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    N A S A T E C H N I C A L

    c 4r/)4z

    N O T E D-4952

    LOAN COPY: RETURN TOAFWL (WLIL-2)KIRTLAMD AFB, N ME X

    SEXTANT SIGHTING MEASUREMENTS FROM ON B O A R D THE GEMINI XI1 SPACECRAFT

    iby Donald W. Smith and Bedford A. LampkinAmes Research CefzzterMoffett Field Cal$

    N A T I O N A L A E R O N A U T I C S A N D S PA C E A D M I N I S T R A T I O N W A S H I N G T O N , D . C . DECEM BER 1 9 6 8

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    TECH LIBRARY KAFB,"IIllllllllll1lllllllllllllllllllllllllIllIll0131709

    NASA TN D-4952

    SEXTANT SIGHTING MEASUREMENTS FRO MO N BOARD THE GEMINI XI1 SPACECRAFTBy Donald W . Smith and Bedford A. Lampkin

    Ame s Research Center Moffett Field, Calif.

    NATIONAL AERONAUTICS AND SPACE ADMINISTRATIONFo r so le b y the Clear inghous e fo r Federa l Sc ien t i f i c ond Techn ica l I n fo rmat ion

    Spr ing f ie ld , V i rg in ia 22151 - CFSTI p r i c e $3.00

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    SEXTANT SIGHTING MEASUREMENTS FROMON BOARD THE G E M I N I X I 1 SPACECRAFT

    By Donald W . Smith and Bedford A . LampkinAmes Resea rch Ce nt er

    SW R Y

    The capab i l i ty o f a s p a c e c r a f t n a v i g a t o r t o make i n - f l i g h t n a v i g a t io nmeasurements from on board t he sp ac ec ra f t us in g a hand-he ld se x t an t has beens t u d i e d e x t e n s i v e l y . Tes t s conducted on board the orbi t ing Gemini X I 1 spacec r a f t were d e si g ne d t o d e t er m in e t h e e f f e c t o f t h e a c t u a l s p a c e - f l i g h t e n vi ronment on na vi ga to r performance. The r e s u l ts show t h a t : (1) hand-heldse xt an t measurement performance i s e x c e l l e n t p r o vi d i ng a s t a n d a r d d e v i a t i o nof measurement e r r o r le ss than 10 a r c seconds ; ( 2 ) s p a c e cr a f t r o t a t i o n a lmot ion and th e ac tu a l spa cec ra f t envi ronment had l i t t l e e f f e c t on t h e n a vi ga to r performance; and ( 3 ) window-induced measurement errors i n the GeminiX I 1 spacec ra f t w e re small and p re d ic t ab le . The op t i ca l hand -he ld s ex tan tappears t o have a pp l i ca t io n t o on -boa rd nav iga t ion f o r fu tu re manneds p a c e f l i g h t s .

    INTRODUCTION

    E a rt h -b a se d e l e c t r o n i c t r a c k i n g s y st em s h av e be en u se d f o r e a r t h o r b i t a lnav ig a t ion of t he manned Gemini sp ac ec ra f t and f o r t ra ns lu na r and in te r p lane ta ry nav iga t ion of var ious unmanned spacecra f t . I t i s p lanned t o u sethe se t r ack ing sy s t ems as an e lement i n the p r imary nav iga t i on sys tem f o rth e manned Apollo sp ac ec ra f t . In t he manned ve h i c l es , th es e sys tems prov ideacc ura te nav iga t io n measurements and re l i e v e th e crew workload a t c r i t i c a ltime p e r i o d s i n t h e m i s s io n .S t u d i e s o f c i rc u ml u na r n a v i g a t i o n ( r e f s . 1 and 2 ) a n d i n t e r p l a n e t a r yn a v i g a t i o n ( r e f s . 3 and 4 ) have i nd i ca t ed th a t p r ec i s e angu la r measurements(s tan dard dev i a t i on of measurement e r r o r I 10 a rc sec) made with an opticaldevice such as a s e x t a n t o r t h e o d o l i t e can b e s u i t a b l y p ro c e ss e d i n a compu te r mechanized nav iga t ion sy s tem t o p rov ide s a t i s f ac to ry midcour se nav iga t i o n . E a rl y i n t h e s p a c e - f li g h t e r a , s i m i l a r s t u d i e s l e d t e c h n i c a l p l an n e rs

    t o cons ide r on -boa rd sy st ems f o r p r imary nav iga t ion . A s i m p l i f i e d h i gh l yre l i ab le on -boa rd nav iga t ion sy s t em f o r manned or b i t a l , lunar , and in te r p l a n e t a r y s p a c e f l i g h t i s d e s i r a b l e :1 . To provide a backup c a p a b i l i t y s u i t a b l e f o r sa f e e a r t h r e t u r nfrom a v a r i e t y o f m i s s io n p ha s es2 . To prov ide a b lunde r check f o r pr imary sy s tem e r ro r s

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    3 . To i n s p i r e t he c r ew ' s c on fi denc e i n t h e pe rf o rm a nc e of t hepr imary naviga t ion and guidance sys tem.On-board navigation of a i r c r a f t and s h i ps ha s e vo lve d i n t o a s ys t e m t ha tdepends t o a l a r g e e x t e n t on t h e u s e o f a p p r o p r i a t e t a b l e s an d c h a r t s , as e x t a n t , a c lock, and a s i m p l e com pu ta t iona l f orm t o e s t a b l i s h ve h i c l ep o s i t i o n on t h e e a r t h ' s s u r f a c e . These s i mp l i f i ed systems a re capable of

    provid ing a p o s i t i o n d e t e r m i n a ti o n w i t h i n a mile . However, t h e na vi ga ti onof s p a c e c r a f t t h a t t r a v e l a t high speeds ove r l a r ge d i s t a nc e s w he r e t heconsequences of small na v i ga t i on e r r o r s w ou l d be g r e a t l y m a gn i f i e d r e qu i r e ssystems based on new sta nd ar ds o f p r e c i s i o n i n b o t h s i g h t i n g and c a l c u l a t i o n .The problem of s i gh t i ng prec i s i on i s b e in g s t u d i e d i n a c t u a l s p a cef l i g h t by t h e A i r Force ( re f . 5) and NASA ( r e f . 6 ) . S i g h t i n g p r e c i s i o n h asa l s o been s t u d i e d i n s i m u l at o r s ( r e f s . 7, 8, and 9) a nd i n h i g h - f ly i n ga i r c r a f t ( r e f . 1 0 ) . The r e s u l t s o f t h e l i m i t e d s p a c e f l i g h t and morecomprehensive si mu la to r and a i r c r a f t e xpe r i m e n t s i nd i c a t e d t ha t a hand-helds e x t a n t c oul d be u s e d as a major element of a s pa c e c r a f t na v i ga t i on s ys t e m .The gen eral o b je ct iv e of Ames' TO02 i n - f l i g h t experim ent was t o make

    nav iga t io n measurements through t he window of th e s t a b i l i z e d Gemini spacec r a f t with a ha nd- he l d s e x t a n t :1. To e v a l u a t e t h e a s t r o n a u t ' s a b i l i t y t o make a c c u r a t e sp a cena vi ga ti on measurements us in g a s i m p l e i n st r um e n t i n anauthent ic space envi ronment2 . To examine th e o pe r a t io na l f e a s i b i l i t y of t he measurementt e c hn i que bo t h w i th p r e s s u r e s u i t he l me t o f f and p r e s s u r es u i t h el m et o n - visor down3 . To e va l ua t e o pe r a t i o na l p r obl em s a s s oc i a t e d w i t h t he s pac e c r a f t environment4. To va l i da te ground-based s i mul a t io n techniques by compari s o n o f t h e i n - f l i g h t d a t a w it h b a s e l i n e d a t a o b t ai n ed byt h e s p a c e c r a f t p i l o t , b o th i n s i m u l at o r s and u s in g a c t u a lc e l e s t i a l t a r g e t s f r o m g r o u n d o b s e r v a t o r i e s .The TO02 exper iment re su l ts a r e compared wit h bas e l in e d a t a obta ine d i na ground-bas ed s i m u l a t i on and w i t h o t h e r f l i g h t da t a , a nd t he po t e n t i a l o f

    the hand-held s ex tan t f o r implementa tion of on-board navig a t ion sys tems fo ri n t e r p l a n e t a r y f l i g h t i s examined.EQUIPMENT

    Sext a n t Des c rip t ionThe two l ine-of-s ight ( L O S ) s e x t a n t shown i n f i g u r e 1 was u se d i n t h eTO02 experiment. I t was des igned t o measure accu ra te ly th e angle be tweenva r i ous types o f c e l e s t i a l t a r g e t s .

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    timersystemconnectorFilter

    primary

    Event timer sWitch

    Figure 1.- Hand-held space sextant used in T002 experiment.

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    ---

    The view through the f ixed LO S f i e l d of t h e s e x ta n t i s imaged i n i t sf oc a l p l a ne t h r ough a p l a t e b e a m s p l i t t e r , o b j e c t i v e l e n s , and p r is m -m i rr o re r e c t i n g sy st em ( f i g . 2 ) . The view through t h e scan ning LOS f i e l d i sr e f l e c t e d from a n a r t i c u l a t e d sc an n i n g m i r r o r ; i t i s then combined witht h e f i x e d LO S f i e l d i n t h e b ea ms pl it

    t e r and imaged ( in th e foc a l p lane )by the same o b j e c t i v e l e n s a nd e r e c t in g sys tem. The op e ra t or , by obse rvi n g t h e f o c a l p l a n e t hr ou gh t h ee ye p i e c e and a d j us t i n g t h e s c a nni ngf i e l d s of view can super impose th es e l e c t e d t a r g e t s i n t h e f i x e d andscanning f i e ld s o f view, and thuse s t a b l i s h t h e a n g u la r s e p a r at i o n oft h e t a r g e t s . The a n g u l a r r o t a t i o n o ft h e s c an n i n g m i r r o r i s c o n t r o l l e d b yth e two-speed scanning con t ro l knobs ,f which p r ov i de t a r g e t op t i c a l m o ti onso f 1 degree and 5 de gr e e s pe r r e vo l u t i o n o f t h e k no bs .

    50 % re f lec t ionI An engraved r e t i c l e i s l o c a t e dI-- - ------ - a t t h e p r i n c i p a l f oc us o f t h e t e l e s co p e o b j e c t i v e l e n s . The r e t i c l eFigure 2.- Schematic diagram o f op t ics ; hand- p a t t e r n was des igned to a s s i s t t h eh e l d s e x t a n t . o p e r a t o r i n k ee pi ng t h e t a r g e t s

    a l i ne d i n t he measurement p lan e oft he i n s t r um e n t w h i l e making t he s i g h t i ngs . The r e t i c l e a l s o d e f i n ed t h earea o f t h e i n st ru m en t f i e l d of view i n which measurements were t o be made t ominimize measurement errors. Ret ic le i l l u m i n a t i o n i s p r ov i de d t o e n a bl e t h eo p e r a t o r t o see t h e r e t i c l e a ga in s t a dark background.

    The sextant i s equipped wit h two removable eye pi ec es , one pro vid ingnormal eye r e l i e f , and th e o t he r , long eye r e l i e f . The normal eye r e l i e feyepiece i s us ed when t he s e x t a n t c an be b rough t d i r e c t l y t o t h e e ye f o rv iewing , whi le the long eye r e l i e f e ye pi e ce a l l ow s t h e s e x t a n t t o be u s edw i t h t he p r e s s u r e s u i t he l m et on and t h e he lm e t v i s o r down.

    Data readout i s accomplished by d i r e c t rea din g of a mechanica l c o u n t e rlo ca t ed below th e ins t ru ment ey epiec e . The measured angl e between th ef ixed and scanning LO S i s i n d i c a t e d on t h e c o u n t e r i n d e g re es , t h e l e a s tcount be ing 0.001" o r 3 . 6 arc seconds .

    A du a l - ce l l r echa rg eable n icke l-cadmium ba t t e r y , c o n ta i n ed w i t h i n t h es e x t a n t , p r ov i de s 2 . 5 v o l t s f o r i l l u m i n a t i n g b o t h t h e d a t a r ea d ou t and t h er e t i c l e .

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    A n event t i m e r but ton and swi tch are l o c a t ed on t h e r i g h t s i d e o f t h einstr umen t . The event t imer swi tch was connected t o t he Gemini XI1 spacec r a f t t e le m e tr y r e c or d e r t hr ou gh t h e s p a c e c r a f t u t i l i t y c or d. Depression oft h e e v e nt t i m e r b u t t o n p u t a t i m e - c o r r e l a t e d s ignal on th e on-board p ul secode modulation (PCM) d a t a r e c o rd e r t a p e f o r u s e i n t h e d a t a a n a l y s i s .

    Two f i l t e r s of d i f f e r e n t d e n s i t y a re provided i n each LOS t o r e du ce t h eamount of l i gh t t r an smi t t ed th rough them. The purpose of the f i l t e r s i s t operm it v iewing of images of widely varyi ng br ig ht ne ss .T h e g e n e r a l c h a r a c t e r i s t i c s of t h e s e x t a n t a re as fo l low s :

    S i z e . . . . . . . . . . . . . . . . . . . . 7 x 7-1/4 x 6-1/16 in.WeightNormal eye re l i e f eyep iece . . . . . . . . . . . . . . 6 lb 4 ozLong eye r e l i e f eyepiece . . . . . . . . . . . . . . . 6 l b 0 ozMagnif ica t ionNormal eyepiece . . . . . . . . . . . . . . . . . . . . . . . 8xLong eye re l ie f eyep iece . . . . . . . . . . . . . . . . . . . 6 ~Field of view . . . . . . . . . . . . . . . . . . . . . . . . . 7"E xi t pup i 1Normal eye re l i e f eyep iece . . . . . . . . . . . . . . . . . mmLong eye re l ie f eyep iece . . . . . . . . . . . . . . . . . . mmE ye r e l i e fNormal eye re l ief eyepiece . . . . . . . . . . . . . . . . 18 mm

    Long eye re l ie f eyep iece . . . . . . . . . . . . . . . . . 60 mmDiopter adju s mentNormal eye re l ief eyepiece . . . . . . . . . . . . . . . 3 t o +SLong eye re l ie f eyep iece . . . . . . . . . . . . . . . . . 3 t o + 3Resolu t ion . . . . . . . . . . . . . . . . . . . . . . 7 s e c of a r cImage . . . . . . . . . . . . . . . . . . . . . . . . . . . E rec tRange . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76"

    A d e t a i l e d d e s c r i p t i o n of t h e i n s t r u m e n t , t h e r e s u l t s o f t h e f l i g h t r a t i n gprogram, and r e s u l t s o f t he func t iona l ve r i f i c a t i on p rogram a re p re sen ted i nr e f e r e n c e 11.

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    0-

    ----

    02 -20-0-2 -40 I I I $ -10 0 10 20 30 40 5o I ;

    Indic ated sextant angle, e,, degFigure 3 . - P r e f l i g h t c a l i b r a t i o n o f ha nd -h el ds pace s ex tan t (GFAE No. E G 2 5 1 0 0 - 1 , s e r i a lno . 4 ) .

    Post f Iighi ca Iibra ionSpecial postflight calibration for actuol GeminiXU measured angles

    0 Preflight calibration from Fig 3P reflight calibration, 0" lo 3"

    IO 01 I II

    0-10 L I I I17 18 19

    100 .p . . . * . I-4-10 I I0 I 2 3Indicated sextant angle, e, , de g

    Figure 4 . - P o s t f l i g h t c a l i b r a t i o n of hand-heldspa ce se xt an t (GFAE No. E G 2 5 1 0 0 - 1 , s e r i a lno . 4 ) .

    6

    Se x t a n t C a l br a t ionP r e f l i g h t . - The f l i g h t s e x t a n t (GFAE No. EG 25100-1, s e r i a l no. 4) was

    c a l i b r a t e d p r i o r t o t h e f l i g h t of t h e Gemini X I 1 us ing the Acceptance T e s tand Opt ica l C al ib ra ti on Proce dure (KTS 41580 00 001) of r e fe re nce 1 2 . Thes e x t an t c a l i b r a t i o n e r r o r , E C Y i s t h e a v e ra g e o f t h e e r r o r s o b t a i ne d a t eachv

    Note: Curve values to be added reading (every lo rom -60 to +700)to sextant reading i n t h r e e c on se cu t iv e c a l i b r a t i o n s .

    The range of the th ree ins t rumentd i s C r e t e i n d i c a t e d s e x t a n t a n g l e

    errors measured a t each ind ica tedFR/\Ih &Ah LQAk$ s e x t a n t a n g le d ur i n g t h e c a l i b r a t i o n~ ~ was v - v " YU" . Ialways l ess than 6 a rc seconds.+ For a c t u a l a ng l e o fn t r u e t a r g e t0" t h e s e x t a n t was c a r e f u l l y a l i n e don an op t i c a l bench t o i nd i c a t e 0" ont he s e x t a n t r e a dou t c oun t e r . Toob t a i n t he a c t ua l m e a s u r e d s e x t a n ta ng l e , t h e i n s t r ume n t e r r o r i s addeda l g eb r a i ca l l y t o t h e i n d i c a t edsextant angle (fig.3 ) .

    P o s t f l i g h t . - A f t er t h e GeminiX I 1 f l i g h t , t h e se x t an t was v i s u a l l yi n s p e c t e d and c a l i b r a t e d t o d et er mi n ewhe the r exposure to th e space andspacecraf t environment had any de let e r i o u s e f f e c t s on t h e s e x t a n t o r i t sperformance . The in sp ec t io n rev ea le dno change i n the phys i ca l condi t ionof th e ins t ru ment . The sex tan t wasc a l i b r a t e d u s i n g t h e p ro c ed u re o fr e f e r e n c e 1 2 , b u t o n ly i n t h er e s t r i c t e d r a n ge s of i n d i c a t e d s ex t a n t a ng l e s , from 0 t o 3', 6 .5 " t o9 .5" , and 16 .5" t o 19 .5" , i n whichs i g h t i n g measurements were made during the Gemini X I 1 f l i g h t . A c a l i b r a t i o n f o r t h e r a nge from 31.5 ' t o34.5" was a l s o made t o check a s i m i -l a r p r e f l i g h t c a l i b r a t i o n . F ig ur e 4compares the post f 1ight ca l br a t iond a t a w it h t h e p r e f l i g h t d a t a off i g u r e 3 and w i t h t h e c a l i b r a t i o nmade i n th e range of s ex t an t angle sfrom 0' t o 3". Tw o s p e c i a l pos t f l i g h t c a l i b r a t i on s w ere made f o rin d i ca t ed sex ta n t angle s of 7 .525'and 18.605', t h e appr oxim ate measuredangles of th e s ig h t in gs per formed onthe Gemini X I 1 f l i g h t .

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    From examination of f igure 4 , it may be s e e n t h a t t h e pos t f l i g h t an dp r e f l i g h t s e x t an t c a l i b r a t i o n e r r o r s d i f f e r g en e r a ll y by a bo ut 5 arc sec w i t ha few as l a r g e as 10 a rc sec . E xce pt f o r t h e f e w l a r g e r e r ro r s , t h e c a l i b r a t i o n s meet t he a c c e p t a nc e t e s t r eq u ir em e nt s f o r o p e r a t i o n a l u s e o f t h e s e x t a n t( r e f . 1 2 , appendix 11, par a . 9 .1 8) : th e di f fe re nc e between th e maximum andminimum e r r o r a t any da t a po i n t ( i n d i c a t e d s e x t a n t a n g l e ) s h a l l n o t e xc ee d6 a r c s e c . I t seems r e as o n ab l e t o c on cl ud e, t h e r e f o r e , t h a t t h e e x p os ur e t oth e spac e - f l igh t envi ronment had l i t t l e o r no e f f e c t on th e performance oft h e s e x t a n t .

    Event Timing SystemThe in tegra l event t i m e r s w i t c h ( f i g . 1) was a c t ua t e d by t he p i l o t whenh e a t t a i n e d t a r g e t s u p e r p o si t i o n i n t h e s ex t an t f i e l d of view. Actua t ion oft h e s wi tc h i n i t i a t e d a t i m e - co r r e l at e d e l e c t r i c a l s i g n a l t o an on-b oard PCMt a pe r e c o r d e r . T h i s e ve n t t i m i ng s yst em was capable of pr ov i d i ng t he t ime ofe ac h s e x t a n t s i g h t i n g w i t h an e r r o r l ess than 20 .2 sec . The data were s t o r e don t h e t a p e and t r a n s m i t t e d t o t h e ground v i a te le met ry equipment a t a f u t u r e

    t ime. I t t h e n became a v a i l a b l e f o r r e d u ct i o n o f t h e s i g h t i n g d a t a .In a pr ev io us exp erime nt on Gemini IV ( r e f . 5 ) , t im e c o r r e l a t i o n d a t awere los t as t h e r e s u l t o f a n equ ip men t f a i l u r e , which s e r i o u s l y r e s t r i c t e dt h e u s e f ul n e s s o f t h e d a t a c o l l e c t e d a nd re co r de d i n t h e p i l o t s l o g an d, i nt h i s c a s e , made i t i m po s si b le t o o b t a i n q u a n t i t a t i v e r e s u l t s . To p r e ve n t d a t al o s s i n t h i s e xp er im en t, a backup t iming system was devised i n which t hecommand p i l o t manually logged t h e time o f s e x t a n t s i gh t in g , which he readfrom a s p a c e c r a f t e lapse d t ime c lock on an or a l "MARK" command from t h e p i l o t .This system proved accu ra t e wi th in about k0.6 sec based on th e event t imess uc c e s s f u l l y t e l e m et e r e d f rom t h e p ri m ar y s yst em du r i ng t h e f l i g h t .

    Sext a n t St owageDuring the launch and en tr y phase of t he Gemini XI1 miss i on, t h e se xt an twas s towed between th e p i l o t s i n a s p e c i a l c o n t a i n e r shown i n f i g u r e 5 . T hi sc o n ta i n er r e s t r a i n e d t h e s e x t a n t d u r in g t h e s e h i gh a c c e l e r a t i o n f l i g h tregimes and a ls o prot ec t ed t h e ins t rum ent f rom damage due t o both t h es u s t a i n e d a c c e l e r a t i o n a nd v i b r a t i o n l o a d s .Durin g t h e o r b i t a l f l i g h t ph a se , t h e i n s t ru m e n t was stowed above theback of th e command p i l o t ' s s ea t where it was restrained from moving by meansof Velcro pads .

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    ---

    c=J.....'. , . . . . . :. .. .\ . . . ., ' . . . .

    Figure S. - Sto\yage of sextan t on board Gemini XI I spacecraft.

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    EXPERIMENTAL METHODS AND PROCEDURES

    P r e f l i g h t T r ai n in gT r a i n i n g i s a c r i t i c a l f a c t o r i n d ev el op in g t h e a b i l i t y o f a s p a c e c r a f tn a v i g a t o r t o m a k e acc ura te nav i ga t io n measurements ( r e f . 7 ) . The Gemini X I 1

    pi lo t , Major Edwin Aldr in , was t r a i ne d f o r t he TO02 exper iment i n t he Geminicab of the Docking Simulator a t NASA's Manned Spacecraft Center ( f i g . 6 ) .Two s im u la te d s t a r t a r g e t s were i n s t a l l e d i n t h e s i m u l a t o r room. The s t a rt a r g e t s c o n s i s t e d o f 1 2 -i n . p a r a b o l i c m ir r o rs t h a t p r o j e c t e d c o l l i ma t e d l i g h ttoward t h e s i g h t i n g s t a t i o n s i m u l a t i n g a s t a r magnitude of about 2 . Usingth e hand-he ld s ex ta n t i n th e darkened Docking S imu la to r , t h e p i l o t p er fo rm ed15 cons ecut ive measurements of th e ang le between t h e s im ula ted s t a r s . A ze rob i a s c o r r e c t i o n was ob ta ined by hav ing th e p i l o t t ake 10 consecu t ive measu re ments when si g h t i n g on one s t a r with bo th se xt an t LOS. The measured se xt an tang les were r e a d o f f o f t h e s e x t a n t c o u n t e r and r e co r d ed . Sextant measurements were r e p ea t e d i n 15 s i g h t i n g s e s s i o ns d i s t r i b u t e d o ve r a pe r iod o f4 days .

    P r ef 1ight Base 1ine ExperimentsA cc ur at e r e f e r en c e b a s e l i n e d a t a were r e q u i r e d f o r e v a l u a t i n g t h e e f f e c to f t h e s p a c e - f l i g h t e nv ir on me nt on t h e p i l o t ' s a b i l i t y t o m a k e accu ra t esextant measurements . A l l b a s e l i n e d a t a were o b t a i n e d a t Ames ResearchC en te r p ri m a r i l y i n t h e A m e s Midcourse Navigation and Guidance Simulator( r e f . 7 ) . The b a s i c components of t he s im ul at or a re a visual scene (moon-s t a r f i e l d ) a n d a movable cab (manned sp ac e v e h i c l e ) . The cab was s t a t i c f o rthe ma jo r i ty o f t he s ig h t in g se s s io ns . Cab mot ion appeared t o have no e f f ec ton s i gh t i n g performance. The two s im ula ted s t a r s used i n t h e i n i t i a l t r a i n

    i n g were employed i n o b t a i n i n g t h e b a s e l i n e d a t a . Using th e hand-held sex ta n t , th e Gemini X I 1 p i l o t made 5 cons ecut ive measurements of t he a ngleob tai ned when viewing th e same s imu la t ed s t a r through bot h s e xt an t LOS t oes ta b l i s h an ins t rume nt-o pera t or measured zero b i a s . Subsequent ly , 10 consecu t ive measurements o f t he ang le between the s e l e c t ed s i gh t i ng t a rg e t s w eremade from which t he mean and st an da rd d ev ia ti on s of t h e measurement e r r o r swere computed. Measurements were made wi th t h e helm et o f f (normal eye r e l i e feyep iece ) and he lme t on, v i so r down ( long eye r e l i e f eyep iece ) . S ex tan tmeasurements were made i n 25 s i g h t i n g s e s s io n s d i s t r i b u t e d o v e r a p e r i o d o f2 days .The t r ue ang les be tween th e s i mu la t or s i gh t i ng ta rg e t s were measuredu s i n g a H i l g e r Watts No. 2 Microp t i c T heodo l i t e w i th a 0 . 1 a rc s e c r e a d ou tand an e r r o r of l e s s t h a n 1 arc s e c .B ase l ine da ta w ere a l so ob ta ined a t t h e Ames ground s i g h t i n g s t a t i o nu s i n g r e a l s t a r s . Measurements were made i n 5 s i g h t i n g s e s s i o n s d i s t r i b u t e dover a p e r i o d o f 2 days .

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    f - 'a

    Figure 6.- MSC docking simulator used in preliminary astronaut trai

    - - - - - - - .----

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    The sex tan t even t t iming sys tem was used t o mark t he t i m e o f s e x t a n tmeasurement on a d i g i t a l r e c o r d e r . An e l e c t r o n i c c l o ck s y nc h ro n iz e d t o t h en a t i o n a l t i m e s t a n d a r d t r a n s m i t t e d o v e r r a d i o s t a t i o n WWV was used as t h etime re fe r ence . T iming e r ro r was l e s s t han +0 ' .25 s e c .

    In-Flight ExperimentIn - f l i gh t p rocedures were car e f u l ly fo rmula ted by the exper imente rs andth e f l i g h t c rew i n the Gemini Miss ion S imula tor a t the Manned Spacecraft andKennedy Space Cente rs . The methods f o r acqu i r ing th e ta r g e t , t ak ing da ta ,measuring t i m e o f t a r g e t s s u p e r p o s i t i o n , and l o c a t i n g s e x t a n t LO S on thewindow were s i mp l i f i ed t o ass ure a maximum probability of experiment success.These p rocedures were f re que nt l y p r ac t i ce d by th e c rew us ing t he v i su a l sceneof t he Miss ion S imula tor .The sextant was taken from i t s s towed loca t ion between t he p i l o t and thecommand p i l o t . The sp ac ec ra f t commander then es ta bl is he d th e sp ac ec ra f to r i e n t a t i o n wi th r e s p e c t t o t h e s e l e c t e d s t a r t a r g e t s s o t h a t t h e p i l o t c ou ld

    se e them through th e r ig ht-ha nd window ( f i g . 7 ) . The spacecra f t was s t a b i l i z e d t o t h i s o r i e n t a t i o n w i t h i n ab ou t _ + 2 " i n pi tc h and yaw and + l o o i n r o l lw i th ve r y low r e s i d u a l a t t i t u d e r a t e s ( l e s s t ha n O . l O o p e r s e c ) . A f t e r t h es p a c e c r a f t was s t a b i l i z e d , t h e p i l o t b r ou g ht t h e s e x t a n t t o t h e window asshown i n f ig ur e 7 , s e t t h e r e t i c l e i l lu m in a ti on t o a comfor tab le leve l , anda cq u ir ed t h e t a r g e t s i n b o th LOS. T he p i lo t t hen supe r imposed the t a rge timages and marked the t ime of sup erp os i t io n by depress i ng the s ex ta n t even tt imer b u t t o n . An o r a l t im e !'MARK" was c a l l e d o u t by t h e p i l o t , and t h espace c ra f t commander r ead h i s space c ra f t c lock , no t in g th e t ime i n the expe r iment log a long wi th t he measured ang le read f rom th e se x t an t by t he p i l o t .This procedure was r e p e a t e d f o r a t l e a s t 13 cons ecuti ve measurements of t heang le betw een th e t a r ge t pa i r and 5 times f o r a s i n g l e s t a r ( the same s t a r i neach LOS) t o p rovide an ind i ca t ion o f t h e measured ze ro b i a s o f t h eins t rument-opera tor combina t ion .

    Dur ing each s igh t i ng ses s i on , th e command pi l o t dete rmin ed and note d ona d iagram con ta ined i n h i s log , th e po i n t on th e window t h a t would be in te r cep ted by th e ex tens ion o f t he lower l e f t co rne r o f t he s ex t an t c a se . T h isp o i n t was used by t he exper imente r i n co r re c t i ng th e d a t a f o r window-inducede r r o r s .The procedure w a s wel l execu ted by th e crew and although some of thet e l eme te red t ime da ta w ere lo s t , th e backup t ime "MARK" procedure providedadequa te redundant da ta .

    Data ReductionThe s i g ht in g performance of t h e p i l o t was e v a l u a t e d u s i n g t h r e ec r i t e r i a : (1) s i gh t i ng measurement e r ro r ; ( 2 ) th e mean o r a r i t hm et ic averageof a group o f s i gh t i ng measurement e r r o r s ; and ( 3 ) t h e s t a n d a rd d e v i a t io n o f

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    ~N

    ----------.. - ~~ ~. . /"

    /'

    ~

    Figure 7.- Sextan t sighting experiment on Gemini XII spacecraft.

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    th e g roup of s i gh t i ng measurement e r ro rs about th e i r mean va lue . The comput a t i o n of t h e va l u es of th e se c r i t e r i a was accompl ished us ing the equa t ionsand c or r ec t ion s exp la ined be low.Si gh ti ng measurement er ro r . - The se x t an t s ig h t in g measurement e r ro rva lues E ( i n a r c sec ) were computed as fo l low s :

    E = ( eM - eT ) - ( e Z mean = s i gh t i ng measurement e r r o r (1)eM = 0R + = measured ta rge t ang le (2)

    O R = sex tan t r eadou t coun te r r ead ingE~ = s e x t a n t c a l i b r a t i o n e r r o r ( f r o m f i g . 3)

    eT = e s + EW + E R = t r u e t a r g e t a n g le (3)es = ce le s t i a l t a rge t ang le ( compu ted )E = window-induced measurement e r r o r ( dete rmi ned bo thexpe r imen ta l ly and ana ly t i c a l ly )E = e r r o r due t o t h e d i f f e r e nc e of t he index o fr e f r a c t i o n o f t h e l i g h t t r a n s m i t t i n g media w i t h i n(n2) and ou t s id e (n l ) o f the space cra f t

    = s i n - ' ( Z s i n al ) - al ( r e f . 13)n l , n 2 = index of r e f r a c t i o n

    a1 = ang le between the inc id en t l i gh t r ay from the s t a rand t h e window normal

    ('Z'mean = mean measured ze ro bi a sez = th e measured zero b i a s o r t he measured ang le when

    the same s t a r i s viewed i n each LOSThe mean measured ze ro b i a s i s used t o c o r r ec t t he measurement da t a f o r pos s i b l e mechanical changes i n th e s ex ta n t due t o env i ronmenta l changes as well asp o s s i b l e changes i n t h e p i l o t ' s v i s i o n .

    Mean s ig ht in g measurement e r r o r . - The mean se xt an t s ig ht in g measuremente r r o r v a l u e s Emean ( i n a rc sec ) were computed as fo l low s :

    Emean = ('M - 'T'mean - ('Z)mean (4 )E = mean s ig h t i n g measurement e r r o rmean

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    St a nda r d de v i a t i on o f s i g h t i n g measurem en t e r r o r . - The s t a nda r d de v i a t i on- _ -of t h e s i gh t i n g m easu rement e r r o r , crE, p r es en t ed i n t h i s r e p o r t was computedus i ng e qua t i on ( 5 ) .

    Greenwich mean tim e (GMT) of si g h t i n g measurement.- The GMT of eachsighting measurement was computed as f o l l ow s :GMT = T L + ATG

    T L = Gemini XI1 launch t ime= 20 h r 46 min 33.419 sec GMTNovember 11, 1966

    ATG = Gemini e lapsed t ime f rom T LWindow-induced measurement e r r or . - Deformat ion of t h e surf ac es of th e

    window panes o f t h e Gemini sp ac ec ra ft (due t o manufac ture , and pr e s s u r e a ndt e m pe r at u r e e nv ir onm en t i n f l i gh t ) c aus es de v i a t i o ns i n t he s e x t a n t LO Sr e s u l t i n g i n er ror s i n t h e m ea su red s e x t a n t a ng l e s . L i ne - o f -s i gh t de v i a t i onsde te r mi ned bo t h e xpe r i m e n t a l ly and a na l y t i c a l l y have be en us ed i n t h i s r e po r tt o c o r r e c t t he m ea su red da t a . An im por ta n t f a c t o r i n c o r r e c t i ng t he e xpe r i menta l da ta was the point on the window a t which each sextant LOS i n t e r sec ted th e window su r f ace ( see p . 11 ) . The in te r s ec t i on poin t s were used i nan expe r imenta l l abo ra to ry se t up and an an a l y t ic a l p rogram t o de te rmine theave rage sex tan t LOS lo ca t i ons f o r each sex tan t s i gh t i ng pe r iod and the angle sand pl an es of in cid en ce of each LOS wit h re sp ec t t o t h e window axi s system.I t was e s t i m at e d by t h e s pa c e c r a f t crew t h a t t h e po s i t i o n o f t h e s e x t a n t LO Sthrough th e window could be de termined t o about + 1 / 2 i nc h . Analys is hasi n d ic a te d t h a t t h i s u n c er t ai n ty i n p o s i t io n c ou ld r e s u l t i n a maximum uncert a i n t y i n t he s e x t a n t m easu rement e r r o r o f a bou t + 2 t o 3 a rc s e c .

    TEST CONDITIONS

    The TO02 experiment was suc cess fu l ly comple ted on o rb i t s 40 , 48, 54,55, and 56 of the Gemini XI1 f l i g h t . The s p a c e c r a f t p o s i t i o n ( l a t i t u d e ,l o n g i t u d e , a n d a l t i t u d e ) as a f u n c t i o n o f t i m e (GMT) f o r each o r b i t i s giveni n t a b l e I .

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    S igh t ing T a rge t sThe s t a r s Betelgeuse and Rigel were the measurement ta rge ts dur ing thes i gh t i ng per io ds on or b i t s 40 , 48, and 56 . Be te lgeuse and Be l l a t r i x were th emeasurement t a r ge t s f o r t h e s igh t i ng pe r iods 54 and 55 . The ce l e s t i a l ang le

    BS between Be telgeuse and Rigel and Betelgeuse and Be l la t r ix were 1836 '17"and 731'47'' , re sp ec ti ve ly . These ang les were computed from the known valueso f r i gh t a scens ion and dec l ina t io n o f e ach t a r ge t ; t hey a re c o r r e c t e d f o rannual abe rr at io n and have been shown t o be l es s t han 1 a rc s e c i n e r ro r .Measurements between t h e moon limb and a s t a r were a l s o pl an ne d f o r t h i sf l i g h t , b u t t h e moon was a t h i n c r es c en t t h a t was a v a i l a b l e as a s i g h t i n gf o r o nl y a s h o r t t i m e a f t e r s p a c e c r a f t s u n s e t . Although the s t a r / s t a r t a r g e tcon f igu ra t ion u sed i s an ide a l i z ed non -nav iga t ion type t a rg e t pa i r , a subs t a n t i a l p o r t i o n o f t h e e x pe ri me nt o b j e c t i v e s were s t i l l m e t .

    Su it Config u r a tionThe p i l o t wore a s tand ard Gemini ty pe pre ssu re s u i t w i th g loves andhe lmet o f f dur ing a l l s i g h t i n g p e r i o ds e xc e pt t h e l a s t . During or b i t 56, hedonned t h e p r e s s u r e s u i t h e l me t , i n s e r t e d t h e l on g ey e r e l i e f e y e pi e c e i nth e s ex ta nt , and performed th e measurement sequence.

    S p a c e c r a f t I n t e r i o r L i g h t i n gDuring t h e s i g h t i n g p e r i o d, t h e s p a c e c r a f t was completely dark exceptf o r a s ha de d r e d u t i l i t y l i g h t p e r m i t t i n g t h e command p i l o t t o w r i t e downthe da t a and r ead h i s e l apsed t ime c lock . The sex tan t r eadou t coun te r wasi l lumina ted w i th a r ed l i g h t , which was turned on only as r e q u i r e d .

    Vehic le At t i tude RatesThe veh ic l e a t t i tu de s measured wi th resp ec t t o a s t a b l e p l a t fo rm wereu se d t o compute t h e v e h i c le a t t i t u d e r a t e s . P r i o r t o t h e s i g h t i n g p e r i o d

    88- 56- 342- t he p l a t fo rm was a l i n e d w i t h r e s p e c tt o t h e l o c a l v e r t i c a l and t h e s pa ce 8 4 - 52- 338 c r a f t o r b i t p l an e and was t o rqued int h e o r b i t p la n e ( p i t c h) a t a r a t e ofabou t 4 .0 /min, t h e o r b i t a l r a t e a tabout 150 mi l e s a l t i t u de . F igu re 8

    i s a t y p i c a l t im e h i s t o r y o f t h ev a r i a t i o n o f t h e v e h i cl e a t t i t u d e sf o r the Gemini e laps ed t ime cor r e

    mber sponding to th e s i gh t i ng measurementsnumbers 14, 15 , 1 6, and 17 of'43 s i g h t i n g p e r i od 1 (o rb i t 40) . Due t o

    Gemini elapsed t ime. hr min a s h o r t ag e o f s p a c e c r a f t e l e c t r i c a lFigure 8.- Typical vehicle attitudes during power, this is the Only sightingsextant sighting period number 1 (Orbit 4 0 ) . pe r io d du r ing which t he s t a b l e

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    p l a t f o rm r e f e r e n c e was a v a i l a b l e f o r measurement of vehicle r a t es anda t t i tu de s . However, th e command p i l o t a s sured th e exper imente rs th a t it wastyp ica l o f a l l t h e s i g h t i n g p er i od s .

    I t can be seen f rom f igure 8 t h a t t h e s p a c e c r a f t i s wel l s t a b i l i z e d i np i t c h and yaw wi t h maximum r a t es of 2" and 4"/min, r e s pe c t i ve ly , whi le th er o l l r a t e dur in g the se s i gh t i ng measurements was about cons tan t a t SO/min.There was l i t t l e e f f e c t o f a t t i t u d e r a t e on se x ta n t measurement performancea t r a t e s of l . S " / se c ( r e f . 8 ) ; t h e r e f o r e , a t t h e s e ra tes o f less t ha n0 . l o / s e c , pe rf o rm a nc e s hou l d no t be a f f e c t e d .

    RESULTS AND DISCUSSION

    The re su l t s o f t he TO02 expe riment co ns i s t o f l ea r n in g curve da tao b t ai n ed d u ri n g t h e i n i t i a l p er i o d o f t r a i n i n g w i th t h e s e x t a n t , b a s e l i n ed a t a f o r c om pa ri so n w i th f l i g h t r e s u l t s , and i n f l i g h t d a t a o b t a i n ed du r in gthe Gemini X I 1 f l i g h t .

    I n i t i a l T r a i n i n gThe Gemini X I 1 p i l o t was t r a i n e d as de s c r i be d p r e v i o us l y . The s t a nda r dde vi a t i on of t he measurement e r r o r from i t s mean value was used as t h em ea su re o f t he p i l o t ' s p r o f i c i e nc y . The s t a nda r d de v i a t i on va r i e d f rom amaximum of about k 1 3 arc s e c e a r l y i n t h e t r a i n i n g pe r io d t o a minimum ofabout k4 a rc se c toward the end.The t r a i n i n g d a t a o f r e f e r e n c e 7 f o r a l a r g e g r ou p o f s u b j e c t s i n d i c a t e dt h a t t he r ange o f s t a nda r d de v i a t i o n o f s i g h t i n g mea su rem en ts a t the end of a

    2-week period was about 14 a rc sec . The TO02 t r a i n i n g da t a, however, wereobta ined f rom an ex cep t io na l ly t a len ted ope ra to r who used an 8-power sex ta n t .I n a d d i t i o n , t h e s e x t a n t u s e d i n o b t a i n i n g t h e TO02 t r a i n i n g d a t a i s a v a s t l yimproved ins t rument op t i ca l l y and mechanical ly , ov e r th a t used i n re fe ren ce 7.The l ow e r s t a nda r d de v i a t i on f o r th e TO02 t ra in in g d a t a compared with t h a t o fHelmet of f Helmet on /visor down r e f e r e nc e 7 may a l s o be due p a r t i a l l yt o t h e i n c r e a s e i n m a g ni f ic a ti o n from3 .0 t o 8 . 0 .

    Standard deviolion

    Base l ine Data - S t a r / S t a r T a r g e t sSextant measurements were madewith t he he lmet of f (normal eye

    F ig ur e 9 . - P r e f l i g ht b a s e l i ne d a t a , TO02 de i i a t io n of t he s ig h t in g measurement-experiment; h e s nav iga t ion s imu la to r andground s i g h t i n g s t a t i o n ; s t a r / s t a r t a r g e t s . error- a bou t t h e i r mean va l ue ( t h eshaded ba rs) and th e mean s ig h t i ng

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    measurement e r r o r ( the o f f se t l i n e ) f o r a l l s i g h t i n g p e ri o d s; t h e s i g h t i n gmeasurement error i s p l o t t e d as t h e a b s c i s s a .The f i gu re a l so summarizes ba se l in e da ta ob ta ined a t a ground s igh t ings t a t i o n u si ng r ea l s t a r s . The s i g h t in g measurement e r r o r i s c o r r e c t e d f o rannua l abe r r a t ion and a tmosphe ri c r e f r a c t io n . The s t anda rd dev ia t ions o fth e s i gh t in g measurement e r r o r s ob ta ined w i th t he helmet o f f , bo th i n th esimulator and from the ground observa tory us ing ac tua l s t a r s , agree w e l l withva lues of +5 and +4 arc s e c , re spe c t iv e l y . S im i la r measurements wi th th ehe lmet on and v is or down, bo th i n th e s imu la t or and f rom the observa tory ,a l s o a g r e e w e l l , hav ing s t anda rd dev ia t ions o f + 7 and +8 a r c s e c ,re sp ec t i ve ly . The mean s i gh t i ng measurement e r ro rs a re smal l , ranging from

    1 t o 5 a rc s e c .

    Gemini X I 1 I n - F l i g h t DataThe Gemini X I 1 in - f l i gh t se x t an t measurements were , as no ted p rev ious ly ,made from w i t h i n t h e s t a b i l i z e d s p a c e c r a f t wh i l e t h e p i l o t was looking

    through the righ t-h and window, which was of good op t i c a l q u al i t y . Themeasurement da t a a r e p re sen ted i n t ab le 11. The s t anda rd dev ia t ion o f t h esi gh ti ng measurement er ro rs and the mean s i gh t i ng measurement er r or a resummarized i n f ig ur e 10 where t he s i gh t i ng measurement er r o r i s a g a i n p l o t t e das t h e a b s c i s s a . For t h e f i r s t f o u r

    -4

    Helmet of f Helmet on /visor d o w nSighting s i g h t i n g p e ri o ds , he measurementsperiod were made wit h th e helmet o f f . The

    5 s t a n d ar d d e v i at i o n f o r t h e s e s i g h t i n g-2 per io ds was l es s than +9 a r c s e c ,and th e average s tand ard dev i a t i onf o r a l l f o u r s i g h t i n g p e ri o d s was 70 a r c s ec . The measurement b i a s er ro rs

    -9-9- I f o r t h e f i r s t two s igh t i ng pe r iods i nwhich B etelg euse and Rig el were used-2- I- I as t a r g e t s w e r e - 2 and 0 a r c s e c ,I

    Measurement6error, orcsec Measurement error,0 orcsec r e s p e c t i v e l y, whereas t h e measurementb i a s e r r o r s f o r s i g h t i n g p e ri od s_Figure 10.- In -f l ig h t s ig h t i ng measurement da ta 3 and 4 , i n which Betelgeus e andTO02 experiment; Gemini XI1 s p a c e c r a f t ; B e l l a t r i x we re u sed as t a r g e t s , w e r es t a r / s t a r t a r ge t s . - 4 and - 2 a r c s e c , r e s p e c t i v e l y . Theaverage mean s i gh t i ng measurement e r r o r f o r a l l f o u r p e r i o d s was - 2 a rc s e c .D ur ing the f i f t h s i gh t i ng pe r iod , t h e measu remen ts were made with th e helm eton, v i s o r down, and wit h t he long eye r e l i e f e ye p ie ce i n s t a l l e d i n t h e s e xta n t . The s tand ard dev i a t i on of measurement e r ro rs f o r th es e measurementswas 8 a rc se c, while t he mean s ig ht in g measurement e r r o r was -11 a r c s e c .The s ta nda rd dev ia t i on of t he measurements f o r a l l s i g h t i n g c o n d i t i o n s

    i s below 9 a rc sec , agree ing wel l w i th th e ba se l in e da ta . The mean s i gh t i ngmeasurement e r r o r s o f t he in - f l i g h t da t a a re g e n e r a l l y sma l l , less t han 4arc s e c f o r t h e h el m et o f f c o n f i g u r a t i o n , w hich a l s o a g r ee s w e l l w i t h t h eba se l i ne da t a . The la r ge mean s i gh t i ng measurement e r ro r , f o r th ehe lme t on con f igu ra t ion da ta (o rb i t 56) i s i n c o n s i s t e n t w i t h b o t h t h e17

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    p r e f l i g h t b a s e li n e d a t a and t h e o t h e r i n - f l i g h t d a t a . The mean sightingmeasurement e r r o r , mean com pri ses many components as i n d i c a t e d i n e q u a ti o ns(1) t o ( 4 ) . The magni tudes o f the se e r ro r components f o r t h i s s e t o f d a t awere c a r e f u l l y s c r u t i n i z e d i n a n e f f o r t t o e x p l ai n t h e i n c on s is t en c y. A l lt he e r r o r components seemed rea son abl e excep t t h e mean z ero bi a s measuremente r r o r (0z)mean ( t ab le 1 11) , which had both a large mean value and a l a r g es t anda rd dev ia t i on . T h i s l a rge s t anda rd dev ia t i on ind ica t e s tha t t h e meanze ro b ia s measurement e r r o r (0z)mean i s no t w e l l known and th e s i gn if ic an ceof t he la rge mean s i gh t i ng measurement er ro r , E m e m , may th er ef or e be opent o q u es t io n .

    The mean s ig ht in g er r or s prese nte d her e a re corr ect ed f o r window-inducedmeasurement e r ro r s , f o r e r r o r s due t o the d i f f e r e nce of t h e index o f ref ract i o n o f t h e l i g h t - t r a n s m i t t i n g media w i th i n and o u t s i d e t h e s p a c e c r a f t , f o rmeasured zero b i as , and f o r ins t rument c a l ib ra t i on .

    Subjective CommentsThe p i l o t s t a t e d t h a t , i n g e ne r a l , t h e o p e r a t i o n o f t h e TO02 s e x t a n t i nzero g w a s much simpler and eas i e r t o manage than had been an t i c i pa te d fromh i s p r e f l i g h t t r a i n i n g and s i m u l a ti o n . During t r a i n i n g , t h e p i l o t i n d i c a t e dt h a t t h e we ig ht o f t h e s e x t a n t c a us ed f a t i g u e , b u t t h i s was a l l ev i a te d i n t h eweigh t less env i ronment o f ac tua l space f l i g h t . H e a l s o s t a t e d t h a t a c qu i si t i o n o f t h e s t a r p a t t e r n s f o r t h e e xp er im en t was m a rg i na l w i th t h e r e s t r i c t e df i e l d of view of t h e window. A la rg er window i n th e s pace cra f t and eas i e raccess t o it would probab ly s imp l i fy acq u i s i t i o n o f t he s t a r p a t t e r n s .

    Star /Star Star / Lunar I m bComparison of Baseline

    Standard and F l igh t Dataerrory,,devatonInf ight The p i lo t ' s per formance as i n d i c a t e d by t h e b a s e l i n e d a t a was v i r t u a l l y t h e same as t h a t i n th e

    +5rcr5* Baseline I space- f l igh t env i ronment as s e e n i nf i g u r e 11, t h u s i n d i c a t i n g t h e u s e f ul -ness o f s imula tors and ear th -basedo b s e r v a t o r i e s i n e v a l u a t i n g s pa cena vi gat io n measurement t ech niq ues .

    I 10 0 Figure 11 shows that navigat ion typeMeasurement error, arcsec Measurement error, arcsec measurements (star/luna? limb) were

    made with a s t anda rd dev ia t ion o f +6Figure 11.- Compar i s on o f in - f l igh t and bas e l ine a r c sec i n t h e s i m ul a to r . I n - f l i g h td a t a , TO02 exper iment ; helmet of f . d a t a t o s u p p o rt t h i s p er fo rm an ce awaitf u tu r e f l i g h t s .

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    Space Navigation Using a Hand-Held SextantFor th e Apollo lunar miss ion th e p r imary sp ace cr a f t nav iga t ion sys tem

    w i l l u t i l i z e ea r th -based r ada r t r a ck i ng measu remen ts . A s im p l i f i ed on-boardbackup system i s s t i l l de s i r ab l e , however , i n which t he hand-he ld se x ta n tcou ld b e a key elem ent . The minimum fu nc ti on s of backup syste m hardware a re :(1) t o make an gul ar nav ig at io n measurements; ( 2 ) t o p r o vi d e a r e f e r en c e f o rh o l d i n g s p a c e c r a f t a t t i t u d e d u r i n g a v e l o c i t y c o r r e c t i o n ; and (3) p o s s i b l y t oprov ide a r e f e ren ce f o r a l in i ng an in e r t i a l measurement un i t t o measure theAV app l i ed . The sextant obviously i s designed t o measure a ngles wi th goodaccuracy. The sex ta nt with a l i g h t e d r e t i c l e cou ld a l s o pe rform func t ions2 and 3 i f i t were mounted on a b r a c k e t a t th e sp ac ec ra f t window and bore-s ig h ted w i th the spacec ra f t axes . Such a mount i n t h e Gemini X I 1 s p a c e c r a f tappeared t o pe rfo rm sa t i s f ac to r i ly du r ing rendezvous.

    P re l imina ry s tud ie s a t Ames have i nd ic at ed t h a t with on ly a simpleco l l ima ted r e t i c l e on the spa cec r a f t window it i s p o s s i b l e t o ho l d t h es p a c e c r a f t a t t i t u d e ma nu all y w it h s u f f i c i e n t a cc ur ac y t o p e rf or m a v e l o c i t yco rre ct io n. The se xt an t with 8-power mag nif ica t ion should improve t h i sper formance . A l in ing an in e r t i a l measurement un i t by th i s techn ique has no tbeen s tud ied .

    Resu l t s o f bo th the D - 9 autonomous o r b i t nav iga t ion i n - f l ig h t exper iment( r e f . 5) on Gemini V I 1 and th e NASA rendezvous n av ig at io n ex per im ent onGemini V I ( r e f . 6) i n d i c a t e t h a t t h e ha nd -h el d s e x t a n t i s s u i t a b l e f o rn a vi g at i on i n t h e s e f l i g h t p ha s es .This exper iment has shown th a t sa t i s f ac to ry na v iga t i on measurements f o rsevera l phases of sp ace - f l ig h t (e .g . , midcourse , rendezvous , ea r t h o r b i t ) canbe made using a hand -he ld s ex tan t . Therefore , it appea r s t ha t t he hand-he ldse xt an t co uld be used t o implement an autonomous on-board n avi ga ti on s ystem.I t i s r ec o gn iz ed t h a t t h e s e x t a n t s u s ed i n t h e s e t e s t s a r e e x p er i me nt a lins tru men ts manufactured t o prove th e desi gn concept. Design changes may benecessary t o p rov ide an ins t rument compat ible wi th t he oper a t i ona l sys temrequi rements .

    CONCLUSIONS

    From an in spec t ion o f t he r e su l t s o f t he in - f l i gh t spac ec ra f t experiments presented, it may be concluded t h a t :1 . The ang le between s t a r s can be measured wit h a hand -he ld s ex tan t .The t o t a l measurement e r r o r (as tro na ut + s e x t a n t + sp ac ec ra ft window) h ad as t anda rd dev ia t io n of l e s s than 510 a r c sec and an average mean si g h ti n gmeasurement e r r o r of onl y 2 a r c s e c .

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    2. Sexta nt measurements of th e ang le between s ta rs w i th th e he lme t on,visor down, in d ic a t e th a t t he s t anda rd dev ia t ion o f s ig h t i ng measuremente r r o r s was less than k10 arc sec .3. The TO02 in - f l i gh t da t a and the p re f l ig h t b a se l ine da ta ob ta ined i nth e s imul a tor and from ground obse rva tor i es were a lmos t id en t i ca l . I t

    appea r s tha t a t l eas t f o r t h e c o n d i t i o n s o f t h i s e xp er i me nt , s i m u l a t o r s andground observ a tor ie s can be us efu l i n ev a lua t in g space nav iga t ion measurementtechniques .4 . In - f l i gh t expe r ience ha s demons t r at ed th e po te n t i a l o f t he hand -he ldsex t an t f o r u se i n midcou rse nav iga t ion (NASA TO02 exp er im en t) , o r b i t na vi ga t i o n (A ir Force D-9 ex per ime nt) , and rendezvous na vi ga ti on (NASA rendezvousexperiment on Gemini VI).

    Ames Research CenterNation al Aeronautics and Space Admi nis tra t ionMoffe t t F ie ld , C a l i f . , 94035, Aug. 20, 1968125-17-02- 10-00-21

    REFERENCES

    1. McLean, John D . ; Schmidt , Stanley F . ; and McGee, Leonard A . : OptimalF i l t e r in g and L inea r P red ic t ion A ppl ied t o a Midcourse NavigationSystem f o r th e Circumlunar Mi ssi on. NASA TN D-1208, 1962.2 . Chris tensen , Jay V . ; and Kipping, E . David: Midcourse Nav iga tio n UsingS t a t i s t i c a l F i l t e r Theory, A Manual Theodolite, and Symbolic Computer

    Contro l . NASA TN D-3875, 1967.3 . White, John S . ; Cal las , George P . ; and Cico la n i , Lu ig i S . : Appl ica t ionof S t a t i s t i c a l F i l t e r Theory t o t h e I n t e r p l a n e t a r y N a v ig at io n andGuidance Problem. NASA TN D-2697, 1965.4 . Cicolan i , Lu ig i S . : In te rp la ne ta ry Midcourse Guidance Using RadarTra cki ng and On-Board O bse rva tio n Data. NASA TN D-3623, 1966.5. Si lva , Rober t M . , Captai n , USAF; J o r r i s , Terry R . , Capta in , USAF; andVal le r ie , Eugene M . , 111, Captain , USAF: The A i r Force Space Navigat i o n Experim ent on Gemini (DOD/NASA Gemini Experim ent D-9, Gemini I V

    and V I 1 F l i g h t s ) . Tec hni cal Report AFAL-TR-66-289, Se pt 1966.6 . Murtagh, T . B . ; P r i c e , C . R . ; and Smith, H . E . : Analysis of Gemini7 -Sta r S igh t ings U t i l i z ing a Space Sex tan t i n Gemini 6 . J . S pacec ra f tand Rockets, vol. 4 , no. 5, 1967.

    20

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    7 . Lampkin, Bedford A . ; and Randle, Rober t J . : I n v e s t i g a t i o n o f a ManualS e x t a n t - S i g h t in g T ask i n t h e A m e s Midcourse Navigat ion and GuidanceSi m ul a to r. NASA TN D-2844, 1965.

    8. Lampkin, Bedford A . : Sex t an t S igh t in g Performance f o r Space Nav iga t ionUsing Simulated and Real C e l e s t i a l T a r g e t s . N a v i g a t i o n : J . I n s t .Navigat ion , v ol . 12 , no . 4 , Winter 1965-66.

    9 . Lampkin, Bedford A . : Navigator Performance Using a Hand-Held S ex ta nt t oMeasure the Angle Between a Moving Flashing Light and a S i m u l a t e d S t a r .NASA TN D-4174, 1968.10. Acken, Richard A . ; and Smith, Donald W . : Navigat or Per formance S t ud ie sf o r Spac e Na vi ga ti on Us ing t h e NASA CV-990 Rese arch A i r c r a f t . NASA TND-4449, 1968.11. Lampkin, Bedford A . ; and Smith, Donald W . : A Hand-Held Sex tan t Qu al i f ie dfor Spac e F l i g h t . NASA TN D-4585, 1968.1 2 . Anon.: "Environmental Q u al if ic at io n and Acceptance Te st Report ,"Hand-Held Space Sex ta nt , GFAE NO. EG25100. Kollsman In st ru me ntCorporation. CR-73073.13. Walsh, Thomas M . ; Warner, David N . ; and Davis, Michael B . : The Effectsof a Gemini Left-Hand Window on Exp eri men ts R eq ui ri ng Accuracy i nS i g h t i n g o r R e s ol u ti o n . NASA TN D-3669, 1966.

    2 1

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    N N TABLE 1 . - SPACECRAFT O R B I T A L POSITION O rb i t 40; November 14, 1966 O rb i t 48 ; November 15, 1966

    ~~ ~

    A 1t i t u d e A 1t itudeGreenwich Lati tude, Longitude, above an Greenwich above anmean time, ob la te mean tim e, Lat i ude , Longitude, o b l a t ehr:min:sec deg deg e a r t h , hr:min:sec deg deli e a r t h ,n m i n m i12:Ol: 16 2.12N 101. OOE 140.81 0 0 :03 :30 4.83s 71.22W 140.51 I1 2 :03: 25 2.03s 108 OOE 140.59 00 :05 :30 8. 65 s 64.58W 140.6112 : 05:14 5.58s 114.00E 140.63 0 0 : 07:30 12.33s 57.80W 140.9212: 07: 20 9.57s 121.OOE 140.91 00 :0 9 :30 15.81s 50.83W 141.431 2 :09 :23 13.30s 128.OOE 141.42 00:11:30 19.02s 43.60W 142.1012:11:23 16.68s 135 .OOE 142.12 0 0 :13 :30 21.90s 36,lOW 142.9212: 13:18 19.70s 142.00E 142.93 00: 15 :30 24.38s 28.29W 1 143.841 2 :15 09 22.30s 149 OO E 143.84 00 :17 :30 26.38s 20 I19W 144.83 i1 2 : 17 : 11 24.73s 157 O O E 144.92 0 0 : 19 :30 27. 85s 11.84W 145.8512:19:09 26.63s 165.O O E 146.03 00:21:30 28.73s 03.29W 146.8712: 2 1 : 18 28.08s 174 O O E 147.26 0 0 :23:30 29.02s 05,34E 147.8712:23 :10 28.82s 178.OOW 148.31 00: 25 :30 28.68s 13.97E 148.8212:25:15 28.98s 169 .OOW 149.44 0 0 :27:30 27.73s 22.48E 149.701 2 : 27: 2 1 28.48s 160. OOW 150.51 00: 29 :30 26.21 s 30.78E 150.5212:29:14 27.47s 152 OOW 151.39 00 :31: 30 24.12s 38.83s 151.2512: 31: 10 25.92s 144.00W 152.01 00 :33:30 21.67s 46.57E 151.9112 :33: 11 23.85s 136.OOW 152.98 0 0 :35 :30 18.78s 54.01E 152 .50

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    above

    TABLE 1 . - SPACECRAFT ORBI TAL POSITION - ContinuedOrbi t 54; November 15, 1966 Orbi t 55; November 15, 1966

    L

    A 1t itude A1t i t udeG reenwichmean t ime , Lat i tude , Longi t ude, above an Greenwich L at it ud e, Longitude, oblateanob la te mean time,h r :min :sec

    10:31:30 10: 33: 30 10:35: 30 10:37: 30 10:39: 3010: 41: 3010: 43:3010:45:3010: 47:3010:49:3010: 51: 3010:53: 3010 : 55: 3010:57:3010: 59:3011: 01:3011: 03: 3011: 05: 30

    Nw 11:07:30

    deg deg ea rt h,n m i hr:min:sec deg d eg e a r t h ,n m i

    3. 32s 125.28E 140.68 12: 01: 30 3.67s 102. 89E 140.487. 17s 131.88E 140. 60 12:03: 30 7. 51s 109.50E 140.33

    10. 91s 138.60E 140. 73 12: OS:30 11. 24s 116.23E 140.4014. 47s 145.48E 141.06 12:07:30 14. 79s 123.14E 140- 6717. 80s 152.61E 141.58 12:09:30 18. 09s 130.29E 141.1220. 82s 160. O1E 142.25 12: 11:30 21. 08s 137.71E 141.7423. 46s 167.70E 143. 03 12:13: 30 23. 68s 145.43E 142.4625. 65s 175.68E 143.90 12: 15: 30 25. 83s 153.45E 143.2927. 33s 176.05W 144.84 12:17:30 27. 47s 161.74E 144.1928. 46s 167. 70W 145. 79 12: 19: 30 28. 54s 170.24E 145. l l28. 98s 158. 95W 146. 74 12: 21: 30 29. 01s 178.87E 146.0328. 88s 150. 31W 147.65 12: 2 3 : 30 28.85s 172.48W 146. 9428. 17s 141.73W 148.52 12:25 :30 28. 08s 163.92W 147.8126. 87s 133 33W 149. 33 12 : 27:30 26. 72s 155.53W 148. 6325. 02s 125. 18W 150. 08 12: 29: 30 24. 83s 147.40W 149.4022.70s 117. 32~ 150. 77 12 :31:30 22.45s 139.56W 150.1319. 95s 109.761V 151. 41 1 2 :3 3 :30 19. 67s 132. 02W 150. 8016. 85s 102.481.V 151. 98 12:35:30 16. 53s 124. 78W 151. 4313. 46s 95. 48W 152. 52

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    13 P TABLE I . - SPACECRAFT ORBITAL POSI TI ON - Concl uded

    Orbi t 56; November 15, 1966Greenwchmean t i me,hr : m n:sec13: 31:30 13:33: 3013: 35:3013: 37: 30 '13:39:3013: 41:3013: 43:3013: 45:3013:47:3013:49:3013: 51: 3013: 53: 3013:55:3013:57: 30 13:59:3014: O : 3014:03: 30 14: 05 :30

    Lat i tude, deg

    4. 02s 7. 86s

    11. 58s 15. 61s 18. 38s 21. 34s 23. 91s 26. 01s 27. 598 28. 61s 29. 01s 28. 80s 27. 97s 26. 57s 24. 62s 22. 21s 19. 39s 16. 22s

    Longi tude, deg

    80. 51E 87. 12E 93. 87E

    100.81E 107.98E 115.42E 123.17E 131. 22E 139.53E 148.05E 156.68E 165.32E 173.88E 177.76W169.65W161.84W154.33W147.12W

    A1ti tude above an obl at e earth, n m 140.46 140.31 140.39 140.66 141.12 141.73 142.43 143.28 144.17 145.24 146.14 147.01 147.85 148.64 149.38 150.07 150.71 151.32

    14: 07:30 12. 79s 140. 15W 151. 89

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    --

    TABLE 11.- IN-FLIGHT

    Orbit 40S i g h ti n g t a r g e t s :

    Pr imary LOS - Betelgeuse Scanning LOS - Rigel Zero bias measurement - Aldebaran

    b i a s 3 63:21:33.5 99.9994 63:22:09.0 0 0 . 0 0 05 63:22:53.5 , 0 0 . 0 0 1

    SEXTANT SIGHTING DATA, TO02 EXPERIMENT, GEM IN I XI1

    Orbit 48Sigh t ing t a rge t s :

    Primary LOS - Betelgeuse Scanning LOS - Rigel Zero bias measurement - Aldebaran

    I I i b i a s , 3 75:21:45,0 99,995I , 5 75:23:29.0 00.003 I6 75:28:44.0 18.604 76.918.605 I

    II18.60818.605

    I 4 75:22:35.0 0 0 . 0 0 5

    18.60918.60418.60818.60618,60618.60516 75:39:00.0 18.60417 75:39:33.5 18,60518 75:40:29.0 18.60619 75 :41:11 . O 18.604

    2 0

    6 63: 28 :2 2 . O7 63:30:31.58 63 :31 :38.5

    63: 32 :53 O63:34:27.063: 3 5: 26 . O63:37:13.5sta rs 13 63:38:46.0

    18.61118.60618.60418.60818.60418.60418,609, 18.606

    63: 39 :36.5 Void63:40:21.0 18.60863 :41: 15 . O 18.61163:42:07.0 18.60518 63:43:53.0 18.60563:44:51.0 ' 18.60520

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    --

    TABLE 11.- IN-FLIGHT SEXTANT SIGHTING DATA, TO02 EXPERIMENT, GEMINI XI1 - Continued

    I rb i t 54; i g h t i n g t a r g e t s :

    Primary LOS - BetelgeuseScanning LOS - B e l l a t r i xZero bias measurement - Aldebaran

    hit conf igurat ion: Helmet o f f

    Orbit 55S i g h ti n g t a r g e t s :

    Primary LOS - BetelgeuseScanning LOS - B e l l a t r i xZero bias measurement - Aldebaran

    Sui t conf igur at io n: Helmet o f f

    Measure-ment-

    Geminie1apsedtimehr :min: sec

    S ex tan treadoutang le ,

    deg

    Cabintemp. ,

    O F

    Cabinp r e s -s u r e ,p s i

    1 87:19:23.5 00.005 70.6 5.26Zero 2 87 : 20: 24 .O 00,002b i a s 3 87: 20: 53.5 00.0004 87: 2 2 : 28 . O 99.9955 87:23:15.5 00.0036 87 :25 :49 .5 07,5297 87:27:16.3 07.531-

    8 87: 28: 29.5 07.5329 87: 29 :28 .O 07,52910 87 :30 :13.5 07.52911 87:31:35.0 07,530

    GeminielansedI t imehr :min:sec1 85:50:06.5!ero 2 85: 51 :06 . Oi i a s 3 85 :51:49.54 85:52:31.05 85:53:15.56 86:02:05.57 86:03:51.08 86:04:56.09 86:05:57.510 86: 06: 56 . O

    11 86:07:51.5Two 1 2 86:08:53.0s tars 1 3 86:09:31.014 86:11:02.015 86:13:23.586: 14:35 . O

    86:15:56.086:17:03.086:17:50.086:18:53.5

    S ex tan t Cabin Cabi nreadout temp. , p res -ang le , OF s u r e ,de g p s i00.002 71.3 5.29 0 0 . 0 0 1 0 0 . 0 0 0 00.002 00.005 07.536 07.531 07.529 07.530 07.529 07.528 07.528 rwo 1 2 87:32: 24 . O 07.52907.528 s t a r s 13 87: 33: 14 O 07.52907.531 14 87 :33:45 . O 07.52807.529 15 87: 35 :02 . O 07.52907.528 16 87: 35 :50.5 07.53007.529 17 87: 36 :30 . O 07.52907.528 18 87 :37: 27 . O 07.52907.531 19 87:38:06 . O 07.53207.531 20 87 :38 :54 .0 07.529

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    12345--7891011121314151617181920

    TABLE 11. - I N-FLI GHT SEXTANT SI GHTI NG DATA, TO02 EXPERI MENT, GEM NI XI 1 - Concl udedOr bi t 56 Si ghti ng targets:

    Pri mary LOS - Betel geuse Scanni ng LOS - Ri gel Zero bi as measurement - Al debaran Sui t conf i gurat i on: Hel met on. Vi sor down Measure ment

    Zero bi as

    Two stars

    Gem ni el apsed t i me hr : mn:sec

    88: 48: 53. 0 88: 49: 30. 0 88: 50: 29. 1 88: Sl : l S. S 88: 51: 59. 5 88: 58: 03. 0 88: 58: 28. 5 88:Sg:O . O 88: 59: 32. 0 89: OO l O O 89: 00: 48. 3 89:01:33. 0 89: 02: 19. 0 89: 03: 10. 5 89: 04: 05. 1 89:04:57. 1 89: 05: 27. 0 89: 06: 09. 0 89: 06: 43. 0 89:07:44. 5

    Sextant readout angl e,deg

    00. 003 00. 009 00. 007 99. 995 00. 003 18. 605 18. 605 18. 604 18. 607 18. 607 18. 607 18. 608 18. 610 18. 607 18. 611 18. 610 18. 610 18. 607 18. 609 18. 609

    Cabi nCabi n prest emp. , sure,"F p s i70. 0 5. 26

    70. 6

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    b i a s +13.7

    Nco

    I I Ii Zero40 1 bias iZerob i a s48 Two s t a r

    i 1 5 5 i b i a s3 I Twoi s t a rN ! i Zero I? 56 INa N '1 TwoVI s tar

    TABLE 111.- SUMMARY OF SIGHTING MEASUREMENT DATASextant CorrectedMean value ands tandard dev ia t ion Window induced c a l i b r a t i o n meanof measurement measurement error, measurementr e r r o re r r o ra rc s e c

    Mean Standard deviat ion Mean

    Standard deviat ion Mean

    Standard deviat ion Mean Standard deviat ion Mean S tandard dev ia t io n Mean

    S tandard dev ia t io n Standard deviat ion

    Mean Standard deviat ion Standard anedev ia t ion

    MeanS tandard dev ia t io n

    e r r o r , Lc' E W a rc sec mean 'I I [ arc sec I+ 2 . 2 -1.6 02 4 . 1+5.8 +o . 4 -4 -2.429.0 j-5 . o218.0 i -7.6 0 1+1. 4+5. 4 j -4.8 - 4 -0.4+6.8 -9.7 0k6.8-1.1 -9.5 I +4 I -4.5k7.6t13.7 I-1.8 -9.5 +4 -1.6k4.5

    k19.3rr'9. 7 i -10.8+ 7 , 5 I

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    A N D S P A C E ADMINISTRATION POSTAGE AND FEES PAIDERONAUTICSD. C. 20546 NATIONAL AERONAUTICS WASHINGTON, SPACE ADMINISTRATIONFIRST CLASS MAILFFICIAL BUSINESS

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