ADVANCED SPACE PROPULSION

Robert H. Frisbee, Ph.D.

Jet Propulsion Laboratory California Institute of Technology Pasadena California

Transportation Beyond 2000: Engineering Design for the Future

September 26-28, 1995

693 ABSTRACT

This presentation describes a number of advanced space propulsion technologies with the potential for meeting the need for dramatic reductions in the cost of access to space, and the need for new propulsion capabilities to enable bold new (and, ultimately, space exploitation) missions of the 21st century. For example, current -to- (e.g., , LEO) launch costs are extremely high (ca. $10,000/kg); a factor 25 reduction (to ca. $400/kg) will be needed to produce the dramatic increases in space activities in both the civilian and overnment sectors identified in the Commercial Space Transportation Study (CSTS). imilarly, in the area of space exploration, all of the relatively "easy" missions (e.g., robotic flybys, inner solar system orbiters and landers; and piloted short-duration Lunar missions) have been done. Ambitious missions of the next century (e.g., robotic outer-planet orbiters/probes, landers, rovers, sample returns; and piloted long-duration Lunar and Mars missions) will require major improvements in propulsion capability. In some cases, advanced propulsion can enable a mission by making it faster or more affordable, and in some cases, by directly enabling the mission (e.g., interstellar missions).

As a general rule, advanced propulsion systems are attractive because of their low operating costs (e.g., higher specific impulse, Isp) and typically show the most benefit for relatively "big" missions (i.e., missions with large payloads or &V, or a large overall mission model). In part, this is due to the intrinsic size of the advanced systems as compared to state-of-the-art (SOTA) chemical propulsion systems. Also, advanced systems often have a large "infrastructure" cost, either in the form of initial R&D costs or in facilities hardware costs (e.g., laser or microwave transmission ground stations for beamed energy propulsion). These costs must then be amortized over a large mission to be cost-competitive with a SOTA system with a low initial development and infrastructure cost and a high operating cost. Note however that this has resulted in a "Catch 22" standoff between the need for large initial investment that is amortized over many launches to reduce costs, and the limited number of launches possible at today's launch costs.

Some examples of missions enabled (either in cost or capability) by advanced propulsion include long-life station-keeping or micro- applications using electric propulsion or BMDO-derived micro-thrusters, low-cost orbit raising (LEO to GEO or Lunar orbit) using electric propulsion, robotic planetary missions using or electric propulsion, piloted Mars missions using aerobraking and/or propellant production from Martian resources, very fast (100-day round-trip) piloted Mars missions using fission or fusion propulsion, and, finally, interstellar missions using fusion, antimatter, or beamed energy.

The NASA Advanced Propulsion Technology program at the Jet Propulsion Laboratory (JPL) is aimed at assessing the feasibility of a range of near-term to far- term advanced propulsion technologies that have the potential to reduce costs and/or enable future space activities. The program includes cooperative modeling and research activities between JPL and various universities and industry; and directly- supported independent research at universities and industry. The cooperative program consists of mission studies, research and development of ion engine technology using C60 (Buckminsterfullerene) propellant, and research and development of lithium-propellant Lorentz-force accelerator (LFA) engine technology. The university/industry-supported research includes modeling and proof-of-concept experiments in advanced, high-lsp, long-life electric propulsion, and in fusion propulsion.

694 INTRODUCTION

Jill LAUNCH COSTS > $10,000 / kg WITH EXISTING LAUNCH VEHICLES

25,000 S_I'S Space Shuttle

Titan IV (SRMU) 20,000

m Titan IV (SRM) Payload 15,000 / Mass to Titan III 200 km Circular Gold at I Orbit I_RST I $ 400 I Troy ounce I (kg) 10,000 (Joel I Atlas Atlas IIA Atlas Atlas I 5,000 Delta 7920 mm

Titan IIG Tsrus Pegasus XL Scout 0 0 5 10 15 20 30 40 50 60 Payload Launch Cost ($ K / kg of Payload) ($1,000 I kg - $ 454 / pound) r

MAJOR ADVANCES IN PROPULSION TECHNOLOGY REQUIRED FOR FUTURE SPACE MISSIONS

105

HEDM Alpha Centaurl '-- Chemical (50 Years One-Way) "1 (H-) Delivered Mass 4 10 J

10 3.

Fast Piloted Mars _ ._'. (00 Days Round-Trip) 1,000 A.U. (50 Years One-Way) 102. 3

Single Stage to GEO Single Stage 16 to LEO 106 108 1010 1012 1014 10 lO 18

Energy Density (J/kg)

695 POTENTIAL TO REDUCE COST

JPL ADVANCED PROPULSION CAN REDUCE COSTS

• Advanced propulsion shows State-of-the-Art

• Issue of Infrastructure Total most benefits for"big" missions System ] _ "Rich" versus "Poor" systems (Mass,

• Beamed Energy, Maglifter, etc. Cost) j _ Advanced systems minimize vehicle I _'f_ Technology propulsion requirements at _ / I System expense of large infrastructure I / Cross-Over • All- SSTO, HEDM, etc. systems put emphasis on V improvements in vehicle propulsion (and minimize infrastructure) Mission "Size" to yield more payload per launch (Payload Mass, AV, Number of Missions)

• Either approach results in a "Catch 22" standoff between need for large initial investment that is amortized over many launches to reduce costs, and the limited number of launches possible at today's launch costs

ADVANCED PROPULSION LAUNCH VEHICLE CONCEPTS

• Very Advanced (Exotic) Chemical - High Energy Density Matter (HEDM) Propulsion (Free Radicals, Excited States, Metastables)

• Near-term "additives" to existing propellants and vehicles for incremental improvements in performance • Far-term, totally new propellant combinations and vehicles for quantum improvements in performance

• Nuclear Thermal (Fission, Antimatter)

• Safety (public acceptance ?) as a launch vehicle • Infrastructure for development, test, operations

• Beamed Energy (Laser / Microwave) Earth-to-Orbit

• Large infrastructure - high powers (~ 100 MW/MT) needed for launch

• Chemical / Electromagnetic Guns / Catapults

• Cannon, Light Gas Gun, • Rail Gun, , MagLifter

• Tethers (Skyhooks, Launch Loops)

696 POTENTIAL TO REDUCE COST

JIlL GUN LAUNCH CONCEPT COMPARISON

10 • Cannons LIGHT GAS GUNS LIGHT GAS GUNS RamLight AcceleratorsGas Guns • [] • Rail Guns Ideal Low RAM ACCEL. • Coil Guns Performance 8 Earth Orbit • MagLifter ...... (LEO) uirements Insertion Required TYPICAL I Demonstrated Velocity REQUIREMENT 5-Year Projection • Payload Plus O Projected Full-Up On-Board 6 COIL GUNS V Prop. System System • lop . 4$0 • RAIL GUNS ,_ Muzzle (Aberdeen) • TF - 0.1 • Mp Velocity MINIMUM REQUIREMENT • Sabot plus Heat Shield Mile • Payload Plus On-Board (kin/s) _ RAIL Propellant (lap = 4S0 o) (1/3 of Total 4 Performance • No Prop. System Dry ProJoctllo) • NO Sabot or Heat Shield • AIr Drag: 1 km/s :apabilities ::::::::::::::::::::::::::i::iii::i::house _::_::LIGHT GAS GUNS RAM ACCEL O (U. Wish.) CANNONS iiiiiili!i CANNONS (Aberdeen 2 COIL GUNS ( (uss Polytech U, MAG (ssl) ourl) LIFTER

0 0.010 0.100 1 10 100 1,000 10,000 100,000 Projectile Mass (kg) Exiting Gun • Use Regime Appropriate Technology (RAT) to reduce overall costs • MagLifter (Vel. = 0 to Mach 0.9, AIt. = 0 to 1 mile) • Ramjet (Vel. = Mach 0.9 to -5, AIt. = 1 to 20 miles) • Pure rocket (Vel. = Mach 5 to 25, AIt. = 20 to 200 miles)

TETHERS AS SKYHOOKS AND LAUNCH LOOPS

• Currently under development for orbit-to-orbit transfers * Use momentum instead of

• Major paradi_lm shift in the concept of "launch vehicle" • Potential Tor large launch system infrastructure

SKYHOOK LAUNCH LOOP

SkyHook Orbit Insertion Bum "Station" ...... _-- _¢:3 --_...... LEO* ..Q=_E e L.irnitof-.. • Tether (3EO Atm°sphere t/ ^ ..... ,..^.^ [] t Payload Ill _uiiU_lJll_l_ I Launch "D Payload _.: / Loop Launch Loop _ "Station" --'+ / ' !111,_.

697 POTENTIAL TO ENABLE NEW MISSIONS

.IPl. ADVANCED PROPULSION CAN ENHANCE I ENABLE NEW CLASSES OF MISSIONS

• Advanced propulsion shows most benefits for "big" missions • Don't use 1000-MT fusion rocket to transport I-MT Comsat to GEO • Sample Missions:

._Ur.[_UI_UJDIIE Example Systems _ ExamDle SYstems

Station- N2H4, ReslstoJet, L0ng-Llfe Station-Keeping, Ion, Keeping ArcJet Micro-Spacecraft Pulsed Plasma

Orbit Raising Chemical "Slow" Orbit Raising SEP iv/ Xe-lon (LEO->GEOIMoon) (Solids, Liquids) "Fast" Orbit Raising SEP wl C60-1on, Russian Hall or TAL; NEP w/ LI-LFA

Planetary Chemical Planetary BMDO Micro-Chain, SEP, (Robotic) (Solids, Liquids) (Robotic, Micro-S/C) Aerobrsklng

Piloted Mars Chemical iv/ Aerobrake, Piloted Mars Fusion, (Slow) ET Propellant Production (Fast) Gas-Core Fission

Interstellar MW-Clses NEP Interstellar Fusion, Antimatter, Precursor Beamed Energy

ELECTRIC PROPULSION CAN ENABLE LOW-COST, NEAR-TERM ROBOTIC PLANETARY, CIS-LUNAR, AND MARS CARGO MISSIONS

• Requires thrusters with high efficiency at low Isp (Optimum Isp decreases as specific mass Increases)

lap (a) lap (s) 0 2,000 4,000 6,000 8,000 0 2,000 4,000 6,000 8,000 80 u , ...... U'J_'_'-" 7075 I0 f' - /,//,,,,,,/l, I "__ 20.40 - LI-L A_

100 I o" soo -==- I _r;_;'";:'" I

:" . " ' ...... Atl. :0 2s°r ..... [ Lorentz Force .... I

_ 200 ,9, P .J 150_ 0 2,000 4,000 0,000 8,000 600 800 1,000 1,200 lap (s) Earth-to-Mars Trip Time (Days)

698 POTENTIAL TO ENABLE NEW MISSIONS JilL BENEFITS OF AEROCAPTURE FOR A NEPTUNE ORBITER MISSION

20 250O

EGA I JGA I .t¢

I t _*****_- F21H21 £ 2000 I Trajectory I O .." I 1$ o l' / o, F21N2H4 c teptunl \ 41 1500 Z r .,: .... NTOIMMH I- 1 I _ > m 1000 w :rblt_S_:ps InsertionBurn_ 'ID ...;.),/ w 500 m Injection (from LEO) / •tel I

I il I I I z I I I I i 6 10 14 18 10 14 10

Flight Time (Years) Flight Time (Years)

ANTIMATTER-CATALYZED MICRO-FISSION/FUSION PROPULSION FOR FAST PILOTED MARS MISSIONS

Concel)t PROPELLANT (Pb) (300 g) GOLD • Uranium (or Pu) enriched DT (or D-He3) pellet compressed (by Ions, lasers, etc.) • At the time of peak compression, the target Is -2 1 gram) bombarded with a small number (~10^8) _m _: SHIELD of antiprotons to catalyze fission / DT CORE • The fission energy release triggers a high- LI._, T" (1 gram @ efficiency fusion burn to heat the propellant Lasers 1 U : 9 DT) • Resulting expanding plasma used to produce thrust

Features mm _ I"_OLD ::,ELD -0.1 _ • Uses a small amount of antimatter - an amount that we can produce today with existing technology and facilities • Mission benefits of 100-day Earth-Mars round trip GOLD PUSHER • Potential benefits of "easier" drivers / aneutronlc fuels

MARS _EARTH ARRIVAL / DEPARTURE Feasibility Issues • Pellet Implosion dynamics • Fission burnup (number of sntlprotons needed) = • Fusion Ignition and burn (total gain) MARSh, I D._y%. I| • Transfer of fission/fusion energy to propellant • Transfer of propellant energy to vehicle DEPART_UR_- °_ °'_sUN )) EARTH_ . • Research Partners ARI_iVA'L_I AVtot.- to kin/el • Pennsylvania State University "1 Thrust ,, 70 kN I • JPL, AFOSR, NSF p_22,000 S I • Rocketdyne

699 SUMMARY

Jill SELECTION CRITERIA REQUIRED TO DOWN-SELECT AMONG MANY COMPETING CONCEPTS

• Must have projected performance which offers unique capabilities for a well defined class of missions

• Must use an environmentally acceptable propellant (no Hg, etc.) • Must be an area where small amounts of funding can have a large impact, especially with co-funding from other agencies

1 _ NERVA Gas-Core Fission ...... "/I//I/_//II,_ J//lll//llll/_. Efficlency H E DM _ - Chemical ,_C60_Xi/K_rlA-r]on (P<0.1MW) Laser

(PJet/Pinput) _ _i'°_L'_ " 'i _ _ _" LFA (P>0 tMW) Sail -- A_I!! _ Beam Cor. _iEi;_'_rlc Antimatter ___ropulslon (asP NEP) o I I I I _____J 7 lap (Ibf-_lbm) 3o0 1,000 3,000 10,000 30,000 10 I I I I --_I I ET°IMr'I IFas,Maral Typical Mission / C:L I ...... Highlhrust/_/elght...... Applications

I LEOFastGEO[ IT:::r w PlanetJMarsllFastLow MarsThrustJWeightJlnterstelllrI I sow I I l Interstellar Precursor II Interstellar I

NASA-JPL ADVANCED PROPULSION TECHNOLOGY PROGRAM

• Current Advanced Propulsion Technology program contains a mix of near-term to far-term technologies in both cooperative and directly-supported university / industry tasks

Near Term ) Far Term

ow) _r _:_ F(,,t) _j_:_

Pulsed EP C60 Ion High-lap TAL Li-LFA Fusion A/M (Princeton) (JPL, CIT, (Olin- (JPL, FTFC, (PSU, LPP) (PSU) MIT, CSU, TsNIIMASH) USC, MIT, MAI, USC) Thermacore, Princeton)

700 SUMMARY

JPL OPPORTUNITIES FOR LaRC

• Need to Reduce Cost, Enable New Classes of Missions

• Low-Cost Earth-to-Orbit (ETO)

• NASP et al. - Propulsion / Aeroframe Integration Issues (Common to many advanced concepts)

• Launch Assist (MagLifter, etc.) - Regime Appropriate Technologies (RAT)

• Laser Power and Propulsion (Solar-Pumped, Diode Lasers)

• Mission Enabling

• Detonation Propulsion (Venus Sample Return)

• Aero-Capture/Brake/Maneuver - WaveRider Aero- (Very high speed, high L/D)

• High Altitude Aero. (e.g., low ambient pressure) - Mars Airplane (UAV), Balloon

701