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N 8 4 - 2 1 6 5 8 NASA Technical Memorandum 85772 OPERATIONAL MODULES FOR SPACE STATI ON CONSTRUCT ION L , ROBERT JACKSON,PAUL L, MOSES, STEPHEN J, SCOTTI, AND MAX L, BLOSSER APRIL 1984 National Aeronauticsand Space Administralion Langley ResearchCenter 1 lampton,Virginia 23665

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OPERATIONAL MODULES FOR SPACE S T A T I O N CONSTRUCTION L. Robert Jackson, Paul L. Moses*, Stephen J. S c o t t i * and Max L. B l o s s e r NASA Langley Research Center SUMMARY c o n s t r u c t i o n concept f o r space s t a t i o n s i s a I d e n t i f i c a t i o n o f an e f f e c t i v e c u r r e n t o b j e c t i v e o f NASA s t u d i e s ( r e f . 1). A novel c o n s t r u c t i o n concept i s desc r i b e d i n t h i s t e c h n i c a l memorandum. With t h i s concept, t h e space s t a t i o n i s cons t r u c t e d by r e p e t i t i v e assembly o f o p e r a t i o n a l modules. The i n i t i a l space s t a t i o n component i n s e r t e d i n t o o r b i t i s a f u l l y o p e r a t i o n a l manned module. T h i s c o n s t r u c - t i o n concept minimizes o n - o r b i t s t a y t i m e o f t h e s h u t t l e , because t h e s h u t t l e i s n o t needed f o r l i f e s u p p o r t d u r i n g assembly o f t h e s t a t i o n . The modules may be p r e - assembled i n a ground-based f a c i l i t y t o enable i n t e g r a t i o n and v e r i f i c a t i o n o f systems. T h i s f e a t u r e improves r e l i a b i l i t y o f space o p e r a t i o n s over s t a t i o n s c o n s t r u c t e d i n space. For t h i s concept, t h e s t r u c t u r e o f t h e modules a l s o p r o v i d e s t h e p r i m a r y r s t r u c t u r e o f t h e space s t a t i o n . This f e a t u r e e l i m i n a t e s t h e need f o r a l a r g e t r u s s - t y p e p l a t f o r m , so s h u t t l e t r i p s a r e minimized and s t a y t i m e i s f u r t h e r reduced. The modules c o n t a i n a 44 f t long compartment t h a t may be p r e s s u r i z e d h a v i n g e i t h e r a 10.5 f t o r 14.5 f t diameter. Once i n o r b i t , t h e s m a l l e r compartment module i s f u l l y o p e r a t i o n a l and ready f o r immediate occupancy. The l a r g e r compartment module uses b a t t e r i e s f o r temporary o p e r a t i o n , b u t must be connected t o a s m a l l e r , f u l l y o p e r a t i o n a l module o r have s o l a r - c e l l a r r a y s a t t a c h e d i n o r b i t t o become f u l l y o p e r a t i o n a l , The l a r g e r compartment, however, p r o v i d e s more u s e f u l volume. A l l modules have a common o v e r a l l space requirement o f 14.5 ft diameter and 46 ft l e n g t h t o enable t r a n s p o r t t o o r b i t by t h e s h u t t l e . * Kentron I n t e r n a t i o n a l , I i l c .

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A i The modules a r e i n t e r c h a n g e a b l e , and any module may be r e p l a c e d w i t h o u t d i s m a n t l i n g t h e space s t a t i o n . Various arrangements and numbers o f modules may be s e l e c t e d t o form a space s t a t i o n c o n f i g u r a t i o n . Convenient a c c e s s i b i l i t y i s p r o v i d e d by i n t e r c o n n e c t i n g t u n n e l s f o r personnel and an assembly t r a n s p o r t v e h i c l e on t r a c k s f o r t r a n s p o r t of personnel and cargo. This novel c o n s t r u c t i o n concept makes maximum use o f Skylab and Spacelab t e c h n o l o g i e s . Moreover, space s t a t i o n growth i s p r o v i d e d by adding modules when needed. discusses space s t a t i o n s u s i n g t h e novel T h i s memorandum d e s c r i b e s and c o n s t r u c t i o n concept. O p e r a t i o n a l modules and an assembly t r a n s p o r t vehi c l e a r e a l s o described. Seven space s t a t i o n c o n f i g u r a t i o n s and s o l a r - c e l l - a r r a y o r i e n t a t i o n s are presented, and analyses o f s o l a r power requirements a r e i n c l u d e d . I N T R O D U C T I O N P r i n c i p a l j u s t i f i c a t i o n s f o r t h e space s h u t t l e were t o p r o v i d e t h e capab i l i t i e s t o c o n s t r u c t and s e r v i c e a space s t a t i o n , and a p r i n c i p a l j u s t i f i c a t i o n f o r a space s t a t i o n i s t o enable p r o d u c t i o n of s p e c i a l i z e d m a t e r i a l s i n t h e z e r o - g r a v i t y and vacuum o f E a r t h o r b i t . Z e r o - g r a v i t y and t h e n e a r - p e r f e c t vacuum o f space u n i q u e l y enable p r o d u c t i o n o f s e l e c t e d pharmaceuticals and growth of s i n g l e - s t r u c t u r a l a p p l i c a t i o n s . A f u r t h e r j u s t i f i - c r y s t a l m a t e r i a l s f o r e l e c t r o n i c and c a t i o n f o r a space s t a t i o n i s t o p r o v i d e a space p o r t f o r o r b i t a l t r a n s f e r v e h i c l e s used t o p l a c e payloads i n t o d i s t a n t o r b i t s . The c o n s t r u c t i o n of a space s t a t i o n i s a f o r m i d a b l e t a s k r e q u i r i n g i n n o v a t i v e s o l u t i o n s t o be e f f e c t i v e . Various space s t a t i o n c o n s t r u c t i o n concepts a r e b e i n g . considered, b u t these concepts general l y r e q u i r e e x t e n s i v e and expensive on-orbi t c o n s t r u c t i o n and d i f f i c u l t system checkout i n o r b i t , which may c o n t r i b u t e t o poor r e l i a b i l i t y . Some o f t h e s e conceptual space s t a t i o n c o n s t r u c t i o n s a r e massive y e t s t r u c t u r a l l y f l e x i b l e , have low n a t u r a l frequencies making a t t i t u d e so t h e y

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3 control d i f f i c u l t o r impractical. Other construction concepts make use of e i t h e r extensive t r u s s structures t o which functional compartments are attached o r i n t e r - connected modules that are n o t fully operational u n t i l completion of the s t a t i o n . Either of these concepts may require numerous s h u t t l e f l i g h t s and excessive onorbit s t a y time for construction. Some concepts require d i f f i c u l t , awkward transand cargo t o the extremities of the station. None of the portation of personnel above construction concepts provides immediate occupancy of the f i r s t space station component inserted into o r b i t . The shuttle o r b i t e r , therefore, must remain on-orbit for a period of time t o provide l i f e support and i t s use rate i s degraded. A n e f f i c i e n t , s t i f f , compact, user-oriented, reliable and economical, spacestation-construction concept i s needed t h a t offers a minimum of t r i p s and onorbit s t a y time for the shuttle. The purpose of t h i s memorandum i s t o describe such a concept. SYMBOLS A solar-cell -array area f Ratio of amount of sunlight transmitted into solar c e l l s a t an angle of incidence compared t o amount transm t t e d a t normal incidence (contains reflection and cosine losses) f average o f f over an orbit of Earth n i index of refraction i n media o f incident l i g h t n t index of refraction i n media of refracted l i g h t PB power continuously supplied t o the bus P S / A power o u t p u t of the solar-cell array R r a t i o of reflected t o incident power normalized t o zero a t normal i nci dence P Angle hetween o r b i t a l plane and Earth-sun l i n e

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4 Y s o l a r - c e l l a r r a y " r o l l " angle (see t e x t ) 'I1 power d i st rib u tion e f f ic i ency '12 energy s t o r a g e system e f f i c i e n c y P r a t i o of r e f l e c t e d t o i n c i d e n t power i n c i d e n t power a t normal i n c i d e n c e r a t i o o f r e f l e c t e d t o o r b i t p o s i t i o n angle o f t h e space s t a t i o n ( z e r o f o r sun a t z e n i t h ) o r b i t p o s i t i o n angle o f t h e space s t a t i o n when a v a i l a b l e s o l a r - c e l l - a r r a y power j u s t equals bus demand o r b i t p o s i t i o n a n g l e o f t h e day-ni g h t t e r i n i n a t o r angle of l i g h t i n c i d e n t on array p l a n e (measured from plane norma1 ) angle of l i g h t r e f r a c t e d by a r r a y p l a n e ANALYSES Regardless o f t h e concept s e l e c t e d t o c o n s t r u c t a space s t a t i o n , t h e l a r g e area o f s o l a r - c e l l a r r a y s necessary t o supply power t o t h e s t a t i o n i s t h e dominant f e a t u r e . Therefore, t h e c o n s t r u c t i o n approach must i n c l u d e p r o v i s i o n s f o r s u p p o r t i n g a l a r g e area o f s o l a r - c e l l a r r a y s . The most i m p o r t a n t f a c t o r s determi n i ng t h e amount o f sol a r - c e l 1- a r r a y a r e a r e q u i r e d t o meet a s p e c i f i e d , continuous power demand a r e t h e space s t a t i o n C o n f i g u r a t i o n and o r i e n t a t i o n o f t h e a r r a y s . I n t h i s study, t h e schematic c o n f i g u r a t i o n shown i n f i g u r e 1 i s used t o d e s c r i b e s e v e r a l d i f f e r e n t c o n f i g u r a t i o n s and o r i e n t a t i o n s . The v a r i o u s l o c a t i o n and number o f s w i v e l j o i n t s employed t o c o n f i g u r a t i o n s r e s u l t f r o m t h e e f f e c t t h e a r r a y o r i e n t a t i o n and E a r t h - p o i n t i n g c a p a b i l i t y . The c o n f i g u r a t i o n s ' a r e discussed i n more d e t a i l i n a l a t e r s e c t i o n o f t h i s memorandum. The remainder & o f t h i s s e c t i o n d e s c r i b e s t h e a n a l y t i c a l method used t o r e l a t e power o u t p u t t o s o l a r - c e l l - a r r a y o r i e n t a t i o n s and areas.

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5 For a g i v e n minimum continuous power r a t i n g ( 7 5 kW i n t h i s s t u d y ) , t h e s o l a r - c e l l - a r r a y o r i e n t a t i o n o f a c o n f i g u r a t i o n w i t h r e s p e c t t o t h e sun d e t e r - energy it can c o n v e r t t o e l e c t r i c i t y ; and t h u s , t h e mines t h e amount o f s o l a r I - o r i e n t a t i o n s i z e s t h e a r r a y s . I - The p r i m a r y o p t i c a l l o s s e s of s o l a r energy a v a i l a b l e f o r c o n v e r s i o n t o some o r i e n t a t i o n s and n i g h t t i m e l o s s f o r e l e c t r i c i t y a r e t h e c o s i n e l o s s f o r a l l o r i e n t a t i o n s . The c o s i n e l o s s occurs when t h e a n g l e between t h e normal t o ( s i ) i s non-zero. The a v a i l a b l e power t h e s o l a r c e l l s and t h e sun d i r e c t i o n i s t h e n reduced by t h e c o s i n e o f t h i s angle. The n i g h t t i m e l o s s i s due t o t h e shadowing of t h e a r r a y by t h e E a r t h . F i g u r e 2 i l l u s t r a t e s t h e geometry o f t h i s problem. The a n g l e B i s t h e angle between t h e o r b i t a l p l a n e and t h e sun-Earth l i n e . T h i s angle v a r i e s s l o w l y w i t h t h e p r e c e s s i o n o f t h e o r b i t a l p l a n e and t h e a maximum r a t e o f 3.50/day f o r a 28.80 i n c l i n a t i o n o r b i t . change o f seasons a t The a n g l e Y i s d e f i n e d f o r a c o n f i g u r a t i o n l i k e t h a t shown i n f i g u r e 1 where t h e o r b i t a l v e l o c i t y v e c t o r . Then y i s t h e l o n g i t u d i n a l a x i s i s a l i g n e d w i t h arrays. The a n g l e Y = 0 when a r r a y s a r e a " r o l l " angle f o r t h e s o l a r - c e l l h o r i z o n t a l and f a c i n g away from t h e Earth. The a n g l e 0 i s t h e o r b i t a l p o s i t i o n a n g l e w i t h 6 = 0 a t o r b i t a l noon (sun a t z e n i t h ) , and O s i s t h e a n g l e when t h e E a r t h begins t o shadow t h e arrays. c o s i n e l o s s i s : With t h i s d e f i n i t i o n o f geometry, t h e COS s i = cos @ cos e cos Y + s i n @ s i n Y. s o l a r - c e l l a r r a y s f o r o r i e n t a t i o n s h a v i n g a Another o p t i c a l l o s s o f t h e c o s i n e l o s s i s r e f l e c t i o n o f i n c i d e n t l i g h t . S o l a r c e l l performance measurements i n c l u d e t h e l o s s due t o r e f l e c t i o n o f t h e normal i n c i d e n t l i g h t , b u t t h e r e f l e c - t i o n i n a n g l e - o f - i n c i d e n c e must be considered. A loss r e s u l t i n g from i n c r e a s e s t y p i c a l s i l i c o n s o l a r c e l l c o n s i s t s o f an o p t i c a l l y a b s o r b i n g semiconductor t o i s a d h e s i v e l y bonded. T h i s composite which a f i l m - c o a t e d g l a s s covarslic!e

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6 c o n s t r u c t i on makes exact a n a l y s i s very d i f f ic u l t. However, because t h e r e f 1e c - t i v i t y o f b o t h d i e l e c t r i c s and a b s o r b i n g m a t e r i a l s v a r y i n t h e same q u a l i t a t i v e manner w i t h i n c i d e n t angle, one e q u a t i o n i s used t o c h a r a c t e r i z e t h e amount of l i g h t t r a n s m i t t e d t o t h e c e l l . This e q u a t i o n i s based on t h e r e f l e c t a n c e (R) o f a d i e l e c t r i c , which i s n o r m a l i z e d t o z e r o r e f l e c t i o n a t normal i n c i d e n c e . The f r a c t i o n o f i n c i d e n t energy t r a n s m i t t e d i n t o t h e c e l l i s t h e n ( 1 - H ) (Ref. 2) ; where : c a l c u l a t i o n s were 1.0 and 1.5, r e s p e c t i v e l y . The q u a n t i t i e s n i and n t used f o r R e s u l t s u s i n g t h i s e q u a t i o n compare w e l l w i t h t e s t s o f s o l a r c e l l s r e p o r t e d i n Reference 3 up t o an 800 angle o f i n c i d e n c e . The r a t i o o f t h e amount o f s o l a r r a d i a t i o n t r a n s m i t t e d i n t o a s o l a r c e l l a t an a n g l e o f i n c i d e n c e compared t o t h e amount t r a n s m i t t e d i n t o a c e l l a t normal i n c i d e n c e i s f; where: The r a t i o f i n c l u d e s b o t h c o s i n e and r e f l e c t i o n l o s s e s and i s d e f i n e d t o be z e r o when ci > 90'. To determine t h e power o u t p u t of t h e s o l a r - c e l l a r r a y , t h e a r r a y e f f i c i e n c y and d e g r a d a t i o n w i t h t i m e i n o r b i t must be considered. The performance o f a s i l i c o n SEP-type a r r a y ( r e f . 4) a t b e g i n n i n g - o f - l i f e i s 10.0 w a t t s / f t * f o r sun-

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7 l i g h t a t normal i n c i d e n c e ( v a l u e obtained from John Dunning, NASA Lewis Research Center (PIR No. 29, June 1983)). The a r r a y d e g r a d a t i o n a t e n d - o f - l i f e ( 1 0 y e a r s ) w i l l decrease t h e performance t o 8.32 w a t t s / f t 2 , based on t h e measured d e g r a d a t i o n o f Skylab a r r a y s (Ref. 5). The s o l a r - c e l l - a r r a y power a t end o f l i f e i s g i v e n by : PS/A = 8.32 f A, where A i s t h e a r r a y area. To determine t h e s o l a r - c e l l - a r r a y area r e q u i r e d t o meet a c o n t i n u o u s powerbus demand, PB, b o t h t h e power d i s t r i b u t i o n e f f i c i e n c y q 1 and t h e energy s t o r - age system e f f i c i e n c y '12 need t o be considered. The s o l a r - c e l l - a r r a y power a v a i l a b l e f o r use i n t h e space s t a t i o n i s r 1 1 P s / A , and t h e amount o f a v a i l a b l e be used t o charge t h e s t o r a g e system. When power t h a t exceeds t h e demand Pg can a v a i l a b l e power i s l e s s t h a n t h e demand, t h e s t o r a g e system must s u p p l y power pB - r l l Ps/A; and t h e power t h a t was r e q u i r e d t o charge t h e system t o meet t h a t demand i s (PB - '11 P s / A ) / I ~ ~ . The a r r a y area must be s i z e d so t h a t t h e excess power, which i s c o l l e c t e d and s t o r e d d u r i n g an o r b i t , equals t h e amount r e q u i r e d t o meet t h e demand when t h e r e t h e f o l l o w i n g e q u a t i o n s : and O D = P ~ / ( 8 . 3 2 '11 A f ) . i s no excess. T h i s r e l a t i o n i s g i v e n by The a n g l e eb i s t h e o r b i t p o s i t i o n of t h e s t a t i o n when t h e a v a i l a b l e s o l a r - c e l l - a r r a y power j u s t equals t h e demand. When t h e a v a i l a b l e s o l a r - c e l l - a r r a y power cannot meet t h e demand throughout d a y l i g h t hours, t h e two e q u a t i o n s must be s o l v e d s i m u l t a n e o u s l y f o r OD and A. When t h e a r r a y can s a t i s f y t h e

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8 simp i f i e s t o g i v e t h e s o l a r - c e l l - a r r a y d a y l i g h t demand, t h e f i r s t e q u a t i o n area; g i v e n as: A = C(n - os)/(os n2) + 11 P ~ / C 8 * 3 2( n / o s ) 7 ~ 1 1 , where 7 i s t h e average o f f over an o r b i t and g i v e n by t h e f o l l o w i n g e q u a t i o n : O S T = 1 / 7 1 f d o . 0 The s o l a r - c e l l - a r r a y area c a l c u l a t i o n s u s i n g t h e s e equations assumed '11 = 0.85 f o r power d i s t r i b u t i o n e f f i c i e n c y and 112 = 0.80 f o r b a t t e r y s t o r a g e e f f ic i ency . ( Va H a r o l d Huie, MSFC, by personal communicat o n ) . ues were obtained from RESULTS AND D I S C U S S I O N Space S t a t i o n C o n f i g u r a t i o n s and O r i e n t a t i o n s The o p e r a t i o n a l modules d e s c r i b e d i n t h i s paper may be arranged t o f o r m v a r i o u s space s t a t i o n c o n f i g u r a t i o n s w i t h d i f f e r e n t s o l a r - c e l l a r r a y o r i e n t a - t i o n s . Two types o f s w i v e l j o i n t s , shown as A and B i n f i g u r e l , were cons i d e r e d f o r improving t h e o r i e n t a t i o n of t h e s o l a r - c e l l a r r a y s w i t h r e s p e c t t o t h e sun and t o p r o v i d e an E a r t h - p o i n t i n g c a p a b i l i t y f o r some c o n f i g u r a t i o n s . The " A " s w i v e l allows a l l s o l a r a r r a y s t o be s i m u l t a n e o u s l y r o t a t e d abo.ut t h e l o n g i - t u d i n a l a x i s o f t h e s t a t i o n . T h i s r o t a t i o n i s about an a x i s tangent t o t h e o r b i t a l f l i g h t path when t h e l o n g i t u d i n a l a x i s o f t h e s t a t i o n i s i n t h e d i r e c t i o n t o t h e a n g l e Y i n t h e a n a l y s i s ) . The "B" o f motion ( T h i s corresponds d i r e c t l y s w i v e l a l l o w s each s o l a r - c e l l a r r a y t o be r o t a t e d about i t s l o n g i t u d i n a l a x i s . were considered. For each c o n f i g u r a t i o n t h e Seven space s t a t i o n c o n f i g u r a t i o n s r e l a t i v e e f f e c t i v e n e s s of t h e s o l a r - c e l l a r r a y o r i e n t a t i o n was c a l c u l a t e d , and p r o v i d e a minimum of 7 5 kW of continuous power. The t h e a r r a y s were s i z e d t o L a r r a y s i z e was c a l c u l a t e d f o r each c o n f i g u r a t i o n a t o r b i t s o f 235 and 270 n.mi . and a t t h e l i m i t i n g B angles o f 0 and 5 2 degrees, and r e s u l t s a r e shown i n

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9 Table I . The range o f c o n t i n u o u s power o u t p u t a v a i l a b l e over a y e a r l y c y c l e i s shown i n Table 11. The seven c o n f i g u r a t i o n s considered and t h e i r r e l a t i v e a r r a y areas and power o u t p u t ranges a r e described as f o l l o w s : 1. Sun-synchronous space s t a t i o n C o n f i g u r a t i o n : T h i s c o n f i g u r a t i o n has space s t a t i o n i s o r i e n t e d so t h a t t h e s o l a r no s w i v e l j o i n t s . The e n t i r e r a d i a t i o n i s always normal t o t h e s o l a r - c e l l a r r a y s (E.i = 0, R = 0). The a r r a y s do n o t shade each o t h e r and, consequently, o p e r a t e a t f u l l c a p a c i t y when n o t i n t h e shadow o f t h e E a r t h . T h i s c o n f i g u r a t i o n o f f e r s t h e l e a s t s o l a r - c e l l - a r r a y area, b u t i t has h i g h aerodynamic d r a g and no E a r t h - p o i n t i n g capab i l i t y . When s i z e d t o p r o v i d e a minimum o f 75 kW o f continuous power, t h e s o l a r - c e l l a r r a y s o f t h i s c o n f i g u r a t i o n produce between 75 and 87 kW d u r i n g a y e a r l y c y c l e i n t h e 270 n.mi. o r b i t (see Table 11). 2. Sun-synchronous-array c o n f i g u r a t i o n : T h i s c o n f i g u r a t i o n has A and B s w i v e l j o i n t s shown i n f i g u r e 1, and t h e l o n g i t u d i n a l a x i s o f t h e s t a t i o n i s ( t i = 0, R = 0). The a r r a y s must be p e r p e n d i c u l a r t o t h e o r b i t a l plane. spaced w i t h gaps about equal t o t h e a r r a y w i d t h . For a g i v e n module l e n g t h , module as f o r t h e f i r s t c o n f i g u r a t i o n , o r t h e h a l f as many a r r a y s a r e used p e r space s t a t i o n i s t w i c e as l o n g t o a v o i d shadowing. F u l l power c a p a c i t y i s achieved when n o t i n t h e shadow o f t h e Earth. T h i s c o n f i g u r a t i o n shares l e a s t c o n f i g u r a t i o n . It has E a r t h - p o i n t i n g capas o l a r - c e l l - a r r a y area w i t h t h e f i r s t b i l i t y , b u t h i g h dray. The a r r a y s must be r o t a t e d about t h e l o n g i t u d i n a l a x i s o f t h e s t a t i o n d u r i n g each o r b i t o f t h e E a r t h and o s c i l l a t e d s l o w l y about t h e i r v a r i a t i o n s o f b e t a angle. As i n d i c a t e d i n l o n g i t u d i n a l axes t o c o r r e c t f o r Tables I and 11, t h i s c o n f i g u r a t i o n has t h e same a r r a y area and v a r i a t i o n i n y e a r l y power g e n e r a t i o n as t h e sun-synchronous c o n f i g u r a t i o n . 3. R o t a t i n g - a r r a y c o n f i g u r a t i o n : T h i s c o n f i g u r a t i o n a l s o i s o r i e n t e d w i t h l o n g i t u d i n a l a x i s p e r p e n d i c u i a r t o t h e o r b i t a l p l a n e . The "A" s w i v e l (see f i g i i r e

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10 1) i s used t o r o t a t e t h e s o l a r - c e l l a r r a y s r e l a t i v e t o t h e E a r t h - p o i n t i n g modules each o r b i t so t h a t t h e a r r a y o r i e n t a t i o n i n i n e r t i a l space i s n e a r l y c o n s t a n t . This o r i e n t a t i o n has r e f l e c t i o n and c o s i n e l o s s e s when t h e b e t a a n g l e i s n o t equal t o z e r o (ti = 13, R > 0). It has h i g h d r a g and r e q u i r e s 1.4 t i m e s t h e s o l a r - c e l l - a r r a y area o f t h e sun-synchronous space s t a t i o n (see Table I ) . The o u t p u t power ranges from 75 t o 108 kW o v e r a y e a r l y c y c l e (see Table 11). 4. Osci 1l a t i ng-array gamma-control l e d c o n f i g u r a t i o n : This c o n f i g u r a t i o n has b o t h t h e A and B s w i v e l j o i n t s , and i t s l o n g i t u d i n a l a x i s i s tangent t o t h e o r b i t . It o f f e r s E a r t h - p o i n t i n g c a p a b i l i t y and no r e f l e c t i o n l o s s f r o m t h e I s o l a r c e l l s ( R = 0), b u t some c e l l s a r e shadowed by a d j a c e n t a r r a y s and a l l a r r a y s must be o s c i l a t e d d u r i n g each o r b i t (cos c i i s c o n t i n u o u s l y maximized by v a r y i n g t h e Y ang e ) . It o f f e r s less d r a g t h a n t h e f i r s t t h r e e c o n f i g u r a t i o n s . The s o l a r - c e l l -array area i s about 1.9 t i m e s t h a t o f t h e sun-synchronous space s t a t i o n . Over a y e a r l y c y c l e , t h e power o u t p u t v a r i e s from 7 5 t o 142 kW i n t h e 270 n.mi. o r b i t . 5. Gamma-angle-controlled c o n f i g u r a t i o n : T h i s c o n f i g u r a t i o n has o n l y t h e "A" s w i v e l j o i n t , which i s o s c i l l a t e d d u r i n g each o r b i t o f E a r t h (cos i s cont i n u o u s l y maximized by v a r y i n g t h e y a n g l e ) . It has E a r t h - p o i n t i n g c a p a b i l i t y and no shadowing by a d j a c e n t a r r a y s , b u t i t has r e f l e c t i o n and c o s i n e l o s s e s (R > 0). I t s l o n g i t u d i n a l a x i s i s t a n g e n t t o t h e o r b i t . I t s d r a g i s t h e l o w e s t o f a l l c o n f i g u r a t i o n s , b u t it r e q u i r e s about 2.0 t i m e s t h e a r r a y area o f t h e sun-synchronous space s t a t i o n . Over a y e a r l y c y c l e , t h e power o u t p u t v a r i e s f r o m 75 t o 149 kW i n t h e 270 n.mi . o r b i t . 6. B e t a - a n g l e - c o n t r o l l e d c o n f i g u r a t i o n : T h i s c o n f i g u r a t i o n i s very s i m i l a r t o c o n f i g u r a t i o n 5 and has t h e same a x i s o r i e n t a t i o n . However, r a t h e r than o s c i l l a t i n g t h e s o l a r - c e l l a r r a y s every o r b i t , t h i s c o n f i g u r a t i o n o s c i l l a t e s t h e a r r a y s over a longer p e r i o d o f 50 days ( o r b i t a l p l a n e p r e c e s s i o n p e r i o d ) t o

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match t h e b e t a a n g l e a t l o c 1 11 E a r t h - o i n t i n g c a p a b i l i t y and no shadowing, b u t i t has r e f l e c t i o n and c o s i n e losses. T h i s c o n f i g u r a t i o n r e q u i r e s 2.1 t i m e s t h e a r r a y area o f t h e sun-synchronous space s t a t i o n . Over a y e a r l y c y c l e , t h e normal power o u t p u t v a r i e s from 75 t o 136 kW i n t h e 270 n.mi. o r b i t ; however, f o r p e r i o d s of peak power demand t h e o u t p u t v a r i e s f r o m 157 t o sun-synchronous s t a t i o n (see Table 11). Con- 183 kW when r e o r i e n t e d t o become a f i g u r a t i o n 6 i s about equal l e n g t h t o c o n f i g u r a t i o n 2, b u t has 2.1 t i m e s t h e a r r a y area. The s l i g h t i n c r e a s e i n s o l a r - c e l l - a r r a y s i z e over t h e f i f t h c o n f i g - u r a t i o n r e s u l t s i n o n l y a s l i g h t i n c r e a s e i n drag. T h i s c o n f i g u r a t i o n was s e l e c t e d f o r study and r e p o r t i n g i n t h i s memorandum. 7. E a r t h - p o i n t i n g space s t a t i o n : T h i s c o n f i g u r a t i o n has no s w i v e l j o i n t s E a r t h - p o i n t i n g o r i e n t a t i o n (Y = 0, R > 0). It and t h e e n t i r e s t a t i o n i s i n an has r e f l e c t i o n and c o s i n e losses. It r e q u i r e s t h e l a r g e s t s o l a r - c e l l - a r r a y area (about 3.6 times t h a t o f t h e sun-synchronous space s t a t i o n ) a n d has l o w drag. Over v a r i e s from 75 t o 130 kW i n a 270 n.mi . o r b i t . a y e a r l y c y c l e , t h e power o u t p u t c o n f i g u r a t i o n ( 6 ) was s e l e c t e d f o r t h i s study. The b e t a - a n g l e - c o n t r o l l e d s t a t i o n c o n f i g u r a t i o n (1) r e q u i r e s l e s s t h a n Although t h e sun-synchronous space area, it was n o t s e l e c t e d because i t has h i g h d r a g h a l f o f t h e s o l a r - c e l l - a r r a y and no E a r t h - p o i n t i n g c a p a b i l i t y f o r any module. The sun-synchronous a r r a y conf i g u r a t i o n ( 2 ) a l s o r e q u i r e s l e s s than h a l f o f t h e s o l a r - c e l l - a r r a y area o f conf i g u r a t i o n 6 and, a l t h o u g h t h e modules w i t h a r r a y s a r e r o t a t e d d u r i n g each o r b i t about t h e l o n g i t u d i n a l a x i s o f t h e space s t a t i o n , o n l y f r i c t i o n a l f o r c e s i n s w i v e l j o i n t "A" must be overcome t o m a i n t a i n E a r t h - p o i n t i ng capabi 1it y . Keeping t h e a r r a y s p e r p e n d i c u l a r t o t h e s o l a r r a d i a t i o n r e q u i r e s o n l y a slow o s c i l l a t i o n i t s own l o n g i t u d i n a l a x i s t o c o r r e c t f o r t h e (3.50/day) o f each a r r a y about v a r i a t i o n i n b e t a angle. Although t h e second c o n f i g u r a t i o n l o o k s p r o m i s i n g , i t was n o t s e l e c t e d ; because i t has n i g h aerodynamic drag, r e q u i r e s several

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12 s w i v e l j o i n t s and r e q u i r e s a complete r o t a t i o n d u r i n g each o r b i t o f s w i v e l j o i n t " A " , which may c o m p l i c a t e space s t a t i o n c o n t r o l and t r a n s f e r o f personnel and I C o n f i g u r a t i o n 3 i s s i m i l a r t o c o n f i g u r a t i o n 2 b u t m a t e r i a l across t h e j o i n t . does n o t o s c i l l a t e each a r r a y about i t s own a x i s and consequently r e q u i r e s a 40 p e r c e n t l a r g e r array area. It was n o t s e l e c t e d , because i t has h i g h aerodynamic drag and i t s swivel j o i n t i s r o t a t e d 360 degrees d u r i n g each o r b i t ( 2 4 @ / h r ) . The c o n f i g u r a t i o n s 4 and 5 a l s o r e q u i r e r a p i d o s c i l l a t i o n o f s o l a r - c e l l a r r a y s d u r i n g each o r b i t and were n o t s e l e c t e d ; because, a l t h o u g h t h e i r a r r a y s a r e s l i g h t l y s m a l l e r t h a n c o n f i g u r a t i o n 6 ( c o n f i g u r a t i o n 6 has a slow o s c i l l a t i o n ) , t h e r a p i d o s c i l l a t i o n s may r e q u i r e c o n s i d e r a b l e power consumption, produce s t r u c t u r a l dynamic i n s t a b i l i t i e s and r e s u l t i n d i f f i c u l t c o n t r o l o f space s t a t i o n o r i e n t a t i o n . The E a r t h - p o i n t i n g c o n f i g u r a t i o n 7 does n o t have these c o n t r o l problems; however, i t was n o t s e l e c t e d , because i t r e q u i r e s much l a r g e r a r r a y s c o n f i g u r a t i o n ( 6 ) . Moreover, c o n f i g u r a t i o n 6 t h a n t h e b e t a - a n g l e - c o n t r o l l e d o f f e r s f l e x i b l e o p e r a t i o n t h r o u g h i t s a b i l i t y t o double i t s power o u t p u t f o r c o n f i g u r a t i o n s 2 and 6 l o o k promising, t h e p e r i o d s o f peak demand. Although b e t a - a n g l e - c o n t r o l l e d c o n f i g u r a t i o n was s e l e c t e d ; because i t p o t e n t i a l l y o f f e r s t h e b e s t combination o f performance and a r r a y s i z e . Space S t a t i o n D e s c r i p t i o n The p r i n c i p a l r e s u l t o f t h i s study i s a n o v e l , s p a c e - s t a t i o n c o n s t r u c t i o n o p e r a t i o n a l upon o r b i t i n s e r t i o n and a l s o p r o v i d e concept u s i n g modules t h a t a r e s t a t i o n , as shown i n f i g u r e s 3 and 4. The use t h e p r i m a r y s t r u c t u r e o f t h e space of o p e r a t i o n a l modules p e r m i t s assembly of t h e e n t i r e space s t a t i o n i n a groundbased f a c i l i t y i n t e g r a t i o n and v e r i f i c a t i o n of systems. A d d i t i o n a l l y , t o enable c a mock-up c o n s t r u c t e d o f o p e r a t i o n a l modules may be m a i n t a i n e d on E a r t h t o a s s i s t l i f e o f t h e s t a t i o n . These f e a t u r e s should space o p e r a t i o n s throughout t h e u s e f u l

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13 improve r e l i a b l i t y o f s t a t i o n operations o v e r t h a t of s t a t i o n s c o n s t r u c t e d i n space. Operat onal modules enable immediate occupancy upon o r b i t i n s e r t i o n , t h u s a minimum o f o n - o r b i t s t a y t i m e i s r e q u i r e d o f t h e s h u t t l e . That i s , t h e s h u t t l e i s n o t needed t o p r o v i d e l i f e support as i t would be f o r c o n s t r u c t i o n concepts t h a t n i t i a l l y r e q u i r e e i t h e r an e x t e n s i v e t r u s s - t y p e p l a t f o r m p r i o r t o mounting h a b i t a b l e compartments i n t e r c o n n e c t i o n of s e v e r a l n o n - o p e r a t i o n a l o r an modules. Use o f o p e r a t i o n a l modules t o p r o v i d e t h e p r i m a r y s t r u c t u r e o f t h e space s t a t i o n p r o v i d e s a v o l u m e t r i c a l l y e f f i c i e n t , s t i f f s t r u c t u r e f o r t h e s t a t i o n . This f e a t u r e minimizes t h e need f o r a d d i t i o n a l s t r u c t u r e and should reduce t h e number of t r i p s and o n - o r b i t s t a y t i m e f o r t h e s h u t t l e compared t o o t h e r c o n s t r u c t i o n concepts. The s i z e o f t h e s t a t i o n i s based on s u f f i c i e n t s o l a r - c e l l - a r r a y area (40,000 f t 2 ) t o produce 75 kw o f continuous power f o r p e r i o d s o f normal o p e r a t i o n . For p e r i o d s o f peak power demand, t h e s t a t i o n may be t e m p o r a r i l y r e o r i e n t e d t o s t a t i o n p r o d u c i n g 157 kw o f continuous power. become a sun-synchronous space However, d u r i n g t h i s temporary r e o r i e n t a t i o n , t h e space s t a t i o n w i l l n o t have E a r t h - p o i n t i n g capabi 1i t y . Because t h e s o l a r - c e l l a r r a y s a r e o f t h e SEP t y p e ( r e f . 4 ) , t h e y can be r e t r a c t e d f o r t h e r e o r i e n t a t i o n maneuver. To m i n i m i z e aerodynamic drag f o r normal o p e r a t i o n , t h e p l a n e o f t h e s o l a r - c e l l a r r a y s i s m a i n t a i n e d tangent t o t h e o r b i t a l f l i g h t path; and t h e s o l a r - c e l l a r r a y s t r a i l t h e l e a d i n g modules t h a t have no arrays. However, an aerodynamically balanced be c o n s t r u c t e d by l o c a t i n g some o f t h e modules h a v i n g a r r a y s c o n f i g u r a t i o n may forward o f t h e E a r t h - p o i n t i n g modules, b u t a second s w i v e l j o i n t i s needed. I n a d d i t i o n t o p r o v i d i n g l i v i n g q u a r t e r s , a s u f f i c i e n t number o f modules can be p r o v i d e d t o s a t i s f y t h e f o l l o w i n g f u n c t i o n s : research, pharmaceutical p r o d u c t i o n , c r y s t a l manufacturing, e l e c t r i c a l power management, space s t a t i o n c o n t r o l , u t i l i t y management, dockiiig, and propellant s t z r a g e . The prcpe!!ants

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14 a r e needed f o r r e f u e l i n g o r b i t a l t r a n s f e r v e h i c l e s based a t t h e space s t a t i o n . 1ife-support systems, t h u s s a f e t y i s enhanced The i n h a b i t e d modules have on-board i n event o f u t i l i t y management module f a i l u r e . Space s t a t i o n growth i s p r o v i d e d by adding modules o n l y when needed s i n c e a l l modules have common i n t e r f a c e s ( i n t e r c h a n g e a b i l i t y f e a t u r e ) ; t h a t i s , i t i s n o t necessary t o i n i t i a l l y c o n s t r u c t an o v e r s i z e d support s t r u c t u r e f o r f u t u r e expansion o f t h e space s t a t i o n . As i n d i c a t e d , t h e use o f a s w i v e l j o i n t i n t h e s t r u c t u r e o f t h e space s t a t i o n s o l a r - c e l l a r r a y s w h i l e p e r m i t t i n g an E a r t h - p e r m i t s e f f i c i e n t o r i e n t a t i o n of t h e p o i n t i n g c a p a b i l i t y f o r modules n o t h a v i n g a r r a y s . S w i v e l i n g about t h e l o n g i t u - d i n a l a x i s o f the . s t r u c t u r e enables simultaneous r e o r i e n t a t i o n o f a l l s o l a r - c e l l i n t h e P angle, r e s u l t i n g from seasonal changes a r r a y s t o c o r r e c t f o r v a r i a t i o n s This o s c i l l a t i o n i s slow--a maximum r o t a - and precession o f t h e o r b i t a l plane. t i o n a l r a t e of 3.5 degrees p e r day f o r a 28.80 i n c l i n a t i o n o r b i t . The use o f an E a r t h - p o i n t i n g c a p a b i l i t y and a low dray o r i e n t a t i o n o f t h e a r r a y s r e s u l t i n a need t o more than double t h e area o f t h e s o l a r c e l l s ( f o r a g i v e n power) over t h a t of a sun-synchronous o r i e n t a t i o n of a space s t a t i o n . T h i s increased s o l a r - c e l l - a r r a y area i s needed because of h i g h c o s i n e and r e f l e c t i o n losses t h a t occur f o r p e r i o d s other than noon i n an o r b i t . However, as i n d i c a t e d , t h i s i n c r e a s e d d u r i n g p e r i o d s o f peak power demand. The s e l e c t e d a r r a y area may be b e n e f i c i a l c o n f i g u r a t i o n , u s i n g t h e o p e r a t i o n a l module c o n s t r u c t i o n concept, p r o v i d e s cons i d e r a b l e useful volume f o r each s e t o f s o l a r - c e l l a r r a y s ; and t h e need f o r many a r r a y s a u t o m a t i c a l l y r e s u l t s i n an abundance o f h a b i t a b l e volume. An optimum r a t i o of power t o u s e f u l volume may warrant c o n s i d e r a t i o n o f a r g e r s o l a r - c e l l a r r a y s t h a n selected f o r t h i s study. . removed from t h e space s t a t i o n w i t h o u t d i smantl ing t h e Any module may be disconnected and r e s t r a ned by t h e assembly space s t a t i o n . S o l a r - c e l l a r r a y s a r e b

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15 module. As shown i n f i g u r e 5, t o remove t r a n s p o r t v e h i c l e p r i o r t o removal o f a a module, t h e d i s c o n n e c t sequence i s u t i 1it y c o n d u i t s , a i r l o c k s - t o - t r a n s p o r t t u n n e l , inter-module c o n n e c t i o n devices and p r e s s u r i z e d compartment-to-truss s t r u c t u r e . When t h e i n t e r - m o d u l e connection d e v i c e s a r e disengaged, a 3-inch c l e a r a n c e i s p r o v i d e d between adjacent modules t o f a c i l i t a t e removal o f a module. s t a t i o n p e r p e n d i c u l a r t o t h e t u n n e l . T h i s w i t h - The module i s withdrawn from t h e by t h e assembly t r a n s p o r t v e h i c l e o r by t h e drawal may be accomplished e i t h e r r e a c t i o n - c o n t r o l system p r o v i d e d i n each module, b u t n o r m a l l y used t o maneuver t h e space s t a t i o n . module i s r e q u i r e d t o r e - e s t a b l i s h t h e o r i g i n a l A replacement s t r u c t u r a l o p e r a t i o n o f t h e space s t a t i o n , and t h i s modu1e s t i f f n e s s and normal disconnect sequence. Replacement modu es may be i n s t a l l e d by r e v e r s i n g t h e r e q u i r e no t u n n e l s t r u c t u r e when d e l i v e r e d t o o r b i t because o r s u r r o u n d i n g t r u s s once t h e t u n n e l and t r u s s s t r u c t u r e are i n s t a l l e d , t h e y n o r m a l l y remain an i n t e g r a l p a r t of t h e s t a t i o n . F i g u r e connect i o n d e v i ce. S i x t e e n such d e v i ces 6 shows an inter-module a r e spaced about one end r i n g o f each module, and m a t i n g f i t t i n g s a r e spaced about t h e o p p o s i t e end r i n g . Each device c o n s i s t s o f two components--the f i r s t component p r o v i d e s l o c a t i n g and l a t c h i n g f u n c t i o n s , and t h e second component completes t h e s t r u c t u r a l t i e between modules. Each component i s a c t i v a t e d by e l e c t r i c - m o t o r - d r i v e n leadscrews. S i m i l a r c o n n e c t i o n d e v i c e s a r e used f o r t h e attachment o f t h e compartment t o t h e t r u s s s u r r o u n d i n g t h e t r a n s p o r t t u n n e l . Operational Modules O p e r a t i o n a l modules a r e t h e basic c o n s t r u c t i o n components o f t h e space s t a t i o n . A l l modules have a common o v e r a l l space requirement o f 14.5 f t d i a m e t e r by 46 f t l e n g t h , and each module c o n t a i n s a compartment t h a t may be p r e s s u r i z e d . Two compartment diameters a r e used, b u t t h e compartments (and modules) a r e

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16 interchangeable. The modules can be d e s i yned empl o y i ng Sky1ab and Spacelab t e c h n o l o g i e s and assembled t o p r o v i d e a d e s c r i b e and discuss t h e s e modules. space s t a t i o n . The f o l o w i n g subsect on s Small, F u l l y Operational Module.- The small , f u l l y o p e r a t i o n a l module i s shown i n f i g u r e 7 and c o n s i s t s o f a 10.5 f t diameter by 44 f t l o n g p r e s s u r i z e d w i t h o t h e r components a f f i x e d . A t each end compartment o f welded aluminum a l l o y of t h e compartment, a s k i r t extends t o i n t e r - m o d u l e attachment r i n y s r e s u l t i n g i n a module l e n g t h o f 45.75 ft. A l o n g i t u d i n a l l y - s t i f f e n e d - s k i n i s used f o r t h e s k i r t s , which a r e a l s o r i n g s t i f f e n e d . Inter-module connection devices ( 1 6 s e t s ) a r e spaced around one i n t e r - m o d u l e attachment r i n g , and m a t i n g f i t t i n g s a r e spaced around t h e o p p o s i t e end r i n g . Reaction c o n t r o l motors a r e mounted w i t h i n t h e s k i r t s , and s i n c e each module has motors, t h e t h r u s t and i n e r t i a l bending moments by l o a d a l l e v i a t i o n . A loads a r e d i s t r i b u t e d , which minimizes compartment. U t i l i t y c o n d u i t s , u t i l i t y t a n k s f l o o r i s provided w i t h i n t h e ( a i r , water, sewage, e t c . ) and b a t t e r i e s a r e l o c a t e d between t h e f l o o r and t h e compartment w a l l . The u t i l i t y c o n d u i t s extend over t h e l e n g t h o f t h e module. A t one end o f the module q u i c k d i s c o n n e c t - t y p e f i t t i n g s a r e t r a n s l a t e d a d i s - t a n c e o f about s i x inches t o mate w i t h t h e u t i l i t y c o n d u i t s of t h e a d j a c e n t module. F l e x i b l e c o n d u i t s a r e used a t t h e movable end of t h e quick-disconnect f i t t i n g s t o enable t h e t r a n s l a t i o n . When t h e attachments between modules a r e engaged, t h e o v e r a l l l e n g t h o f t h e module i s 46 ft. Above t h e p r e s s u r i z e d compartment i s a t r a n s p o r t t u n n e l , surrounded by a frame and t r u s s - t y p e s t r u c t u r e . The frames surround t h e t u n n e l and a r e i n t e r - connected by t r u s s members. Tracks, i n t e g r a l w i t h t h e t r u s s s t r u c t u r e , a r e used assembly t r a n s p o r t v e h i c l e . A i r l o c k s a r e f o r attachment and guidance of t h e U p r e s s u r i z e d compartment. These a i r l o c k s enable p r o v i d e d a t each end o f t h e t r a n s f e r o f personnel f r o m t h e t u n n e l and t h e compartment. Removable doors a r e p r o v i d e d a t t h e ends o f t h e t r a n s p o r t t u n n e l .

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17 On e i t h e r s i d e o f t h e p r e s s u r i z e d compartment, two a r r a y s o f s o l a r c e l l s a r e shown deployed i n f i g u r e 7. A r a d i a t o r i s a t t a c h e d a t t a c h e d , and t h e a r r a y s a r e t o t h e l o w e r s u r f a c e of t h e module. T h i s r a d i a t o r i s s e m i - c i r c u l a r t o p r o v i d e a maximum r a d i a t ion area w i t h o u t r e q u i r i ng depl oyment o r assembly in space The c r o s s s e c t i o n o f t h e completed module f i t s w i t h i n a 14.5 f t diameter mold l i n e . compartment, equipment s u i t e d t o t h e u s e r i s i n s t a l l e d I n s i d e t h e p r e s s u r i z e d p r i o r t o s h u t t l e launch of t h e module. Moreover, t h e u t i l i t y t a n k s may be f i l l e d t o a l l o w immediate occupancy of t h e module upon o r b i t i n s e r t i o n . T h i s s m a l l , f u l l y o p e r a t i o n a l module i s t h e f i r s t component o f t h e space s t a t i o n t o be in s e r t e d i n t o o r b i t. F i g u r e 8 shows t h e s m a l l , f u l l y o p e r a t i o n a l module i n s t a l l e d w i t h i n t h e payload bay of t h e s h u t t l e . As shown, t h e c o n t r a c t e d s o l a r - c e l l a r r a y s a r e r o t a t e d about a l o n g i t u d i n a l a x i s t o f i t w i t h i n t h e payload bay. A r e a r w a r d l o c a t i o n o f t h e module w i t h i n t h e payload bay i s necessary t o s a t i s f y s h u t t l e c e n t e r o f g r a v i t y requirements. A tunnel i s p r o v i d e d between t h e module and t h e crew compartment o f t h e s h u t t l e . This t u n n e l enables s h u t t l e t r a n s p o r t o f t h e space s t a t i o n crew. Once i n o r b i t , t h e crew can t r a n s f e r i n t o t h e module and p e r f o r m systems p r i o r t o module r e l e a s e f r o m t h e s h u t t l e . A a f i n a l checkout o f f u l l y equipped module may have a gross l i f t o f f w e i g h t o f about 55,000 l b , and a l a n d i n g weight o f about 35,000 l b . However, t h e l i f t o f f w e i g h t a p p l i e s t o an o r b i t a l p l a n e i n c l i n a t i o n o f 28.8 degrees. Should a much h i g h e r i n c l i n a t i o n module w e i g h t may be h a l v e d by u s i n g 23 ft l o n g modules a n g l e be d e s i r e d , t h e t o s a t i s f y t h e reduced payload c a p a b i l i t y o f t h e s h u t t l e . T h i s small be designed t o be a p r o p e l l a n t s t o r a g e t a n k , volume module may and when used f o r t h i s purpose, i t equipped a c c o r d i n g l y ; however, a r a d i a t o r i s may be p r e i n s t a l l e d on t h e t a n k s t o supplement r a d i a t o r s p r o v i d e d by t h e h a b i t a b i e modules.

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Large-Useful -Volume--Module.- The l a r g e - u s e f u l -volume module i s shown i n f i g u r e 9 and c o n s i s t s of a 14.5 ft diameter by 44 f t l o n g p r e s s u r i z e d compartment l e n g t h t o 45.75 ft. When i n s t a l l e d i n t o t h e space w i t h end s k i r t s e x t e n d i n g t h e s t a t i o n , t h e t o t a l l e n g t h i s 46 ft; so t h e l a r g e and small compartment modules have i d e n t i c a l space requirements o f 14.5 ft diameter by 46 f t l e n g t h . A l l s t r u c t u r a l and u t i l i t y i n t e r f a c e connections a r e i d e n t i c a l t o t h o s e o f t h e s m a l l e r compartment module. T h i s l a r g e , u s e f u l volume module has no t u n n e l , s u r r o u n d i n g t r u s s or s o l a r - c e l l a r r a y s a t t a c h e d when mounted i n t o t h e payload bay o f t h e i t e m s a r e t a k e n t o o r b i t by a separate s h u t t l e s h u t t l e . Several s e t s of t h e s e l a u n c h and attached t o t h e modules i n space. As w i t h t h e s m a l l e r compartment module, r e a c t i o n c o n t r o l s , two a i r l o c k s , a r a d i a t o r and a f l o o r , which covers u t i l i t y conduits and t a n k s , b a t t e r i e s , etc., a r e p r o v i d e d . These i t e m s and u s e r - o r i e n t e d equipment a r e i n s t a l l e d i n a ground-based f a c i l i t y p r i o r t o launch. I T h i s l a r g e compartment module i s n o t immediately h a b i t a b l e upon i n s e r t i o n i n t o upon c o n n e c t i n g i t t o a s m a l l , f u l l y operao r b i t , b u t becomes h a b i t a b l e e i t h e r t i o n a l module or upon i n s t a l l i n g i t s s o l a r - c e l l a r r a y s . Temporary h a b i t a t i o n l i s p o s s i b l e by u s i n g i t s on-board b a t t e r i e s f o r power, thus t h e l a r g e - u s e f u l - volume module may be c o n s i d e r e d an o p e r a t i o n a l module, b u t f o r a l i m i t e d p e r i o d . T h i s large-useful-volume module a l s o may be designed t o be a p r o p e l l a n t s t o r a g e t a n k w i t h o r w i t h o u t a supplementary r a d i a t o r . Assembly Transport Vehi c l e F i g u r e 10 shows an assembly t r a n s p o r t v e h i c l e (ATV) used t o assemble t h e modules and l a r g e antennas o r o t h e r p e r i p h e r a l equipment needed f o r space s t a t i o n - f u n c t i o n s . The ATV c o n s i s t s o f a p r e s s u r i z e d capsule, f o u r d r i v e wheels, two a r t i c u l a t i n g arms and a s t o r a g e rack. c The c a p s u l e p r o v i d e s a s h i r t - s l e e v e e n v i r o n - ment f o r t h e operator. Windows and a i r l o c k s a r e p r o v i d e d a t each end. A deploy- -

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19 a b l e a i r l o c k i s a l s o p r o v i d e d through t h e f l o o r o f t h e capsule, and t h i s a i r l o c k tunnel o f each module. The a r t i c u l a t i n g arms can be connected t o t h e t r a n s p o r t t h e capsule. C o n t r o l consoles a r e p r o v i d e d a t a r e l o c a t e d a t t h e m i d - l e n g t h of each end o f o p e r a t i o n o f t h e ATV from e i t h e r end. On t h e t h e capsule t o enable upper s u r f a c e o f t h e capsule, a rack i s p r o v i d e d t h a t has two s e t s o f b i - f o l d doors o f t r u s s c o n s t r u c t i o n . T h i s rack p r o v i d e s a means o f t r a n s p o r t i n g v a r i o u s c o n s t r u c t i o n m a t e r i a l s . The four-wheel d r i v e system c o n s i s t s o f f o u r r a c k and p i n i o n d r i v e s , powered by s e p a r a t e e l e c t r i c motors. The wheels a r e p i n i o n s ; and t h e t r a c k s , b u i l t i n t o t h e t r u s s s t r u c t u r e s u r r o u n d i n g t h e t r a n s p o r t t u n n e l , a r e g e a r - t o o t h racks. A s m a l l r e t a i n i n g wheel, connected t o t h e ATV, presses on t h e the ATV t o t h e t r a c k s . Support s t r u c t u r e f o r o p p o s i t e s i d e of t h e rack t o clamp t h e wheels i s s u f f i c i e n t l y deep t o allow t h e ATV t o pass o v e r a c o r n e r a t t h e end o f t h e space s t a t i o n w i t h o u t c o n t a c t between t h e c a p s u l e and t h e t r a n s p o r t t u n n e l . E l e c t r i c a l power f o r t h e ATV i s p r o v i d e d by a t h i r d r a i l s i m i l a r t o subway c a r s o f our l a r g e r c i t i e s . B a t t e r i e s and l i f e - s u p p o r t p r o v i s i o n s a r e s t o r e d w i t h i n t h e capsule, so t h e ATV i s e s s e n t i a l l y an independent s p a c e c r a f t c a p a b i l i t y (it has no r e a c t i o n c o n t r o l , guidance o r w i t h l i m i t e d l i f e - s u p p o r t p r o p u l s i o n systems). CONCLUDING REMARKS A novel space s t a t i o n c o n s t r u c t i o n concept employing o p e r a t i o n a l modules t h a t p r o v i d e t h e p r i m a r y s t r u c t u r e f o r t h e space s t a t i o n and enable ground-based i n t e g r a t i o n and v e r i f i c a t i o n o f systems i s d e s c r i b e d i n t h i s t e c h n i c a l memorandum. The space s t a t i o n i s c o n s t r u c t e d by c o n n e c t i n g i n t e r c h a n g e a b l e modules t h a t have common i n t e r f a c e j o i n t s . The modules have an i d e n t i c a l o v e r a l l space requirement (14.5 f t diameter by 46 f t l o n g ) t o enable t r a n s p o r t t o o r b i t by t h e s h u t t l e . Two o p e r a t i o n a l modules a r e proposed--one has a 10.5 f t dSaiiieter p r e s s u r i z e d

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20 compartment, and t h e o t h e r has a 14.5 ft d i a m e t e r compartment. Each compartment i s serve as a p r o p e l l a n t s t o r a g e t a n k . The 44 ft l o n g and may be designed t o module w i t h the s m a l l e r compartment has s o l a r - c e l l a r r a y s , a r a d i a t o r , a i r l o c k s , a t r a n s p o r t t u n n e l , t r a c k s , u t i l i t y c o n d u i t s , s t o r a g e t a n k s and s u f f i c i e n t l i f e - immediately as a f u l l y o p e r a t i o n a l v e h i c l e when support c a p a b i l i t y t o o p e r a t e i n s e r t e d i n t o o r b i t . T h i s f u l l y o p e r a t i o n a l module i s t h e f i r s t component o f t h e space s t a t i o n t o i n s e r t e d i n t o o r b i t . The l a r g e - u s e f u l - v o l u m e module be immediate power, and be e i t h e r connected must use i t s on-board b a t t e r i e s f o r module o r have i t s s o l a r - c e l l a r r a y s i n s t a l l e d t o t h e s m a l l , f u l l y o p e r a t i o n a l i n space t o become f u l l y o p e r a t i o n a l . A space s t a t i o n c o n s t r u c t e d o f o p e r a t i o n a l modules may b e n e f i t from module f a b r i c a t i o n , assembly and t e s t i n g i n ground-based f a c i l i t i t e s . A d d i t i o n a l l y , t h e e n t i r e space s t a t i o n i s p o s s i b l e on t h e pre-assembly and system checkout of ground p r i o r t o launch. These f e a t u r e s minimize o n - o r b i t c o n s t r u c t i o n t i m e and enhance r e l i a b i l i t y . The modules p r o v i d e e f f i c i e n t , s t i f f p r i m a r y s t r u c t u r e f o r t h e space s t a t i o n . Very few a d d i t i o n a l s t r u c t u r a l members a r e needed, t h u s t h e use o f modules f o r space s t a t i o n s t r u c t u r e should m i n i m i z e o n - o r b i t s t a y t i m e s h u t t l e t o complete t h e s t a t i o n . Addiand number o f t r i p s r e q u i r e d f o r t h e t i o n a l l y , s i n c e each h a b i t a b l e module i s capable of l i f e support upon o r b i t i n s e r t i o n , t h e o n - o r b i t s t a y t i m e of t h e s h u t t l e i s f u r t h e r minimized. Convenient t r a n s p o r t i s p r o v i d e d between modules by t u n n e l s f o r personnel and by an assembly t r a n s p o r t v e h i c l e on t r a c k s f o r personnel and cargo. The assembly t r a n s p o r t v e h i c l e enables assembly o f t h e modules and f a b r i c a t i o n o f antenna o r o t h e r s t r u c t u r e s on t h e space s t a t i o n , and t h e space s t a t i o n may be adding modules. Any module may be removed w i t h o u t c enlarged--as requi red--by d i s m a n t l i n g t h e space s t a t i o n . A replacement module i s r e q u i r e d t o r e - e s t a b l i s h t h e o r i g i n a l s t r u c t u r a l s t i f f n e s s and normal o p e r a t i o n of t h e space s t a t i o n .

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21 A high volumetric e f f i c i e n c y i s provided by the modular space s t a t i o n c o n s t r u c - t i o n c o n c e p t ; t h a t i s , e s s e n t i a l l y a l l of the structure r e q u i r e d t o s u p p o r t the n e c e s s a r i l y extensive s o l a r - c e l l a r r a y s p r o v i d e s u s e f u l volume. These o p e r a t i o n a l modules may be used t o c o n s t r u c t space s t a t i o n s having any of the o r i e n t a t i o n s considered i n t h i s s t u d y . Two of these seven s o l a r - c e l l - a r r a y s p a c e s t a t i o n c o n f i g u r a t i o n s a r e a t t r a c t i v e - - a sun-synchronous a r r a y and a b e t a - a n g l e - c o n t r o l l e d c o n f i g u r a t i o n . T h e l a t t e r was s e l e c t e d f o r s t u d y , because i t has fewer swivel j o i n t s , l e s s drag and an a b i l i t y t o i n c r e a s e power o v e r normal o p e r a t i o n for p e r i o d s of peak demand. The use of o p e r a t i o n a l modules makes maximum use of Skylab and Spacelab t e c h n o l o g i e s . Operational modules t h a t provide the primary structure of the s p a c e s t a t i o n have p o t e n t i a l t o s a t i s f y the need f o r an e f f i c i e n t , s t i f f , compact, u s e r - o r i e n t e d , r e l i a b l e and economical , space-station-construction concept t h a t o f f e r s a m i n i m u m of t r i p s and o n - o r b i t s t a y t i m e f o r the space shuttle. REFERENCES 1. Mikulas, Martin M . , J r . ; B u s h , Harold G . ; Wallsom, Richard E . ; Dorsey, John T.; and Rhodes, Marvin D.: A Manned-Machine Space S t a t i o n Construction Concept, NASA TM 85762, February 1984. 2. Rauschenbach, M . S . : S o l a r Cell Array Design Handbook, Van Nostrand Reinhold Co., C. 1980. 3. Opjorden, R . W . : S o l a r Cell Optical Design C o n s i d e r a t i o n s . Presented a t N i n t h IEEE P h o t o v o l t a i c S p e c i a l i s t s Conference, May 1972. 4 . " S o l a r Array Technology Development f o r SEP, Final Report ,I' Lockheed Mi s s i l e s and Space Company, NASA CR-161634, LMSC-D715820, NAS8-31352, January 9, 1981. 5. White, W . J.: Skylab Reactivation Data Analysis Final Report. McDonnell Douglas A s t r o n a u t i c s Company - Huntington Beach, NASA CR 159074, June 1979.

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22 TABLE I.-SOLAR-CELL-ARRAY RELATIVE AREAS AND AREAS FOR A M I N I M U M CONTINUOUS POWER OF 7 5 KW FOR V A R I O U S CONFIGURATIONS AND ALTITUDES. -- ----.---I - -- - -- CONFI (;URATION+ 235 N. M i . O R B I T 270 N. M i . O R B I T 1 and .2 1.oo 3 1.45 4 1.85 5 1.95 6 2.07 7 3.58 .-I_I-_---------- - R e l a t i v e Area I Area ( f t 2 ) _ 18920 1.oo 18650 27 380 1.43 26730 35080 1.86 34770 36980 1.96 36640 39150 2.10 39150 67750 3.63 67750 t See t e x t f o r d e s c r i p t i o n o f c o n f i g u r a t i o n s . TABLE 11.- RANGE OF CONTINUOUS POWER OUTPUT AVAILABLE OVER A YEARLY CYCLE FOR V A R I O U S CONFIGURATIONS, B ANGLES AND ALTITUDES. Power, kW - Power. kW Power, kW 1 and 2 75 .Of 3*** 108.5 4*** 75.0" 139.8 5*** 75.0* 147.1 270 N. M i . O R B I T tJ B = 0 0 - m - 86.2 75.0* 87.1 75.0* 107.5 75.0* 75.0* 141.9 75 .O* 149.2 6 normal 75.0" 134.3 75.0* 135.9 peak** 155.3 178.4 7*** 129.8 157.5 182.9 75 .O* 129.8 75 .O* t See t e x t f o r d e s c r i p t i o n of c o n f i g u r a t i o n s . * Design p o i n t . ** When r e o r i e n t e d t o become a sun-synchronous s t a t i o n . *** Power output may be i n c r e a s e d if r e o r i e n t e d t o become a sun-synchronous s t a t i o n .

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c3 7 \ I / ', W c3 Q) w I \ 1 ' L L J c3 I w z 0 0 J -2 --I w > 7 - 0 7 -I W > 1, U .. .-- L M It_i 3 u3 I--1 1-i

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24

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8 W =r 3 -J 0 > I 2 3 LL w v, =) I w c3 5 I -- I 25 3 U 0 E U aJ r 0 V m Q, L

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26 1 0 W I I- 4: . I - J cll -1 W W M \ \ / 1 -0 0 1 E t F m E 0 k- *r- I c, W a 0 L aJ -7) n 0 Y- O ,I T3 aJ c, V 3 I- L = c, W v) FQ E 0 0 E 0 .C n c, a I- c, LL v) M - M 00 X

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. 27 I 7-01LI 0 I- 7 W Z E I- = & 0 0 n W N w cx 3 v, v, w n5 a, - - I I m I - 4 c I c 51 I -0 I 2 c I m c 0 1 % *It- C, I d : a L aJ I = s3: 0 I = L 0 J , 1 YaJ I L 3 U I a, v 0 I L a I I I I I I L n I aJ L 3 I cn 5 nnna' I I I I I - - >--t = ] .. -.1 ...

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W 0 U > W a z 0 .z tw W 4 + A 0 w W z z U 7 0 0 c 0 4 z 0 W 0 0 U J -J 3 cn CI z u 0 W z v) + 4 3-c W I I 4 e a W 0 c t U 3 W z z o I- w - 1 I t - W Z V Ir W 0 w z n v z x 2 0 0 4 0 LJ W 4 c c W 4 x v) v) Z I W - r x 0 W U / -I+ > ok- - zW M - a c t: 0 u W Y I W W L 3 cn .F LL ii I

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W C C LI3 t- V 3 kv, tn v, 3 C Y 7- ~ ?- =I -0 0 11-1 E . - rd S 0 're, fd L 0) 0. 0 r- 2 'Cr - r-

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30 w -I => a 0 ZI -J z 0 W It L 'a X z 0 .I- C, a L aJ a 0 . a, ?-

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r-w N N 0 7 0 u I-r z z 0 w W zz I-- c u Q: w cc CZI w N W v) v) w E e v) cn 3 cx I- I 0 I- I c Ic?L 31 c3 7 0 1 I- LL Lo J X cd w cx 0 I- < Y z w ZE u-l Lx cn U aJ 3 L. U II w (3, Lx I I- C-( II3 n 7 0 V

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32 c 0 ln 0 c-, c, L a L c, 8

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r-l-Report No. 2. Government Accession NO. 3. Recipient's Clbiog No. i NASA TM-85772 4 T I t k and Subtitle i 5 Report Date . A p r i l 1984 -- I O p e r a t i o n a l Ciodules f o r Space S t a t i o n C o n s t r u c t i o n 6. Perforrninp Organization Code I , -__- I Author(sJ 506-53-43 -- 8 Perforrniriy Organitation Report N o L. Robert Jackson, Paul L . Moses*, Stephen J . S c o t t i * and Max L. B l o s s e r .--~~- 9 Ptvforrriing Orydniidtion Name dnd Address I NASA Langley Research Center I Hampton, VA 23665 I I FI S L Z c--II-_ - _ _ 10 Work Unit No I-_____-_- --.- _.. - 11 Cantrdct or Grant No ---- -.- 13 Type of Report and Period Cuvered 5 T e c h n i c a l Memorandum--- N a t i o n a l Aeronautics and Space A d m i n i s t r a t i o n 14 Sponsoring Agency Code 1 Washington, DC 20546 I t - -. - - i- - - C e y '&urds (Sugyested by Author[$)) 1 Space S t a t i o n s Space S t a t i o n C o n s t r u c t i o n Ground-Based Checkout of Systems I O p e r a t i o n a l Modules I Sol a r - C e l l - A r r a y O r i e n t a t i o n s -- - ______ e 1 18. Distribution Statement U n l i m i t e d - U n c l a s s i f i e d * S u b j e c t Category 18 I 19 Secui t v Classif (of this report) (of this pagel 21 No of Pages 2 2 h x ' 20 Security Classif U n c l a s s i f i e d 33 A0 3 I Uncl a s s i f ied