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Laser Space Propulsion Overview

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1 Laser Space Propulsion Overview
Claude Phipps, Ph. D., managing partner James Luke, partner Photonic Associates, LLC, Santa Fe, NM Wesley Helgeson, senior research associate NMT/IERA, Albuquerque, NM XIV Advanced Laser Technologies Conference Brasov, Romania September 12, 2006

2 Perspective I am now of a certain age where “practical” strictly means “what I’ll see in my lifetime.” So, I’m not going to talk about some gee-whiz laser propulsion possibilities that I avidly discussed years ago Launching 10 tonnes into low Earth orbit with a 4GW laser Deflecting asteroids bent on destroying life on Earth using a multi-GW laser and a 10-km diameter mirror on the moon But I am still quite excited about Assembling space stations from 10 to 20-kg launches of components at 1% of current costs per kg Micro-, mini- and macro-thrusters Several other promising concepts in laser space propulsion

3 Outline Introduction to Photonic Associates, LLC
Terminology and Theory Advantages of Laser Space Propulsion (LSP) Taxonomy Pure Photon Propulsion Propulsion by Laser Gas Detonation Laser Jet Engines Propulsion by Laser Expulsion of Liquids Laser-Electric Hybrids Laser Heat Exchangers Propulsion by Laser Ablation Perspective and Conclusions

4 Terminology for LSP Here are the most important parameters:
1) Momentum coupling coefficient Cm=dJ/W=dmvE/W = F/P 2) Specific ablation energy Q* = W/dm 3) Exhaust velocity vE = CmQ* 4) Specific impulse Isp = dJ/(dmgo) = vE/go 5) Mass usage rate 6) Ablation efficiency hAB = WE/W = dmyvE2/(2W) = yCmvE/2 7) Energy conservation CmvE = CmIsp*go = (2/y)hAB where y = <vx2>/(<vx>2) ≥ 1 is a parameter1 that is often (The CmvE product = 2.0 when hAB = y = 1, but can’t be larger unless hAB >1) [1See Phipps & Michaelis, Laser and Particle Beams, 12(1), (1994)]

5 Conservation of Energy
I would like to make this point very clear. Take a “drift Maxwellian”: 8) 9) 10) 11) ≥1 If M = u/cs = 1, and cs = (kT/mE)1/2 with  = cp/cv =5/3, we have  = 1.60 Comment: forward peaking of most free, high-intensity laser ablation jets2 can give M≈2 and  = 1.15, and we can take  ≈ 1. [2See Kelly and Dreyfus, Nucl. Inst. Meth. B32, 341 (1988)

6 Terminology, cont’d 12) Thrust efficiency hT = heohAB
Here are some ancillary relationships among LSP parameters: 12) Thrust efficiency hT = heohAB 13) Fuel lifetime tAB = go2MIsp2/(2PhAB) Severe penalty paid for Isp = 10s (Yabe) Lots of thrust, but 10,000 times less tAB than if Isp =1000s 14) Optimum coupling fluence Fopt = 480 t0.5 MJ/m2 15) Surface absorber vacuum model3: 16) Volume absorber vacuum model4: Cm2 = (2rt/F)(T - Fd/F - Fp/F - lnx/x) [In Eqs. 12 & 13, A is mean atomic number, Z is mean ionic charge state, y = A/2[Z2(Z+1)]1/3, x = F/Fth, Fth is thrust threshold fluence, Fd and Fp are fluences required for dissociation and plasma formation, r is mass density, t is target thickness and F is incident fluence] 3 Isp is just a matter of intensity! See: Phipps et al. J. Appl. Phys., 64, 1083 (1988) 4 Parameters defined in J. Prop. & Power, 20 no.6, (2004)

7 Advantages of LSP 1) Lower costs with laser launching. Reducing the cost of getting to space by 2 orders of magnitude ($100/kg vs. $10,000/kg today) will change our relationship to space travel. Greater than the price of gold! But it need not be so! [Myrabo Lightcraft flight, White Sands] Today’s LEO launch costs Launch System Minimum Cost (k$/kg) Rockot 10 Shuttle 12 Athena 2 Taurus 20 ISS, commercial 22 Pegasus XL 24 Long March CZ-2C 30 Athena 41 Photo: Courtesy Leik Myrabo

8 Lower costs, cont’d Connection between the charts: 3.3USD/MJ of laser light delivered at 5 flights per day. Is that reasonable5? Compare cost of wallplug energy on the ground (0.03USD/MJ). [5See Phipps & Michaelis, Laser and Particle Beams, 12(1), (1994)] Above: theoretical predictions for flight in vacuum. Laser launching facilitates frequent launches, diluting recurrent and sunk costs. Above: (•) flight simulation results for 1-m diameter craft laser-launched from ho = 30km in air compared to vacuum predictions at left.

9 Advantages of LSP 2) Lower Dead Mass
Do not have to raise turbines, pumps, tanks, exhaust nozzles, etc., along with the payload 3) Variable Exhaust Velocity (crucial!) Accomplished by varying intensity on target (t, As) Uchida6 showed that varying vE during a LEO to GEO transfer mission gave a factor-of-3 lower energy cost than conducting the same mission with a constant vEopt. vE was varied by a factor of 300 according to vE/vEo = C(t/to)0.5 Special case of fact that, when vE = v(t), theoretical maximum efficiency of momentum transfer to flyer can be obtained, because exhaust stream velocity is zero in the starting reference frame in which v is measured. 6Uchida, 1st International Symposium on Beamed Energy Propulsion, Huntsville, AL, 5-7 November 2002, AIP Conference Proceedings (2002)

10 Advantages of LSP 4) Enabling Otherwise Impossible Missions: A recent “BAA”* set the following graduate-level problem: Prime power: kW Spacecraft total mass: kg Engine mass including fuel: 80kg Initial orbit: 500km altitude circular Complete any of 4 missions: Rephase s/c 180 degrees in 12 hours Raise s/c from 500km to 1500km in 2 days, return in 30 days Crank orbital plane 15 degrees in 90 days Drop s/c to 300km, fight ram pressure for a year with 50W prime power, return in 30 days These requirements were set to be impossible with current technology But, a 20-kg laser propulsion engine using a 470W diode-pumped glass fiber laser can accomplish all the tasks, according to our calculations. *See

11 Taxonomy of LSP Pure Photon Propulsion
Earliest LSP concept, before lasers were demonstrated8 Cm is only 2/c = 6.7N/GW (for total reflection) Isp is as large as it can be, 31Ms But: to accelerate 1 tonne at go, requires 1.5TW laser power Möckel9 did not shrink from this, envisioning a 1km diameter xray laser beam with 1Å wavelength impinging on a 1km diameter sail to propel a spacecraft to a-Centauri in 10 years. At present, only two practical applications exist: Bae’s concept10 for intracavity photon thrusters to precisely position nanosats Photon sails (but here the sun or another star is the photon source) 8 Sänger, J. Spacecraft, in Probleme der Weltraumforschung (IV. Internationaler Astronautischer Kongress, Zurich, 1953) Biel-Bienne, Laubscher, p.32 (1955) 9 Möckel, J. Spacecraft and Rockets 9, no. 12, pp (1972) 10 Bae, Final Report, NIAC Phase I Program , April 30, 2006, NASA Institute for Advanced Concepts, 75 Fifth St. NW, Suite 318, Atlanta GA 30308, USA

12 LSP Taxonomy 2) Propulsion by Laser Gas Detonation
The air-breathing Myrabo Lightcraft11,12 would, in principle, require no ablation fuel other than ambient air, in the atmosphere. Biparabolic design: laser light coming from below forms a ring focus under the rim, propels craft via successive detonations in air. Outside atmosphere, the device would use solid ablatants located in the rim. Flown to 71m in spin-stabilized flight, driven by a repetitively-pulsed, 10kW CO2 laser. Cm ranged from about 250mN/W for air to 900mN/W for solid propellant. Materials problems are challenging Apollonov laser jet engine: efficiency and materials survival advantages (later) Photo: Courtesy Leik Myrabo 11Myrabo, AIAA/SAE/ASME 18th Joint Propulsion Conference, Cleveland, OH (1982) 12Myrabo, Proc SDIO Workshop on Laser Propulsion, J. T. Kare, ed., LLNL CONF , Lawrence Livermore National Laboratory, Livermore, CA 94550, pp (1987)

13 Engineering characteristics of the model:
Results of the flight experiments with AeroSpace Laser Propulsion Engine (ASLPE) model Dr. Yuri Rezunkov, NIIKI OEP, Russia Model flight characteristics: Laser power – 5 kW Maximal acceleration – 4-5 m/s2 Maximal velocity – 3.5 m/s Thrust (max) – 1.5 N Flight duration – 3 s Engineering characteristics of the model: Cm = 25 dyne/W (air-breathing mode), and 45 dyne/W (laser-chemical propulsion) Model mass – 150 g 16Rachuk et al., AIP Conference Proceedings 830, pp (2006)

14 LSP Taxonomy 3) Laser Jet Engines
Apollonov has proposed and measured the performance of a model version17 of a laser driven jet engine which can simultaneously achieve Cm = 4.17mN/W and vE = 2,520m/s. These parameters give CmvE = 5.25, an unusual result which is 2.5X larger than permitted by Eq. 7. However, factors of 2 are not a big problem When verified, this is an extremely important result for nonenergetic ablation fuel Device is based on the resonance merging of shock waves generated by an optical pulsed discharge to form a quasi-stationary wave, and has obvious advantages in thrust conversion efficiency and lifetime. 17Apollonov, et al., Quantum Electronics 36, pp (2006)

15 LSP Taxonomy 4) Propulsion by Laser Expulsion of Liquids
In 2002, Yabe18,19 proposed a laser-powered microairplane For, e.g., collecting climate data or observing volcanic eruptions Engine uses shock generated on a laser-irradiated absorber at the back of a liquid container to expel droplets of liquid Result: largest Cm values ever observed, but Isp = 10s (for some applications, OK) Measured Cm’s up to 5mN/W (simulations gave up to 70mN/W) 18Yabe et al., Appl. Phys. Letters, 80, pp (2002) 19Yabe et al. Appl. Phys. A77, pp (2003)

16 LSP Taxonomy, cont’d 5) Laser Heat Exchangers
Kare has proposed20,21 the HX thruster Essentially a laser-heated boiler (simulations give Isp = 600s with 1000C exhaust) Achieves very low specific mass (0.001kg/kW), but assumes a 100MW laser Water injection at low altitude to increase thrust, H2 above atmosphere Launch mass M = 5400kg, m = 180kg delivered to LEO, m/M = 0.033 Rather22 has proposed a similar concept, in which a Shuttle H2 tank with M = 30Mg could be propelled to GEO in 45 days Would use a 10MW laser to heat 4Mg H2 achieving Isp = 1500s Could be used to build a manned GEO station or LEO-GEO shuttle 6) Laser-Electric Hybrids Horisawa and coworkers23 have built and tested a hybrid laser-electric thruster (next slide) 20Kare, J. Prop. and Power, 11, pp (1995) 21Kare, AIP Conference Proceedings 664, pp (2002) 22Rather, AIP Conference Proceedings 664, pp (2002) 23Horisawa et al., AIP Conference Proceedings 830, pp (2006)

17 j F B Laser-Electric Hybrid Acceleration Propulsion System Anode
Research Activities at Horisawa Lab. at Tokai University : Laser-Electric Hybrid Acceleration Propulsion System Coaxial L-EM Hybrid Thruster j Anode F B Cathode Thruster head Anode Ibit vs Charge Energy Feasibility studies of microspacecrafts are currently under development for the mass less than 100 kg with an available power level for propulsion of less than 100 watts. Various potential propulsion systems for microspacecraft applications, such as ion thrusters , field emission thrusters, PPT, vaporizing liquid thrusters, resistojets, microwave arcjets, pulsed arcjets, etc., have been proposed and are under significant development for primary and attitude control applications.1 Cathode Length: 22mm Channel length: 3mm Cu-Anode: f6.0mm Al2O3 –Insulator: f5.0mm C-Cathode & Propellant: f4.0mm Isp vs Charge Energy

18 Taxonomy of LSP 7) Propulsion by Laser Ablation
Kantrowitz24 suggested the first practical approach to LSP, in which a laser is used to heat a solid propellant surface to generate a vapor or plasma jet that provides the thrust. Cm is as much as 8 orders of magnitude larger Watts (rather than GW) of laser power can now do useful tasks Propellant may be inert, or exothermic. Laser may be remote (e.g., groundbased), or onboard. Invariably, these should be pulsed rather than CW Allows achievement of high Isp when necessary Broadens the range in which Isp and Cm can be varied Facilitates clearing plasma from the optical path between pulses 24Kantrowitz, Astronaut Aeronaut. 9, no. 3, pp (1971)

19 The msmLPT Lippert group at PSI25: target photochemistry
Market: attitude & position control for msatellites Patents: we own the patents on this application Total mass 0.5kg Thrust 0.1 – 10mN, 20W max input Thrust efficiency = 133% (chemical input) Isp = 200s, thrust-optimized Minimum impulse bit = 100nN-s Uses GAP:C or GAP:dye fuels Likely to be 1st laser ablation propulsion application to fly in space 25Lippert, et al., Appl. Surf. Sci., 186, (2002)

20 The nsmLPT Isp is just a matter of intensity (Eq. 15). 7ks has been seen in other work26. The nsmLPT, operating at I = 0.25PW/m2, is the basis of our 3,000-s Isp claim Research device, not as completely developed as the msmLPT Benchtop and microchip lasers produced data Fluence ~ 1MJ/m2, t = 4ns Vacuum Torsion Balance Thrust Gage Gold-coated, 2.5-inch IBM hard drive disk (4400 rpm) 26Phipps, & Michaelis, Laser and Particle Beams, 12 (1), (1994) 25nN precision, 1.25 nN/mrad

21 The two LPT’s can be combined
Previously, the only way to obtain the range 3ks < Isp < 200s in one vehicle was to use separate chemical and electrical thrusters A scaled-up macro-LPT with a fiber laser target driver can use the combined operating principles of the two LPT’s All Isp’s based on measured mass loss 3000s at 1MJ/m2, 4ns 137s at 0.25MJ/m2, 1ms msmLPT nsmLPT

22 Requirements for macro-LPT’s
Thrust of order 1N Electrical power of order 1kW 200 < Isp < 3000 seconds Based on what we’ve already demonstrated in solid fuels Diode-pumped fiber lasers will accommodate pulsewidth range ns- and ms-pulse modes in the same laser Liquid fuel Eliminate moving parts, except for a small pump Mass budget 20kg (thanks to fiber lasers!)

23 kW Pavg pulsed fiber lasers
First critical ingredient for the success of this project Yb-doped fiber amplifier MOPA will access 10ns, 1MJ/m2 operating point Based on very large mode area cores ~ 70mm diameter Photonic crystal fibers (“holey fibers”) permit propagating single transverse modes in a structure whose core size is wavelengths Reported at HPLA6: more capability than we need27 3MW peak in a 70-mm core fiber with 200mm OD (we only need 300kW) M2 = 1.1 in a 30W Pavg oscillator-amplifier with 900ps pulses Fiber length: few m heo can be 45% 27di Teodoro, paper N, SPIE 6261 (2006)

24 Liquid Fuels Then add laser absorbing dye Second key ingredient
The only reasonable format for supplying kg quantities of ablation fuel We can illuminate fuel in a way that protects the optics Candidates: Raw GAP [Dm/m = 0.02% in 4 hours at 2 mtorr] Polymerized GAP [dissolves completely in ionic liquids (methyl-trioctylammonium-trifluoroacetate)] Ionic liquids have “immeasurably low” vapor pressure and melting points ~ – 80C Already feature, and are used in, electrospray thrusters Then add laser absorbing dye In a tank,does not have to be protected from UV

25 Anticipated motor performance

26 Perspective and Conclusions
Near term (say, 5 years): Accomplishing near-Earth missions using laser-powered macrothrusters is an exciting new application of laser ablation propulsion This can be done with lightweight, high-power diode-pumped fiber lasers and liquid ablative fuel based on the PSI fuel design Unmatched thrust efficiency derives from exothermic laser ablation fuels Competitive technologies have greater mass/thrust and lower thrust density Using pure photon propulsion to provide very small impulse bits needed to position nanosatelites with nm precision could be the first useful application of this technology Laser jet engines look exciting. Could avoid materials problems in Myrabo designs and increase coupling efficiency and lifetime. Duplication of results will improve acceptance.

27 Perspective and Conclusions
Medium term (say, 10 years): Propelling a lightcraft from Earth surface to proof-of-concept altitude (10km) should be supported However, infrastructure has to be in place, at the same place, and this is costly Large beam director with adaptive optics Zoom optics Laser guidestars Tracking and illuminating lasers Repetitively-pulsed thrust laser with at least 100kW average power Also, it will be relatively easier than Earth launch to send samples into low Mars orbit from its surface in conjunction with MSR Surface atmosphere is similar to Earth’s at 20km, as regards drag Mars’ surface gravity is considerably weaker (38%) Hybrid laser-electric thruster has great promise if efficiency can be increased

28 Perspective and Conclusions
Far term (say, fifteen years): Possible to routinely launch 10-20kg nanosatellites, or parts of a larger satellite, into LEO, as a far cheaper way to carry mass to orbit With 5 launches/day from one site, 3 tonnes can be placed in LEO each month Space hardware can be assembled rapidly on orbit Permits launching completed space vehicles into interplanetary trajectories at very low cost Achieving this goal will entirely change our relationship to space and space travel Whether this is done depends on priority decisions of government scientific and engineering programs (and we know how wise they are).


30 The msmLPT Uses ms-duration diode laser pulses
Thomas Lippert group21 at Paul Scherrer Institut played a major role in its development Suggested the use of energetic ablatants Perfected the chemistry of GAP and other materials to make them suitable for coatings Made a series of sample films for us Highlighted: all 1ms, 0.25MJ/m2 1ms, 9MJ/m2 result with 1XDL laser diode 21Lippert, et al., Appl. Surf. Sci., 186, (2002) Laser input 500kJ/kg

31 ms- and ns-Laser Plasma Thrusters
(Note: macro-LPT will not use T-mode) An LPT is a device which uses self-contained lasers to create thrust via laser ablation of a specially-prepared solid or liquid fuel

32 kW Pavg pulsed fiber lasers
A tentative kW Pavg laser design (courtesy Aculight Corp.) Endcaps avoid fiber damage We anticipate needing N≈14

33 msmLPT commercial laser diodes
MTBF as operated: 200,000 years. Lasers will not limit device life

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