought to my attention about a year ago. This proposed design, termed "Spaceplane" was developed at Teledyne Brown by Dan DeLong (who later became one of the founders XCOR Aerospace and is currently their Vice President and Chief Engineer, and who also currently owns all the rights to the Spaceplane design). Dan's proposed concept was a winged, "assisted" single-stage to orbit (SSTO) design that was launched off of the back of a converted 747. The LOX/LH2 stage, powered by 1x SSME and 6xRL-10s would theoretically be capable of delivering ~14klb of unmanned cargo to a 400km circular orbit. The vehicle would be reusable, using an Inconel-foil over fiberglass insulation concept for its reentry TPS, and using a runway landing for its recovery method.



While the specifics of Dan's proposed design are now a bit dated (the concept was proposed back in the late 80's), the general approach still merits investigation.

To Stage or Not to Stage: That Is The Question

Now, before I go into the specifics of this approach, I know at least a few of you are probably already thinking things along the line of "SSTO? He can't be serious. Everyone knows that SSTOs are totally unrealistic!" While to be honest, I'm mostly a TSTO guy myself (as is Dan DeLong these days), but I think there's a real danger in how quickly and without contemplation people tend to buy into new conventional wisdoms.

The fundamental reason why anyone would even want to stage a rocket vehicle has to do with the physics of the rocket-powered flight. The rocket equation, says that the change in velocity due to a rocket in flight is linearly proportional to the specific impulse of the propulsion system and proportional to the natural logarithm of the vehicle's mass ratio (the ratio of the mass at ignition to the mass at shutdown of the engines).

DV = Isp * g * ln (MR)

Another way of looking at this equation is that the required mass ratio of a vehicle is exponentially proportional to the required velocity change divided by the vehicle's specific impulse:

MR = e^(DV/(Isp * g))

The inverse of the mass ratio is the dry fraction of the vehicle, ie. the percentage of the vehicle's gross takeoff weight that can be allocated to structures, propulsion, payload, recovery systems, controls, power, life-support, etc, etc. The rest is fuel. Rewriting it in terms of dry fraction (df), we get:

df = e^-(DV/(Isp * g))

Now this is a fairly simplistic way of viewing things (ie. the Isp actually varies quite a bit with time based on the altitude at a given time, the engine throttle level, if you're using thrust augmentation, etc, etc.), but shows the crux of the problem. The total delta-V needed to attain a low earth orbit can range anywhere from ~8-10+ km/s, while you'd be lucky to get a mission-averaged Isp much higher than ~400-440s even using the highest Isp propellants in service, LOX and LH2. Now there are all sorts of subtle nuances that we could go into. Things like how dense propellants typically require lower overall delta-V because they end up having less gravity and drag losses, or that depending on what latitude you're launching from you can get a small "boost" due to the earth's rotation. But the crux of the matter is that for a single-stage system, you're dealing with a dry fraction of less than 10% (and typically quite a bit less than 10%).

That 10% has to cover all those categories mentioned above while still providing a high enough payload fraction that your system doesn't have to get too gargantuan to deliver a sufficiently sized payload. And it has to be robust enough to be reused many times. And your system needs to be maintainable. And it needs to have graceful failure modes, and safe abort modes throughout the flight path. And it needs to be buildable on a realistic budget and timeframe.

All of those issues make the concept of staging very desireable. By staging you get to drop off some of your dry mass along the way, instead of having to lug it all up to orbit. This tends to relax the required mass ratios substantially, which makes it a lot easier to do all those things that make a reusable vehicle truly reusable (as opposed to recoverable, refurbishable, or scavengeable).

But that staging comes at a price. Staging creates a lot of complexity, and introduces some potential failure modes that can be hard to actually check-out on the ground. Staging is one of the single highest risks of failure for existing launch vehicles. Additionally, with a TSTO, now you're really designing three vehicles, not just one. A first stage, an upper stage, and a combined entity. You now have to come up with abort modes for all the different configurations.

Probably one of the biggest headaches for TSTOs is how to recover and reuse the first stage. Getting to orbit is only a little bit about going up, and mostly about hurtling yourself sideways fast enough to "throw yourself at the ground and continually miss". Doing so entails gathering quite a bit of horizontal velocity with a first stage, which means that the first stage gets quite a bit of horizontal distance between it and the launch site by the time it releases the upper stage. Most of the TSTO approaches I'll discuss later revolve around how to get that first stage back. This is a real challenge for TSTO vehicles, though as Dan put it about SSTOs, they have their own challenges with getting the stage back (mostly due to trying to pack a robust heat shield and a robust structure into such a limited available mass budget).

So, in spite of the real challenges of developing SSTOs, there is a reason why some sane and rational people still look at them from time to time. There are real drawbacks to all approaches, and if an SSTO can be technically feasible, it might actually be desirable economically.

With that in mind, I'd like to get back to the topic of this post: air-launched "assisted" SSTOs.

The Benefits of Air Launching

One of the lessons I've learned as an engineer is that many times the best way to solve a really nasty and intractable-looking problem is to find a way to not actually solve that problem, but to replace it with an easier problem, and solve that one instead. In the case of an SSTO, trying to make a ground launched, horizontal takeoff and landing SSTO is a horrible challenge. You have very little dry mass to start with, and ground launching requires landing gear rated for the fully loaded weight of your vehicle, wings that have to be able to produce sufficient lift at very low speeds for takeoff, engines that can operate near sea level while still being efficient in vacuum (which entails either really high pressure designs, altitude compensations, or carrying around different engines with some optimized for high thrust at low altitudes, and some optimized for high efficiency in vacuum), and several other challenges. According to Dr Livingston, a Boeing engineer several years ago suggested that such a system was just not technologically feasible with modern materials and propulsion systems. While there have been some improvements on both fronts since he made that comment back in the mid-90s, I wouldn't be surprised if a ground takeoff HTHL SSTO is still unrealistic.

So the real engineer finds a way to cheat.

And a good way to relax all of those constraints is to not try taking off from the ground, but to start at a reasonable altitude, by using a subsonic airbreathing carrier aircraft. Starting, as SpaceShipOne did, at a reasonable altitude gives several distinct advantages over ground launch (the following list comes from Dan DeLong, with some thoughts from me [in brackets]):

1. The airplane carrier contributes to the overall altitude and velocity. These advantages are small. [Total savings are probably on the order of 100-200m/s. While this is a small fraction of the overall delta-V, the exponential nature of the problem means that even a small decrease in required delta-V makes a big difference.]
   

2. Meteorological uncertainties are mostly below launch altitude. Propellant reserves can thus be less. [Or this means that you can fly on a more dependable schedule, and that you can have more robust propellant reserves without paying as much of a penalty for such.]
   

3. Total integrated aerodynamic drag losses are less, as the launch is above much of the atmosphere. [This provides a bigger benefit to low density propellant combinations such as LOX/Methane or LOX/LH2, but overall could be worth several hundred m/s of delta-V, particularly for smaller vehicles]
   

4. Max Q is less, which reduces structural mass, and may allow lower density thermal insulation. [You may also be able to "split the difference" on the structural mass somewhat--allowing for a higher FOS on the structure, which allows much less maintenance/inspection, while still pocketing at least some of the mass savings.]
   

5. Engine average Isp is increased because the atmospheric back-pressure effect affects a smaller fraction of the trajectory. [This means that your mission averaged Isp is going to be much closer to your vacuum Isp than is typical for a booster engine.]
   

6. Engine expansion ratio (non-variable geometry assumed) can be greater because overexpansion is less problematical. [For instance, IIRC, you can light an RL-10 at 30,000ft without risk of unsteady flow-separation caused by overexpansion. This can make a huge difference, as it means you can use an engine with a much higher vacuum Isp. Possibly a benefit of as much as 5-10%, with greater improvements seen by lower pressure systems that often have higher reliability than the ultra-high pressure staged combustion engines preferred for booster applications these days. When combined with benefit #5 above, this can have a large impact on the required propellant fraction due to the exponential nature of the rocket equation.]

7. Wing area can be smaller because the wings do not need to lift the gross weight at low subsonic speed. Air launch Q is greater than runway rotation Q.
   

8. Wing airfoil shape need not be designed to work well at high gross weight and low subsonic speeds.

9. Wing bending structure need not be designed for gross weight takeoffs or gust loads. Wings can reasonably be stressed for 0.7 g working plus margin. This is a large weight advantage made possible by the carrier aircraft flying a lofted trajectory and releasing the orbiter at an initial angle of at least 15 degrees. (25 degrees is much better but not crucial, more than 60 degrees has no value) This initial angle decays in the first 10 seconds of flight but picks up again as propellant is burned and the constant wing stress trajectory yields a better lift/weight ratio. The thing to keep in mind is that the wings are sized and stressed for landing, and that insofar as they exist, are used to augment launch performance. [A comment I heard from a professor of mine back at BYU was that many people try to use composites as "black aluminum", i.e. they don't try to understand the nuances of the material, and thus miss out on most of the benefits. I think that that may often be the case with wings on rocket vehicles--if you design a vehicle to take the maximum advantage of your wings, you can negate some or all of the supposed "penalty" for carrying them in the first place. And that's coming from a VTVL guy!]

10. Thrust/weight ratio can be smaller because the low initial trajectory angle does not have large gravity losses. This allows a smaller engine, propellant feed, and thrust structure mass fraction. I found 1.25 at release to be about optimum. This is a bigger advantage in air launching because total integrated aerodynamic drag losses are less and the trajectory need not get the orbiter out of the thick stuff as fast. [Lower gravity losses due to the flight angle reduces the required delta-V somewhat, and is probably a bigger benefit once again for high performance, low-density propellants, which typically suffer from higher gravity losses. Lower required thrust-to-weight is also big because your propulsion system is often a large part of the dry mass of an SSTO, so being able to get away with a lower required T/W ratio for the vehicle can make a large difference.]
    

11. The lower mass/(total planform area) yields lower entry temperatures. I assumed inconel foil stretched over fibrous blanket insulation for much of the vehicle undersurface. Titanium over blankets, or no insulation worked on the top surface. Payload bay doors peaked at 185 F. [Having a better ballistic coefficient (the relationship of mass to planform area) means that your vehicle starts decelerating at a higher altitude where the atmospheric density is lower. Basically, drag force is proportional to area, while since F=ma, the acceleration is inversely proportional to mass.
    
    In other words, "Fluffy" is good for reentry vehicles, which means that by necessity, a fixed geometry SSTO is probably going to have gentler reentry heating loads than a fixed-geometry TSTO. This is increased by the fact that many of the benefits/constraints of air-launching push vehicles towards lower density propellant combinations like LOX/Methane or LOX/LH2. This is a good thing, because an SSTO has a lot less mass to cram that TPS system into. This is also good, because lower temperatures and more robust TPS systems mean lower maintenance, lower costs, and higher "availability".]
    

12. Mission flexibility is greater. For example, the carrier airplane can fly uprange before release to allow a wider return-to-launch-site abort window. Good ferry capability, etc. [The other major benefit for missions to specific orbital destinations, like say a Bigelow station, is that the carrier airplane can move the launch point around. By being able to place the launch point at just the right position relative to the station, you can provide for first-orbit rendezvous opportunities even if your launch site isn't directly underneath the given station. The ability to move the launch point also potentially opens up longer launch windows. Lastly, being able to move the launch point allows options like operating out of an airport closer to "civilization" while still launching out of an area with low population density, like say over an ocean or a desert.]

13. [Update: A commenter noticed that Dan and I both forgot to include an important additional benefit of this approach--landing gear for an air-launched SSTO can be designed based on landing weight instead of takeoff weight. This is a big deal for SSTO designs. Boeing had another proposed design, RAS-V that used a trolley for takeoff, but would probably be pretty dicey for an abort. Dan also mentioned the point I forgot to bring up that the RL10s on his design could be used to establish a subsonic cruise of a respectable distance, so you wouldn't actually dump propellants, you'd burn them off in your smaller engines. All in all this ability helps Mass Ratio substantially since the landing gear for a ground takeoff HTHL SSTO is typically a large chunk of the dry weight of the vehicle.]
    

As can be seen from this list, by "cheating" a little bit on the boundary conditions, assisted SSTO approaches can avoid many of the typically largest drawbacks of ground-launched SSTOs. What was a probably intractable problem before (ground-launched HTHL SSTO) becomes a lot more feasible by adding the air-launch "assist". Now, technically you could say that the carrier airplane in an air-launched "assisted" SSTO is really a stage, and therefore the idea isn't really SSTO--and you would be technically correct. But, I do think there is a fundamental difference between an airbreathing carrier plane and a true first stage, such as: no worries about TPS for the carrier plane, no need for RCS systems, no need for rocket propulsion (probably), no need for high propellant fractions, etc.

So all in all, there's a fairly compelling case that if you're interested in developing a SSTO vehicle, and a winged one at that, that air-launching is a big win over ground launching.

The Constraints, Challenges, and Drawbacks of Air-Launching

But as with everything in engineering, air-launching is not without its constraints, challenges, and drawbacks. While I'm sure that someone like Dan DeLong, or Antonio Elias of OSC could probably do better justice to this section than I could, I'll try to touch on some of the high-points:

1. There are a limited number of existing aircraft designs that can be used for air launching. What this means is that the design space for gross takeoff weight vs. carrier price is not a smooth continuous function. If you are near the upper limits of a given carrier craft, even a small increase in takeoff weight might end up forcing you to use a much larger carrier craft.
2. Most existing aircraft aren't that great for air-launching large vehicles. If you drop the vehicle from beneath most commercial aircraft, you're very limited on maximum volume beneath the wings or the hull. If you launch off of the back of an aircraft, you now need to have a higher L/D wing (or light the engines before separating) so as to not collide with the carrier after separation. Also, if you use a top-launched configuration, now you have to mount the stage on top of your carrier, which requires a substantial amount of ground handling equipment (compared to a bottom-dropper).
   
3. Due to needing to fit on an existing carrier aircraft, air-launched SSTOs are a lot more Gross Take-Off Weight (GTOW) limited than ground-launched SSTOs (which can grow to arbitrarily big sizes).
   
4. Related to point #3, there are certain systems on a launch vehicle that don't scale down very linearly. There are also minimum gage issues. These two realities mean that as an SSTO gets smaller, the maximum achievable mass ratio for the system gets worse and worse. Below some minimum size, it's no longer possible to reach orbit with any appreciable payload at all. I'm not positive where that exact point is (and it probably depends on a *lot* of details, but it is probably in the ~50klb range.
5. This is still an SSTO, and even if you cheat by air-launching, you still have a very demanding mass ratio to meet while still making the system robust enough for reuse.
6. Air-Launching a cryogenic propellant stage requires either very good insulation, or some sort of propellant storage capabilities on the carrier craft, or at least some sort of propellant conditioning equipment (ie something to pull heat out of the propellants and prevent them from boiling off). Or possibly all of the above.
7. Due to upper limits on the size of available carrier craft, this concept is unlikely to be scalable to payloads much bigger than 20-25klb.
   

Now, none of these are necessarily deal-killers, but its important to know a design choice's drawbacks.

Potential Enabling Technologies

There are a couple of recent technologies that could make a vehicle like this a lot more realistic than back when Dan DeLong first developed the concept. Specifically, cryogenic composite tank materials, some advanced cryogenic insulation techniques that are under development, the White Knight series of carrier aircraft, thrust augmented nozzles, and orbital tugs.

First off, cryogenic composite tank materials (such as XCOR's "NonBurnite" flouropolymer matrix composites) allow for somewhat lighter tank masses, allow for cryogenic "wet wings" if desired, and allow for insulation and the tank to be integrated into the vehicle structure.

The advanced cryogenic insulation technique I mentioned would help a lot with reducing/eliminating boiloff issues for cryogenic propellants (particularly LH2 if you go that way). I can't really go into the specifics on this approach quite yet. I had written an SBIR proposal for pursuing this technology (along with some teaming partners in industry), but we barely lost out, so it may take a lot longer before the idea is proven out. Suffice it to say that it could cut down on boiloff substantially in gravity, and even moreso in microgravity. Keep your fingers crossed.

The benefit of the White Knight series of carrier aircraft should be obvious. Having a large carrier aircraft with a high undercarriage that is purpose-built for carrying large rocket powered vehicles is immense. I don't have exact specs for WK2 (I figured it would be really bad form to try and pump my friends on the Scaled Propulsion team for such info), but my guess is that its at least 40klb, and possibly as much as 60-80klb. Depending on the exact numbers it might be just barely big enough for a fully orbital SSTO, though I'm not sure how much payload you could get with a vehicle that small. I really don't have a great feel for how the scaling performance for the SSTO works. There have also been several rumors (from all sorts of sources) about the possibility of a White Knight 3 down the road. T/Space showed such a vehicle in their original presentations. That would likely be capable of carrying a booster in the 300-500klb range, which is about the weight of Dan's original "Space Plane" proposal. The benefit of using a White Knight 2 or 3 for your carrier plane (above and beyond being able to buy an airplane that is purpose built for air-launching) is that the SSTO wouldn't be the only customer for the carrier aircraft. Which means the SSTO would only have to pay a fraction of the amortization costs of the WK2/3 development. More importantly, if you can get away with something like WK2, there may very well be several of these built for Virgin Galactic (and other customers), which means that the unit price of the airplane will be lower, parts will be more available, there will be a larger operational/maintenance experience base for it, and depending on the required flight-rate, it might even be possible to just rent a WK2/3 from a SS2 operator instead of having to own one outright.

Ok, I'm sure I'm starting to sound like I have a bit of a hobbyhorse thing going, but I think that thrust augmented nozzles would be a very good match for an air-launched SSTO. Especially if they were running in a "tripropellant" configuration (ie with the fuel in the thrust augmentation section being a denser fuel like kerosene, methane, or subcooled propane). The first big advantage is that it would allow an engine with a much higher thrust to weight ratio compared to a more traditional engine. This would allow for a much lighter engine to be used, which directly translates into more mass for the rest of the vehicle (and the payload). Another benefit is that depending on the fuel used (and the construction technique for the wings), a "wet-wing" tank could be used for the TAN fuel, which would allow a lot more fuel to be carried at almost no extra dry-weight. Combine this with the fact that the LOX tank would be bigger, and the LH2 tank smaller, and it ends up giving you a much higher achievable Mass Ratio for a given construction technology. Using TAN, you can also get away with a larger expansion ratio on the nozzle, giving better Isp after the TAN propellants burn out. Also, if the TAN injectors are broken up into quadrants with separate valves, they could possibly be used for Liquid Injection Thrust Vector Control. This would eliminate the need for the gimbal, and possibly allow for the now much bigger rocket engine to package better into the rocket vehicle. Lastly, if the thrust augmentation is light enough, it might allow for the possibility of keeping some "go-around" propellant for increased landing reliability. While adding the denser TAN propellant doesn't give quite the same drag and gravity loss benefits as it would for a vertical ground launched vehicle, it would still likely increase the payload fraction for the vehicle at a slight increase in GTOW. Aerojet was estimating, IIRC, a 3x increase in payload for a less than 50% increase in GTOW.

Lastly, space tugs (possibly based on the Orbital Express design, or possibly based on the Loral/Constellation Services tug designs) could greatly help such a system if it turns out to have lower performance than hoped for. Instead of taking the payloads all the way to their destination, a tug could possibly allow the SSTO to place payloads into a much lower temporary orbit (which would increase payload mass). Having a tug would also reduce the mass and complexity of the SSTO as it would no longer need its own rendezvous and docking hardware. Also, having a tug means that the cargo (or propellant) could be stored in generic containers, which would simplify ground handling and payload installation. A pressurized tug would be necessary if you wanted to fly people on the spaceplane, but that isn't too unreasonable.

All of these new technologies, most of them which have only come out in the past 5 years or so, make a system like this a lot more feasible today than back in 1986.

Preferred Instantiation

[Update: I also forgot to include this section in the original post]

While I think Dan's original design provides a lot of useful ideas, I think that my preferred instantiation of an air-launched "assisted" SSTO would be a lot smaller. After Space Plane, Dan also went the direction of a smaller vehicle--one he called "Frequent Flyer". I don't recall the exact specs for that design, but they were around 40-50klb GTOW, and required a solid strapon "0th stage" to provide enough thrust. I'd go instead with a wet-wing tripropellant design using kerosene in the wings burned in a single RL10 modified for LOX/Kero thrust augmentation. The gross weight would go up a bit, probably to up around 70-75klb (which is hopefully below the upper limit of what White Knight 2 can carry--I don't know for sure), but you'd get a better mission averaged Isp, would have a fully reusable system, and would probably increase the payload a bit over the Frequent Flyer. But Dan would be in a much better position to say. My goal with this instantiation would be basically either two people, or 1-2klb worth of cargo to LEO. If a vehicle this size works, and if it can fit on WK2, it would be possible to do a larger follow-on using something like a WK3 down the road.

That's just my opinion though.

Remaining Unknowns and Some Potential Paths Forward

So the question becomes, where are we at now with regards to this concept? What unknowns are that we currently know about? Where do we go from here?

The key "known unknowns" I can think of include:

1. TPS design and reentry aerodynamics--is it feasible to make a reusable TPS system that will work for this vehicle that is robust enough, and what moldline/airfoil design will provide the best balance of needed subsonic performance, and workable hypersonic aerodynamics?
   
2. Cryogenic propellant tanks and insulation--can tanks be designed that are both light enough and robust enough for the application? Can long-lifetime cryogenic composite tanks be built that work at LH2 tempeatures? Can an insulation technique be found that is adequate enough to prevent boiloff during the ferry to the launch site? Do we need to use some form of subcooling, propellant conditioning, or "top-off tanks" on the carrier plane?
3. Thrust Augmentation--can thrust augmentation actually deliver enough of an advantage to justify its use in this application? Can an existing engine (such as an RL10 variant) be readily modified for use with thrust augmentation? What is the optimal augmentation level? Does the better payload fraction provided allow you to use a smaller vehicle? What TAN fuel is best? Kerosene? Subcooled Propane? LH2? Can the thrust augmentation be combined with an LITVC system? Does that gain you anything? Can you adequately control the CG shift during flight with the TAN fuel in a "wet wing"? Could an RL10 type engine operating on "vapors" in turbine bypass mode provide enough of a core flow to ignite the thrust augmentation for a go-around burn at landing? Or would you need separate go-around thrusters?
4. Vehicle Sizing--what's the smallest vehicle size that can reasonably deliver (with margin) the payload in question? What are the actual carrying capacities of WK2 or 3? Would such a minimal vehicle be small enough to fit under WK2, or would WK3 be necessary?
5. Mass Ratio--what mass ratio would be required for the vehicle? Based on existing technologies, how feasible is that mass ratio to attain? Is the required mass ratio more doable using denser propellants, and if so, can a denser propellant vehicle still keep a low enough GTOW to fit on potential carrier planes?

To me, the most critical questions that are also the most unknown, are the ones regarding the TPS and reentry aerodynamics. Most of the other questions, while important, are much more straightforward to answer.

As for the path forward, I think there are multiple prongs that can be taken.

First off, for the carrier plane, WK2 is mostly built and will probably be flying this year. More exact information about its maximum carrying capacity can probably be had in the relatively near future. Trying to find a way to make a vehicle that closes using WK2 would be the most preferable option.

Second off, the TPS/Reentry Aerodynamics. Some of this can be worked on the "traditional way" using CFD and special wind tunnels (at places like NASA Ames). However at some point, it would probably be worthwhile to move on to subscale models launched from suborbital vehicles. Basically, a suborbital vehicle with a "nanosat launcher" upper stage could probably put up a small, instrumented reentry model to nearly orbital speeds. A lot of care would be necessary in designing the experiment and analyzing the data to get the actual data you want, because there are all sorts of scaling laws going on a the same time. Things like different reynolds numbers, the fact that the standoff distance of the bow shock is going to be proportional to the linear dimensions of the vehicle, so a subscale model is likely going to see more intense heating, etc. It should be possible to design a series of low-cost experiments though that can at least retire some of the risk in advance before trying to build an operational version.

As for overall vehicle integration and Mass Ratio control issues, an HTHL vehicle like Xerus actually provides a useful starting point for working ones way up to an SSTO. Now, the XCOR people aren't SSTO fans. And they're especially not LH2 fueled SSTO fans. But, the best approach for trying this would probably be to hire someone like XCOR to try and build a lower-performance iterative prototype first to test out some of the key functionality, and then work your way up to the performance needed for SSTO. The first prototype might use just a traditional LOX/Methane engine with as high of a mass ratio as possible. Make sure that the handling and basic aerodynamics work out right. Test out the cryo insulation, and air-launch cryo-propellant handling procedures. Make sure that the TPS functions as expected in the suborbital (though relatively high velocity) environment that such a vehicle could provide. Upgrade the engine to a TAN system and get some experience operating that and making sure that the LITVC scheme works. Test out RCS functionality. Test abort modes.

Do a second iteration that has LH2 as well as the TAN propellant. Develop and test out a TAN-modified RL10. Get experience using such an engine. Get in-flight performance data. Make sure the cryo insulation still works. Make sure the tank can handle the cold cycles. See how close you can get to the mass ratio. Instrument the crap out of your vehicle and figure out where you can shave weight, and how robust/reusable the TPS is in an almost orbital situation. Figure out if you need to scale up the vehicle, or what other changes will be needed to reach a sufficient payload target. Start expanding the envelope to orbit.

Now some of these steps might be skippable depending on how previous steps go. Some of them might be doable as part of other programs (for instance figuring out the cryo composite tanks for LH2 or the special insulation system might benefit other projects, developing flightweight propellant conditioning hardware that can fit on a WK2 or 3 might also be useful for other projects). But these are just some thoughts on what has to be done from a technical standpoint to get "there" from "here".

Conclusions

In spite of the bad reputation that SSTOs have earned during the last decade, there are at least some versions, like the air-launched SSTO that aren't entirely crazy. They still might not make sense, but if any SSTO RLV design ever makes it, my guess is it would likely be something like this.