significant fraction of the vehicle/spacecraft mass, and the cost of delivering mass to low .... NASA Lewis has been analyzing the thermal/mechanical interface ...
NASA Technical Memorandum 102065 AIAA-89-2492
. The NASA Low Thrust Propulsion Program
James R. Stone and Gary L. Bennett NASA headquarters Ofice of Aeronautics and Space Technology Washington, D. C.
Prepared for the 25th Joint Propulsion Conference cosponsored by the AIAA, ASME, SAE, and ASEE Monterey , California, July 10- 12, 1989
(NASA-Tn-102065) TfIE N S A LOY THRUST {HASA) 31 p CSCL 10B
PROPULSION PROGRAH
N89-26895
Unclas G3/20. _,02172663
THE NASA LOW THRUST PROPULSION PROGRAM James R. Stone and Gary L . B e n n e t t NASA Headquarters O f f i c e o f A e r o n a u t i c s and Space Technology Washington, DC 20546
SUMMARY
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The NASA OAST P r o p u l s i o n , Power, and Energy D i v i s i o n s u p p o r t s a low t h r u s t p r o p u l s i o n program aimed a t p r o v i d i n g h i g h performance o p t i o n s t o a b r o a d range of near-term and f a r - t e r m m i s s i o n s and v e h i c l e s . Low t h r u s t p r o p u l s i o n has a major impact on t h e m i s s i o n performance Of e s s e n t i a l l y a l l s p a c e c r a f t and v e h i c l e s . On-orbi t 1 i f e t i m e s , payloads, and t r i p t i m e s a r e s i g n i f i c a n t l y impacted by low t h r u s t p r o p u l s i o n performance and i n t e g r a t i o n f e a t u r e s f o r E a r t h - t o o r b i t (ET01 v e h i c l e s , E a r t h - o r b i t and p l a n e t a r y s p a c e c r a f t , and l a r g e p l a t f o r m s i n E a r t h o r b i t . M a j o r emphases of t h e program a r e on low t h r u s t c h e m i c a l , b o t h s t o r a b l e s and hydrogen/oxygen; low-power ( a u x i l i a r y ) e l e c t r i c a r c j e t s and r e s i s t o j e t s ; and high-power ( p r i m a r y ) e l e c t r i c p r o p u l s i o n , i n c l u d i n g ion, magnetoplasmadynamic (MPD), and e l e c t r o d e l e s s concepts. T h i s paper w i l l p r e s e n t t h e major r e c e n t accomplishments of t h e program and d i s c u s s t h e i r i m p a c t s .
INTRODUCTION The i d e n t i f i c a t i o n and development of new p r o p u l s i o n systems i s fundament a l t o t h e c o n t i n u e d e f f e c t i v e n e s s of NASA. A c c o r d i n g l y , NASA c o n t i n u e s t a m a i n t a i n a t e c h n o l o g y program which spans focused development on E a r t h - t o - o r b i t (ETO) and chemical t r a n s f e r p r o p u l s i o n , b a s i c p r o p u l s i o n r e s e a r c h and t e c h n o l ogy (R&T>, and advanced p r o p u l s i o n concepts ( r e f . 1 ) . E s s e n t i a l l y a l l spacec r a f t and v e h i c l e s i n c o r p o r a t e low t h r u s t p r o p u l s i o n systems which c o n t r i b u t e a s i g n i f i c a n t f r a c t i o n of t h e v e h i c l e / s p a c e c r a f t mass, and t h e c o s t o f d e l i v e r i n g mass t o low E a r t h o r b i t (LEO) i s a major f r a c t i o n o f t h e c o s t o f any m i s s i o n . For example, on t h e G a l i l e o m i s s i o n , p r o p e l l a n t accounts f o r 43 p e r c e n t o f t h e t o t a l mass and f o r t h e more c h a l l e n g i n g ( l a r g e r v e l o c i t y i n c r e m e n t ) comet r e n dezvous a s t e r o i d f l y b y ( C R A F ) m i s s i o n , t h e p r o p e l l a n t f r a c t i o n i s 76 p e r c e n t ( r e f . 2). The o b j e c t i v e of t h e l o w - t h r u s t p r i m a r y and a u x i l a r y p r o p u l s i o n p r o gram, which i s t h e focus of t h i s paper, i s t o p r o v i d e t h e b a s i s f o r i n c r e a s e d performance and o p e r a t i o n a l l i f e of s m a l l t h r u s t e r systems by d e v e l o p i n g f u n damental u n d e r s t a n d i n g i n t h e areas of h i g h - t e m p e r a t u r e m a t e r i a l s , f l u i d p h y s i c s , e l e c t r i c a l and magnetic f i e l d s , and i o n p h y s i c s . The emphasis of t h i s program i s on h i g h - r i s k , h i g h - p a y o f f t e c h n o l o g i e s such as chemical t h r u s t e r s , a r c j e t s , r e s i s t o j e t s , i o n engines, and magnetoplasmadynamic (MPD) t h r u s t e r s . The work i s p r i n c i p a l l y b e i n g c a r r i e d o u t through two NASA c e n t e r s : t h e J e t P r o p u l s i o n L a b o r a t o r y (JPL) and Lewis Research Center (NASA L e w i s ) . Both c e n t e r s a r e w o r k i n g on a complementary program t o advance t h e t e c h n o l o g y for l o w - t h r u s t p r o p u l s i o n systems f o r a broad range of f u t u r e space p l a t f o r m s , s p a c e c r a f t , launch, and o r b i t t r a n s f e r v e h i c l e s . JPL has been f o c u s i n g p r i n c i p a l l y on ( 1 ) i m p r o v i n g i o n e n g i n e l i f e ; (2) s i m p l i f y i n g mu1 t i e n g i n e system a r c h i t e c t u r e ; and ( 3 ) d e v e l o p i n g t h e technology necessary t o b u i l d and t e s t an MPD t h r u s t e r capable o f s t e a d y - s t a t e o p e r a t i o n a t power l e v e l s and s e v e r a l megawatts. NASA Lewis has been f o c u s i n g
p r i n c i p a l l y on ( 1 ) i m p r o v i n g chemical systems; ( 2 ) r e s e a r c h on high-performance a r c j e t s ; and ( 3 ) b a s i c p h y s i c s and s c a l a b i l i t y o f i n e r t - - g a s i o n t h r u s t e r s and high-power MPD t h r u s t e r s . There i s a c l o s e i n t e r c h a n g e between JPL and NASA Lewis, and t h e two programs b o t h complement and supplement each o t h e r . T h i s paper focuses p r i m a r i l y o n p r o g r e s s beyond t h a t r e p o r t e d a t t h e 2 4 t h J o i n t P r o p u l s i o n Conference ( r e f . 31, b u t some r e f e r e n c e s t o e a r l i e r work a r e inc 1 uded f o r c l a r i t y and c o n t i n u i t y . CH EM1CAL
Low t h r u s t chemical p r o p u l s i o n f i n d s a p p l i c a t i o n t o a b r o a d c l a s s o f v e h i c l e s i n c u d i n g ET0 v e h i c es, E a r t h - o r b i t a l and p l a n e t a r y s p a c e c r a f t and l a r g e p l a t f o r m s , i n c l u d i n g Space S t a t i o n Freedom, i n E a r t h o r b i t . On E T 0 v e h i c l e s s t o r a b l e p r o p e l l a n t s a r e c u r r e n t l y used f o r o n - o r b i t p r o p u l s i o n , b u t f u t u r e s y s t e m s may t a k e advantage o f u s i n g r e s i d u a l p r i m a r y p r o p e l l a n t s (hydrogen or hydrocarbons and oxygen) f o r these f u n c t i o n s . Advantages may a c c r u e from b o t h t h e use o f scavenged r e s i d u a l s and from t h e i n c r e a s e i n s p e c i f i c i m p u l s e ( I s p ) . New a r c h i t e c t u r e s i n c l u d i n g p r o p e l l a n t r e s u p p l y c r e a t e emphasis o n extended l i f e as w e l l a5 i n c r e a s e d performance. A h i g h - t e m p e r a t u r e t h r u s t e r e f f o r t i s b e i n g conducted u s i n g advanced m a t e r i a l s and d i a g n o s t i c t e c h n i q u e s and i s aimed a t i n c r e a s e d performance and l i f e w i t h s t a t e - o f - t h e - a r t and advanced s t o r a b l e p r o p e l l a n t s . Both s t o r a b l e ( m o n o p r o p e l l a n t h y d r a z i n e ) and gaseous hydrogenloxygen (HI01 systems have been i n v e s t i g a t e d f o r Freedom.
Due i n p a r t t o problems w i t h G a l i l e o ' s 10-N t h r u s t e r s , i n t e r e s t has been neightened i n u n d e r s t a n d i n g t h e fundamentals o f small r o c k e t s . S u p p o r t f o r small r o c k e t fundamental r e s e a r c h i s p r o v i d e d b y t h e Advanced T r a n s p o r t a t i o n P r o p u l s i o n and Low T h r u s t P r o p u l s i o n programs. T h i s e f f o r t , which was i n i t i a t e d under t h e Low T h r u s t P r o p u l s i o n program, i s d i s c u s s e d b r i e f l y h e r e i n . Storable Propellants Low-thrust, s t o r a b l e , m o n o p r o p e l l a n t and b i p r o p e l l a n t p r o p u l s i o n i s w i d e l y used on a v a r i e t y o f s p a c e c r a f t , r a n g i n g from small s a t e l l i t e s t o t h e space s h u t t 1e . B i p r o p e l l a n t . - S t o r a b l e b i p r o p e l l a n t s a r e used f o r many E a r t h - o r b i t a l and p l a n e t a r y s p a c e c r a f t . A major accomplishment a t NASA Lewis and A e r o j e t t h i s p a s t year has been t h e achievement o f an e x t r a o r d i n a r y i n c r e a s e (-900 K ) i n chamber o p e r a t i n g temperature for a 22-N advanced s t o r a b l e r o c k e t u s i n g n i t r o gen t e t r o K i d e (N2O4 or NTO) and monomethyl h y d r a z i n e (MMH) ( r e f . 4). The t h r u s t e r , shown o p e r a t i n g i n f i g u r e 1 , c o n s i s t s o f i r i d i u m - c o a t e d r h e n i u m f a b r i c a t e d by a chemical vapor d e p o s i t i o n ( C V D ) process wherein t h e i r i d i u m c o a t i n g i s f i r s t d e p o s i t e d on an expendable mandrel o f molybdenum and t h e n t h e t h i c k e r rhenium l a y e r d e p o s i t e d on t o p of i t ( r e f . 5 ) . The rhenium o f f e r s t h e d e s i r e d high-temperature s t r e n g t h w h i l e i r i d i u m p r o v i d e s t h e needed o x i d a t i o n r e s i s t a n c e . Because o f t h e h i g h m e l t i n g p o i n t o f i r i d i u m temperatures approaching 2700 K a r e p o s s i b l e . T h i s can a l s o t r a n s l a t e i n t o a g r e a t e r than t e n f o l d increase i n the o p e r a t i n g l i f e . T h i s t e c h n o l o g y c l e a r l y overcomes t h e problems t h a t e x i s t i n g t h r u s t e r s have p r e s e n t e d t o NASA and o t h e r s p a c e c r a f t users.
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Aerojet f i r s t t e s t e d two i r i d i u m - c o a t e d rhenium t h r u s t chambers w i t h 8 : l expansion r a t i o , and o v e r 15 h r o f o p e r a t i o n was demonstrated a t t e m p e r a t u r e s from 2250 t o 2530 K w i t h o u t f a i l u r e or any evidence o f c o r r o s i v e a t t a c k or measurable change i n t h r o a t dimensions. S i m i l a r r e s u l t s were r e c e n t l y demons t r a t e d on a 22-N t h r u s t e r w i t h 1 5 0 : l expansion r a t i o f a b r i c a t e d from t h e same m a t e r i a l s by t h e same t e c h n i q u e ( r e f . 6 ) . The s i g n i f i c a n c e o f t h i s can be seen i n f i g u r e 2 which compares t h e s t a t e - o f - t h e a r t (SOA) d i s i l i c i d e - c o a t e d n i o b i u m a l l o y chamber w i t h t h e I r / R e chamber. Not o n l y does t h e I r / R e chamber o f f e r extended l i f e t i m e s b u t i t o f f e r s h i g h e r Isp. Because o f t h i s performance advance, NASA i n i t i a l l y s e l e c t e d t h i s t e c h n o l o g y f o r t h e M a r i n e r Mark 11 comet rendezvous a s t e r o i d f l y b y (CRAF) m i s s i o n . The reduced p r o p e l l a n t mass (-600 k g ) enabled t h e a d d i t i o n of t h r e e experiments t o t h e s p a c e c r a f t . To assure t h e r e a d i n e s s of t h i s technology f o r t h e m i s s i o n , t h e NASA O f f i c e of Space Science and A p p l i c a t i o n s supported A e r o j e t , under t h e management of t h e JPL, f o r f a b r i c a t i o n and t e s t of a 440-N i r i d i u m - c o a t e d rhenium t h r u s t e r , w i t h t h e CVD p r o c e s s i n g performed by U l t r a m e t . A 4-hr t e s t i n d i c a t e d f e a s i b i l i t y o f t h e d e s i r e d performance and l i f e ( r e f . 7). While some s p a l l i n g o f t h e i r i d ium has o c c u r r e d because of contaminants t h a t a f f e c t e d t h e i r i d i u m d e p o s i t i o n b o t h engines a r e s e r v i c e a b l e and a w a i t a d d i t i o n a l t e s t i n g . NASA Lewis i s cont i n u i n g t o work w i t h U l t r a m e t to improve t h e f a b r i c a t i o n process. A d e l a y i n t h e CRAF m i s s i o n has r e c e n t l y o c c u r r e d , r e s u l t i n g i n l e s s c h a l l e n g i n g p r o p u l s i o n requirements and a d e c i s i o n t o use a p r o p u l s i o n system p r o v i d e d by NASA's European p a r t n e r i n t h i s m i s s i o n . M o n o p r o p e l l a n t . - A l t h o u g h m u l t i p r o p e l l a n t r e s i s t o j e t s and hydrogen/ oxygen were base1 i n e d for Freedom p r o p u l s i o n , t h e t e c h n o l o g y o f monopropel l a n t h y d r a z i n e p r o p u l s i o n was advanced t o p r o v i d e a d e s i g n o p t i o n which m i g h t have l o w e r development c o s t ( a l t h o u g h o p e r a t i n g c o s t s would be h i g h e r due t o t h e r e q u i r e m e n t for p r o p e l l a n t r e s u p p l y ) . A l i f e t e s t o f a 22-N t h r u s t e r was conducted under a c o o p e r a t i o n program between t h e Rocket Research Co. and NASA Lewis. The t o t a l impulse c a p a b i l i t y of 4 . 8 ~ 1 0 6 N-s demonstrated i s t h e g r e a t e s t r e p o r t e d f o r small h y d r a z i n e r o c k e t s ( r e f . 8 ) . Hydrogen/Oxygen
Space Station Freedom. - Based o n earlier studies manned s p a c e stations, two p r o p u l s i o n systems were i n v e s t i g a t e d f o r d i f f e r e n t f u n c t i o n s ( r e f s . 9 t o 1 1 ) . A s d i s c u s s e d elsewhere i n t h i s paper, low power m u l t i p r o p e l l a n t r e s i s t o j e t s were s e l e c t e d f o r d r a g make-up. for t h e h i g h - t h r u s t (110 t o 220 N) f u n c t i o n , gaseous H / O t h r u s t e r s were i n v e s t i g a t e d ( r e f s . 9 t o 15). I n i t i a l t h r u s t e r designs had an ISp goal of g r e a t e r t h a n 400 s e c l and, t h u s , had m i x t u r e r a t i o s from 3 : l t o 5 : l . Subsequent s t u d i e s of p r o p e l l a n t a v a i l a b i l i t y f o r v a r i o u s s t a t i o n f l u i d management s t r a t e g i e s l e d t o t h e r e q u i r e m e n t t o o p e r a t e a t an 8 : l m i x t u r e r a t i o w i t h t h e p r o d u c t s o f water e l e c t r o l y s i s and t h u s reduced t h e Isp goal t o 346 sec. T h i s l e d t o t h e need f o r t h r u s t e r d e s i g n m o d i f i c a t i o n s and an e x p e r i m e n t a l d e m o n s t r a t i o n o f t h e 8 . 9 ~ 1 0 6N-s d e s i g n g o a l . These s u c c e s s f u l r e s u l t s have l e d t o H/O p r o p u l s i o n b e i n g basel i n e d f o r t h e h i g h t h r u s t f u n c t i o n on t h e Freedom.
] I n t h i s paper Isp i s d e f i n e d as t h r u s t p e r u n i t w e i g h t f l o w and has u n i t s o f seconds ( s e c ) i n b o t h U.S. customary and '5.1. u n i t s .
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F u t u r e l a u n c h v e h i c l e s . - S t u d i e s a t NASA Lewis have shown t h a t advanced a u x i l i a r y p r o p u l s i o n subsystems ( A P S ) can s i g n i f i c a n t l y i n c r e a s e t h e p a y l o a d o f advanced ET0 v e h i c l e s ( r e f s . 16 and 17). The concept i s based on u s i n g an i n t e g r a t e d H / O p r o p u l s i o n system i n which p r o p e l l a n t s scavenged from t h e l a u n c h v e h i c l e would be used f o r a l i q u i d h y d r o g e n l l i q u i d oxygen (LH2/L02) p r i m a r y r e a c t i o n c o n t r o l system (RCS) and a gaseous hydrogenlgaseous oxygen (GH2/G02) v e r n i e r RCS. U n l i k e p r e v i o u s s t u d i e s conducted d u r i n g t h e space t r a n s p o r t a t i o n s y s t e m (STS) t e c h n o l o g y program, these s t u d i e s have avoided any p r o p e l l a n t cond i t i o n i n g r e q u i r e m e n t s and have suggested t h e development o f hardware t o use t h e p r o p e l l a n t s i n t h e a s - d e l i v e r e d s t a t e . F i g u r e 3 shows t h e proposed i n t e g r a t e d H / O s y s t e m i n comparison w i t h a 1960's v i n t a g e RCS concept. The advantages o f t h e c u r r e n t l y proposed system i n c l u d e : ( 1 ) g r e a t e r ( b y about 100 sec) system s p e c i f i c impulse; ( 2 ) s i m p l i f i e d system t h r o u g h e l i m i n a t i o n o f h e a t e x c h a n g e r j g a s i f i e r , gas accumulator, and compressor; and ( 3 ) a decoupled t h r u s t e r / p r o p e l l a n t management system. F i g u r e 4 shows t h e p a y o f f i n t e r m s o f i n c r e a s e d p a y l o a d mass for t h e i n t e g r a t e d H/O s y s t e m . A p o t e n t i a l payload b e n e f i t o f 4800 k g i s p r o j e c t e d for Space S h u t t l e 1 1 . Such a p a y l o a d b e n e f i t may a l s o o f f e r s i g n i f i c a n t o p e r a t i o n a l b e n e f i t s i n terms o f t h e t y p e s of o r b i t s t h a t can be used. An i n d u s t r y s t u d y t o v e r i f y these p o t e n t i a l benef i t s i s b e i n g i n i t i a t e d by NASA Lewis. Rocket Fundamentals Present computer codes do n o t c o r r e c t l y p r e d i c t t h e performance o f s m a l l r o c k e t s . As a r e s u l t , NASA Lewis has s i g n i f i c a n t l y m o d i f i e d a N a t i o n a l Aerospace Plane (NASP) combustor code and extended i t t o space s t a t i o n H / O r o c k e t s . T h i s code o f f e r s t h e advantage o f i n c l u d i n g t h e e f f e c t s o f a shear l a y e r t o c o o l t h e n o z z l e ( f o r a small r o c k e t t h e boundary l a y e r i s n o t so t h i n i n r e l a t i v e t e r m s ) and o f n o t h a v i n g numerical "patches" a t t h e t h r o a t . The i n i t i a l o u t p u t s o f t h e code i n c l u d e combustion shear l a y e r m i x i n g , t r a n s o n i c flow, and v i s c o u s n o z z l e flows. The r e s u l t s a r e encouraging and NASA Lewis w i l l work w i t h N A S A ' s Ames Research Center (ARC) t o use t h e computational c a p a b i l i t y o f t h e N a t i o n a l Aerospace S i m u l a t o r (NAS) f o r t h e c o n t i n u i n g work ( r e f . 1 8 ) . ELECTROTHERMAL Electrothermal propulsion using subkilowatt r e s i s t o j e t s i s c u r r e n t l y perf o r m i n g n o r t h - s o u t h s t a t i o n k e e p i n g (NSSK) on geosynchronous (GEO) s a t e l l i t e s ( r e f s . 19 and 20) and w i l l be used f o r Freedom and man-tended p l a t f o r m s ( r e f . 2 ) . The NASA e l e c t r o t h e r m a l a u x i l i a r y p r o p u l s i o n program i n c l u d e s t h e development o f r e s i s t o j e t o p t i o n s f o r h i g h s p e c i f i c impulse and f o r l o n g durat i o n c o m p a t i b i l i t y w i t h m u l t i p l e propellants. Kilowatt-class a r c j e t s are being developed t o p r o v i d e i n c r e a s e d l i f e f o r h i g h e r power geosynchronous s a t e l l i t e s . Power e l e c t r o n i c s technology i s r e q u i r e d for a l l these concepts and i s , t h e r e f o r e , an i n t e g r a l p a r t o f t h e program, as i t i s a l s o i n t h e h i g h power, p r i m a r y p r o p u l s i o n area. Arc j e t s
1-kW p r e f l i g h t development. - NASA Lewis has been s t u d y i n g a r c p h y s i c s ; e l e c t r o d e m a t e r i a l s and t h e i r c o m p a t i b i l i t y w i t h p r o p e l l a n t s ; h e a t t r a n s f e r , 4
plasma a r c , and f l u i d mechanics models. The NASA Lewis experiments have i n c l u d e d plume fundamentals, a r c l f l o w s t a b i l i t y , and t h r u s t e r / p o w e r p r o c e s s o r i n t e g r a t i o n fundamentals. NASA i s w o r k i n g toward a f l i g h t t e s t o f an a r c j e t i n t h e e a r l y 1990's. NASA Lewis s u c c e s s f u l l y completed a lOOO-hr, 500-cycle l i f e t e s t o f a 1.3-kW a r c j e t t h i s p a s t y e a r , t h e r e b y d e m o n s t r a t i n g system autonomy ( r e f . 21). No l i f e - l i m i t i n g mechanisms were i d e n t i f i e d as a r e s u l t of t h e t e s t . The a r c j e t met t h e p r e t e s t g o a l s o f 35 p e r c e n t t h r u s t e f f i c i e n c y and 450 sec s p e c i f i c i m p u l s e . F i g u r e 5 shows t h e s p e c i f i c impulse as a f u n c t i o n of t h e r a t i o of t h e power. NASA Lewis a l s o demonstrated r e l i a b l e , c o n s i s t e n t s t a r t u p s o f t h e a r c j e t ( r e f s . 2 2 and 23). F i g u r e 6 shows t h e a r c v o l t a g e as a f u n c t i o n o f c y c l e number; n o t e t h a t most o f t h e v o l t a g e r i s e o c c u r r e d i n t h e i n i t i a l 10-hr b u r n - i n p e r i o d ( r e f . 2 1 ) . Before a r c j e t t e c h n o l o g y can be a p p l i e d t o s p a c e c r a f t , however, a number of s p a c e c r a f t i s s u e s must be addressed. One o f these i s t h e thermal impact t h e a r c j e t w i l l have on b o t h t h e s p a c e c r a f t and on t h e power c o n n e c t i o n t o t h e power p r o c e s s i n g u n i t . NASA Lewis has been a n a l y z i n g t h e thermal/mechanical i n t e r f a c e between t h e a r c j e t and t h e s p a c e c r a f t . The goal i s t o keep t h e back temperature low enough (~400K ) and t h e conducted h e a t low enough ( < l o W ) t o m i n i m i z e problems i n d e s i g n i n g t h e r e a r e l e c t r i c a l c o n n e c t o r . An o b v i o u s approach would be t o extend t h e l e n g t h s of t h e a r c j e t ; however, t h e s t r u c t u r a l a n a l y s i s showed t h a t t h e a r c j e t cannot be made l o n g enough t o g e t t h e d e s i r e d temperature because of e x c e s s i v e h e a t l o s s e s . T h i s p o i n t e d o u t t h e need f o r h i g h e m i s s i v i t y surfaces. F u r t h e r analyses showed t h a t a c o a t i n g such as z i r conium d i b o r i d e w i t h an e m i s s i v i t y of about 0.6 would meet t h e thermal i n t e r faces ( r e f . 24). Under NASA Lewis c o n t r a c t , supported by t h e OAST F l i g h t P r o j e c t s O f f i c e , Rocket Research Co. has f a b r i c a t e d a f l i g h t - t y p e , k i l o w a t t - c l a s s a r c j e t , which i s shown i n f i g u r e 7 . The e l e c t r o d e c o n f i g u r a t i o n has been v e r i f i e d by p e r formance d e m o n s t r a t i o n s and l i f e t e s t i n g . The a r c j e t has been s u c c e s s f u l l y i n t e g r a t e d w i t h t h e power p r o c e s s i n g u n i t (PPU) and has m e t t h e t h e r m a l i n t e r f a c e s . The dynamic s t r u c t u r a l a n a l y s i s of t h e a r c j e t has been completed and t h e e l e c t r o m a g n e t i c e f f e c t s on sate1 1 i t e communications have been assessed. While many major i s s u e s such as e l e c t r o d e l i f e and r e l i a b i l i t y have been addressed ( e . g . , r e f . 21) l i t t l e has been done t o improve t h e e f f i c i e n c y o f t h e d e v i c e . P r e l i m i n a r y e x p e r i m e n t a l work has shown t h a t t h e o p e r a t i n g c h a r a c t e r i s t i c s o f a r c j e t s depend on t h e l o c a t i o n o f t h e a r c attachment zone i n t h e anode/nozzle. An a n o d e l n o z z l e c o n s i s t i n g of f i v e p i e c e s o f t u n g s t e n i n s u l a t e d from each o t h e r by boron n i t r i d e spacers was used i n a r a d i a t i o n - c o o l e d , segmented anode t o s t u d y t h e p h y s i c s of t h e a r c attachment zone ( r e f . 2 5 ) . Large p o t e n t i a l g r a d i e n t s were shown t o e x i s t i n t h e n o z z l e d u r i n g o p e r a t i o n w i t h a l l t h e segments a t t a c h e d t o a common p o i n t . P r e f e r r e d modes o f o p e r a t i o n were i d e n t i f i e d by f o r c i n g t h e p o i n t of attachment t o d i f f e r e n t p o s i t i o n s . F u r t h e r , use o f t h e segments as f l o a t i n g probes gave rough e s t i m a t e s o f plasma potent i a l , and, by s u b t r a c t i o n , t h e anode drop. A knowledge o f t h e fundamental o f a r c j e t s i s i m p o r t a n t because o f t h e e x i s t i n g low e f f i c i e n c y (33 t o 38 p e r c e n t ) o f a r c j e t s caused, i n p a r t , because i t expends so much energy i n b r e a k i n g bonds l e a d i n g t o a " f r o z e n flow" w i t h about 80 t o 85 p e r c e n t o f t h e energy i n t h e gas i t s e l f . C o m p u t a t i o n a l l y . n o z z l e s t u d i e s a r e d i f f i c u l t because o f t h e e x t r e m e l y small dimensions, low Reynolds number o p e r a t i o n , and c o m p l i c a t e d a r c p h y s i c s i n t h e c o n s t r i c t o r / n o z z l e r e g i o n . The plasma and flow f i e l d s a r e s t r o n g l y coupled, which c o m p l i c a t e s t h e a n a l y s e s . F i g u r e 8 shows t h a t t h e n o z z l e geome t r y a f f e c t s t h e a r c j e t c h a r a c t e r i s t i c s ( r e f . 26). While t h e performance i s
5
i n s e n s i t i v e t o t h e upstream design of' t h e t h r u s t e r , i t appears t h a t a c o n i c a l d i v e r g i n g n o z z l e i s t h e optimum d e s i g n . A s p a r t o f i t s e f f o r t t o understand t h e fundamentals o f a r c j e t (and i o n engine) performance, NASA Lewis has e s t a b l i s h e d a l a s e r - i n d u c e d f l u o r e s c e n c e ( L I F ) f a c i l i t y and i s now i d e n t i f y i n g t h e pliime species as p a r t o f i t s i n v e s t i g a t i o n of t h e e l e c t r o d e l o s s e s and s p a c e c r a f t i n t e r a c t i o n s . Under i n t e r n a l f u n d i n g , JPL w i l l be measuring t h e v e l o c i t y and temperature p r o f i l e s i n t h e exhaust stream of a 30-kW a r c j e t u s i n g L I F . F i g u r e 9 shows t h e JPL L I F experi m e n t a l setup ( r e f . 2 7 ) .
Plume i m p a c t s . - As t h e a r c j e t t h r u s t e r moves c l o s e r t o b e i n g a f l i g h t ready p r o p u l s i o n s y s t e m onboard communications s a t e l l i t e s f o r a p p l i c a t i o n s such as NSSK, s p a c e c r a f t i n t e g r a t i o n concerns become of s i g n i f i c a n t i n t e r e s t . A key i s s u e c e n t e r s on t h e p o t e n t i a l impact t h a t t h e a r c j e t plume may have on t h e t r a n s m i s s i o n o f RF s i g n a l s i n common use for s a t e l l i t e communications. A f i r s t o r d e r s t u d y u s i n g Langmuir probe d a t a i n d i c a t e d t h a t t h e impacts appear n e g l i g i b l e i n t h e antenna f a r f i e l d , except for p r o p a g a t i o n paths near t h e a r c j e t source ( r e f . 28). More r i g o r o u s numerical techniques a r e necessary t o f u l l y d e f i n e t h e i n t e r a c t i o n processes and e f f e c t s which would o c c u r i f t h e plasma were t o expand w i t h i n t h e antenna near f i e l d . Recent r e s u l t s ( r e f . 29) e x t e n d t h e p r e v i o u s work and p r e s e n t a body of s y s t e m a t i c e x p e r i m e n t a l d a t a which c o r r e l a t e measured plasma p r o p e r t i e s i n t h e a r c j e t plume w i t h a wide range o f t h r u s t e r o p e r a t i n g c o n d i t i o n s and c o n s t r i c t o r geometries and c o n f i r m t h e e a r l i e r f i n d i n g t h a t communications impacts should be n e g l i g i b l e . 5-kW System t e c h n o l o q y . - Recent i n t e r e s t i n a r c j e t s has l e d t o t h e development and l i f e t e s t s o f b o t h 1 and 30 kW (e.g., r e f . 30) a r c j e t systems f o r a p p l i c a t i o n t o GEO s a t e l l i t e s t a t i o n k e e p i n g and prime p r o p u l s i o n . O r b i t t r a n s f e r m i s s i o n s from LEO t o GEO m i g h t s i g n i f i c a n t l y b e n e f i t from a r c j e t systems i n t h e 5-kW power range coupled w i t h t h e use o f h i g h t h r u s t chemical h y d r a z i n e p r o p u l s i o n t o r a p i d l y t r a n s v e r s e t h e Van A l l e n r a d i a t i o n b e l t s . The h y d r a z i n e a r c j e t s y s t e m would t h e n be used t o complete low t h r u s t , h i g h Isp t h e o r b i t r a i s i n g and i n c l i n a t i o n changes r e q u i r e d t o achieve geosynchronous o r b i t . Such high-power a r c j e t systems w i l l l i k e l y be e n e r g i z e d from h i g h v o l t a g e buses s i n c e h i g h bus v o l t a g e r e s u l t s i n low s p a c e c r a f t power s y s t e m mass. A 5-kW c l a s s a r c j e t system was r e c e n t l y developed a t NASA Lewis ( r e f . 31) u s i n g a f u l l - b r i d g e , pulse-width-modulated power c o n v e r t e r w i t h e l e c t r i c a l i s o l a t i o n . P r e v i o u s l y , a 1-kW c l a s s p u l s e - w i d t h modulated p a r a l l e l c o n v e r t e r was used. For h i g h bus v o l t a g e s , a b r i d g e c o n v e r t e r has advantages o v e r t h e p a r a l l e l c o n v e r t e r . The b r i d g e c o n v e r t e r power t r a n s i s t o r s w i t c h e s o p e r a t e a t bus v o l t a g e whereas t h e p a r a l l e l c o n v e r t e r t r a n s i s t o r switches must s u p p o r t t w i c e t h e bus v o l t a g e . T h i s advantage i s p a r t i a l l y o f f s e t by h a v i n g two switches i n s e r i e s , b u t lower v o l t a g e t r a n s i s t o r s a l s o have l o w e r ON r e s i s tance. Another advantage of t h e b r i d g e c o n v e r t e r i s t h a t t h e power t r a n s f o r m e r i s s i m p l e r and lower mass than t h e p a r a l l e l c o n v e r t e r power t r a n s f o r m e r . The l a b o r a t o r y 1-kW, r a d i a t i o n - c o o l e d a r c j e t used for t h i s work i s an e x t e n s i o n of a design d e s c r i b e d elsewhere ( r e f . 2 1 ) . S p e c i f i c d i f f e r e n c e s from t h e 1-kW c l a s s a r c j e t i n c l u d e m o d i f i c a t i o n s i n t h e cathode, c o n s t r i c t o r , and t h r u s t e r h e a t r a d i a t i n g area.
6
Resistojets High performance. - To advance s t o r a b l e p r o p e l l a n t r e s i s t o j e t s beyond t h e c u r r e n t s t a t e - o f - t h e - a r t 300 sec mission-averaged Isp ( r e f . 32), s e v e r a l e f f o r t s have been undertaken. NASA Lewis i s w o r k i n g t h r o u g h a four-phase cont r a c t e d i n d u s t r i a l development program t o d e s i g n , f a b r i c a t e , and c h a r a c t e r i z e a h y d r a z i n e r e s i s t o j e t t h r u s t e r capable of about 320 sec I s pThe . first phase, which was conceptual d e s i g n and a n a l y s i s , has been completed and Rocket Research was chosen for t h e d e s i g n f i n a l i z a t i o n and performance c h a r a c t e r i z a t i o n . C u r r e n t l y t h e program i s a s s e s s i n g t h e t r a d e o f f on immersed h e a t e r s versus r a d i a t i v e l y - c o u p l e d h e a t e r s . Improved h e a t exchanger performance, l o n g e r - l i f e h i g h e r - t e m p e r a t u r e h e a t e r s ( r e f s . 33 and 341, arid improved n o z z l e performance ( r e f s . 35 and 361 a r e b e i n g sought. The importance o f h i g h q u a l i t y t e s t f a c i 1 it i e s for e v a l u a t i n g performance has been demonstrated ( r e f . 3 7 ) . NASA Lewis has been modeling t h e supersonic v i s c o u s flow i n a r e s i s t o j e t by s o l v i n g t h e Navier-Stokes e q u a t i o n i n c o n s e r v a t i v e form w i t h a f i n i t e - v o l u m e f o r m u l a t i o n . A t y p i c a l s o l u t i o n i s shown i n f i g u r e 10, which g i v e s a p l o t of Mach number c o n t o u r s for an a x i s y m m e t r i c c o n v e r g i n g - d i v e r g i n g n o z z l e w i t h a 20" d i v e r g e n t h a l f - a n g l e , a r e a r a t i o of 20, and 1086 Reynolds number ( r e f . 3 8 ) .
M u l t i p r o p e l l a n t . -. A s p r e v i o u s l y mentioned, m u l t i p r o p e l l a n t r e s i s t o j e t s have been b a s e l i n e d f o r freedom. The r e q u i r e m e n t s a r e q u i t e d i f f e r e n t from most o t h e r p r o p u l s i o n a p p l i c a t i o n s i n t h a t l o n g l i f e and i n t e g r a t i o n f e a t u r e s a r e much more i m p o r t a n t t h a n performance ( r e f s . 9 t o 11). U t i l i z i n g freedom wastes as p r o p e l l a n t m i n i m i z e s r e s u p p l y r e q u i r e m e n t and may e l i m i n a t e t h e need t o r e t u r n some wastes t o E a r t h . E n g i n e e r i n g model t h r u s t e r s have been b u i l t and d e l i v e r e d t o NASA f o r t e s t i n g ( r e f . 39). Performance c h a r a c t e r i s t i c s on a wide range of p o s s i b l e p r o p e l l a n t s have been o b t a i n e d ( r e f . 40). and l o n g - t e r m l i f e t e s t s have been conducted f o r o v e r 10 000 h r w i t h o v e r 140 deep thermal c y c l e s ( r e f . 41). A power c o n t r o l l e r was developed t o enable t h e Freedom r e s i s t o j e t s t o o p e r a t e on high-frequency power ( r e f . 42). To f a c i l i t a t e t h e i n t e g r a t i o n of t h i s t e c h n o l o g y on Freedom, p r o p e l l a n t and f e e d system o p t i o n s w e r e assessed ( r e f . 4 3 ) , and i n t e r f a c e s w e r e d e f i n e d ( r e f . 4 4 ) . The exhaust plumes o f t h e t h r u s t e r s a r e of concern because of p o t e n t i a l e f f e c t s on sensors and experiments and p o t e n t i a l a t t e n u a t i o n o f s i g n a l s p r o p a g a t i n g t h r o u g h t h e plume. A n a l y t i c a l and e x p e r i m e n t a l techniques have been developed ( r e f . 4 5 > , and a p r e l i m i n a r y assessment made o f t h e e f f e c t o f n o z z l e geometry on plume c h a r a c t e r i s t i c s ( r e f . 46). The exhaust o f t h e e n g i n e e r i n g model r e s i s t o j e t was i n v e s t i g a t e d u s i n g r o t a r y p i t o t probes and a r o t a t i n g q u a r t z c r y s t a l m i c r o balance. The e f f e c t of a plume s h i e l d has been e v a l u a t e d and f o u n d t o be small, b u t t h e a b s o l u t e mass f l u x i n t o t h e b a c k f l o w r e g i o n was v e r y low (-7x10-7 g/cm2-sec> ( r e f . 47). Water. - I n t e r e s t i n water r e s i s t o j e t s developed as a s p i n - o f f t o t h e Freedom m u l t i p r o p e l l a n t r e s i s t o j e t development. for man-tended, s h u t t l e s e r v i c e d p l a t f o r m s such as t h e proposed i n d u s t r i a l space f a c i l i t y ( I S F ) , ease and s a f e t y of p r o p e l l a n t r e s u p p l y and ground h a n d l i n g o p e r a t i o n s a r e c r i t i c a l issues, which leads t o i n t e r e s t i n water as a p r o p e l l a n t . W i t h a r e s i s t o j e t capable o f steam o p e r a t i o n a l r e a d y under development f o r Freedom. w a t e r r e s i s t o j e t s were b a s e l i n e d for t h e ISF ( r e f . 4 8 ) . T h i s n e c e s s i t a t e d t h e development of a z e r o - g r a v i t y steam g e n e r a t o r when i t was determined t h a t a v a i l a b l e steam generators, such as t h a t developed f o r t h e Manned O r b i t i n g Research Laborat o r y , d i d n o t perform s t a b l y and r e l i a b l y and t h a t o p e r a t i o n o f t h e freedom 7
resistojet with liquid water feed could be quite unstable (ref. 40). A cyclone steam generator was developed after evaluation of a number of boiler concepts studied for space power application. Further development of this concept led to an integrated vaporizer/resistojet utilizing a single heater (ref. 49). This concept is shown in figure 11; the liquid water is swirled to the outer wall and boiled by heat radiated from the central heater which also heats the resistojet by conduction. Thermal losses are reduced since the outer water operates at temperatures below saturation. This design also overcomes the many stability and phase separation problems typically encountered in zero-gravity boilers. Laboratory models have been built and performance mapped over a range of conditions, and flow visualization results obtained (ref. 5 0 ) . Initial studies of the plume characteristics of steam resistojets has recently been conducted (ref. 51). Mass flux dnd flow angle measurements were obtained in the plume using a variable temperature quartz crystal microbalance. PRIMARY (HIGH POWER) ELECTRIC Prospects now appear good fcjr broad acceptance and application of electric propulsion systems (ref. 20). However, current applications are limited to low-power stationkeeping and orbit control (refs. 19, and 52 to 5 4 ) . The successful operation of these systems has led to increased user confidence, and further operational use of electric propulsion appears imminent. The National Commission on Space advocated a number of challenging missions, such as a return to the Moon, unmanned and manned exploration of Mars and its moons, and unmanned scientific exploration of the rest of the solar system (ref. 5 5 ) . Many of these missions would be enhanced, and some would be enabled by high ISp electric propulsion. To perform the challenging future missions, high power and high ISp systems will be required. Candidate systems include electrostatic (ion) and MPD engines, with electrodeless approaches representing a longer term possibility. Electric propulsion is also applicable to advanced robotic exploration missions, offering both decreased propellant mass (and/or increased payload) and reduced trip times for deep space missions. Furthermore, this technology may be applicable to manned spacecraft using artificial gravity, where speed is not so critical. There are also many potential applications for high Isp electric propulsion at the tens of kilowatts available from large solar power systems. High specific impulse clearly offers propellant mass savings, but in order to practically exploit that benefit for space missions, it is necessary for the overall vehicle to exhibit acceleration levels sufficient to meet mission time lines. This requirement necessitates low specific mass and high efficiency propulsion and power systems in order to keep power system mass low. Mission and System Analyses Mission analyses covering spacecraft from small, so ar electric propulsion (SEP) (refs. 2 and 56) to large, megawatt nuclear e ectric propulsion ( N E P ) spacecraft (refs. 57 to 61) show enhancing to enab ing levels of capability for exploration of the planets and beyond (ref. 5 2 ) . JPL considered a small, 180-kg demonstration spacecraft with a 1.5-kWe solar array using ion propulsion for transportation from LEO to lunar orbit (ref. 56). This Lunar Get Away Special (LGAS) mission would carry one instrument, nominally an Apollo gamma ray spectrometer, and would carry 36 kg of xenon propellant. JPL has 8
a l s o s t u d i e d a deep space m i s s i o n concept, wherein t h e Thousand A s t r o n o m i c a l U n i t (TAU) E x p l o r e r , p r o p e l l e d by NEP, would reach 1000 A.U. i n 50 y e a r s w i t h a s i g n i f i c a n t s c i e n c e payload ( r e f . 5 7 ) . Both o f these s p a c e c r a f t a c c o m p l i s h t h e m i s s i o n p r o p u l s i o n w i t h a minimum o f p r o p e l l a n t mass and, t h e r e b y , maximize t h e s c i e n c e payloads a t t h e i r d e s t i n a t i o n s . A s t u d y was conducted by JPL ( r e f . 60) o f t h e b e n e f i t s i o n p r o p u l s i o n m i g h t p r o v i d e t o t h e CRAF m i s s i o n i f i t were used i n s t e a d of s t o r a b l e b i p r o p e l l a n t s . Even though t h e m i s s i o n and i t s s c i e n c e package w e r e n o t o p t i m i z e d f o r use of e l e c t r i c p r o p u l s i o n , a 3-year t r i p t i m e r e d u c t i o n c o u l d be achieved a l o n g w i t h a 600-kg i n c r e a s e i n l a u n c h mass margin. A range of s o l a r - and nuclear-powered E a r t h o r b i t a l m i s s i o n s have been s t u d i e d and show costjmass r e d u c t i o n s b e n e f i t s ( r e f s . 62 t o 64). I n a USAF s t u d y i t was shown t h a t a s o l a r e l e c t r i c o r b i t t r a n s f e r v e h i c l e f o r d e l i v e r y of s a t e l l i t e c o n s t e l l a t i o n s t o t h e i r o p e r a t i o n a l o r b i t s c o u l d o f f e r s i g n i f i c a n t savings ( r e f . 62).
Nuclear e l e c t r i c p r o p u l s i o n system t e c h n o l o g y f o r an e l e c t r i c c a r g o v e h i c l e has been i d e n t i f i e d as a major r e q u i r e m e n t f o r e v o l u t i o n a r y s o l a r system e x p l o r a t i o n ( r e f . 65). The use of an e l e c t r i c , l o w - t h r u s t c a r g o v e h i c l e i n t h e Lunar O u t p o s t t o E a r l y Mars E v o l u t i o n case c o u l d p o t e n t i a l l y reduce t h e i n i t i a l mass i n LEO (IMLEO) by o n e - t h i r d o v e r a s t a n d a r d c h e m i c a l l y p r o p e l l e d v e h i c l e . S t u d i e s have shown t h a t f o r a Mars c a r g o v e h i c l e l a r g e enough t o s u p p o r t a manned m i s s i o n , h i g h performance e l e c t r i c p r o p u l s i o n w i t h s p e c i f i c impulses o v e r 4000 sec a t multimegawatt power l e v e l s can o f f e r major r e d u c t i o n s i n p r o p e l l a n t r e q u i r e m e n t s a t a c c e p t a b l e t r a n s i t t i m e s . Compared w i t h an a e r o b r a k i n g c a r g o v e h i c l e u s i n g hydrogen/oxygen p r o p u l s i o n , and n o n a e r o b r a k i n g h i g h performance e l e c t r i c v e h i c l e can r e s u l t i n e l i m i n a t i o n o f a t l e a s t t h r e e Heavy L i f t Launch V e h i c l e (HLLV) launches, and savings a r e even g r e a t e r when compared w i t h nonaerobraking chemical p r o p u l s i o n ( r e f . 66). T h i s r e d u c t i o n i n t h e numb e r o f launches m i g h t p e r m i t t h e m i s s i o n t o be completed more r a p i d l y i f HLLV launch r a t e s a r e low. To perform these c h a l l e n g i n g f u t u r e m i s s i o n s , t h e t o t a l impulse c a p a b i l i t y must be advanced from t h e c u r r e n t l y demonstrated 106 N-s f o r b o t h i o n and MPD engines t o a t l e a s t 108 N-s ( r e f . 67).
Ion I o n engines have demonstrated s p e c i f i c impulses from l e s s t h a n 2000 sec t o more t h a n 10 000 sec, t h r u s t e f f i c i e n c i e s t o o v e r 0.75 ( e . g . , r e f . 681, and t o t a l t h r u s t impulse as h i g h as 106 N-s for 10-kW c l a s s t h r u s t e r s . Prop e l l a n t s have i n c l u d e d mercury, argon, k r y p t o n , and xenon. I o n t h r u s t e r techn o l o g y has been demonstrated w i t h f l i g h t t e s t i n g o f t h e Space E l e c t r i c Rocket Test (SERT 1, 11) i o n t h r u s t e r s ( r e f . 69). E l e c t r o s t a t i c ( i o n ) p r o p u l s i o n i s planned f o r i t s first o p e r a t i o n a l use on t h e Japanese E n g i n e e r i n g T e s t S a t e l l i t e V I ( r e f . 54). T h r u s t e r s i z e i s a d j u s t a b l e t o f i t m i s s i o n r e q u i r e m e n t s ( f i g . 12). But t o advance t o s i g n i f i c a n t l y h i g h e r power, t h e key i s s u e s a r e scale-up o f i o n a c c e l e r a t i o n subsystems for h i g h power o p e r a t i o n and t h r u s t e r l i f e . High power o p e r a t i o n i s l l m i t e d by i o n o p t i c s , and e x t r a c t i o n a r e a must be increased w i t h i n c r e a s i n g power. I o n p r o p u l s i o n systems i n t h e range o f 10 t o 50-kW o f f e r s i g n i f i c a n t payload and t r i p t i m e advantages o v e r chemical systems f o r l u n a r ferry and o u t e r p l a n e t e x p l o r e r m i s s i o n s ( i n c l u d i n g m u l t i p l e t a r g e t m i s s i o n s ) , as w e l l as for m i s s i o n s o u t s i d e t h e s o l a r system A nearterm t a r g e t for p l a n e t a r y and E a r t h o r b i t a l m i s s i o n s i s about 5 t o 30 kW p e r i o n t h r u s t e r u s i n g xenon as a p r o p e l l a n t . The planned P a t h f i n d e r Cargo V e h i c l e
9
P r o p i i l s i o n program w i l l f o c u s on a t a r g e t of 0.1 t o 1 MW p e r i o n t h r u s t e r u s i n g argon o r k r y p t o n . While t h e performance e n g i n e e r i n g o f i o n engines i s w e l l i n hand t h e s c a l a b i l i t y , system, l i f e t i m e , and power p r o c e s s i n g i s s u e s r e m a i n open and a r e b e i n g addressed i n t h e NASA program. L i f e t i m e . - I n t e r e s t i n near-term a p p l i c a t i o n o f i o n t h r u s t e r s f o r s o l a r e l e c t r i c p r o p u l s i o n i n n e a r - E a r t h m i s s i o n s ( r e f s . 62 and 70) has l e d t o a program t o i d e n t i f y and extend t h e o p e r a t i n g l i m i t s o f i o n t h r u s t e r s o r i g i n a l l y developed for 3-kW o p e r a t i o n w i t h mercury t o t h e IO-kW range u s i n g i n e r t gas p r o p e l l a n t s ( r e f s . 71 and 7 2 ) . The o r i g i n a l mercury i o n engines p r e s e n t e d l i f e l i m i t i n g phenomena l i k e s p a l l i n g o f metal f l a k e s eroded f r o m t h e d i s c h a r g e chamber s u r f a c e s which c o u l d s h o r t o u t t h e screen a c c e l e r a t i n g g r i d s as w e l l as t h e problem o f u s i n g a t o x i c , c o n d e n s i b l e p r o p e l l a n t . As a r e s u l t t h e program i s now focused on i n e r t gas p r o p e l l a n t s , p r i m a r i l y xenon. JPL m o d i f i e d t h e 0.3-m J - s e r i e s mercury i o n engines, which had p r e v i o u s l y been h i g h l y developed and were r e a d y f o r space q u a l i f i c a t i o n t e s t i n g a t 2 . 2 kW, t o use xenon. Recogn i z i n g t h a t t h e xenon s p u t t e r r a t e s a r e g r e a t e r t h a n f o r mercury and t h e xenon engine o p e r a t i n g powers a r e 2 t o 5 times those f o r mercury engines, l i f e t i m e i s a c r i t i c a l i s s u e . An i o n t h r u s t e r system f o r p l a n e t a r y a p p l i c a t i o n s has been designed and i s undergoing e n g i n e e r i n g t e s t s ( r e f . 73). The f o c u s o f these a c t i v i t i e s i s on r e d u c i n g system c o m p l e x i t y , w i t h t h e goal o f r e d u c i n g t h e c o s t o f development and f l i g h t q u a l i f i c a t i o n . Proposed d e s i g n changes a r e e v a l u a t e d i n t e r m s o f m i s s i o n impact ( r e f . 7 4 ) .
To overcome cathode e r o s i o n problems, JPL has been t e ; t i n g a 1.27-cm diame t e r h o l l o w cathode shown i n f i g u r e 13 ( r e f . 7 5 ) . The cathode was s u c c e s s f u l l y o p e r a t e d f o r 1200 h r on argon, o f which 1050 h r were a t 100 A and 24 h r w e r e a t 150 A. The cathode was s t i l l o p e r a t i n g when t h e t e s t i n g was t e r m i n a t e d ; c r a c k i n g a l o n g t h e t a n t a l u m b a r r e l a t t h e upstream end and t u n g s t e n d e p o s i t s which were i n t h e process o f c l o s i n g o f f t h e i n s e r t b o r e were two o f t h e problems observed i n o p e r a t i n g these cathodes a t h i g h power. There may have been a cathode j e t formed which c o u l d have been r e s p o n s i b l e for t h e h i g h e r o s i o n r a t e a t t h e upstream s i d e o f t h e b a f f l e . P r e l i m i n a r y d a t a o b t a i n e d by JPL i n 1987 showed t h a t t h e i n t r o d u c t i o n of n i t r o g e n i n t o t h e xenon p r o p e l l a n t reduced t h e b a f f l e e r o s i o n . N i t r o g e n may a l s o reduce t h e e r o s i o n o f t h e a c c e l e r a t i n g g r i d s . The work w i l l be c o n t i n u e d ( r e f . 7 6 ) . I n a d d i t i o n , a l t e r n a t i v e s t o t a n t a l u m w i l l be t e s t e d as b a f f l e m a t e r i a l s and e r o s i o n and d e p o s i t i o n r a t e s on c r i t i c a l s u r f a c e s and d e p o s i t s t r u c t u r e w i l l be c h a r a c t e r i z e d . S c a l i n g i s s u e s . - R e s u l t s have p r e v i o u s l y been r e p o r t e d f o r 30- t o 50-cm diameter xenon t h r u s t e r s a t power l e v e l s up t o 20 kW. However, t h e o n l y extended o p e r a t i o n o f a h i g h . p o w e r xenon i o n t h r u s t e r has been w i t h a 30-cm J-series d i v e r g e n t - f i e l d t h r u s t e r a t 10 kW. T h i s t h r u s t e r had i n s u f f i c i e n t l i f e f o r h i g h t o t a l impulse m i s s i o n because o f cathode b a f f l e e r o s i o n . NASA Lewis has addressed i t s c a t h o d e - b a f f l e e r o s i o n , which was r u n n i n g about 0.5 mm/hr, by e l i m i n a t i n g t h e b a f f l e i p o l e p i e c e and g o i n g t o t h e r i n g cusp design shown i n f i g u r e 14. T h i s d e s i g n w i l l r e q u i r e t h e a p p l i c a t i o n of a magn e t i c f i e l d on t h e o r d e r of 500 t o 1000 G a t t h e boundary ( r e f s . 77 and 7 8 ) . Measurements made by NASA Lewis have shown t h a t t h e e r o s i o n r a t e s a r e v e r y s e n s i t i v e t o t h e d i s c h a r g e c u r r e n t . I n o r d e r t o understand e r o s i o n b e t t e r , NASA Lewis i s d e v e l o p i n g a model o f s p u t t e r i n g . NASA Lewis has demonstrated t h e t e c h n o l o g y t o f a b r i c a t e 0.5-m i o n t h r u s t e r s ( r e f . 79) as shown i n f i g u r e 15. F i g u r e 1 6 shows t h e i o n beam e x t r a c t i o n c a p a b i l i t y o f a 0.3-m i o n engine and t h e new 0.5-m i o n engine. The 0.5-m
10
engine doubles t h e power c a p a b i l i t y and extends t h e s p e c i f i c impulse c a p a b i l i t y . (The t h r u s t e r e f f i c i e n c y i s n e a r l y independent o f s i z e and magnetic circuit. ) E a r l y i o n t h r u s t e r g r i d s ( i o n o p t i c s ) were f l a t and were s u b j e c t t o severe, u n c o n t r o l l e d b u c k l i n g when r a d i a l temperature g r a d i e n t s became too steep. The g r i d s were t h e n d i s h e d t o c o n t r o l b u c k l i n g . I n c r e a s i n g t h e t h r u s t of i o n engines w i l l r e q u i r e i n c r e a s i n g g r i d s i z e . W i t h t h e l a r g e r g r i d s and p o t e n t i a l l y n o n c i r c u l a r geometries now under c o n s i d e r a t i o n , computer modeling has been developed and e x p e r i m e n t a l l y v e r i f i e d f o r u n d e r s t a n d i n g s t r u c t u r a l response ( r e f . 8 0 ) . Engine s y s t e m t e c h n o l o q y . - JPL has been w o r k i n g on a s i m p l i f i e d system d e s i q n arid i m p r o v i n g t h r o t t l i n g s t r a t e g y f o r p l a n e t a r y m i s s i o n . A s shown i n f igu;e 1 7 , JPL has d e t e r m i ned t h a t i o n - e n g i ne; o p e r a t i ng a t f i xed p r o p e l 1 a n t flow r a t e s can be t h r o t t l e d o v e r an i n p u t power range o f 3 . 2 : l w i t h o n l y a small i n c r e a s e i n p r o p e l l a n t consumed and small decrease i n p a y l o a d d e l i v e r e d as compared t o o p e r a t i n g t h e engines a t a v a r i a b l e flow r a t e . The improved t h r o t t l i n g s t r a t e g y seeks t o s e l e c t t h e most optimum number o f o p e r a t i n g engines, o p e r a t i o n a l d u t y c y c l e s , and s p e c i f i c i m p u l s e . The systems s t u d i e s have shown t h a t t h i s o p t i m i z e d t h r o t t l i n g s t r a t e g y r e s u l t s i n a r e d u c t i o n i n t h e r e q u i r e d engine l i f e t i m e o f 25 p e r c e n t t o p e r f o r m t h e base m i s s i o n , which was a rendezvous w i t h Comet K o p f f , when compared t o t h e c o n v e n t i o n a l t h r o t t l i n g t e c h n i q u e . O b v i o u s l y t h e c o n s t a n t flow s t r a t e g y e l i m i n a t e s t h e flow c o n t r o l l e r s and p e r m i t s o p e r a t i o n a t f i x e d d i s c h a r g e c o n d i t i o n s - and i t may a l s o s i m p l i f y t h e PPU. JPL p l a n s t o c o n f i g u r e t h e l a b o r a t o r y PPU f o r a twoengine o p e r a t i o n and o p e r a t e t h e two-engine module on a s i n g l e screen s u p p l y . Computer c o n t r o l a l g o r i t h m s f o r m u l t i e n g i n e c o n t r o l w i l l be developed. NASA Lewis has examined i n p a r a m e t r i c f a s h i o n t h e impact o f v a r i o u s t h r u s t e r t e c h n o l o g i e s and o p e r a t i n g c o n d i t i o n s and system t e c h n o l o g i e s on t h e d e s i g n and performance o f a 10-kW c l a s s i o n p r o p u l s i o n system for o r b i t a l maneuvering and t r a n s f e r . A methodology i s d e s c r i b e d w h e r e i n a computer code i s used f o r p r e c i s e d e t e r m i n a t i o n of i o n t h r u s t e r performance (based upon p r e d e f i n e d and u s e r - d e f i n e d t h r u s t e r t e c h n o l o g i e s ) , a d e t e r m i n a t on o f o v e r a l l p r o p u l s i o n system d e s i g n i n c l u d i n g a complete mass breakdown. and f i r s t - o r d e r c a l c u l a t i o n s o f t o t a l impulse and d e l t a - V c a p a b i l i t i e s . Resu t s a r e o b t a i n e d f r o m t h i s code t o examine t h e impact of t h r u s t e r t e c h n o l o g i e s ( e n g i n e d i a m e t e r , 2- and 3 - g r i d i o n o p t i c s , t h r u s t e r o p e r a t i n g c o n d i t i o n s (power l e v e l p r o p e l l a n t , and s p e c i f i c i m p u l s e ) ) , and subsystem t e c h n o l o g i e s on system d e s i g n and m i s s i o n c a p a b i l i t y . These a n a l y s e s w e r e a l s o conducted for a r c j e t systems ( r e f . 81).
MAGNETOPLASMADYNAMIC Multimegawatt MPD t h r u s t e r t e c h n o l o g y o f f e r s p a y l o a d g a i n s o f a f a c t o r o f 10 o v e r chemical p r o p u l s i o n f o r t y p i c a l o r b i t r a i s i n g , l u n a r base f e r r y , and manned i n t e r p l a n e t a r y m i s s i o n s . The MPD t h r u s t e r combines h i g h s p e c i f i c impulse (1000 t o 5000 sec) w i t h moderate t h r u s t l e v e l s ( 1 0 t o 100 N ) . Histori c a l l y , steady s t a t e MPD t h r u s t e r s have t y p i c a l l y been r u n a t or below t h e f e w hundred k i l o w a t t range ( e . g . , r e f s . 82 t o 84), w h i l e MPD t h r u s t e r s o p e r a t e d i n a p u l s e d mode have been r u n a t power l e v e l s exceeding 1 MW ( e . g . , r e f s . 84 t o 8 7 ) . P r o p e l l a n t s have i n c l u d e d H 2 , A r , He, L i , Ne, "3, and N2H4. 11
High s p e c i f i c impulse (3000 t o 6000 sec) a t e f f i c i e n c es o f 30 t o 50 p e r c e n t have been demonstrated u s i n g hydrogen ( e . g . , r e f s . 88 and 891, though i n gene r a l t h r u s t e f f i c i e n c i e s have n o t exceeded 30 p e r c e n t f o r most p r o p e l l a n t s ( f i g . 18). P r e s e n t l y , MPD t h r u s t e r l i f e t i m e s a r e l i m t e d by severe cathode e r o s i o n ( r e f s . 90). MPD p r o p u l s i o n i s l e s s advanced han i o n . H i g h e r e f f i c i e n c i e s and s p e c i f i c impulses a r e g e n e r a l l y o b t a i n e d w i t h a p p l i e d magnetic f i e l d s , b u t t h e fundamental t h e o r e t i c a l u n d e r s t a n d i n g o f t h i s mode o f o p e r a t i o n i s l a c k i n g . The h i g h e s t t o t a l impulse demonstrated i s 106 N-s, a t a b o u t 25 kW ( r e f . 91). C u r r e n t l y , NASA Lewis i s i n v o l v e d i n b o t h e x p e r i m e n t a l and t h e o r e t i c a l r e s e a r c h i n t h e areas of cathode e r o s i o n and MPD t h r u s t e r performance. NASA Lewis has made o p e r a t i o n a l i t s high-power MPD t h r u s t e r t e s t s t a n d and successf u l l y demonstrated an o p e r a t i n g power o f 130 kW i n a h y b r i d MPD/electrothermal mode and GO kW i n t h e MPD mode ( r e f . 91) NASA Lewi(; has extended t h e magnetic f i e l d t o 0.3 T and shown reduced anode damage on s t a r t - u p and an extended s t a b l e s t e a d y - s t a t e o p e r a t i n g range as shown i n f i g u r e 19 ( r e f s . 92 and 9 3 ) . A high-power MPD t h r u s t s t a n d ( r e f . 94) and n o n i n t r u s i v e plasma d i a g n o s t i c s ( r e f . 9 5 ) a r e b e i n g developed, and hardware i s b e i n g assembled for a s e r i e s of cathode e r o s i o n e x p e r i m e n t s . Codework i s b e i n g w r i t t e n t o s i m u l a t e t h e magnetoplasmadynamic i n t e r a c t i o n s ( r e f . 96), and w i l l be used t o e v a l u a t e t h r u s t e r d e s i g n changes ( r e f . 9 0 ) . JPL i s a l s o w o r k i n g on such a t e s t s t a n d and b o t h Centers a r e d e v e l o p i n g n o n i n t r u s i v e d i a g n o s t i c s f o r MPD t e s t i n g . The p o t e n t i a l impact o f h i g h - t e m p e r a t u r e s u p e r c o n d u c t i v i t y developments on MPD t e c h n o l o g y was assessed i n a j o i n t e f f o r t b y Argonne N a t i o n a l L a b o r a t o r y and NASA Lewis ( r e f . 97).
Work a t JPL has demonstrated t h a t cathode e v a p o r a t i o n can be m i n i m i z e d by d e s i g n i n g for t h e r m i o n i c e m i s s i o n d u r i n g s t e a d y - s t a t e o p e r a t i o n . T h i s may l e a d t o p r a c t i c a l t h r u s t e r l i f e t i m e s (21000 h r ) . I n t h e n e a r t e r m , JPL i s f o c u s i n g on d e m o n s t r a t i n g MPD t h r u s t e r o p e r a t i o n f o r p e r i o d s g r e a t e r t h a n 100 h r . Prev i o u s l y , u s i n g t h e t h r u s t e r concept shown i n f i g u r e 20, JPL had completed 85 r u n s t o t a l i n g 1 3 h r o f o p e r a t i o n , r e a c h i n g a maximum power o f o v e r 72 kW a t 2245 A . The e n g i n e o p e r a t e d f o r an 83-min p e r i o d w i t h no e x c e s s i v e a r c s p o t damage on t h e cathode. The cathode t i p t e m p e r a t u r e was l e s s t h a n 2240 K f o r o p e r a t i o n up t o 1700 A w i t h an argon p r o p e l l a n t mass f l o w r a t e o f 0 . 1 6 g / s e c . JPL has observed two d i s t i n c t s t e a d y - s t a t e o p e r a t i n g modes as shown i n f i g u r e 21. The f i r s t mode i s c h a r a c t e r i z e d by a luminous cathode j e t w h i l e t h e second mode has a cooler cathode t i p and no cathode j e t . A t t h e same c u r r e n t t h e t e r m i n a l v o l t a g e i s as much as 40 p e r c e n t l o w e r i n t h e second mode. I t may t u r n o u t t h a t t h e second mode c o u l d p r o v i d e t h e more e f r i c i e n t a c c e l e r a t i o n of t h e plasma, due t o a more c o n t a i n e d r a d i a l c u r r e n t p a t t e r n . Work i s c o n t i n u i n g t o understand t h e c o n d i t i o n s under which t h e two modes o c c u r . A s p a r t o f i t s e f f o r t t o improve MPD t h r u s t e r performance JPL has designed a r a d i a t i o n - c o o l e d , a p p l i e d f i e l d h y b r i d e n g i n e as shown i n f i g u r e 2 2 . T h i s w i 1 1 be f a b r i c a t e d and t e s t e d . J D L has a l s o been r e v i e w i n g t h e l i t e r a t u r e t o de termine i f designs p r e v i o u s l y d i s c a r d e d because of t h e p r e v i o u s l y e x i s t i n g technology l i m i t a t i o n s may now- be u s e f u l . R e c o g n i z i n g t h a t e e c t r o d e sheaths have a s i g n i f i c a n t e f f e c t on MPD t h r u s t e r o p e r a t i o n a l l i m i t a t ons and p e r formance, (JPL i s s p o n s o r i n g t h e development o f a more s o p h i s t c a t e d twodimensional model t h a t w i l l p r o v i d e a b e t t e r u n d e r s t a n d i n g o f MPD t h r u s t e r o p e r a t i o n s than c u r r e n t one-dimensional models. 12
ELECTRODELESS DISCHARGE THRUSTERS E l e c t r o d e t h r u s t e r concepts o f f e r t h e p o t e n t i a l f o r very h i g h energy coup l i n g e f f i c i e n c y , and a r e t h e r e f o r e , of g r e a t i n t e r e s t f o r h i g h power a p p l i c a t i o n s ( r e f s . 98 t o 104). L i m i t a t i o n s imposed by e l e c t r o d e e r o s i o n i n o t h e r e l e c t r i c p r o p u l s i o n t h r u s t e r d e s i g n s a r e p o t e n t i a l l y avoided. C u r r e n t l y NASA Lewis i s e v a l u a t i n g t h e microwave e l e c t r o t h e r m a l (MET) t h r u s t e r ( r e f . go), which absorbs a p p l i e d microwave power i n a plasma d i s c h a r g e and heats t h e gas p r o p e l l a n t by h i g h p r e s s u r e t h e r m a l i z a t i o n ( f i g . 2 3 ) . Advantages i n c l u d e a h i g h e f f i c i e n c y for power a b s o r p t i o n ; a h i g h power d e n s i t y ; and e x t e r n a l c o n t r o l of t h e d i s c h a r g e l o c a t i o n , shape, and volume. The MET t h r u s t e r s h o u l d r e a d i l y s c a l e w i t h power (a1 though performance may n o t ) and i t i s c o m p a t i b l e w i t h h i g h power o p e r a t i o n . The c u r r e n t t e c h n o l o g y MET, b e i n g developed i n c o n j u n c t i o n w i t h M i c h i g a n S t a t e U n i v e r s i t y , o p e r a t e s a t a m i c r o wave f r e q u e n c y o f 2450 MHz and a power c o u p l i n g e f f i c i e n c y i n excess of 95 p e r c e n t . Power l e v e l s up t o 2.5 kW have been t e s t e d , and s p e c i f i c impulse v a l u e s up t o 600 sec have been o b t a i n e d w i t h h e l i u m . Recent r e s u l t s show energy e f f i c i e n c i e s a p p r o a c h i n g 65 p e r c e n t a t low power ( r e f . 105). Gases t e s t e d i n c l u d e He, N2, H2, and 02, and a v a r i e t y of microwave a p p l i c a t o r designs have been demonstrated. P r e s e n t l i m i t a t i o n s i n performance a r e due t o m a t e r i a l c o n s t r a i n t s and MET t h r o a t / n o z z l e d e s i g n ( r e f . 90). F u t u r e work a t NASA Lewis w i l l f o c u s on power l e v e l s o f 30 kW a t a f r e quency o f 915 MHz, u s i n g H2, He, and N2 a t d i s c h a r g e p r e s s u r e up t o 10 atm. A magnetic n o z z l e , produced by a low temperature s u p e r c o n d u c t i n g magnetic magnet (peak f i e l d 5.7 T I , w i l l be used t o i n c r e a s e t h e plasma d e n s i t y i n t h e d i s charge chamber w a l l s . Computer modeling w i l l be used t o p r e d i c t performance w i t h magnetic n o z z l e s , and t o compare performance 1 i m i t s w i t h o t h e r e l e c t r o d e l e s s concepts i n c l u d i n g e l e c t r o n c y c l o t r o n resonance (ECR) and i o n c y c l o t r o n resonance ( I C R ) heated t h r u s t e r s ( r e f s . 90, 99, 105, and 106)). JPL i s a l s o c o n d u c t i n g r e s e a r c h on t h e ECR concept ( r e f . 104). ELECTROMAGNETIC LAUNCHERS The p o s s i b l e a p p l i c a t i o n of e l e c t r o m a g n e t i c l a u n c h e r s t o d e l i v e r nonfragile materials from t h e Moon t o LEO or other nodes was suggested by t h e N a t i o n a l Commission on Space ( r e f . 55). Several y e a r s ago NASA Lewis complet e d an i n v e s t i g a t i o n o f e l e c t r o m a g n e t i c l a u n c h e r s for d e l i v e r y o f n o n f r a g i l e payloads from E a r t h i n t o v a r i o u s o r b i t s ( r e f s . 107 t o 109). These s t u d i e s i n d i c a t e d s i g n i f i c a n t c o s t b e n e f i t s f o r Earth-based launchers i f t h e l a u n c h r a t e o f a p p r o p r i a t e c a r g o i s h i g h enough. S t u d i e s have a l s o c o n s i d e r e d t h e u t i l i t y o f EML's for t h e l a u n c h o f raw m a t e r i a l s and n o n f r a g i l e c a r g o from t h e l u n a r s u r f a c e ( r e f s . 110 t o 113). However t h e l a u n c h r a t e s would have t o be h i g h e r than those e n v i s i o n e d i n any o f t h e e x p l o r a t i o n case s t u d i e s before an Earth-to-space r a i l l a u n c h e r would be c o m p e t i t i v e w i t h chemical l a u n c h e r s . Advances i n h i g h temperature s u p e r c o n d u c t i v i t y c o u l d c o n t r i b u t e s i g n i f i c a n t l y t o t h e u t i l i t y o f such l a u n c h e r s ( r e f . 114) and make them t h e most economical means o f b u l k t r a n s p o r t from t h e surface of t h e Moon f o r such m a t e r i a l s as p r o p e l l a n t s ( r e f . 115).
13
CONCLUDING REMARKS The ongoing NASA program i n l o w - t h r u s t p r i m a r y and a u x i l i a r y p r o p u l s i o n c o n t i n u e s t o make g r e a t s t r i d e s . The development of h i g h - t e m p e r a t u r e chemical t h r u s t e r s o f f e r s o r d e r - o f - m a g n i t u d e l i f e t i m e improvements and h i g h e r s p e c i f i c i!iipulses. The t e c h n o l o g y f o r r e s i s t o j e t s has been t a k e n t o t h e p o i n t where t h e a r e b a s e l i n e d f o r space s t a t i o n . Work i s advancing on a r c j e t s l e a d i n g t o a p anned f l i g h t d e m o n s t r a t i o n . Both i o n and MPD t h r u s t e r t e c h n o l o g y i s s u e s a r e b e i n g addressed w i t h t h e goal t o f l i g h t demonstrate these systems so t h e y w i l be ready f o r f u t u r e m i s s i o n s such as a c a r g o v e h i c l e f l i g h t t o Mars. ACKNOWLEDGMENTS The a u t h o r s acknowledge t h e c o n t r i b u t i o n s made by P . G a r r i s o n , J . K e l l e y , D . K i n g , T . P i v i r o t t o , J . B a r n e t t , K . G o o d f e l l o w , W . D e i n i n g e r , and C . Garner o f JPL and b y D. Byers, F . Curran, R. Myers, S . Schneider, J . Sovey, and L . Carney o f NASA Lewis. The a u t h o r s a l s o acknowledge t h e c o n t i n u e d s u p p o r t o f G. Reck and E . VanLandingham of NASA Headquarters which a l l o w e d us t o comp l e t e t h i s paper. RE F ERE NC E S
1 . Reck, G.M., "NASA D i r e c t i o n s i n Space P r o p u l s i o n f o r 2000 and Beyond," NASA TM-102281 , 1989. 2 . Palaszewski, B., and E n g e l b r e c h t , C . , " L i g h t w e i g h t S p a c e c r a f t P r o p u l s i o n System S e l e c t i o n , " A I A A Paper 87-2022, J u l y 1987. 3. Stone, J.R., "Recent Advances i n Low T h r u s t P r o p u l s i o n Technology," A I A A Paper 88-3283, J u l y 1988. 4. Whalen, M.V., Lansaw, P . T . , and Wooten, J.R., "High Temperature, O x i d a t i o n R e s i s t a n t T h r u s t e r s , " 1987 JANNAF P r o p u l s i o n M e e t i n q , Vol. 1 , CPIA-480VOL-1, P . S . E g g l e s t o n and K . L . S t r a n g e , eds., Chemical P r o p u l s i o n I n f o r m a t i o n Agency, L a u r e l , MD, 1987, pp. 413-420.
5. Harding, J.T., Kazaroff, J.M., and Appel, M . A . , T h r u s t e r s by CVD, NASA TM-101309, 1988.
I r i d i u m - C o a t e d Rhenium
6 . Wooten, J.R., and Lansaw, P . T . , "High-Temperature, O x i d a t i o n - R e s i s t a n t T h r u s t e r Research," A e r o j e t Techsystems Co., Sacremento, C A , NASA C o n t r a c t NAS3-24643, (NASA C R , t o be p u b l i s h e d , 1989). 7. Appel, M . , Schoenman, L . , F r a n k l i n , J . , and Lansaw, P . T . , " F e a s i b i l i t y Demonstration o f 445-N High Performance Rocket Engine," Proposed f o r t h e 1 8 9 JANNAF P r o p u l s i o n M e e t i n g , C l e v e l a n d , OH, May 1989. 8. Meng, P . R . , Schneider, S . J . , Morgan, C I J . , Jones, R . E . , and P a h l , D.A., " A L i f e Test o f a 22 Newton ( 5 - l b f ) Hydrazine Rocket," NASA TM-100232, 1987. 9 . Jones, R . E . , "High and Low-Thrust P r o p u l s i o n S y s t e m s f o r t h e Space Stat i o n , " A I A A Paper 78-0398, Jan. 1987, ( N A S A TM-88877). 14
10. Jones, R.E., Meng, P . R . , Schneider, S.J., Sovey, J.S., and Tacina, R.R., "Space S t a t i o n P r o p u l s i o n System Technology," A c t a A s t r o n a u t i c a , Vol. 15, No. 9, Sept. 1987, pp. 673-683.
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12. H e c k e r t , B.J., Yu, T . I . , A l l u m s , S.L., and C a r r a s q u i l l o , E.A., " 2 5 t h l b f Gaseous OxygenlGaseous Hydrogen T h r u s t e r for Space S t a t i o n A p p l i c a t i o n , " 1986 JANNAF P r o p u l s i o n M e e t i n g , Vol. 1, K.L. Strange and D.S. E g g l e s t o n , eds., CPIA-PUBL-455-VOL-I, Chemical P r o p u l s i o n I n f o r m a t i o n Agency, L a u r e l , MD, 1986, pp. 539-546. 13. Robinson, P.J., and Rosenthal, S . E . , "A Proven 2 5 - l b f H2/02 T h r u s t e r f o r Space S t a t i o n A u x i l i a r y P r o p u l s i o n , " A I A A Paper 86-1560. June 1986. 14. S e n n e f f , J.M., and R i c h t e r , G.P., "A L o n g - L i f e 50 l b f H2/02 T h r u s t e r f o r Space S t a t i o n A u x i l i a r y P r o p u l s i o n , " A I A A Paper 86-1404, June 1986. 15. R i c h t e r , G.P., and P r i c e , H.G., "Proven, L o n g - L i f e HydrogenlOxygen T h r u s t Chambers f o r Space S t a t i o n P r o p u l s i o n , " 1986 JANNAF P r o p u l s i o n Meeting, Vol. 1, K.L. S t r a n g e and D.S. E g g l e s t o n . eds., CPIA-PUBL-455-VOL-I, Chemi c a l P r o p u l s i o n I n f o r m a t i o n Agency, L a u r e l , MD, 1986, pp. 547-564 (NASA TM-88822). 16. Schneider, S . J . , " A u x i l i a r y P r o p u l s i o n Technology f o r Advanced E a r t h - t o O r b i t V e h i c l e s , " NASA TM-100237, 1987. 17. Schneider, S.J., and Reed, B.D., "Weight Savings i n Aerospace V e h i c l e s t h r o u g h P r o p e l l a n t Scavenging," SAWE Paper 1818, S o c i e t y o f A l l i e d Weight Engineers, May 1988 (NASA TM-100900). 18. Schneider, S . J . , Personal Communication, NASA Lewis Research C e n t e r , C1 eve1 and, OH, 1988. 19. Sackheim, R.L., and H o w e l l , G.W., "Trends i n P r o p u l s i o n Systems f o r Geosynchronous S a t e l l i t e s , " 1 4 t h I n t e r n a t i o n a l Symposium on Space Technology and Science, M. Nagatomo, ed., AGNE P u b l i s h i n g , Tokyo, Japan, 1984, pp. 245-254.
20. Byers, D.C., and Wasel, R.A., "The NASA E l e c t r i c P r o p u l s i o n Program," A I A A Paper 87-1098, May 1987 (NASA TM-89856). 21. Curran, F.M., and Haag, T.W., "An Extended L i f e and Performance T e s t o f a Low-Power A r c j e t , " A I A A Paper 88-3106, J u l y 1988 (NASA TM-100942). 22. Haag, T.W., and Curran, F . M . , " A r c j e t S t a r t i n g R e l i a b i l i t y : A M u l t i s t a r t T e s t on Hydrogen/Nitrogen M i x t u r e s , " A I A A Paper 87-1061, May 1987 (NASA TM-89867). 23. Sarmiento, C.J., and Gruber, R . P . , "Low-Power A r c j e t T h r u s t e r P u l s e I g n i t i o n , " A I A A Paper 87-1951, June 1987 (NASA TM-100123).
15
24. Curran, F.M., B r u c k n e r , R . , and Haag, T . , "Low Power A r c j e t Thermal Cons i d e r a t i o n s , " Proposed f o r t h e 1989 JANNAF P r o p u l s i o n Meeting, C l e v e l a n d , OH, May 1989. 25. Curran, F.M., and M a n z e l l a , D . H . , "The E f f e c t of E l e c t r o d e C o n f i g u r a t i o n on A r c j e t Performance," A I A A Paper 89-2722, J u l y 1989. 26. Curran, F.M., Sovie, A . , and Haag, Thomas, " A r c j e t Nozzle Design I m p a c t s , " NASA TM-102050, 1989 (Proposed for t h e 1989 JANNAF P r o p u l s i o n M e e t i n g ) . 2 7 . D e i n i n g e r , W.D., 1988.
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28. Carney, L.M., " E v a l u a t i o n of t h e Communications Impact o f a Low-Power Arcj e t T h r u s t e r , " A I A A Paper 88-3105, J u l y 1988 (NASA TM-100926). 29. Carney, L.M., and Sankovic, J.M., "The E f f e c t s o f A r c j e t T h r u s t e r Operat i n g C o n d i t i o n and C o n s t r i c t o r Geometry on t h e Plasma Plume," A I A A Paper 89-2723, J u l y 1989. 30. P i v i r o t t o , T.J., K i n g , D . Q . , D e i n i n g e r , W.D., and Brophy, J . R . , "The Design and O p e r a t i n g C h a r a c t e r i s t i c s of a 30-kW Thermal A r c j e t Engine f o r Space P r o p u l s i o n , " A I A A Paper 86-1508, June 1986.
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33. B a r r , F . A . , and Page, R.J., " S l i p C a s t i n g and E x t r u d i n g Shapes o f Rhenium w i t h M e t a l Oxide A d d i t i v e s , P a r t I 1 - Development o f G r a i n S t a b i l i z e d Rhenium P a r t s for R e s i s t o j e t s , " NASA CR-180851, 1987. 34. Page, R.J., S t o n e r , W . A . , and B a r k e r , L . , " P r e l i m i n a r y Design Study o f Hydrogen and Ammonia R e s i s t o j e t s for Prime and A u x i l i a r y T h r u s t e r s , NASA CR-182176, 1988.
35. G r i s n i k , S . P . , Smith, T . A . , and S a l t z , L.E., "Experimental Study o f Low Reynolds Number N o z z l e s , " A I A A Paper 87-0992, May 1987 (NASA TM-89858). 36. Whalen, M . V . , 1987.
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37. Manzella, D . H . , Penko, P . F . , OeWitt, K . J . , and K i e t h , T . G . , "An E x p e r i mental I n v e s t i g a t i o n o f t h e E f f e c t o f Test C e l l Pressure on t h e Performance o f R e s i s t o j e t s , " A I A A Paper 87-3286, J u l y 1988.
38. Penko, P . F . , Smith, C . C . , D e W i t t , K . J . , and K i e t h , T . G . , " A Numerical and Experimental I n v e s t i g a t i o n of R e s i s t o j e t Nozzle Flow," A I A A Paper 89-2839, J u l y 1989.
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39. Shephard, C.B., M c K e v i t t , F.X., and Finden, L.E., " M u l t i p r o p e l l a n t Resist o j e t , " Rept. No. RIiRD88-150, Rockwell I n t e r n a t i o n a l , Rocketdyne D i v i s i o n , Canoga Park, CA, O c t . 1988, NASA CR-182199. 40. B r a u n s c h e i d e l , E.P., "Performance c h a r a c t e r i z a t i o n and T r a n s i e n t I n v e s t i g a t i o n o f M u l t i p r o p e l l a n t R e s i s t o j e t s , " A I A A Paper 89-2837, J u l y 1989. 41. Tacina, R.R., Personal Communication, NASA Lewis Research Center, Clevel a n d , OH, Mar. 1989. 42. Gruber, R . P . , " R e s i s t o j e t C o n t r o l and Power f o r H i g h Frequency AC Buses," A I A A Paper 87-0994. May 1987 (NASA TM-89860). 43. H e c k e r t , B.J., "Space S t a t i o n R e s i s t o j e t System Requirements and I n t e r f a c e D e f i n i t i o n Study," RI/RD87-109. Rocketdyne D i v i s i o n , Rockwell I n t e r n a t i o n a l Corp., Canoga Park, CA, Feb. 1987, NASA CR-179581. 44. Bader, C.H., " P o t e n t i a l P r o p e l l a n t Storage and Feed Systems f o r Space S t a t i o n R e s i s t o j e t P r o p u l s i o n O p t i o n s , " NASA CR-179457, 1987. 45. Zana, L.M., Hoffman, D.J., B r e y l e y , L.R., and S e r a f i n i , J.S., "An Analyt i c a l and E x p e r i m e n t a l I n v e s t i g a t i o n of R e s i s t o j e t Plumes," A I A A Paper 87-0399, Jan. 1967 (NASA TM-88852). 46. B r e y l e y , L.R., S e r a f i n i , J . S . , Hoffman, D.J., and Zana, L.M., " E f f e c t o f Nozzle Geometry on t h e R e s i s t o j e t Exhaust Plume," A I A A Paper 87-2121, June 1987. 47. Carney, L.M., and B a i l e y , A.B., " E x p e r i m e n t a l E v a l u a t i o n o f R e s i s t o j e t T h r u s t e r Plume S h i e l d s , " I E P C Paper 88-091, Oct. 1988 (NASA TM-101363). 48. L o u v i e r e , A.J., Jones, R . E . , Morren, W.E., and Sovey, J.S., "WaterP r o p e l l a n t R e s i s t o j e t s for Man-Tended P l a t f o r m s , " IAF Paper 87-2519, 1987 (NASA TM-100110).
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49. Morren, W.E., and Stone, J.R., "Development o f a Liquid-Fed Water Resist o j e t , " A I A A Paper 88-3288, J u l y 1988 (NASA TM-100927). 50. Morren, W.E., and Stone, J.R., " O p e r a t i o n a l C h a r a c t e r i z a t i o n s o f a L i q u i d Fed Water R e s i s t o j e t , " A I A A Paper 89-2836, J u l y 1989. 51. M a n z e l l a , D.H., and Carney, L.M., "Plume Impacts o f a L i q u i d - F e d Water R e s i s t o j e t , " A I A A Paper 89-2840, J u l y 1989. 52. Stone, J.R., Byers, D . C . , and K i n g , D.O., "The NASA E l e c t r i c P r o p u l s i o n Program," I E P C Paper 88-002, O c t . 1988 (NASA TM-101324).
53. B r i l l , Y . , E i s n e r , A . , and Osborn, L . , "The F l i g h t A p p l i c a t i o n o f a Pulsed Plasma M i c r o t h r u s t e r , The NOVA S a t e l l i t e , " A I A A Paper 82-1956, Nov. 1982. 54. Shimada, S . , Takegahara, H., Kimura, H . , and K a j i w a r a , K., " I o n Engine System for North-South S t a t i o n - K e e p i n g o f E n g i n e e r i n g T e s t S a t e l l i t e V I , " A I A A Paper 87-1005, May 1987.
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55. P i o n e e r i n g t h e Space F L o n t i e r , N a t i o n a l Commission on Space, Bantam Books, New York, 1986. 56. Nock, K . T . , Aston, G., S a l a z a r , R . P . , and S t e l l a , P . M . , "Lunar Get Away S p e c i a l (GAS) S p a c e c r a f t , " A I A A Paper 87-1051, May 1987. 57. Nock, K . T . , "TAU - A M i s s i o n t o a Thousand A s t r o n o m i c a l U n i t s , " A I A A Paper 87-1049, May 1987. 58. G a l e c k i , D.L., and P a t t e r s o n , M.J., "Nuclear Powered Mars Cargo T r a n s p o r t U t i l i z i n g Advanced I o n P r o p u l s i o n , " A I A A Paper 87-1903, June 1987 (NASA TM-100109). 59. Sauer, C . G . , J r . , " A p p l i c a t i o n o f S o l a r E l e c t r i c P r o p u l s i o n t o F u t u r e P l a n e t a r y M i s s i o n s , " P.IAA Paper 87-1053, May 1987.
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Vol 1 :
Technical
66. N i e h o f f , J . , "Humans on Mars: A Space L e a d e r s h i p Program," B r i e f i n g t o NASA Headquarters, Science A p p l i c a t i o n s I n t e r n a t i o n a l C o r p o r a t i o n , 1987. 67. Sovey, J . S . , and Mantenieks, M . A . , "Performance and L i f e t i m e Assessment o f MPD A r c T h r u s t e r Technology," A I A A Paper 88-3211, J u l y 1988 (NASA TM-101293). 68. R a w l i n , V . K . , and P a t t e r s o n , M . J . , "High Power I o n T h r u s t e r Performance," NASA TM-100127, 1987. 69. K e r s l a k e , W . R . ,
" I o n P r o p u l s i o n f o r S p a c e c r a f t , " NASA TM-79502,
1977.
70. Garner, C . , " I o n P r o p u l s i o n System Technology f o r O r b i t R a i s i n g and Maneuvering," Proposed for 1989 JANNAF.Propu1sion Meeting, C l e v e l a n d , OH, May 1989.
18
71. Rawlin, V.K., " I n t e r n a l E r o s i o n Rates o f a 10-kW Xenon I o n T h r u s t e r , " A I A A Paper 88-2912, J u l y 1988 (NASA TM-100954). 72. P a t t e r s o n , M.J., and Rawlin, V.K., "Performance o f 10-kW Class Xenon I o n T h r u s t e r s , " A I A A Paper 88-2914, J u l y 1988 (NASA TM-101292). 73. Aston, G., Brophy, J.R., Garner, C.E., and P l e s s , L.C., " O p e r a t i n g Chara c t e r i s t i c s of a IO-kW Xenon I o n P r o p u l s i o n Module," A I A A Paper 87-1006, May 1987. 74. Garner, C.E., Brophy, J.R., and P l e s s , L.C., " I o n P r o p u l s i o n System Design and T h r o t t l i n g S t r a t e g i e s for P l a n e t a r y Missions," A I A A Paper 88-2910, J u l y 1988. 75. Brophy, J.R., and Garner, C.E., "Tests of High C u r r e n t Hollow Cathodes f o r Ion Engines," A I A A Paper 88-2913, J u l y 1988. 7 6 . Garner, C., "Techniques for Reduced S p a l l i n g and I n c r e a s e d O p e r a t i n g L i f e o f Xenon I o n Engines," A I A A Paper 89-2714, J u l y 1989. 77. Rawlin, V.K., "Performance of Large Area I o n T h r u s t e r s for O r b i t T r a n s f e r M i s s i o n s , " NASA TM-102049 (1989 JANNAF P r o p u l s i o n M e e t i n g ) . 78. Patterson, M.J., and Verhey, T.R., "Performance and L i f e t i m e C h a r a c t e r i z a t i o n o f a 10 kW Xenon Ring-Cusp I o n T h r u s t e r , " A I A A Paper 89-2713, J u l y 1989. 79. Rawlin, V.K., and M i l l i s , M.G., " I o n O p t i c s for High Power 50 cm Diameter I o n T h r u s t e r s , " A I A A Paper 89-2717, J u l y 1989. 80. MacRae, G.S., " S t r u c t u r a l Analyses of I o n O p t i c a l Systems U s i n g t h e MARC F i n i t e Element Code," A I A A Paper 89-2719, J u l y 1989. 81. P a t t e r s o n , M.J., and Curran, F.M., " E l e c t r i c P r o p u l s i o n O p t i o n s f o r 10 kW Class Earth-Space Missions," Proposed for 1989 JANNAF P r o p u l s i o n Meeting, Cleveland, OH, May 1989. 82. Auweter-Kurtz,
M., K u r t z , H.L., Schrade, H.O., and S l e z i o n a , P . C . , "Numeri c a l Modeling o f t h e Flow Discharge i n MPD T h r u s t e r s , " A I A A Paper 87-1091, May 1987.
83. K u r t z , H.L., Auweter-Kurtz, M., Merke, W., and Schrade, H O., " E x p e r i mental MPD T h r u s t e r I n v e s t i g a t i o n s , " A I A A Paper 87-1019, May 1987. 84. King, D.Q., and Brophy, J.R., "Design and O p e r a t i o n o f a lOO-kW, Subscale MPD Engine," A I A A Paper 87-1020, May 1987. 85. Myers, R.M., Suzuki, N . , K e l l y , A.J. , and Jahn, R.G., "Cathode Phenomena i n a Low Power, Steady S t a t e MPD T h r u s t e r , " A I A A Paper 88-3206, J u l y 1988. 86. Myers, R.M, K e l l y , A.J., and Jahn, R.G., " E l e c t r o t h e r m a l - E l e c t r o m a g n e t i c H y b r i d T h r u s t e r Research," A I A A Paper 87-1018, May 1987.
19
87. C h o u e i r i , E.Y., K e l l y , A.J., and Jahn, R . G . , "MPD T h r u s t e r Plasma, I n s t a b i l i t y S t u d i e s , " A I A A Paper 87-1067, May 1987. 88. Yoshikawa, T., Kagaya, Y . , Yokoi, Y . , and Tahara, H . , "Performance Chara c t e r i s t i c s o f Quasi-Steady S t a t e MPD T h r u s t e r s , " 1 7 t h I n t e r n a t i o n a l E l e c t r i c P r o p u l s i o n Conference, Japan S o c i e t y f o r A e r o n a u t i c a l and Space Sciences, Tokyo, 1984, pp. 396-403. 89. Uematsu, K . , Mori, K., Kuninaka, H., and K u r i k i , K., " E f f e c t o f E l e c t r o d e C o n f i g u r a t i o n on MPD A r c j e t Performance," 1 7 t h I n t e r n a t i o n a l E l e c t r i c P r o p u l s i o n Conference, Japan S o c i e t y f o r A e r o n a u t i c a l and Space Sciences, Tokyo, 1984, pp. 79-86.
90. LaPointe, M., Rawlin, V., and Power, J., "High Power E l e c t r i c P r o p u l s i o n Technology a t t h e NASA Lewis Research C e n t e r , " Prepared f o r 6 t h Symposium on Space N u c l e a r Power Systems, Albuquerque, NM, Jan. 9-12, 1989. 91. Sovey, J . S . , and Mantenieks, M.A., "Performance and L i f e t i m e Assessment o f MPD A r c T h r u s t e r Technology," AIAA-88-3211, J u l y 1988 (NASA TM-101293). 92. Sovey, J . S . , Mantenieks, M.A., Haag, T.W., R a i t a n o , P., and Parkes, J.E., " T e s t F a c i l i t y and P r e l i m i n a r y Performance o f a 100 kW C l a s s MPD T h r u s t e r , " NASA TM-102021, 1989 (1989 JANNAF P r o p u l s i o n M e e t i n g ) .
93. Mantenieks, M.A.,
Sovey, J . S . , Myers, R., Haag, T.W., R a i t a n o , P., and Parkes, J.E., " C h a r a c t e r i z a t i o n of a 100-kW Class A p p l i e d - F i e l d MPD T h r u s t e r , " A I A A Paper 89-2710, J u l y 1989.
94. Haag, T.W., "Design of a T h r u s t Stand for H i g h Power E l e c t r i c P r o p u l s i o n Devices," Proposed for t h e 1989 JANNAF P r o p u l s i o n Meeting, C l e v e l a n d , OH, May 1989. 95. Myers, R.M., "Plume C h a r a c t e r i s t i c s o f MPD T h r u s t e r s : Examination," A I A A Paper 89-2832, J u l y 1989.
A Preliminary
96. LaPointe, M.R., "Numerical S i m u l a t i o n o f A p p l i e d F i e l d Steady S t a t e MPD T h r u s t e r s , " proposed for t h e 1989 JANNAF P r o p u l s i o n M e e t i n g , C l e v e l a n d , OH, May 1989. 97. Reed, C.B., and Sovey, J.S., "The Use of H i g h Temperature Superconductors i n Magnetoplasmadynamic Systems," NASA TM-101219, 1988. 98. P o l l a r d , J.E., L i c h t i n , D . A . , and Cohen, R . B . , "RF D i s c h a r g e E l e c t r o thermal P r o p u l s i o n : R e s u l t s for a Lab-Scale T h r u s t e r , " A I A A Paper 87-2124, June 1987. 99. W h i t e h a i r , S . , Asmussen, J . , and Nakanshi, S . , "Microwave E l e c t r o t h e r m a l T h r u s t e r Performance on H e l i u m Gas," J o u r n a l o f P r o p u l s i o n and Power, Vol. 3, No. 2, Mar.-Apr. 1987, pp. 136-144. 100. Morin, T.J., and Hawley, M.C., "The E f f i c a c y of H e a t i n g Low-Pressure H2 i n a Microwave D i s c h a r g e , " Plasma Chemistry and Plasma P r o c e s s i n q , Vol. 7, No. 2, June 1987, pp. 181-199.
20
101. Hawley, M.C., Asmussen, J., Filpus, J.W. Frasch, L.L., Whitehair, S . , Morin, T.J., and Chapman, R., "A Review of Research and Development on the Microwave-Plasma Electrothermal Rocket," AIAA Paper 87-1011, May 1987. 102. Frasch, L.L., Griffin, J.M., and Asmussen, J., "An Analysis of Electromagnetic Coupling and Eigenfrequencies for Microwave Electrothermal Thruster Discharges," AIAA Paper 87-1012, May 1987.
103. Filpus, J.W., and Hawley, M.C., "A Computer Model for the Recombination Zone of a Microwave-Plasma Electrothermal Rocket," AIAA Paper 87-1014, May 1987. 104. Sercel, J., "Electron-Cyclotron-Resonance (ECR) Plasma Thruster Research," AIAA Paper 88-2916, July 1988. 105. Whitehair, S., and Asmussen, J., "The Experimental Performance of a Compact Microwave Electrothermal Thruster," Michigan State University, East Lansing, MI, 1988 (to be published). 106. Whitehair, S., Frasch, L.L., and Asmussen, J . , "Experimental Performance of a Microwave Electrothermal Thruster with High Temperature Nozzle Materials," AIAA Paper 87-1016, 1987.
107. Zana, L.M., Kerslake, W.R., and Sturman, J.L., "Rail Accelerators for Space Transportation - An Experimental Investigation," NASA TP-2571, 1986. 108. Rice, E.E., Miller, L.A., and Earhart, R.W., "Preliminary Feasibility Assessment for Earth-to-Space Electromagnetic Rai lgun Launchers NASA CR-167886, 1982. ,I'
109. Miller, L.A., Rice, E.E., Earhart, R.W., and Conlon, R.A., "Preliminary Analysis of Space Mission Applications for Electromagnetic Launchers," NASA CR-174748, 1 984. 110. Kolm, H., "An Electromagnetic Slingshot for Space Propulsion," Lechnology Review, Vol. 79, June 1977, pp. 60-66.
1 1 1 . O'Neil, G.K., and O'Leary, B., eds., Space Based Manufacturing from Nonterrestrial Materials, Progress in Astronautics and Aeronautics, Vol. 57, AIAA, New York, 1977. 112. Heppenheimer, T.A., "Achromatic Trajectories and Lunar Material Transport
for. Space Colonization." Journal of-Spacecraft and Rockets, Vole 15. No. 3 , May-June 1978, pp. 176-183. 113. Billingham, J., Gilbreath, W.P., O'Leary, B. , and Gosset, B., eds., Space Resources and Space Settlements, NASA SP-428, NASA, Washington, DC, 1979.
114. Hull, J.R., and Carney, L.M., "Application of Superconducting Technology to Earth-to-Orbit Electromagnetic Launch Systems," NASA TM-101134, 1988. 115. "Exploration Mission/Technology Planning Workshop." Workshop Proceedings, Vols. I & 11, Washington, DC, Nov. 14-17, 1988.
21
ORIGINAL PAGE BLACK AND WHlTE PHOTOGRAPH
I r ON Re
SOA ( S i ON Nb) 1000
r
1500 FIGURE 1.
2000
(Isp
=
306-311s)
2500 3000 3500 4000 CHAMBER TEMPERATURE. OF
-l 1000
4500
FIGURE 2 . - PERFORMANCE AND L I F E EXTENSION PROVIDED BY IRIDIUM-COATED RHENIUM THRUST CHAMBER,
- ADVANCED 22-N Bi-PROPELLANT THRUSTER.
1960’s RCS CONCEPT
( I s p = 280-290s)
PROPOSED RCS CONCEPl SHUTTLE II SORTIE MISSION’ 50
r LOADED PROPELUNI
OMS
TANK
oms
PRQPhlANl CONOlllOWlNG
ORY MASS
TANK
GHylGOz RCS THRUSTERS PROPELLANT CONDITIONING
LHz1LOz RCS THRUSTERS NO PROPELLANT CONDITIONING
S 0 A EARlH
STORABLE SYSTEM
SCAVENGING HI0 SYSTEM ILn=l27 I ~ C
SCAVENOING HI0 SYSTEM I.”=lll rec
Itp=31068c
A PAYLOAD BENEFIT OF 10,700 Ib PROJECTED FOR SHUTTLE II MAY OFFER SIGNIFICANT OPERATIONAL BENEFITS
* ELIMINATED COMPONENTS
- HEAT EXCHANGERIOASIFIER
FIGURE 3.
-
-
OAS ACCUMULATOR -COMPRESSOR OECOUPLEO THRUSTERIPROPELLANT MANAGEMENT
‘VEHICLE MASS AND MISSION REQUIREMENTS SUPPLIED BY LaRC
I D ‘1R.31PI4
cD-BB-11311
FIGURE 4.
INTEGRATED HI0 AUXILIARY PROPULSION SYSTEM.
22
- PAYOFF OF INTEGRATED H/O PROPULSION.
MASS FLOW RATE.
OptGlMAL PAGE IS POUR QUALITY
KG/SEC
o 0
0
47c
4.1~10-~ 4.6~10-~ 5.0~10-~
OPEN SYMBOLS DENOTE DATA TAKEN BEFORE L I F E TEST CLOSED SYMBOLS DENOTE DATA TAKEN AFTER 144 CYCLES HALF SYMBOLS DENOTE DATA TAKEN AFTER 335 CYCLES THREE QUARTER SYMBOLS DENOTE DATA TAKEN AFTER L I F E TEST CONCLUSION
45c U v)
W v) a -1
8
43c
:
LL W V
w
410
POWER. W FIGURE 5. - LIFE-TEST 1-KW ARCJET SPECIFIC IMPULSE AS FUNCTION OF POWER.
250
0
250
-
0FIGURE 6.
- LONG-TERM VOLTAGE TRENDS FOR LIFE-TEST
23
1-KW ARCJET.
ELECTRODE CONFIGURATION VERIFIED BY:
- PERFORMANCE DEMONSTRATIONS - LIFE TESTING
i PPU INTEGRATION DEMONSTRATED THERMAL INTERFACES MET DYNAMIC STRUCTURAL ANALYSIS COMPLETED COMMUNICATIONS IMPACTS ASSESSED
FIGURE 7. - FLIGHT-TYPE,
150
1
m
KILOWATT-CLASS ARCJET
i BASELINE
ox ox
DOWNSTREAM CONTOUR
A
DUAL CONTOUR
>
: : 100 . + W
9
I
450
400
I
I
r
0 0
'
U v1 Y
10
I
15
20 P/M,
I
25
30
J/Kg
FIGURE 8. - NOZZLE GEWETRY EFFECTS ON ARCJET CHARACTER I S T I C S .
PULSED TUNABLE
DETECTOR 7 I NARROWBAND INTERFERENCE FILTER
WICH CONTOURS
VOLUME
COOLED VACUUM TANK 1.2X2.1
AXISYM NOZZLE, AR M
= 20. 41
x 21 GRID. RE
=
1086,
DT
=
. O l e 500
STEPS
c
CONTOURS:
TO PUMP
8
=
2 =
0.5. 3
= 1.0,
4
=
1.5. 5 = 2.0. 6 = 2.5. 7
LIQUID
6
A INTERNAL THERMOCOUPLE LOCATIONS EXTERNAL THERMOCOUPLE LOCATIONS
SUPERHEATER INSERT
H
-FLOW
BOILER CHAMBER
RESTRICTOR
/-LIQUID
INJECTOR
u 1
SUPERHEATER-’
FIGURE
11.
3.0,
FIGURE 10. - COMPUTED R4CH NUMBER CONTOURS FOR LOW REYNOLDS NUMBER CONVERGING-DIVERGING NOZZLE.
FIGURE 9 . - JPL LASER INDUCED FLUORSCENCE (LiF) EXPERIMENTAL SETUP.
*
=
3.5.
- INTEGRATED WATER VAPORIZER/RESISTOJET.
25
2 cm
NEAR TERM PLANETARYlEARTH ORBIT MISSION TARGET = 5 TO 30 LWITHRUSTER, Xe PATHFINOER CARGO MISSION TARGET 0.1 TO 1 MWITHRUSTER, At OR Kr
Ar.Kt
loo THRUSTER POWER, kW
H
i
XE
lono
&
lJ
STATIONKEEPING
SEPS CIRCA 1980
SEPS CLASS CARGO PLANETARY/ VEHICLE EARTH ORBIT PROPULSION TRANSFER
FIGURE 12. - I O N ENGINE POWER RANGE FOR VARIOUS MISSIONS.
AFTER 170 HR AT 100 A
NEW
- JPL 1.27 CM
FIGURE 13.
DIAMETER HOLLOW CATHODE.
DIVERGENT FIELD
RING CUSP
. Ulolrll
.
VOLUME BAFFLE FOR DISCHARGE IMPEDANCE CONTROL USED FOR SERT I, SERT It, IAPS, AND SEPS FIGURE 14.
-
BOUNDARY MAGNETIC FIELD NO BAFFLE
DIVERGENT-FIELD AND RING-CUSP ION THRUSTERS.
26
ORIGINAL PAGE BLACK AND WHiTE PI-iOTOCRAPH
FIGURE 15.
- 50
CM
ION THRUSTER.
0 CONSTANT FLOW STRATEGY ELIMINATES FLOW CONTROLLERS AND PERMITS OPERATION AT FIXED DISCHARGE CONDITIONS - MAY SIMPLIFY PPU 0 ENGINE L I F E REQUIREMENT REDUCED 24% BUT REQUIRES 9% MORE PROPELLANT 3000 Kg PAYLOAD
LARGE AREA ION OPTICS PROVIDE:
25
TITAN I V LAUNCH 75 KW ARRAY
STRATEGY
2X INCREASE IN POWER OVER 30 cm DIA. THRUSTER EXTENDED SPECIFIC IMPULSE CAPABILITY
XENON
POWER, kW
IO50 2000
3000
I
HOURS
4000
SPECIFIC IMPULSE,
5000
REQUIRED ENGINE L I F E
s
FIGURE 16. - ION EXTRACTION CAPABILITIES OF 30 cn AND 50 cn THRUSTERS.
FIGURE 17.
27
N-S TOTAL IMPULSE
Kg PROPELLANT MASS
- ION ENGINE THROTTLING STRATEGY.
ORIGINAL PAGE BLACK AND W.MjTE P l
r
.8
I
0 HYDROGEN
0
?! I
0 FLAG:
0
AMMONIA
-
m
STEADY STATE
"A" APPLIED FIELD
D NITROGEN
0
HYDRAZINE
0 ARGON
u
U
0
.4
OA
ARC VOLTAGE. V
A,
"1/
-
ARC PRESSURE 100 TORR
MAGNETIC FIELD
I 0 101
11111
I
I I 1 1 1 1 1 1
I
I
I
I I
102 103 INPUT POWER, KW
FIGURE 18.
lld
MAGNETIC FIELD.
02
TESLA
01
0
104
5w
ELECTROMAGNET CURRENT, A
- DEMONSTRATED EFFICIENCY FOR MPD THRUSTERS.
FIGURE 19.
0.1
0.2
MAGNETIC FIELD. TESLA APPLIED MAONETIC FIELD EXTENOEO TO 0.3 TESLA REDUCED ANODE DAMAGE ON START-UP EXTENDED STABLE STEADV.STATE OPERATING RANGE CU-81-37102
- OPERATING RANGE FOR LERC APPLIED-FIELD NPD THRUSTER.
DISTINCT STEADY-STATE OPERATING MODES OBSERVED BY D. KING IN 1987 ONE MODE IS CHARACTERIZED BY A LUMINOUS CATHODE JET. A SECOND MODE HAS A COOLER CATHODE TIP AND NO CATHODE JET; THE TERMINAL VOLTAGE IS LOWER. ANODE
(+)7
SECOND MODE MAY PROVIDE MORE EFFICIENT PLASMA ACCELERATION
/
I/ FIGURE 20.
, LBUFFER ELECTRODE
- JPL STEADY-STATE, SELF-FIELD MPD THRUSTER.
F I G U R E 21. - STEADY-STATE,
28
S E L F - F I E L D MPD MODE CHANGES.
-RADIATOR
ELECTROMAGNET
FIGURE 22. DESIGN.
-
-.
JPL RADIATION-COOLED,
y
REGENERATIVE THROAT-NOZZLE COOL I NG 7 1
F
A P P L I E D - F I E L D MPD.THRUSTER
THROAT-NOZZLE ASSEMBLY
-
e
VIEW I NG WINDOW
CENTER C O N D U C T O R - U L v -\-
I
PROPELLANT INFLOW (PAR T I A L )
1 IN. FIGURE 23. - ELECTRODELESS. MICROWAVE PLASMA TORCH THRUSTER DESIGN.
29
Report Documentation Page Spice Adin,nislr,i c -_ . ___
I
~
1 Report No _ .
--
___
NASA TM-,02065 AIAA-89- 2492
7
__
__
-_
.
~- - _ _ - -
.-
3. Recipient's Catalog No
Government Accession No
-_______
__
5 . Report Date
4 Title and Subtitle
The N .\SA Low Thrust Piopulsion Program 6. Performing Organization Code
_____-
_____.-_
8 Performing organization Report No
7 Author@)
E-4822
James R. Stone and Gary L. Bennett
10. Work Unit No. --
506-42-3 1
-
-~~~
9 Perforniiny Organization Name and Address 11. Contract or Grant No.
NASA Headquarters Office of Aeronautics and Space Technology Washington. D.C. 20546-OOO 1
13. Type of Report and Period Covered
Technical Memorandum
I
2. Sponsoring Agency Name and Address
National Aeronautics and Space Administration Washington. D.C. 20546-0001
14. Sponsoring Agency Cod;
~
5. Supplementary Notes
Prepared for the 25th Joint Propulsion Conference cosponsored by the AIAA, ASME, SAE, and ASEE, Monterey, California, July 10-12, 1989.
The NASA OAST Propulsion, Power, and Energy Division supports a low thrust propulsion program aimed at providing high performance options for a broad range of near-term and far-term missions and vehicles. Low thrust propulsion has a major impact on the mission performance of essentially all spacecraft and vehicles. Onorbit lifetimes, payloads. and trip times are significantly impacted by low thrust propulsion performance and integration features for Earth-to-orbit (ETO) vehicles. Earth-orbit and planetary spacecraft, and large platforms in Earth orhit. Major emphases of the program are on low thrust chemical propulsion, both storables and hydrogen/ oxygen; low-power (auxiliary) electric arcjets and resistojets; and high-power (primary) electric propulsion, including ion, magnetoplasmadynamic (MPD), and electrodeless concepts. This paper will present the major recent accomplishments of the program and discuss their impacts.
_
_
_
_
_
.
_
~
7 . Key Words (Suggested by Author@))
Electric propulsion Low thrust
Unclas\ified - Unlimited Sublcct Category 20
_______-9 Sycurity Classif (of this report)
Unclassified NASA FORM 1626 OCT 86
I
Unclassified
I
30
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