Apollo Experience Report Evolution of the Attitude Time Line

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1. Report No.

NASA TN D- 7086

7. Author(s)

Rocky D. Duncan, MsC

2. Government Accession No.

9. Performing Organization Name and Address

Manned Spacecraf t CenterHouston , Texas 77058

17. Key Words (Suggested by Author(s))

T i m e L i ne* Fl ight P lanCoordina te Sys temAtt i tude Time Line

12. Sponsoring Agency Name and Address

National Aeronau t ics an d Space Adm inist rat ionWashington, D. . 20546

15. Supplementary Notes

18. Distribution Statement

3. Recipient's Catalog No.

19 . Security Classif. (of this report) 20. Security Classif. (of this page) 21. No. of Pages

None None 8

~ ~~

5. Rewrt Date

22. Price

$3.00

M a r c h 19736. Performing Organization Code

8. Performing Organization Report No.

M s c s-353

10. Work Unit No.

924-22-20-00-72

11. Contract or Grant No.

13. Type of Report and Period Covered

Technical Note14 . Sponsoring Agency Code

The MSC D ire cto r waived the us e of the Internat ional System of Uni ts (SI) fo r thi s Apollo Exp eri -ence Repor t , because , i n h i s judgment, us e of SI uni t s would impai r t he usefu lness of the re po r to r r e su l t i n exces si ve cos t .

16. Abstract

The evolution of the a t t i tude t im e l ine is d i scus sed . E m phas i s is placed on the operat ional needfo r and con s t r a i n t s on the t ime l ine and on how these fac tors w ere involved in the t im e l ine generat ion pro ced ure . Examples of c ons t ra in t s on and appl ica t ions of t he com pl et e t i m e l ine a r e g i ven.



APOLLO EXPERIENCE REPORT

EVOLUTION OF THE ATT ITUDE T IM E L IN EB y R o ck y D . D u n c a n

M an ne d Spacecra ft Cente r

S U M M A R Y

The a t t i tude t im e l ine is a comp le te t ime his tory of the sp ace craf t or ienta t ionwith r e sp ec t t o a r e f e r enc e coord ina te sys t em . The need fo r a com ple te a tt i tude t im el ine tha t sa t i s f ies miss ion req ui re me nts within opera t iona l and equipment const ra ints

is expla ined. The proce dure tha t was used to gene ra te the de ta i led a t t i tude t im e l ineis di scu ssed , and pa r t i cu la r a t ten t ion is given to m iss ion-or i en ted p rob lem s and toproblem -solving methods . The di f fe rent needs for the t im e l ines of ear th -orbi ta l andluna r -orb i t a l m i ss ions are c i ted. A s y s t e m of pointing-con straint envelopment analy-sis that is s u p e r i o r t o t he X-, -, -body coordinate system is p r e s e n t e d . The t i m el ine gem ra t in n e f fo r t is explained with r e f e r ence to mission p h i x i f i g i n geileral and toi n t e r f ace r eq u i r em ent s w i th va r ious work ing g roups in pa r t i cu la r .

INTRODUCTION

A deta iled a t t i tude t im e l ine is now a requ i red pa r t of the f l ight p lan fo r a lunarmiss ion. The onboard f light p lan conta ins loca l-hor izonta l a t t i tudes and iner t ia l meas-u r e m e n t u n i t g i m b a l a n g l e s f o r e v e r y p h a s e of the mis s ion ac tivi ty f r om l if t-of f tolanding. Included in the f l ight plan are i l lustrat ion s of c r i t ic al a t t itude-dependent ac-t i v i t i e s ( such as l andm ark t r ack ing p rocedures , photography pro ced ures , and com m andand se rv ic e module (CSM) and lunar module (LM) high-ga in antenna (HGA) pointing re -q u i r e m e n t s ) a n d o t h er aids t h at s e r v e as r e f e r enc e fo r the c r ewm en dur ing eve ry phaseof the m i s s i o n .

The CSM and LM c rew proc edure s m a n u a l s are m ore de ta i led than the f l ight plan .Th e CSM an d LM d ocum ents contain a descr ipt ion of each s tep in the pro ced ura l tech-niques that have been defined fo r ev ery phase of the miss ion. Spec if ic a t t i tude req ui re -

m e n t s are i n t r i n s i c i n m o s t of these proc edu res . Although som e a t t i tudes can becomp uted on bo ard , many of the at t i tudes cannot. Also, the onboa rd so lu t ions are nota lways us ed b ecause the se a t t i tude computat ions are u s e d t o s o l v e f o r a spec i f ic case.(In mo st a t ti tude-pointing pro ble m s, usua l ly there are many solut ions that wil l sat isfythe a t t i tude const ra ints . ) The onb oard solut ions al so do not include con siderat ion of at o t a l a t t i t ude and m aneuve r sequence . Fo r th is r ea son , the proc edure s docum ent s con-ta in many a t t i tude s computed pref light tha t a r e opt imized for com mun ica t ions , mini -m um m aneuve r r equ i r em ent s , and v i sua l cues.



The a t t itude t ime l ine is used in com m unica t ions , t he rm a l , and nav iga t iona l ana l -y s e s . T h e t i m e l in e a l s o has b e en u s e d f o r t r a je c t o r y d i s p e r si o n a n a l y s e s , s u c h as th emodel ing of venting e f fec ts , was te dum ps, and the di rec t io n an d magni tude of t ran s la -t iona l veloci ty inc r em ent s tha t r e su l t f r o m uncoupled a t ti t ude m aneuve r s ( a t ti t ude m a-neuvers us ing unbalanced thrus t in g) . The f ina l a t t i tude t ime l ine the refo re m ust be theres ul t of much d e ta i led planning to minimize m aneu vers and to me et all t r ack ing , t he r -m a l , and com m unica tions r equ i r em e nt s and to m ee t any o the r spacec r a f t - a t t i tude r e -

qu i r em en t s dur ing all phases of the miss ion.

REQUIREME NT FOR A C O MP LE TE A T T I T U D E T I M E L I N E

A deta i led a t t i tude t im e l ine did not ex i s t f o r M ercury , Gem in i, or e a r l y e a r t h -orbi ta l Apol lo m iss io ns . The first lunar -orbi ta l miss ion (Apol lo 8) was the first m i s -s ion fo r which a n a t t em pt wa s m ade to p roduce a de ta i led a t t it ude t im e l ine . Som ephases o f the ea r ly m iss ions did have pref l ight p lanned a t t i tudes , but th is pref l ight a t t i -tude planning was l im i ted to spec i f ic ex per im ents o r t r ack ing ex e rc i se s . The l im i teda t t it ude p lann ing was poss ib l e f o r se ve ra l r ea s on s . For an ea r th -orb i t a l m i ss ion , no

m a jor a t ti tude p rob lem s o ccu r r ed tha t i nvo lved com m un ica tions because h igh -b i t - r a tete le me try and good voice com munica t ions could be obtained by th e u s e of the CSM andLM om nid i r ect iona l an tennas . Howeve r , f o r l una r d i s tances , high-bi t - ra te communi-ca t ions nec ess i ta te the us e of the CSM high-ga in antenna or the L M s t ee r ab le an tenna(SA) . Many opera t io ns requ i re the u se of a t t i tu des tha t conf l ict with pointing thes ean tennas a t t he ea r th ; t he r e fo r e , t he f li gh t c r ew and ground con t ro l l e r s m u s t know theexac t spacec r a f t a t t it ude p rof i l e f o r each t r ack ing pe r iod s o tha t the high-bi t - ra te com-m unicat ions r equ i r em e nt s can be scheduled . In e a r t h o r b i t , no major t h e r m a l p ro b -l e m s o c c u r r e d . For a l u n a r m i s si o n , a l m o s t all of the t r ans luna r and t r an sea r th coa s tp h a s e s are in d i r ec t sun l igh t . To m ain ta in even hea t ing f ro m s o l a r r ad ia t ion , an a t t i -t ude and tu rn ing r a t e tha t a l lows pass iv e the r m a l con t ro l m us t be es t ab l i shed . Also,spec i f ic a t t itude guid e l ines are e s ta b l is h e d f o r t h e r m a l c o n s t r a i n t s d u r in g c r e w m e m b e r

r e s t pe r iods in luna r o rb i t .

In lunar orbit, t he t im e l ine is m o r e t i m e c r i t i c a l a n d e v e n t c r i t i c a l t ha n d u r in go the r m iss ion phases. If a pa r t i cu la r sec t ion of the c r ew ac t iv i ty tim e l ine we re no tcomp le ted on a pas s dur ing ea r th o rb i t and the f li gh t p l an had to be de layed one revolu-t ion, the con sequen ces would not be as s e v e r e as f o r t he s am e s itua t ion dur ing luna rorbit . Although the ea r th -o rb i t a l m i ss ions we re invo lved and de ta il ed , no requ i r em en tex i s t ed t o m a in ta in a cont inuous d e ta i led a t t i tude and pointing t im e l ine fo r all m i s s i o npha ses . The luna r -l and ing m iss ion p lann ing is based on m any t im e-c r i t i c a l cons ide r a -t ions , such as Manned Space Flight Network comm unica t ions coverag e , exp er ime nt ac -t iv i t i e s , c r ew r e s t /work cyc le s , spacec r a f t housekeep ing r equ i r em e nt s , and l igh t ingcondi t ions a t the lunar landing s i te . An example of a t im e-c r i t i c a l and even t - c r i t i c a lt im e l ine is as fol lows.

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F o r the Apollo 11miss ion, the lunar -orbi t t ime l ine on the day of d escen t wa s ther e s u l t of months of con cent ra ted e f for t . The e ffor t involved a lm os t every m ajo r groupa t t he Manned Spacec ra f t Cen te r (MSC). T h e b a s ic p r o b l e m s w e r e t o a c c om p l i sh the

following ob jec t ives .

1. To ac t iva te and check ou t the LM

2. To pe r fo rm l andm ark t r ack ing fo 'r de scen t t a rge t ing

3 . To undock , pe r fo rm descen t -o rb i t i nse r t ion , t hen pe r fo rm po wered-descen tini t ia t ion one-half rev olution la te r

4 . To p e r f o r m all these ac t iv i t i e s with in a t i m e f r a m e that would pe rm i t ex t r a -vehicular a c t ivi ty a f t e r landing

In i ti a l ly , t he se p rob lem s d id not s ee m to be par t icular ly di f f icul t , but c loser ex-aminat ion resul te d in unexpec ted prob lem s. Most of the LM checkout per io d requ i redcont inuous LM high-ga in SA cov erage , the landm ark t racking nec ess i ta ted th e u s e of

a t t i tude s an d man euvers tha t w ere incompat ible with SA point ing coverage , and a se-quent ia l schedul ing of th ese ac t ivi t ies re sul ted in an unacceptable c re w workday (m or ethan 20 ho ur s ) . The on ly so lu tion wa s to schedule sec t ion s of the LM checkout with ana t t i tude for good comm unica t ions and then accept a b r e a k i n high-ga in-antenna commu-nica t ions dur ing the se tup and execution of the landm ark t racking. Al l the se s te ps wer et im e c r i t i c a l because the l andm ark t r ack ing exe rc i se is a pre c i se op e ra tion tha t in -vo lves spec i f i c a t t it ude and p it ch r a t e s and the consequence of not complet ing th e LMcheckout or of not per form ing the t ra ckin g would be t o delay the l an d in g f o r o n e r e v o h -t io n o r m o r e . This si tuat io n would be undes i r ab le becau se the desc ent ta rg e t ing wouldhave t o b e updated and a n addi t iona l fue l co s t would be r equ i r ed . Dur ing th i s pe r iod ,many othe r ac t iv i t i e s ( such as undocking, L M inspec t ion rend ezvo us- rad ar checkout ,and burn m oni to r ing) r equ i r ed pa r t i cu la r a t t i tudes . A ll of t h e s e r e q u i r e m e n t s i m p l y

that, f o r h igh ly com plex m iss io ns , it is not des i r ab le f o r t he c r ewm en to de te rm ine theprope r a t t i t ude for comm unica t ions , undocking, o r othe r m an euve r s . The conf l ic t sshould be r e so lv ed p r e f ligh t , and the ine r t i a l m easurem ent un i t g im ba l ang le s and othera s s o c i a t e d data should be provided as a p ar t of th e onb oard data file.

BACKG ROUN D DEVELOPMENT- ONSTRAINTS

A ND B A S I C A N A L Y S IS

Many spec i f i c and sys t em s-c r i t i c a l cons t r a in t s we re e s t ab l i shed in the planningf o r a l una r m iss ion . Th ese con s t r a in t s app li ed to all p h a s e s of t he m iss ion ; t ha t is,

a t a n y t i m e d u r in g t h e m i s s i o n (a rest p e r io d , i n c i s l u n a r s p a c e , or i n luna r orbit),spec i f i c a t t i tude s are n e c e s s a r y t o m e e t t h e r m a l , c o m m u n i c at io n s , o r o t h e r r e q u i r e -m ent s . The de te rm ina t ion of the se a tt i tudes nece ss i t a t e s a com ple te a t ti t ude t im e l ine ,w h ic h, i n t u r n , r e q u i r e s a compi led se t of all t h e a t t it u d e r e q u i r e m e n t s for all p h a s e sOf t he m iss ion . The in i t i a l e f fo r t i n this compi la t ion w a s a thorough review of the CSMand LM O pera t iona l Data Book and the jo int MSC /Rlarshal l Space F l ight Cen ter Jo intRe fe r ence Cons t r a in t s docum ent . The cons t r a in t s w e re o f ten poor ly o r im prope r lyw o r de d a n d s o m e t i m e s w e r e o u t of da te . A l so , m any cons t r a in t s we re not p r e se n tedin a usab le m ann e r ; f o r exam ple , m any were de linea ted in t e rm s of X-, Y - , Z-body

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The col lec t ion and documenta tion of these co ns t ra in ts were not easy to accompl ish.Of ten , data w ere not ava i l ab le and con tac t s had to be made with th e prop er MSC groupto have the data gene ra t ed . Fo r exam ple , t he data books would conta in informat ion onth e fiel d of v iew of all f ive CSM windows, but these fields of view w er e base d only onda ta on v iews f ro m the couch. Data w ere needed fo r fields of view 12 inc he s f r o m thewindow, 6 i n c h e s f r o m the window, and so f o r t h . Another example w a s the extent towhich the LM blocks the CSM optic s when the vehic les are docked. T h e data bookblockage con tours we re only approximat ions of the re a l b lockage . Deta i led blockagecontour s were gene ra t ed because m any of the l andm ark t r ack ing p rof i l e s r e qu i r ed exac tdata to def ine when the l andm ark w a s in a n acceptable viewing region.

Of ten , o ld cons t r a in t s were i nva l id o r ove r ly conse rva t ive . Som e cons t r a in t s thathad or ig ina ted dur ing t e s t ing in ea r ly spacec r a f t deve lopm ent pha ses (Block I s p a c e c r a f t )had rem ain ed only because they had never been cha l lenged. An exam ple was th e CSMenvi ronm enta l con t ro l sys t em (ECS) r ad ia to r cons t r ain t f o r l una r o rb i t . The cons t r a in twas w orded as fol lows.

"The ECS rad ia to rs impo se res t r ic t io ns upon the or ienta t ion of th e CSM i n luna rorb i t . Fo r convenience of ex pre ss io n, the ef fec t ive sur fac e area of the r a d i a t o r s m aybe exp ress ed by ' chorda l p lanes ' def ined as two planes pa ra l le l to the X-axis of the

CSM, ach con ta ining the c i r cum fe ren t i a l ex t r em e t i e s of t he r e spec t iv e r ad ia to r s .T h e s e p la n e s m u s t be within 25" of t he loc al ve rtic al when the CSM is within 25" of thesub so la r po in t on the m oon . A devia t ion f ro m this con st ra int is a d m i s s i b l e f o r a m axi -m um of th r e e consecu t ive o rb i t s f o r a t o t a l of e ight t im e s pe r m iss ion . '*

Opera t iona l ly , this cons t r a in t w a s untenable. Comp l iance would have requi r edtha t one c r ewm an be awake at all t im es , and the a t t i tude s would have conf l ic ted wi tho the r ac t iv i t i e s dur ing the c r ew work pe r iocb , The conf l ic t tha t res ul te d frcrrr? th is con-s t r a i n t w a s d i s c u s s e d , a n d a r e q u e s t w a s m ade tha t t he spa cec r a f t con t r ac to r and MSC

r eexam ine this cons t r a in t f o r B lockII

spacec r a f t . The cons t r a in t w a s found to be notapp l i cab le f o r a Block I1 spacec r a f t and w a s deleted. Many con fl icts occ ur between op-e r a t i o n a l r e q u i r e m e n t s a n d data book co ns t r a in t s , and these p rob lem s had to be nego-t ia ted as t he m iss ion p rof i l e changed .

GENERATION OF THE ATTITUDE TI M E LIN E

Theore t i ca l ly , t he r e su l t of t he in i t i a l effort would be a com plete se t of at t i tud er e q u i r e m e n t s that would be the d e s ig n c r i t e r i a f o r a l una r m iss ion . A m iss ion des ignedwithin this f ram ew ork would involve min imal reac t ion cont ro l sy s tem us ag e by minimiz-

in g all a t t i tu d e s a n d m a n e u v e r s f o r a m iss ion w h i l e meet ing all t he rm a l , com m unica -t ions , naviga t iona l , and photographic requ i remen ts . However , in pr ac t ic e , num erousc o m p r o m i s e s are nece ssa ry to m ee t va r ious seconda ry ob jec t ives (such as te levis ionc o v e r a g e ) . F o r this rea so n, the development of an at t i tude t im e l ine is a n i t er a ti v ep r o c e s s , the re su l t of which is an opt imiza tion of all a t ti t udes fo r all phases of the mis-s ion without sac r i f ic in g s impl ic i ty of ope ra t ion, crew p r e f e r e n c e , o r m i s s i o n f l e x ib i l it y .

T he first a t t i tude document w a s prepa red fo r u se on the Apol lo 8 m i s s i o n . T h i se f fo r t wa s d if fi cul t f o r sev e ra l r ea son s . One p rob lem w a s t h a t a s im i l a r docum ent had

n e v e r b e e n p r e p a r e d b e f o re a n d t h e e f f o rt w a s not a p a r t of t he r equ i r e d m iss ion

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docum ent s o r i nc luded on any schedule . Anothe r f ac to r was tha t , i n the pa s t , m anygroups had been de te rm in ing a t t i t udes fo r t he i r own pa r t i cu la r segm ent of t he m iss ion .For ins tance , the L M pro ced ures docum ent con ta ined bas i c a t t i t udes fo r undocking anda few oth er ph ases . No a t tem pt had been made to produ ce a comple te a t t i tude documentfor use dur ing ea r th -o rb i t a l m i ss ion s because the a t ti t ude -gene ra tion t eam d id not ex i s t .The da ta p r io r i ty e f fo r t was a f ac to r con t ribu ting to the accep tance of one g roup as th eof fi c ia l source fo r a l l a t t it udes . Mee t ings w ere he ld to def ine the m iss ion t echn iquesf o r all phase s of the m iss ion and w ere su ppo r ted by all the ma jor planning gro up s . In

the d i scuss ion of t he luna r m iss ion t echn iques , i t becam e ev iden t tha t the com plexity ofthe a t t i tu de planning ef for t ( for all t h e r e a s o n s m e n ti o ne d p re v i o u sl y ) w a s a n o r d e r o fm agnitude g r ea te r t han fo r ea r th -orb i t a l m i s s ion s . The m os t com ple te list of all re-

q u i r e m e n t s was compiled by a gro up of en gin eer s who had been planning this type ofe f fo r t f o r som e t im e , had an t i c ipa ted the need , had co l lec t ed the r equ i r e m e nt s , andthrough com pute r p rogram deve lopm ents had des igned the too l s needed to pe r fo rm the

r e q u i r e d a n a l y s e s . T h e r e f o r e , t h e e n t i r e t a s k w a s g i ve n t o t h i s gr o u p , w ho a l s o h adq u ic k a n d c o m p l et e a c c e s s t o t h e t r a j e c t o r y d a t a .

The development of a n a t t i tude t im e l ine fo r a l u n a r m i s s i o n r e q u i r e s a c l o s e i n -t e r f ace w i th many group s , i ncluding the c r ewm en, f li gh t p l an ne r s , f l igh t p ro ced urespe r son ne l , and f li gh t con t ro l pe r son ne l . These peop le def ine the gene ra l r equ i r em ent s( such as photography and l andm ark t r ack ing) f o r a m i s s i o n i n the f o rm of a f l ight p lan .T h e s e m i s si o n r e q u i r e m e n t s are then integra te d into a de ta i led a t ti t ude t im e l ine fo rt h e m i s s i o n . C o n s i d e ra b l e in t e r a c ti o n i n t h i s p r o c e s s o c c u r s b e c a u s e t h e e v e n ts s c h e d -uled in the fl ight p lan of ten a r e a t t i tude dependent . Th ere for e , deve lopment of the a t t i -tude t im e l ine for each m iss ion is a n e v o lu t io n a ry p r o c e s s t h a t h a s i np u t f r o ms im ula t ion s , f r om pr io r i ty des igna tions (when conf l i c ts a r i s e ) , and even f ro m c r ew-m e m b e r p r e f e r en c e s .

The g roups who deve lop , us e , and ve r i f y the a t t i t udes m u s t ana lyze the t im e l ineto de te rm ine whe the r the a t ti t udes sa t i s fy co ns t r a in t s t ha t are a s s o c i a t e d w ith p a r t i c u l a rs y s t e m s . T he r e s u l t is an o pe ra t iona l at t it ude t im e l ine tha t is di s t r ibu ted wide ly to

rea l - t im e suppor t pers on nel , tha t can be used wi th conf idence tha t no a t t itude-dependentprob lem s wi ll be encounte r ed , and tha t t r ack ing r eq u i r em ent s w i l l be accep tab le f o r allp h a s e s of t he m iss ion .

C O N C L U D I N G REMARKS

The a tt it ude t im e l ine gene ra tion fo r luna r m is s ion s becam e a r ecognized r equ i r ede f fo r t . Th i s work becam e inc r eas ing ly im por t an t as t h e m i s s i o n s b e c a m e i n c r e a s in g l ycomplex. The advan ced lunar explora t ion provid ed b y t h e J-series l una r m iss ions in -c ludes p l ans fo r a l a rg e num ber of e xpe r im enta l packages tha t are u s e d i n l u n a r o r b i t

f o r f u r the r exp lor a tion of the m oon . Th ese expe r im en t s have p r ec i se po in t ing r equ i r e -m e n t s a n d o p e r at io n a l c o n s t r a i n t s . T h e s e e x p e r i m e n t s , t h e i r o p e r a t i o n a n d s ch e d u l in g ,a n d t h e c o n fl ic ts t h a t a r i s e r e q u i r e a t horough ope ra t ion a l a t t i t ude and po in ting con-s t r a i n t analysis if t h e h i g h es t a n d b e s t r e t u r n is to be r e a l iz e d f o r t h e m i s s i o n .

Manned S pacecraf t Cen terNat iona l Aeron aut ics and Space Adm inis t ra t ion

Houston, T ex as , Oc tob er 9, 1972924-22-20-00-72

6NASA-Langley, 1973- 1 s-353



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Apollo Experience Report Evolution of the Attitude Time Line