Laser launcharchitecture

Modular Laser Launch Architecture:
Analysis and Beam Module Design
NIAC Phase I Fellows Meeting
24 March 2004
Jordin T. Kare
Kare Technical Consulting
908 15th Ave. East
Seattle, WA 98112
206-323-0795
jtkare@attglobal.net
Revised 3/23/04
Kare Technical Consulting 3/23/04 1

The Laser Launch Concept
Leave The Hard Parts
On The Ground!
Launch many small payloads
on demand -- up to 10 per hour Leave The Hard Parts
!
On The Ground!
Laser and Beam Projector
• Big
• Heavy
• Expensive
• STATIONARY
Vehicle
• Small
• Simple
• Cheap
• Inert
30,000 launches per year x 100 kg
= 3000 Metric tons per year!!
Rule of Thumb:
1 kg of payload
per MWof laser

Why Laser Launch?
• Massive launch capacity
– A 100-kg launcher can put 3000 tons per year in LEO
• Very low marginal cost to orbit
– Electricity, vehicle, and propellant easily <$100/lb
• Potentially low total cost to orbit
– If the system is cheap enough to buy and run, and…
– If there are enough payloads to launch
• Maximum safety -- no stored energy on vehicles
– Enables all-azimuth launch from any site
• High reliability, easy to maintain
– The hard parts stay on the ground
– Vehicles are simple, mass-produced, and testable
• Ultimate launch-on-demand -- FedEx to space

Pulsed Laser Propulsion Works...

… But Has The Same Problems As Everything Else
• Development cost
– Even at $10/watt, $1 Billion for 100 MW
• Technical risk
– You don’t know if it will work at all without spending $$$
• In this case, for a multi-megawatt test laser
• Programmatic risk
– You don’t know what it will actually cost until you’ve built it
• Big lasers have had cost/schedule/performance problems for 40
years!
– Reality is always different from theory; operational systems
are always different from prototypes

The Heat Exchanger Thruster
Primary (H2) Propellant Tank
Pump
(optional)
Lightweight
Heat Exchanger
Secondary
(Dense)
Propellant
Nozzle(s)
Laser
Beam
Dense propellant
injection trades lower Isp
for higher thrust,
matches exhaust velocity
to vehicle velocity
• Exhaust Temperature ~1000 C
• Specific Impulse ~600 seconds

Heat Exchanger Thruster Advantages
• Works with any laser wavelength and pulse format
• Nearly 100% efficient
– high absorption, negligible reradiation
• Simple to design
– Steady flow
– Simple propellant properties (especially for H2)
• Simple to build
– Electroplating technique demonstrated at LLNL
– Modular design scales easily to any area
• Simple to test
– Works with any radiant source; doesn’t even need a laser

Current 100 MW Vehicle Concept
Dense propellant tanks Avionics
!
Drop tank
Stage 2 tank
Total H2 tank volume ~25 m3 Payload
Aeroshell
Pressurant tank
Drop tank
!
~6 meters
!
Heat exchanger
(25 m2)

What Do We Do About The #%&@ Laser?
• Lasers cost too much
– Absolute cheapest high power laser is $20-50/watt
• CO2 electric discharge, with very poor beam quality
• Should scale to 100 MW, but not easily or cheaply
– Stay-on-all-day lasers above ~10 kW don’t exist
• AVLIS copper vapor lasers were 10 kW total, at a cost of
>>$1000/watt
• No one will pay to develop a large laser
– Too many bad memories: CO2, HF/DF, Excimer, FEL…
– “There are liars, damn liars, and laser builders”

Laser Diode Arrays
• >50% efficient DC to Light at ~800 nm
• 10,000 hour lifetime (60,000 launches!) CW operation
• Run on DC current; water cooled
• Commercially available from multiple vendors
• $4 - $10/watt NOW
• $2/watt in a few years in
100 MW quantities
• BUT -- not coherent; not
high enough radiance to
beam 500 km
A 1200 Watt CW “stack”
from Nuvonyx, Inc. --
a catalog item!
A 1200 Watt CW “stack”
from Nuvonyx, Inc. --
a catalog item!
1 cm

The Beam Module Concept
• DON’T build one big laser and beam director
• Build MANY small “Beam Modules”
– Completely independent laser and beam director
– Minimal common services, ideally only power and water
“This division of the laser source among many apertures was initially
regarded only as a necessary evil, required by the low radiance of
noncoherent [laser diode] arrays. However, we have recently realized that
the fact that the laser and optical aperture can be subdivided into small
independent “beam modules” is a fundamental advantage of laser
propulsion over other advanced propulsion systems, and may well be the
key to making laser launch the best option for a future launch architecture”
-- J. Kare 7/03
“This division of the laser source among many apertures was initially
regarded only as a necessary evil, required by the low radiance of
noncoherent [laser diode] arrays. However, we have recently realized that
the fact that the laser and optical aperture can be subdivided into small
independent “beam modules” is a fundamental advantage of laser
propulsion over other advanced propulsion systems, and may well be the
key to making laser launch the best option for a future launch architecture”
-- J. Kare 7/03

Advantages of Beam Modules
• Scalability
– System grows smoothly by adding beam modules
• Reliability and maintainability
– Failed modules have no effect on launch (even in progress)
– Beam modules can be replaced as units
• Cost
– Everything in the system is mass-produced
– Plausible cost goal: comparable to a modern automobile
(excluding laser)
• Development
– All the technical risk is in the first few units: $M, not $B
– No failure costs very much -- you can’t “crash the prototype”

Conceptual Beam Module (as of last year)
Optics module
• 6 kW* diode array
• Stacking optics
• Tip-tilt mirror
• Tracking sensor
Support module
• Diode power supply (16 kW* DC)
• Diode temperature controller
• Cooling water pump/regulator
• Tracking sensor controller
• Mount controller and drivers
• Tip/tilt controller and drivers
Telescope
• 3-m replica primary
• Secondary
• 2-axis alt-az mount
(possibly alt-alt to avoid
zenith singularity)
A 100 MW launch
system might have
~20,000 of these* --
But you can build ONE
A 100 MW launch
system might have
~20,000 of these* --
But you can build ONE
to start with
to start with
*Based on 2x1013 radiance and 500 km range;
better radiance or shorter range would increase
unit power and decrease number required

At Least Three Solutions
• Fiber Lasers
• Spectral Beam Combining
• Diode Pumped Alkali Laser (DPAL)
All made breakthroughs within the last year!

Fiber Lasers
See www.spiphotonics.com
• Converts non-coherent diode array light to single-mode laser
output with up to 90% efficiency; 75% is routine
• Demonstrated at 1 kW; 10 kW projected within 1-2 years
• Simple and mass-produceable; already in commercial production

Spectral Beam Combining (SBC)
lmax
lmin
Diffraction
Grating
Diode bars
Field lens
2-D Microlenses
• Diodes operate independently in external cavity
Output
Coupler
– Antireflection coating on laser diode output facets
– Each diode automatically operates at the “correct” wavelength
• Demonstrated* with ~700 diodes in 7 bars (26 watt output)
– >1000-fold stacking should be feasible
• SBC efficiency ~50% (power out compared to raw diode bars)
•AcuLight, Inc., Bothell, WA, 2004

Diode Pumped Alkali Laser (DPAL)
4 kW 795 nm Rb laser concept
• Diode array pump 6.08 kW @ 780 nm
• 66% light-to-light efficiency
• New concept (2003) developed by W. Krupke et al. (ex-LLNL)
• Rb (785 nm) or Cs (895 nm) vapor in He buffer gas
– Absorption line pressure-broadened to match diode linewidth
– High efficiency requires tight control of diode wavelength, spectrum
• Demonstrated at ~30 W level
– Performance predicted accurately with no free parameters

Laser Subsystem: Alternatives
DPAL
Rubidium vapor cell
795 nm
Baseline Fiber Laser SBC Diodes
8 x 125 W diode bars
805 - 810 nm
Yb-doped double-core
fiber
Lasing medium
Wavelength 1.08 mm
Module output power 50 kW 10 kW 50 kW
10 kW
6
1.2
1.1 x 1016
54%
18.5 kW
50%
27%
222 kW
162 kW
~300 liter/min*
Unit laser power 10 kW 600 W
# of lasers/module 6 20
2
2.3 x 1014
60% SBC eff.
1000 W
50%
30%
40 kW
28 kW
~50 liter/min*
Beam quality (M2) 1.5
Radiance (P / l2 (M2)2) 3.8 x 1015 W/m2-sr
Laser Efficiency (P 80% out / Pdiode)
Pump Power per laser 12.5 kW
Diode Efficiency 50%
DC efficiency (P 40% out / PDC)
DC Power (module) 150 kW
Cooling Requirement 90 kW
Water flow ~100 liter/min

10
9
8
7
6
5
4
3
2
1
0
How Much Will They Cost? Diode Arrays
Current
Price
Range
Diamond Optical est.
$4/W @ 1000 bars,
~20% drop per 10X qty
95% learning curve
90% learning curve
Likely price range
@ 200 MW quantity ~$2 - 3.50/W
0.1 1.0 10.0 100.0 1000.0
Total power (MW)
$10/W
$6/W
$/Watt
$/W

Laser Diode Cost Trends
– Substantial reductions in bar cost
• $100/bar, 100 W bars in 1-2 years (F. Way, Diamond Optical)
• $10/bar (50 W bars?) “to stay competitive” (a major manufacturer)
– Substantial reductions in packaging cost
• LLNL, Oriel, others developing low-cost packaging
– Oriel “TO-220” package aimed at 50% of late-’03 price; available in mid 2004
• Diamond Optical willing to quote ~50 cents/watt
– Unpredictable gains in performance
• Bars have been stuck at 60 W for several years (100 W Real Soon Now)
• Major improvement may require radical approach (e.g., VCSEL arrays)
– But...Current market does not support large investments in improved
processing/packaging
• ~$100M/year for all high power arrays, vs. $4B/year for discrete diodes at
peak of telecomm market
• ~$1B market for launch system would drive industry

How Much Will They Cost? Complete Lasers
• Current commercial fiber lasers are $500/watt* -- Too Much.
BUT
– Relatively low unit power: 100 W
– Based on discrete packaged diodes @ $100 - 150/watt, not bars
– Semi-custom production: typically ~10 units
• Best prediction for high-volume, multi-kW lasers: $7 - 10/W
– 3 - 4X diode cost
– Best estimate of component cost in quantity
– Consistent with projected cost of fiber ($2K / 1 kW)
– Consistent with ~85% learning curve for complex assemblies
• Other laser options in same range

Telescope Requirements
• Total Area
– Set by laser radiance (W/m2-sr) and vehicle flux requirement
• e.g., fiber laser @ 3.8 x 1015 W/m2 sr requires ~330 m2 of optics
– Secondary limits from mirror heating, thermal blooming
• Still need to double check blooming
• Mirror size and quality
– Diffraction: Dmirror > f l R / d
• R / d ~ 105 (500 km / 5 m) f ~ 2 (2.44 for classical limit)
• ~ 16 cm @ 0.8 mm, 22 cm @ 1.08 mm
– Wavefront error: Slope < 0.5 x 10-6
• ~5 waves per meter (vs. 1/10 wave for astronomical telescope)
• Pointing and tracking
– Pointing range (nominal) +/- 80° along track, +/- 45° crosstrack
– Closed loop tracking to <<10 mrad; open loop pointing to ~1 mrad

Optics Options
Cassegrain
• Simple optics
• Compact mount
• Obscuration losses (few %)
Off-axis Cassegrain
• Low loss
• Asymmetric optics
• Bulky
Diffractive primary
• Potentially low cost primary
• Potentially light weight
• No obscuration
• No current technology
• Chromatic aberration
Stationary telescope
with tracking flat
• All hardware is stationary
• Minimum moving mass
• Cheap primary
• Additional large optic (flat)
• Field rotation
Multiple small telescopes
on common mount
• Lower optics cost/mass
• Compact
• More tracking hardware
• Alignment problems

Optimum Primary Diameter
Diffraction
limit ~0.2m
Production
optics ~50 cm
Max. blank diam.
0.95 - 1.4 m
Largest monoliths
made to date 8m
Tracking hardware
Const * N ~ D-2
Mirror cost
~ N* D2.5
System
Cost
0.1 m 1 m 10 m
Primary Diameter
• Minimum size set by tracking hardware cost or diffraction
• Maximum set by rapid increase in mirror cost with size
• Small jumps at limits of various “standard” supplier capabilities

TANSTAACT(TAG)
• There Ain’t No Such Thing As A Cheap Telescope
(That’s Any Good)
– Many advanced technologies not necessary (or cheap)
• Non-glass substrates (SiC, Graphite Epoxy)
• Advanced polishing techniques (magnetorheological polishing)
• Active/Adaptive primary (PAMELA)
– Several possibilities still to look at
• Replica optics
• Electrodeposited metal optics
• Lightweight mount (up to half the cost of a telescope)
• Shifts optimum toward fewer, smaller telescopes than
original concept
– “Only” 1000 - 2000 x 1 m, vs. 10,000 x 2 - 3 m
– Allowed by improved (higher radiance) laser options

Telescope Baseline
• ~1 meter f/2.5 Cassegrain
– Afocal (technically a Mersenne)
– Borosilicate (Pyrex) primary
• “Few-wave” accuracy
– Multilayer coated for low
absorption
• Small (10 cm) secondary
– Minimize obscuration
– Limited field of view is OK
• Alt-Alt mount
– Tracks smoothly through zenith
~$100K each @ 1000 units ($22K for primary)
$2 - 5M investment to be able to make 1/day
~$100K each @ 1000 units ($22K for primary)
$2 - 5M investment to be able to make 1/day

Photonic Crystal Fibers
Left:
“Air-clad” double core fiber
Right:
Visible-wavelength high power
single-mode guiding
J. Limpert, et al. "Thermo-optical
properties of air-clad photonic crystal
fiber lasers in high power operation,"
Opt. Express 11, 2982-2990 (2003)
• Transport kW power with low loss (<<1 dB/meter)
www.blazephotonics.com
–“Holey” fiber region guides single mode; forbids higher modes
– Most power is transported in void space; avoids nonlinear effects
• Enabling for low cost beam projectors
– Eliminates multiple mirrors in beam path
• Lossy, difficult to align, difficult to clean
– Isolates laser from telescope motion, dust, etc....

Tracking Subsystem
• Requirement: point beam to ~5 mradians
– Track vehicle (control mount) 500 mr @ <10 Hz
– Compensate atmosphere <100 mr @ ~100 Hz
“Fast” CMOS camera
drives tip-tilt mirror;
100 mr FOV, 500 Hz
“Slow” CCD camera
controls mount;
1 mr FOV, 60 Hz readout
controller
3-axis
(tip/tilt/focus)
actuated
mirror
From laser

Beacon Options
• Reflected laser light
– Too much local scattered light
• Thermal radiation from hot heat exchanger
– Start/restart problem
– No pointahead for atmospheric correction
• Ground-based laser with retroreflector
– Possible, but requires high power (kW), good tracking
• Beacon on vehicle
– Narrow-angle with pointing mechanism
– Wide-angle -- simplest possible system
• A laser diode and a pingpong ball

Baseline Beam Module
1-m Cassegrain Telescope
• f/2.5 primary
• Alt-Alt Mount
Optics module
• Fiber output optics
• Tip-tilt mirror
• Tracking sensor
Laser assembly:
6 x 10 kW
fiber lasers
Support module
• Diode power supply (250 kW DC)
• Cooling water pump/regulator
• Tracking sensor controller
• Mount controller and drivers
• Tip/tilt controller and drivers
• Allows for 20% losses in optics, 10% loss in
transmission, and 10% of modules offline for
maintenance/repair

100 MW System Capital Cost
• Laser 1020
– 120 MW Fiber lasers @ $8/watt 960
– 300 MW DC supply @ $.20/watt 60
• Optics 144
– 2000 Primary mirrors @ $22 K 44
– Other optics, pointing, tracking @ $25 K 50
– Mount and pad @ $25 K 50
• Facilities 161 - 350
– H2 plant (1000 - 30,000 launches/year) 2 - 60
– Power buffer 15
– Power line 11-48
– Launch stand 30
– Physical plant 100 - 195
• TOTAL 1325 - 1514
My long-standing Rule Of Thumb estimate: ~$2 Billion

What Happens To Space?
Architectural Implications 1
• Cheap small payloads (common to all laser launch)
1. Microsats/Nanosats: any mission that can be done in 100
kg pieces will be cheapest that way
– But that will only account for a few % of launch capacity
2. Modular satellites/Constellations: Divide up functionality
into 100 kg co-orbiting blocks (cf. NIAC work on constellations)
3. On-orbit fueling/refueling/resupply
– Stimulates development of autonomous microspacecraft
rendezvous and docking, “tug” spacecraft
– Opens up high-mass-ratio mission space: Moon/Mars with
storable propellants
4. On-orbit assembly: large structures constructed on orbit
5. True space industry?

What Happens To Space Industry?
• Routine, on-demand launch; very high reliability
– Shift in spacecraft reliability criteria; “ground spares” OK
• A change in space industry
– Large aerospace company resources are not required
– To build vehicles
– To build beam modules
– To build payloads
– “Learning curve” for participation is much less costly
– A change in space politics
– More countries can have their own launchers, or “rent
time” on larger launchers and provide vehicles or payloads

What Happens To Human Space?
• Immediate shift in logistics for human LEO missions
– Missing/broken widgets replaceable by Next Day Space
• Scaling and reliability enable growing human presence
– Laser launch is uniquely testable to ~ 10-8 failure probability
• e.g., 104 launches AND 104 abort/recoveries before flying a
person
– Initial human launch capability at TBD payload/laser power
• Mercury capsule was ~1500 kg; surely we could do better?
• Potential driver for launch system growth to ~1 GW
– Growth to 2 or more person vehicle opens up passenger
launch -- to thousands or 10’s of thousands per year

In-Space Power and Propulsion
• Providing electric power shifts module design goals, but
“power” modules can also be used for launch
– PV-compatible wavelength preferred (nominally 700 - 900 nm)*
– Higher beam quality (adaptive optics) may be desired
– However, dedicated pulsed lasers may be preferred for high-Isp
pulsed propulsion
• Low cost modules open design space for space power
– For GEO power, each satellite can have a dedicated source
– For LEO/MEO power, modules can be distributed to many sites
worldwide
• Launcher site can provide 100-MW power levels anywhere
out to GEO
– Relay architectures to be explored

Beam Module Satellite Solar Power System
• Small (10 cm) optics in GEO generate practical (<1 km)
spot size on Earth
– Ideal application for diffractive optics?
• Optics-sized solar panel produces a convenient amount
of power: ~3 W for 100 cm2
• SO... build self-contained ~10x10x10 cm beam modules
and simply stack them up to make a powersat
– No high power cables
– No phase locking;
• No minimum satellite size to deliver power
• Power can be shared among any number of receivers
– Modules simply clip to a frame

Beam Module SSPS
Module array on
simple grid
Flat film
reflector
rotates 1/day
tilts 1/year
for sun tracking
Stationary
flat film reflector
Ground
PV array
Beacon/
command
transmitter
Offset from
ground array
Possibility:
Aerostat w.
microwave
or fiber bundle
downlink?
Note added 3/30/04:
We have been referred to a similar SSPS
configuration for microwaves, with a phased
array transmitter, proposed by Nobuyuki Kaya,
e.g., in Space Energy and Transportation 1 (3)
1996, pp. 205-213. Modular laser configurations
have also been considered; we are still seeking
details to compare against the concept proposed
here.

Solar Power Satellite Beam Module
PV Cell
10 x 10 cm
3..5 W out
Laser
Driver
3 W in
Electronics
power 1/2 W
Main mirror or diffractive lens ~10 cm dia
Laser diode
1.5 W out
Guide
sensor
Controller
3-axis MEMS
actuator
3 cm
fold
mirror
Actuator driver

Conclusions 1: Technology Is Ready
• Lasers crossed the threshold within the last year
– Performance is sufficient, and nearly certain to improve
– Costs are still high, but not inherently so
• Costs will drop with volume and time
• Current optics technology is dull, but adequate
– Modern glass optics are cheap enough with high-radiance lasers
• Optimum primary size is ~1 meter or less
– Innovative but unproven technologies are waiting in the wings
• No show-stoppers elsewhere in the system
– Mounts, pointing and tracking, etc. are straightforward
• On-vehicle “omni” beacon looks best for pointing/tracking and makes
adding adaptive optics straightforward if required
– Power storage is ripe for innovative tech (advanced batteries,
flywheels) but not a system driver

Conclusions 2:
Architecture Implications Are Profound
• Laser launch in general shifts paradigms
– Small unit payloads, routine prompt access => on orbit industry
• Modular launcher technology changes industry
– Small companies can play -- modules can come from many sources
– Small countries can play -- buy their space launch “by the yard”
• Crewed flight is a new game
– Continuous scaling from support (100 kg payloads) to solo
launches (~1000 kg) to taxi (tour bus?) service
– Inherently high reliability, inherently testable -- tourist friendly!
• Significant effects on in-space power and propulsion
– Requirements are different, but overlapping
– Low-enough unit costs open new options, e.g., laser-per-satellite
power systems, distributed power belt for orbit raising
• Spinoffs: powersats, power beaming, industrial lasers...

Where to go?
• Technology development -- only small niches
– Most technology is being driven by other uses
– Some leverage in low-cost optics, SBC lasers
• Technology integration and demonstration
– Integrated subscale module
• COTS fiber laser(s) or SBC laser array (~100 W)
– Upgradeable to higher power as lasers become available
• Optics TBD: at least half-scale; full-scale if possible
• Full tracking system
– Full scale beam module is a bit much to bite off: ~$10-20 M
• Higher power-per-module than originally conceived
• System integration and architecture studies
– Many, many issues barely touched: siting, markets, safety...

Laser Launch Architecture With Modular Ground-Based Laser Array
Large spacecraft are
assembled and serviced
at a LEO assembly facility
(Crewed or robotic)
(Optionally) Vehicles
discard aeroshell,
drop tanks at
top of atmosphere
Heat Exchanger
(HX) vehicle
with side-facing
heat exchanger
Propellant
(LH2) storage
Launch catapult
boosts vehicles to
~100 m/s
Vehicle prep Payload handling
To GEO, Moon, Mars...
Supply vehicles
rendezvous with
Space Station and
other future facilities
Individual beams from
Beam Modules
add incoherently at
the vehicle
Failed modules do
not affect launch
Main Beam
Module Array
(100 - 10,000 units)
Power generation/
energy storage
Array control
Independent payloads
go directly to LEO
Baseline:
expandable
vehicles
discarded.
Vehicles could
also be reused
Secondary Beam
Module array(s) for
orbit raising, reentry,
rendezvous
propulsion, etc
Recovery
area

Laser launcharchitecture

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