apollo experience report guidance and control systems engine simulation program

8/8/2019 Apollo Experience Report Guidance and Control Systems Engine Simulation Program

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9L.EC O P Y

APOLLO EXPERIENCE REPORT -

GUIDANCE AND CONTROL SYSTEMS

Engineering Simulation Program

by David W. Gilbert

Manned Spmecrdft Center

Hoztston, Texas 77058

N A T IO N A L A E R O N A U T IC S A N D S PA CE A D M IN IS T R A T IO N W A S H IN G T O N , D . C. JUNE 1 9 7 3



I. Report No. 2. Government Accession No.

NASA TN D-7287

1. Title and Subtitle

A P O L L O E X PE R IE N C E R E P O R TGUIDANCE AND C ONT ROL SYSTEMS-

3. Recipient's Catalog No.

5. Report Date

June 1973

6. Performing Organization Code

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

* Simulat ion ' Cert i f i ca t ion Tes t ing' Hybrid Simulat ion ' Software Veri f icat ion

' Eng ineer ing S imula t ion S imula tion* Guidance and Cont ro l

R ea l -T i m e S i m u l a t i on * Man-in-the-Loop

ENGINEERING SIMULATION PROGRAM

David W. Gilbert , MSC

8. Performing Organization Report No.7. Author(sJ

MSC S-318

10. Work Unit No.

914-50-17-08-72. Performing Organization Name and Address

11. Contract or Grant No.Manned Spacecraft CenterHouston , Texas 77058

18. Distribution Statement

13. Type of Report and Period Covered

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

None None 14

2. Sponsoring Agency Name and Address

Nat ional Aer ona ut i cs and Space Admini s t ra t ionWashington, D.C . 20546

22. Price

3.00

14. Sponsoring Agency Code

I5. Supplementary Notes

6. Abstract

T h e A p ol lo P r o g r a m e x p e r i e n c e f r o m e a r l y 1962 o July 1969 w i th r e sp ec t t o t he eng i nee r ing -s i m u l a t i on suppo r t and t he p rob l em s encoun te red is s u m m a r i z e d i n t h i s r e p o r t . Engineer ingsim ula t ion in su pp ort of the Apol lo guidance and control sy ste m is d i scu s sed in t e r m s of de -s ign ana ly s i s and ver i f i ca tion , cer t i f i ca t ion of hard ware in c losed- loop opera t ion , ver i f i c a-t ion of har dw are / so f twa re compat ib i l it y , and ver i f i ca tion of bo th sof twa re and pro ced ure sf o r e a c h m i s s io n . The magni tude , t im e, and co s t of t he eng i nee r ing s i m u l a t i ons are d e -scr ibed wi th resp ec t t o hardwa re ava i l ab i l it y , NASA and cont ra c tor fac i l i t i e s ( for ver i f i c a-t ion of the comm and module, the lun ar module, and the prim ar y guidance, n avigat ion, andcon t ro l sy s t e m ) , and schedul ing and p lanning cons idera t ions .

are m ade r ega rd i ng i m p l em en ta t ion of s i m i l a r , l a rge - sca l e s i m u l a t i ons fo r fu t u re p rog ram s .

F ina l ly , recommendat ions

* F o r s a l e by the National Technical In formation Service, Spr ingf ie ld, Vi rg in ia 22151



APO LLO EX PER I ENCE REPORT

GUIDANCE AND CONTROL SYSTEMS-

ENG INEER ING S IM U L A T IO N P R O G R A M

By D a v i d W . G i l b e r t

M a n n e d S p ac e cr af t C e n t e r

S U M M A R Y

Engineering s imulat ion in support of the Apol lo Program guidance and controlsy s t em s w as used ex tens ive ly fo r des ign ana lys i s and ver i f i ca tion , fo r cer t i f i ca t ion ofha rdw are opera t ion under c losed-loop cond i tions, and fo r ver i f i ca t ion of hard ware /software compat ib i l i ty and of sof tware and procedures on a miss ion-by-miss ion bas i s .The magni tude o f the s imula t ion e f fo r t w as jus ti f ied by the l imi ted t i m e and funds ava i l -ab l e fo r d ev e l o p men t a l mi s s i o n s an d t h e r e s u l t an t n eces s i t y fo r s u cc es s o n ea ch mi s -s i o n . T h e s i m u l a t o r s p rov ed t o be unexpectedly important in the development andver i f icat io n of the onboard digi tal sof twa re. The magni tude of the ta sk and the t im e re-q u i r ed t o i mp l emen t l a rg e h y b r i d -mi s s i o n ev a lu a ti on - ty p e s i m u l a t o r s w e r e i n it ia l lyundere s t imated . The t imely ava i l ab i l ity of sub sys tem hardw are fo r eva luat ion in thes i m u l a t o r s w a s an ea r l y p ro b lem. L a t e r , f o r m a l mi s s io n -v e ri f ic a t io n s i mu l a t i o n s

w er e h amp ered b ecau s e d e ta i led mi s s i o n p l an s, t r a j ec t o r i e s , and p ro ced u re s we r e n otava i l ab le e ar ly enough to m ake a comple te ver i f i ca tion job poss ib le . Expe r ience ind ica test h a t th e ap p ro a ch t o mi n imi z i n g u n ex p ec ted p ro g ram co s t s i n co n s t ru c ti n g l a rg e , co m -p l ex , f i n a l -v e r i f i c a t i o n s i mu l a t o r s is to use highly compe ten t , exper ien ced personne land to start p lann ing ea r l y in g re a t de ta i l , bu t to de lay implementa t ion as long as p o s -s i b l e s o the many changes and res imula t ions encoun tered as t h e p ro g ram d ev e lo p s canbe avoided. However , th i s approach mu s t be ba lanced against the r is k of not having the

hav ing the l a r ge hardw are- type s im ula to r cons truc ted and opera ted by the con t rac to r ata Governm ent fac i l i ty . Thus , l a t e in the p rogram , when needed on ly occas iona l ly , thes i m u l a t o r can b e o p e ra t ed by c i v i l s e rv i ce p e r s o n n e l so tha t a con t inuous con t rac to rcapab i l i ty d oe s no t have to be main ta ined fo r a long period .

s i mu l a t o r o p e ra t i o n a l at the op t imum time. F ina lly , c ons idera t ion should be given to

INTRODUCTION

M a ny t y p e s of a c t i v it i e s a r e s o m e t i m e s r e f e r r e d t o as s i mu l a t i o n s . T h e s e ac t iv -i t i e s inc lude env i ronmen ta l t es t ing , c re w tra in ing , and many types of d ig i t a l computa-t ion . The ac t iv i ty tha t is d i s c u s s e d i n t h i s r e p o r t is cha rac te r i zed by the fo llowingb a s i c f e a t u r e s . T h e a c ti vi ty is pr im ar i ly gu idance and con t ro l (G&C) o r i en ted ; is



p e r fo rmed i n real t i me , u s u a ll y u n d e r l ab o ra t o ry o r ro o m-am b i en t en v i ro n men t a l co n-d i t ions ; use s genera l -purpo se ana log and d ig i t a l comput ing equ ipment ; and typ ica l ly con -sists of a crew -s ta t ion mockup and var io us amoun ts of sub sys te m hard w are and spe c ia lin te r f ace equ ipment. Th i s ac t iv i ty is r e f e r r e d t o as eng ineer ing s imula t ion to d i f fe ren-tiate t h i s t y pe f r o m t h e o t h e r t y p es of s i mu l a t i o n s co nd u c ted i n th e Ap o ll o P ro g ra m .

Th e m ajo r i ty of the eng ineer in g s imula t ion conducted at non-NASA faci l i t ies was

. p e r fo rm ed by t h r ee co n t r ac t o r s : o ne r e s p o n s ib l e fo r t h e co mman d and s e rv i ce mo d u l e(CSM) des ign and cons t ru c t ion , one respo ns ib le fo r the luna r m odule (LM) des ign andcons t ruc t ion , and one respons ib le fo r the des ign and p rog ram ing of the p r im ar y gu id -ance, nav iga tion , and con t ro l sys tem (PGNCS). The PGNCS wa s bu i l t by a g r o u p Of

s u b co n t r ac t o r s r e s p o n s i b l e t o a NASA Manned Spac ecraf t C en te r (MSC) co n t r ac to r ;t h u s , all s y s t e m h a rd ware an d s o f t wa re were Go v ern men t - fu rn is h ed eq u i pmen t f o r t h etwo module co n t ra c to rs . Some eng inee r ing s imu la t ion of a r e l a t i v e l y mi n o r n a t u re wasconducted a t the PGNCS con t ra c to r fa c i l i ty in the latter pa r t of the p ro gra m . How ever ,a s o mewh a t l a r g e r p o r t io n of s y s t e m s i mu l a t i o n w as co n d u ct ed ea r l y i n t h e p ro g ram bya major command module (CM) s t ab i l i za t ion and con t ro l sys tem (SCS) subcon t rac to r asp a r t of t h e o v e ra l l p r i m e CM co n t r ac t o r e f fo r t .

A s i m i l a r s i t u at io n di d n o t ex i s t o n t h e LM s y s t e m, b ecau s e t h e p r i m e c o n t r a c t o rr e t a i n ed s y s t em s r e s p o n s ib i l it y fo r th e SCS, p ro cu re d co m p o n en ts f ro m s u b co n t r ac t o r s ,and p rov ided s imula t ion suppor t at t h e i r f ac i li ty . An o t h e r d i f f e r en ce wa s t h e r eq u i r e -men t f o r t h e L M ab o r t g u i dan ce s y s t em (AGS) fo r wh ich no co u n t e rp a r t exists on theCM. The AGS prov ides a t t i tude con t ro l and gu idance to the rate s tab i l i za t ion and con-t r o l s y s t em d ev e lo p ed by t h e p r i me LM co n t r ac t o r , who r e t a i n ed s y s t em s r e s p o n s i b i li t yand p rov ided s imula t ion supp or t fo r the AGS, which w as bu i l t under a subcon t rac t . Anex cep ti o n t o t h i s p ro ced u re o ccu r r ed i n th a t t h e MSC c o n t r ac t ed s ep a ra t e l y wi t h t h es a m e s u b co n t r ac t o r fo r t h e s o f t wa re u s ed w i th th e AGS. In addi t ion, MSC personnelp rov i ded s u p p l emen t a ry i n -h o u s e en g i n ee r i n g s i mu l a t io n t o s u p p o r t t h e s u b co n t r ac t o rin the deve lopment and ver i f i ca t ion of AGS pr og ra m s fo r miss io n use .

BACKGROUND

In e a r l y 1964, t h e Apo ll o Sp acec ra f t P ro g r am Office a r r an g e d f o r a s e p a r a t e e n g i-n ee r i n g s u b s y s t em man ag e r , so tha t opera t iona l methods cou ld be s i m i l a r t o t h o se t he nb e in g e s t ab l i sh ed fo r man ag in g co n t r ac t o r ac t i v i t y i n th e d ev e l o p men t of t h e s p acec ra f th a r d w a r e s u b s y s t e m s . T h e s e s u b s y s te m m a n a g e r s w e r e r e s p o n s ib l e t o t h e p r o g r a mma n ag e r fo r t h e t e ch n ica l d i r ec t i o n an d mo n i t o r i n g of co n t r ac t o r ac t i v i t i e s r e l a t i v e t oa g iv en s u b s y s t em. W i th t h e ex cep t io n s p r ev i o u s l y n ot ed , t h e co n t r ac t o r en g i n ee r i n gs i mu l a t i o n s were co n du c ted p r i m ar i l y at th e facilities of t h e p r i m e c o n t r a c t o r s f o r t h e

CM, LM, and PGNCS. The eng inee ring s im ula t ion s conducted at e a c h o f t h e c o n t r a c t o r

o v e r a l l p r o g ra m , s o m e p r o b le m areas, a nd r e c o m m e n d a t i o n s f o r f u t u r e p r o g r a m s .. f ac i l i t i e s and at the MSC are d es c r i b ed i n t h i s r ep o r t , f ol lo wed by a d is cu ss io n of the

2



S I M U L A T I O N A T C O M M A N D M O DU LE C O NT RA CT OR F A C I L I T I E S

62 I 6 3 1 6 4 I 6 5 I 6 6 I 6 7 1 6 8 I 6 9

O O ......or none at all) w er e u s ed d u r i n g t h i s p h as e Unmanned CSM missions 0 0

Manned CSM missionsof ac t iv i ty , which l as t ed app rox im ate ly18 mon ths whi le two eva lua to r fac i l i t i es Type 1 studies- Block II mission evaluation

entry. coast

and maneuver, vector contr ol

vector con tro l Coast and n

w ere b e i ng b u i lt . T h e s e ev a l u a t o r s , Boost abort,,Al

wooden mocku ps of the CM with displa ysand con t ro l s connec ted to a hybrid cornput- and t h r us t [-+valuator

i n g f ac i li t y , w e re u s ed d u r i n g t h e n ex t2 y e a r s f o r a series of detai led s imulat ionsof the va r iou s m iss ion phases .

Entry. boost abort, an d th ru st 'g B I o c kSpacecraft 0121evaluation

M)9maneuver\= 0 s acecraft 01 1

OSpacecraft 0171020;~;;(;~plsslo3/~Block Ilsystem { n om p h a s i scertification OSpacecraft 012. crew tra inin g

p l if i ed cockp i t and v i sua l rep re sen ta t ions

w as p l aced o n G&C s y s t e m s ev a l u at io n andrelated c r e w p r o c e d u r e s . D u r in g t h a te a r l y p e r i o d, a series of docking sim ul a-t i o n s w as co n du c ted at one of the contrac-t o r f a c i l i t i e s w h e r e s c e n e- g e n er a ti o n

L a t e r , t h e h a rd ware - t y p e s i mu l a t io n s we re r ep ea t ed u s i n g B l o ck I1 G&C equip-men t t o ce r t i f y t h e s y s t em s f o r f l ig h t . T h es e s i mu l a t i o n s w e re ex p an d ed t o in c l u de a

deta i l ed ver i f i c a t ion of the d ig i t a l au top i lo t (DAP) and compat ib i l i ty wi th the G&C hard-w a r e , b e c a u s e t h e DAP w a s a new fea tur e of the Block I1 s y s t em . Re ru n s of t h i s andt h e p r e v i o u s B l oc k I1 h a rd w are s i mu l a t io n s we re r eq u i r ed t o u pd a te t h e r e s u l t s as the

*

s t ru c t u ra l -b en d i n g -mo d e d a t a for the CSM/LM docked configurat ion w er e better definedand t h e t h r u s t v e c t o r co n t ro l (T VC) mo d e co mp en s at io n w a s changed in th e SCS and inth e DAP.

; Manned

Spacecraft 104

Spacecraft 106

Spacecraft 107

E v a l u a t o r I w as m odi fi ed and updated to rep r ese n t the B lock I1 CM, and the s im u-l a t io n co m p u t e r co mp l ex was r ep ro g ra me d f o r co mp a t ib i li ty wi th th e B l ock I1 s y s t e m sand t h e r eq u i r emen t s o f t h e l u n a r mi s s i o n s . A series of miss ion-veri f icat ion

3



s i mu l a t i o n s w as p e r fo rm ed t o v e r ify t h e G&C s o f t w a r e an d p r o c e d u r e s f o r e a c h m i s s io n .T h i s p a r t i cu l a r s i m u l a t o r wa s p laced u n d e r co n f ig u rat io n co n t ro l , and a f o r m a l s y s t e mof r ep o r t i n g and c l ea r i n g any d i s c r ep an c i e s was i n i t ia t ed fo r t h e s i m u l a t i o n s .

The mode of op era t ion f o r the se s im ula t ions evo lved in to a t wo -co mp l ex a r r an g e -men t . T h e fo r m a l mi s s i o n -b y -mi s s i o n s i mu l a t i o n wa s p e r fo rm ed o n t h e mi s s i o n ev a l -ua to r , wh ich is a l a rg e h y b r id co mp u t e r co mp l ex wit h a c rew-s t a t i o n mo ck u p , ex t e rn a l

s cen e -g en e ra t i o n eq u i p men t, and a h a rd w are g u i d an ce co mp u t e r . In add i t ion , the sys -t e m s h a rd ware i n th e G&C l ab o ra t o ry w as i n t e r f aced wi th a r e l a t iv e l y s m a l l amo u n t ofana log equ ipment and wi th the Ev alua to r 11 mo ck up t o fo rm a h a r d w a r e e v a l u a t o r c o m -p l ex . T h i s en t i r e co mp l ex wa s u sed s ep a ra t e l y t o d ev e l op an d v e ri fy ch an g es t o t h eG&C h a rd ware , ev a l u at e s t ru c t u ra l -m o d e s t ab i li t y an d co mp en s a t io n , and v e r i f y p r o c e -du re s fo r mal func tion de tec t ion . Th i s mode of opera t ion w as main ta ined a lm os t con t in -uous ly un t i l a f t e r the first l u n a r- l an di n g mi s s i o n , wh en th e co mp u t e r co mp l ex w asred u ced in s u c h a m a n n e r t h a t o n ly t h e m i s s i o n e v a lu a t o r o r th e h a r d w a r e e v a l u a t o rcould be o p e ra t ed at one t ime.

SI MU LA TIO N AT LUNAR MODULE CONTRACTOR F AC IL I T IE S

T h e ma j o r s i mu l a t i o n s co nd u c ted b y th e p r i m e L M co n t r a c t o r an d th e r e l a t i o n s h i pto the manned and unmanned miss ions are s ho wn i n f i g u re 2. T h e p r i m e L M co n t r ac t o rbegan work 1 y e a r later t h an t h e p r i m e CMco n t r ac t o r . Du r i n g t h e first 18 mo nths oft h e co n t r ac t , t h e p r i m e L M co n t r ac t o r s u b -con t rac ted a d o cki n g s i mu l a t io n t a s k t o o n ef i rm an d an ab o r t - f ro m-p o wered -d es cen ts im u l a ti o n t a s k t o a n o t h e r f i r m ; th e p r i m eL M co n t r ac t o r ex i s t i n g f ac i l i t i e s we re u s ed

to per fo rm hover -and- land ing and ren dez -vous s im ula t ions whi le tw o detai led LMs i m u l a t o r s w e r e b e in g c o n s tr u c te d . T h efirst d e t a il ed s i m u l a t o r wa s i n o p e ra t i o napprox imate ly 26 months after the LM con-tract w a s let. The hove r , landing, andd o ck in g s i m u l a t o r , called th e 111-B, w a s ana l l-ana log s im ula to r tha t had a deta i l edwooden mockup of the LM cre w s tat io n wi thfunc t iona l d i sp lays and co n t ro l s and an ex-t e rn a l s cen e of t h e l u n a r t e r r a i n o r of t h e

62 1 6 3 1 6 4 I 6 5 I 6 6 I 6 7 1 6 8 I 6 9

I LM missions - M 1" 0..

I u n m a nn e d 3 4 5 6

I M a n n e d L Rm I551on5

l a k i n g '0 bor tubccjntract subcontract

mdH o v e r a n d l a n d0

Rendezvous

I " 5 a nd , ad dockIm I

m-8 Descent . ascenr . and abor tI

S ISI

L M 1

L M 3- M 4Miss ions im ula t ions

(Full m i s s i o n ' L M 5e n g i n e e r i n g

s i m u l a t o r l 0

L M 6

klZ l

V II

I

II

CM. The 111-B w as used extens ive ly f o r a

ye ar to s tudy the LM land ing and dock ingman eu v e r s . T h e d es cen t , a s cen t , andab o r t man eu v e r s we re s t u di ed on an o t h e rs im ula tor (11-B) that contained a s i m i l a r c r e w - s t a t i o n m o c ku p b u t us e d h y b ri d c o m p u t a -t io n ; th e 11-B w a s s c a l e d t o a c c o m m o d a t e t h e o v e r a l l t r a j e c t o r y g e o m e t r y r a t h e r t h a njus t the c lose- in m iss ion phas es s imula ted in the II I-B. Th e 111-B and I I -B s im ul a to rsw ere p h as ed o u t i n ea r l y 1 9 6 6; t h e c r ew s t a t i o n f ro m t h e 11-B s i mu l a t o r w as u p d a t ed andused in the f u l l m i s s io n e n g i n e e r in g s i m u l a t o r ( F M E S ) .

F i g u r e 2 . - Si mu l a t i o n s co n d u c ted at p r i m e

LM c o n t r a c t o r facilities.

4



T h e FME S is a l a rg e , h y b ri d s i mu l a t o r wit h a c r ew s ta t io n , ex t e rn a l v i s u a ls cen es , an d an i n t e r f ace wi th t h e f l i g h t co n t ro l i n t eg ra ti o n (FCI ) l ab o ra t o ry , wh i ch co n -t a i n s all t h e G & C s y s t e m h a r d w a r e . The gyroscopes and the inertial m e a s u r e m e n t u nitw e r e m o u n te d o n a th re e-a x i s f l igh t -a tt i tude tab le , the g im bal -d r ive ac tua to r s of the de-s cen t en g in e wer e mo u n ted i n lo ad r i g s , an d a h a r d w are t h ro t t le -v a l v e ac t u a t o r . w as u s ed ..Ot h e r s u b s y s t em h a rd w are u s ed i nc l ud ed t h e co n t ro l e l ec t ro n i c s , t h e L M g u id an ce co m-

pu ter , and the AGS com puter . In f i n a l o p e ra ti o n a l f o rm , t h e FME S r eq u i r ed a co mp l e t et ie - i n t o s u b s y s t e m h a r d w a r e . Prov i s ion wa s made fo r two mode s of op era t ion , thema them at ica l -m odel mode and the har dw are mode , wi th qu ick changeove r poss ib le .How ever , main ta in ing an acc ura te ma them at ica l mod el of the PGNCS sof tw are requ i r eda l a rg e , co n ti n uo u s e f fo r t as a re su l t of sof tware evolut ions . Be cause of the doubtabou t the va l id ity of the ma them at ica l model ( in the even t of d i sc rep anc ies ) and fo r eco-n o mi ca l r ea s o n s , t h e ma t h ema t i ca l-mo d e l mo d e of opera t ion wa s not main ta ined . Be-cau s e t h e L M d id n ot u n d e rg o an ex t en s iv e mo d i f ica ti o n p ro g ra m s i m i l a r t o th e B l ock I/Block I1 CM conf igura t ion change , no s imula to r modi f i ca t ions of tha t so r t w er e req u i re d .

.

T h e FME S was u s ed t o s u p p o r t t h e ce r t i f ic a t i o n t e s t i n g of t h e G&C s y s t e m s fo r t h eonly unmanned LM m iss io n. Bec ause the first LM miss io n w as unmanned , the G&Cs y s t e m co n ta i ned s o m e s p ec i a l eq u i pmen t i n t h e fo rm of a p r o g r a m r e a d e r a s se m b l y toau t o ma t e s o m e of t h e man u a l f u n c t io n s and t o s u p pl emen t t h e u n t ri ed p r i m ar y s y s t em ,which w a s included as h a rd w are i n th e FME S s i mu l a t i o n s fo r ce r t i f ic a t i o n p u rp o s es .T h e s e s i m u l a ti o n s w e r e e x te n de d t o p r o v id e a detai led veri f icat ion of the PGNCS soft -w a r e p r o g r am (SUNBURST 1 1 6 ); later, a rever i f i ca t ion of SUNBURST 120 af t e r re v i -s i o n s w e r e m a d e; and, still later, a spec i f i c ver i f ica t ion of the D AP func t ions in the sep ro g r am s . T h e s i mu l a t o r w as p ut u n d e r co n f ig u rat io n co n t ro l , an d a f o r m a l s y s t e m ofr ep o r t i n g an d c l ea r i n g all d i s c r e p a n c i e s wa s in i t ia ted . Th i s type of s imu la t ion w as re-p ea t ed fo r ea ch s u cceed i n g L M mi s s i o n .

Fo rm a l ce r t i f i c a ti o n r e q u i r em en t s ex i s ted u n t il a f t e r t h e Apo llo 11 mi s s i o n , b e -

ca u s e ea ch m i s s i o n i n vo lv ed a n ew r e q u i r e m e n t o r a potent ial appl icat ion of the sys temfunct ion. S i g ni fi can t s o f t wa re ch an g es a l s o we re ma d e after each mi s s i o n . In f ac t ,desp i t e an add i t iona l LM s imula to r at the PGNCS con t rac to r fac i l i ty and the ad d i t iona ly e a r o r m o r e of t i m e a v a i la b le as a res u l t of the spa cec raf t 012 acc iden t , the de gr ee oft h e p r i m e L M c o n t r ac t o r s i mu l a ti o n s u p p o r t d i r ec t l y co n ce rn ed wit h t h e LM s o f t w a redeve lopment and ver i f i ca t ion was f a r g r ea t e r t han an t ic i p a ted o r in t en d ed . T h i s s i t u a -t ion redu ced the t im e ava i l ab le f o r s imula t ion ver if i ca t ion of backup modes , of the AGS,and of mal func t ion-de tec t ion p roce dur es . To a l l ev ia te th i s s i tua t ion , th e simula t iono p e r a t i o n at t h e p r i me L M co n t r ac t o r f ac i l i t y was put on a t h r ee - s h i f t b a s i s and t h ef a c i l i t i e s at MSC w er e o p e ra t ed by s u b c o n t r ac t o r p e r s o n n e l t o s u p p l emen t th e AGS s i m -ulat ion and evaluat ion. This s i tuat ion cont inued through May 1969, when the s imulat ionr e t u r n e d t o a n o rm a l o n e -s h i ft o p e ra ti o n .

SI M U L A T IO N A T PGN C S C ON TR AC TOR F A C IL IT IE S

The de s ign of the PGNCS and assoc ia ted so f tware w as the spec i f i c conc ern of thePGNCS co n t r ac t o r . T h e t y pe of r ea l - t i me s i mu l a ti o n g e r m an e t o t h i s r ep o r t was con -d u c t ed ea r l y i n t h e p ro g ra m fo r ev a lu a ti o n of ce r t a i n c r ew t a s k s an d of s y s t e m co mp o -n en t s i n c l o s ed - lo o p o p e ra ti o n . A combined CSM o r LM hybrid faci l i ty wi th funct ion alc r e w s t a t io n s w a s i m p l em e n te d later to aid in the development of the software and,

5



espec i a l l y , of t he c r ew p ro ced ure s so f tware i n t e r face . However , t he p r im ary so f tw ared e v e lo p m e n t t o o l w a s t h e n o n - re a l - ti m e d i g i ta l p r o g r a m .

T h e first unmanned Block I m i s s i o n s w e r e r e l a ti v e l y s i m p l e , a nd t h e s i m u l a t i o n sw er e m ore concerne d wi th t he ha rdw are opera t i on . Wi th t he app roach of t he first

manned ( spacec ra f t 012) miss ion , t he magn i tude of t he c re w d i sp l ay and con t ro l i n t e r -

face wi th t he so f tw are first becam e ev iden t on the P GNC S and p r im e C M con t rac to r ss i m u l a t o r s . M any u ne x pe ct ed d i s c r e p a n c i e s a r o s e , r e q u i r i n g c h a n g e s o r a l t e r n a t i v ep roc edu res . At app rox imate ly t he s a m e t ime , it b e c a m e a p p a r e n t t h a t t h e p r o b l e mwould probably be g r e a t e r f o r t h e B l oc k I1 sy s t e m s because t he au top i lo t func t i ons hadbeen added t o t he P GNCS wi th no add i t iona l p rov i s ions f o r c rew d i sp l ay o r co n t ro l ; t ha tis, all crew in t e r fa ce wi th t he com pu te r was only t h rough t he d i sp l ay and keyboard . Asa r e su l t of t he i nc rea s ing so f tw are work load , t he P GNC S con t rac to r added a secondhybr id s im u la to r f ac i l i t y du r ing 1967 so tha t the CSM and LM s im ulat ion s could be con-ducted independent ly . T h e s e s i m u l a t o r s s e r v e d as d e v e l o p m e n t a l t o o l s f o r p o r t i o n s o ft he so f tw are and as ver i f i ca t i on facilities f o r t he a s s e m b l e d p r o g r a m . E a c h s i m u l a t o rconta ined a h a r d w a r e g u id a nc e c o m p u t e r , a s i m u l a te d i n e r t i a l m e a s u r e m e n t u ni t, a

crew-s t a t i on mockup , spec i a l i n t e r fa ce equ ipmen t , and genera l -pu rp ose hybr id com -

p u ti ng e q u ip m e n t f o r s i m u l a t in g th e o t h e r s p a c e c r a f t s y s t e m s , e q u a t i o n s of motion, andso fo r t h . One P GNC S con t rac to r i nnova ti on w as the u se of c losed -c i r cu i t t e l ev i s i onand a v id e o t a p e r e c o r d e r s o th a t p r o c e d u r a l a n d s o f t w a r e d i s c r e p a n c i e s c o uld be re-played and separated .

S o f tware d i s c rep an c i es r ep o r t ed by NASA and con t rac to r o rgan i za t i ons u sua l l yw er e r e -c rea t ed and checked on one of t he PGNC S co n t ra c to r s im u la to r s be fo re ac h a n g e w a s effected. T h i s p r o c e d u r e t e n de d t o e l i m i n a t e "false a l a r m s " t h at w e r e t h er e s u l t of si m u l a t o r p r o b l e m s r a t h e r t h an a c t u a l s y s t e m d i s c r e p a n c i e s .

S I M U L A T I O N AT M S C F A C I L I T I E S

T h e o v e r a l l s i m u l a ti o n a c t i v i t i e s c o n -duc t ed at the MSC are shown in f i g u r e 3 .

Other s imu la t i ons of t he s a m e types t ha twere conducted by the MSC but not shownin f i gu re 3 w e r e p r i m a r i l y t h o se p e r f o r m e don the p rocedures -deve lopmen t s im u la to r sa nd t r a i n e r s .

The s imu la t i ons we re begun i n

Augus t 1962 in t e m p o r a r y q u a r t e r s w hil eth e MSC was be ing cons t ruc t ed . Dur ingth i s pe r iod , wh ich l a s t ed a lmo s t 2 y e a r s ,a series of analog man - in- the- loop s i m -u l a t i ons was p e r f o r m e d t o e v a l u a te basicveh i c l e -con t ro l concep t s and hand l ing qua l -ities f o r t he v a r i o u s m i s s i o n p h a s e s . D u r -

'

6 2 I 63 I 64 I 65 I 66 I 67 1 68 I 69

Preliminary studies

Thrust vector controlHover, docking. ~

Rendezvous siinulations-anding, abort.

and entry

Entry0 0

Lunar landing

n o 0

C S M veri f icationi-M verificdtior

B l o c k l lI~ .--ing the f i r s t half o f 1964, t h e s i m u l a t i o nfaci l i ty was m o ve d t o p e r m a n e n t q u a r t e r s .

F i g u r e 3 . - The G&C s imu la t i ons conduc t edat MSC faci l i t i es .

6



The fol lowing 3 y e a r s w e r e c h a r a c t e r i z e d by a n a l m o s t co n ti nu o us s e r i e s of s i m u l a ti o n sr e s p o n s i v e t o t h e p ro g ram n eed s fo r d ef in i ti o n of d e t a il e d G & C s y s t e m r e q u i r e m e n t sf o r all miss io n p has es in bo th nom ina l and o ff -nomina l cond i tions .

T h e T VC s i mu l a t i o n s first es tab l i she d the feas ib i l i ty of u s ing a d i r e c t - m a n u a l -co n t ro l mo de as a backup . La te r , hea t ing p rob le ms wi th the SPS eng ine g imbal -d r ive

ac t u a t o r s r eq u i r ed l o wer i n g t h e max i mu m rate capab i l i ty . Ex tens ive s imu la t ions ofbo th au tom at ic and manu al TVC m odes we re conducted to iden ti fy the m in imum a l low-a b le a c t u a to r p e r f o r m a n c e a nd t o d e fi n e t h e fli gh t r e s t r i c t i o n s t h a t w e r e r e q u i r e d f o rs o m e of t h e ea r l y s y s t e m s (wh i ch h ad t h e l o w- ra te ac t u a t o r s wi th o ut th e co m p en s a t i n gch an g es i n th e co n t ro l e l ec t ro n i c s ) .

.

T h e l o ng s e r i e s of r en d ezv o u s s i mu l a t i o n s w a s concerned in i t i a l ly wi th manualb ack up p ro ce d u re s fo r L M d i r e c t a s c en t , t h en wi th t h e e f f ec t of t h e c i r cu l a r f l i g h t p l anconcept , and f inal ly , wi th the evaluat ion of a one-man CSM-act ive r es cu e of the LM.Dur ing th i s per iod , s imu la t ions of the Gem in i IV an d Gemi n i VI r en d ezv o u s man eu v e r swere conducted to ob ta in a ch eck b et ween s i mu l a ted and ac t u a l p e r fo rm an ce .

T h e l u n a r -l an d in g s i mu l a t i o n s w e re co n ce rn ed i n i ti a ll y wi th e s t ab l i s h i n g t h econ t ro l -mode def in it ion fo r the f ina l desce n t , the as soc ia ted p i lo t d i sp lay s and con t ro l s ,and the expec ted ve loc i ty d i spers ion at touchdown. La te r , s imu la t ions were co n ce rn edwith the effect of var ious descent-guidance techniques on pi lo t v is ib i l i ty of the landings i t e an d t h e e f fec t on t h e f i n a l ap p ro ach tr a j ec t o ry . S t i l l later, s im u l a ti o ns w e r e p e r -fo rm ed to eva lu a te land ing-po in t - redes ignat ion capab i l i ty as a funct ion of f ue l avai labi l -i ty an d c r ew p ro c ed u re s fo r u s in g t h i s c ap ab i li ty .

T h es e s i mu l a t i o n s (p r i m ar i l y an a lo g s i mu l a t i o n s i nv o lv in g a c rew-s t a t i o n mo ck u pand an ou t- the-window sce ne gen era to r ) we re concerne d wi th G&C as pe c t s of bo th theLM and the CSM sy s te m s . Dur ing the l a t t e r pa r t of 1966 , a Block I g u i d an ce s y s t em

w a s i n t e r f a c e d w i th a CSM s i mu l a t o r t o en ab l e t h e ac t u a l f l ig h t s o f t wa re t o b e ex e rc i s edd u r i n g s i m u l a t e d m i s s i o n p h a s e s . A s a r e s u l t of the impending bui ldup in Block I1 so f t -w a re ac t i v it y , t h e B l ock I in te r fac e w as d i scon t inued and modi f ied to a Block I1 configu-r a t i o n d u r i n g 19 6 7. A s i m i l a r b u il du p of an LM v e r i fi c a t i o n s i mu l a t o r also was i n i t i a t edd u r i n g t h e s a m e p e r i o d . T h e r e s u l t an t B lo ck I1 CSM and LM s i m u l a t o r s w e r e mu chm o r e c o m p l e x a nd m o r e f o r m a l l y c o n t ro l le d an d opera ted than p rev ious conf igura t ions .

T h e CSM s i m u l a t o r w as u s ed t o p ro v id e a fo rm a l v e r i f i c a t io n of t h e en t ry -m o n i t o r -s y s t e m s o f t wa r e and t h e b ack u p r an g i n g capab il it y , t o ev a l u a t e t h e i n i t i a l B lo ck I1 s o f t -w a r e , t o p r o v id e a ch eck f o r t h e co n t r ac t o r s i mu l a t i o n s , and t o i n v es t i g a t e v a r i o u sf a i l u r e - r eco v e r y s i t u a t io n s . T h e L M s i mu l a t o r w as u s ed i n it i al l y as an eva lua t ion fa-c i l i ty fo r the AGS to supp lem ent the l imi ted am ount of fo rm al ver i f i ca t ion th a t cou ld be

done at t h e p r i m e L M co n t r ac t o r f ac i l it y b ecau s e of t h e h eav y wo rk lo ad t h e r e i n s u p -p o r t i n g t h e d ev e l o p men t o f t h e p r i mary s y s t em s o f t wa re . In t h i s r e s p e c t , t h e LM s i m -u l a t o r s e r v e d t h e S a m e fu n c ti o n as t h e h y b r i d s i mu l a t o r s at t h e PGNCS co n t r ac t o rf ac i l i t y i n s u p p o r t i n g t h e d ev e lo p men t of t h e p r i ma ry s y s t em s o f t wa re . In th e case ofthe AGS, th e hybr id fac i l i t y was provided at t h e MSC r a t h e r th an at t h e r e s p o n s i b l e s u b -c o n t r a c t o r f a c i l i ty . A h a r d w a r e a b o r t e le c t r o n i c s a s s e m b l y w a s i n te r f a c ed w i th t h es i m u l a t o r , and t h e a c t u a l fl ig h t p r o g r a m s a nd p r o c e d u r e s w e r e c h ec k ed i n v a r i o u s a b o r ts i t u a t i o n s .

7



Afte rward , the L M s i m u l a t o r w a s u s e d t o de v e lo p a lt e r n at i v e p r o c e d u r e s f o r v a r -i ous failure s i tuat ions that could poss ib ly develop dur ing the LM m iss ion and to evalu atethe de t a il ed p roc ed ur es and pe r fo rmance as soc i a t ed wi th t he use of the landing-pointdes igna to r as actual ly mechanized in the flight sof tware . This latter task requires ah igh -qual it y ex t e rna l s cen e gen era t o r t o ach ieve the r equ i re d accu racy wh i l e ma in ta in -ing the d e s i r e d r e a l i s m . Ano ther som ewhat novel f ea tu re of t he LM s im u la to r w as t he

in terpre t ive s imulat ion of the actual gu idance compu te r ,(No

hardware gu idance cam-p u t e r w a s a v a il a b le f o r this purpose . ) This i n t e rp re t i ve s imu la t i on p rovided ce r t a inopera t i ona l conven i ences no t a s soc i a t ed w i t h the h a r d w a r e a p p ro a c h b ut w a s a l w a ys thefirst suspec t componen t when so f tware anomal i es occu r red . C onverse ly , the locat ionof a problem was not a lways ev ident when anomal ies occurred wi th a h a r d w a r e g u id a nc ec o m p u t e r ip the s imulat ion . T he first suspe c t component wa s u sua ll y the piece of testequipment called the prog ra m-a na lyze r conso l e, wh ich p rov ided a c o m p le t e e r a s a b l em e m o r y f o r t e s t p u r p o s e s a nd s i m u l a t o r o p e ra t io n . The conso l e memory was l oadedwith a punched paper tape. The p r o g r a m - a n a l y z e r c o n so l e w a s a rather t e m p e r a m e n t a lp i ece of equ ipmen t that w as af fec t ed by power su rg es , su r round ing equ ipmen t , e l ec t ro -m a g n e ti c i n t e r f e r e n c e , t e m p e r a t u r e , a nd d i v e r s e e x t e r n a l i n fl u en c e s. A s a r e s u l t , fre-quen t i n t e r rup t i on s that w e r e n e c e s s a r y t o test o r re l o a d t h e m e m o r y l oa d w e r e n o r m a l .

.

D I SC USS ION

cost

T h e s i m u l a t i o n s d e s c r i b e d i n this r e p o r t c o s t a p p ro x i m a t e ly $51 mil l ion throughthe Apollo 11 miss ion , no t including the co s t of the MSC s imu lat ions o r the MSC sup-port con t rac l to r s . Th i s cos t is less than 1 percent of the to ta l c os t of the areas s e r v e d ;that is, th e C S M , the LM, and the onboard G&C sy s t e m s developm ent . In v iew of then a tu re of the! Apollo mi ssio ns (high cos t , l im i t ed numb er , and r e s u l t a n t e m p h a s i s o n the

s u c c e s s of e a c h m i s si o n) , this c o s t d o e s no t s e e m u n r e a s o n a b l e .

However , the f i s ca l prof i le of the t w o s p a c e c r a f t c o n t r a c t o r s w a s q u i te d i ff e r e n t.In the c a s e of the p r i m e CM c o n t r a c t o r , an o v e r a l l b u d g et a ry c o s t f o r s i m u l a t i o n s w a snegotiated con the basis of a s k e tc h y p r o g r a m plan. The p lan p roved to be t oo ambi t i ousf o r th e c o s t and had to be t r i m m e d s e v e r e ly after 2 y e a r s . In the ca se of t he p r im e LMc o n t r a c t o r , a m or e modes t but app rop r i a t e and we l l-de fined s imu la t i on p r og ram w asagreed upon, b u t only a s m a l l f r a c t i o n of the t o t a l co s t wa s inc luded i n the p r o g r a mb u dg e t. T w o y e a r s elapsed befo re t he r equ i red cos t was ac tua l l y de f ined , and it is un-c e r t a i n t h at t h e c o s t w a s e v e r f o r m a l l y n e g o ti a te d as an i den ti f iab l e con t rac t l ine i t em .AS a r esu l t , the LM s imula t i on p rog ram started at a s l o w e r rate and at a l o w e r l e v e lthan t he CM pro g ra m. Although t he LM s imu la t i ons cos t less than half of what the CMsimula t i ons cos t , t he t o t a l fo r the LM w a s 50 p e r c e n t m o r e t h a n th e first comple t e esti-m ate s , P r imar i Iy because of l eng thened p r og ra m sched u les and tasks added by the MSC.The added tasks were concerned p r im ar i l y wi th add i ti ona l ve r i f i ca t ion suppor t fo r the

p r i m a r y G & C s o f tw a r e . The s imu la t i on costs f o r t h e CM w e r e c l o s e t o t h e o r i g i n a le s t i m a t e , despite the f a c t that t h e p r o g r a m had b e e n s e v e r e l y a b b r e v ia t e d i n s c o p e al-though lengthened in sched ule .

8



S chedu I g Problems

As idea ll y env is ioned ea r ly i n t he Apo llo P r og ra m , t he mi s s ion -ver i f ica t i on s i m -ula t ions were to have been completed approximately 4 months before launch so t ha t t hef i n a l 4 months of cre w t ra in ing could be perform ed u s ing a se t of de ta i led p ro ce du resand so f tware t ha t had been ve r i f i ed by eng inee r ing pe r son ne l fo r t he pa r t i cu l a r m i s s ion .

In p r a c t i c e , t h i s id e a l w a s ne ve r r ea l l y pos sib l e, w i th t he r esu l t t ha t t he m ore t yp i ca lo p e r a ti o n a l s e q u e n c e w a s as fol lows.

.

The mi s s ion s imu la t i ons s t a r t ed app rox imate ly 4 months be fo re l aunch becausede t a i l ed mi s s ion de fin it ion , t r a j e c to ry da t a , and f l igh t so f tware no rmal ly w er e no tavai la b le soo ne r . Deta i led s imu lat ions of eac h miss io n phase and re la ted cont ingencys i t ua t i ons were per fo rmed fo r app rox imate ly 2 months. Usua ll y , so m e changes w er e

made t o t he mi s s ion p ro f i l e , t he c re w p rocedures , and, som et imes , t o t he f l igh t so f t -w are du r ing t h i s t im e . A se r i e s of f i na l so f tware -ve r i fi ca ti on t e s t s was conduc ted2 m o n t hs b e f o r e la u nc h . T h e s e t e s t s c o m p r i s e d a s e r i e s of fo rmal ly con t ro l l ed anddocumented s imulat ions us ing the latest ava il abl e mi s s ion t r a j e c to r y p lan , c r ew p roc e-du re s , and f l igh t sof tw are . The s imu lat ions , which had to be comp leted wi th in 2 w e e k sso t ha t the de t a i l ed r es u l t s could be pub li shed and d is t r i bu t ed be fo re l aunch , s e rv ed asusefu l r e f e r en ce s du r ing t he ac tua l m i s s ion . Then , t he s imu la t i on ac t iv i t y fo r t he nex tm i s s i o n w a s b e g u n ; t h a t is , approx imately 6 weeks be fo re one l aunch , s imu la to r ope ra -t i ons fo r the subsequen t m i s s ion had t o be s t a r t ed t o suppor t the t yp i ca l 2 . 5 -mon thl aunch i n t e rva l . Thus , any p ro b l em s requ i r i n g s imu la t i on suppor t du r ing t he 6 w e e k sbef o re l aunch usua l ly en t a il ed the i n t e r ru p t i on of t h e p r e p a r a t i o n s f o r t h e s u b s e qu e n tm i s s io n . T h e s i m u l a t o r s at th e MSC normal ly w ere s chedu led t o p rovide t h i s t ype ofc lo se - in suppor t .

The amoun t of eng inee r ing s imu la t i on pl anned fo r each m i s s ion va r i ed , dependingon the com plexi ty , the amount of new so f twa re , and the miss ion funct ions being pe r-

f o r m e d f o r t h e first t ime , s o t ha t eac h mi s s ion s imu la t i on was ac tua l l y t r ea t ed as as p e c i a l c a s e . W i th r e s p e c t t o s i m u l a ti o n su p p o rt , 4 - m on th l au n ch i n t e r v a l s a r e a l m o s ti dea l , p rov ided t ha t de t a i led mi s s ion de f ini ti on and so f tw are a re ava i l ab l e and t ha t s i g -n i f i can t d i f f e rences exist i n e a c h m i s s io n o r s p a c e c r a f t s y s t e m . L o n g e r i n t e r v a l s t en dto r esu l t i n i d l e pe r iods ; wherea s , 2 . 5 mon ths is approx imate ly t he m in imum l aunchi n t e r v a l t h a t can be suppor ted wi th re su l t s publi shed before launch . The 2 .5-month in-t e r v a l a s s u m e s th a t c h a n g es in th e m i s si o n o r s p a c e c r af t are minimal l o r that the cov-erage wi l l no t be comple t e .

Alm os t w i thou t excep t ion , ev e ry l a rge hybrid s im u la to r r eq u i re d much l onger t oget in to op era t ion than or ig inal ly p lanned . Delays of 6 to 12 mon ths we re typ ical , evenaf t e r a l lowing fo r unexpec ted changes . The bas i c p rob l em appeared t o be a g e n e r a l

lack of ex pe r ie nc e on the par t of the personn el involved , who, fo r thte m o s t p a r t , p r e -v ious ly had no t been concerned wi th such l a rge and complex s im u la to r s . In f ac t , f ewpeop le had had such exper i ence . Th i s genera l lack of exper i ence wa s a s t a t e -o f - t he -a r t -condi tion in 19 63; adequate equipment had only recen t ly becom e avai lab le then and noone ye t had wide spre ad exp er ienc e in the applica tion of ge ner al -p urp ose comput inge q u i p m e n t t o l a r g e h y b ri d s i m u l a t o r s w it h m an y h a r d w a r e i n t e r f a c e s . A s a result, the 'magn i tude of t h e t a sk wa s no t under s tood f u l l y . T h e tr o u b l e so m e a r e a s in c lu d ed t heto t a l hyb r id so f tware - in t eg ra t i on t a sk and t he i ncomple t e under s t and ing o f many o f t heh a r d w a r e i n t e r f a c e d e t a i l s t h a t a f fe c te d t h e s o ft w a re . S o m e ti m e l a t e r , a f t e r t h e s im u -la to r wa s op era t ing rout inely , l i t t l e doubt ex is ted that the sa m e grou p of people could

9



plan and execute a s i m i l a r o p e ra t i o n wi th mu ch b e t t e r s ched u li n g accu rac y an d lesst ro ub le. However , th e p lanned schedule would be long er fr om the start than the firstone . The t endency to undere s t imate the t as k cou ld occ ur on ano ther p ro gr am if t h e p e r -

, sonnel involved have no t had d i re c t exper ien ce in a s i m i l a r o p e ra t io n .

Mode of Operation

The modes of ope ra t ion fo r the two con t rac to r s im ula t ion complex es had d i f fe ren tr e s u l t s , as prev ious ly descr ibed . T h e b as i c r ea s o n w a s the am ount of G&C sy ste mh ard w are t ha t wa s mad e av a il ab le t o each co n t r ac t o r . T h e p r i m e CM co n t r ac t o r w a sprov ided a comple te PGNCS fo r the G&C labora to ry and a p a r t i a l s y s t e m f o r t he s i m u -l a t o r . T h i s co n t r ac t o r a l s o h ad a s i m i l a r co mp l emen t of B l ock I h a r d w a r e , s o m e ofwhich could be m odif ied f o r use wi th the Block I1 s y s t e m o r u se d as p e r i p h e ra l eq u i p -m e n t f o r data handl ing and up-link/down-l ink in te rfa ce . When the ba s ic G&C labora to ryi n teg ra ti o n t e s t i n g wa s co mp l e ted , t h a t s y s t em w as u s ed as a s e p a r a t e h a r d w a r e -ev a l u a t o r - ty p e s i mu l a t o r f o r s t ab i l i ty and co n t ro l and fo r f a i l u re -mo d e ev a l ua t io n . T h ep a r t i a l s y s t em w as u s ed i n t h e mi s s i o n ev a l u a t o r t h a t h ad a l a rg e d i g i ta l co mp u t e r s u i t -

ab le fo r l o n g -t e rm t r a j ec t o ry co mp u ta ti o n as r eq u i r ed fo r mi s s i o n s i mu l a t i o n s . Bo tht h e co mp l e te and p a r t i a l s y s t e m s h ad h a rd wa re g u id an ce co m p u t e r s that requ i red f l igh ts o f tw a r e p r o g r a m s .

The p r im e LM con t rac to r had on ly one PGNCS ass igned to the FCI l abo ra to r y , ye thad to suppor t the s imula to r opera t ion also . A n o th e r p a r t i a l s y s t e m w a s a s s i g n ed t e m -p o ra r i l y f o r r ad a r - i n t eg ra t i o n t e s t in g , b ut th i s s y s t em w as n o t av a i lab l e fo r s i mu l a t i o np u r p o s e s . T h i s d i s s y m m e t r y w a s th e r e s u l t of a combina t ion of fac to r s , such as thep reced en t e s t ab l i s h ed b y th e p r i m e CM co n t r ac t o r d u r i n g t h e B l o ck I por t ion of t h e p r o -g r a m , t h e e x t r e m e l y t i gh t d e l iv e r y s c he d u le r e q u i r e m e n t s f o r e a c h B lo ck I1 s y s t e m ins u p p o r t of s p a cec ra f t s ch ed u l e s , o v e ra l l p ro g ram b u d g e t p ro b l em s , an d t h e g en e ra l l ym o r e c r i t i c a l a nd austere at t i tude of the LM project off ice.

T h e p r i m e CM c o n t r a c t o r t w o -c om p le x a r r a n g e m e n t w a s m o r e f l e x ib l e an d r e -s p o n s i v e , wh i ch was a p p ro p r i a t e b ecau s e t h e CSM co n t ro l s y s t em s had t o co n ten d wi ththe docked LM and the r esu l t in g low-f requency bend ing modes as a b as i c mi s s i o n TVCr eq u i r em en t . I n t h e case of the LM, control of the docked CSM w a s a b a c ku p o r c o n ti n -gency mode and did n ot w a r r an t t he s am e amo u n t of a t t en ti o n . T h e l a rg e mi s s i o n s i m -u la to rs d id no t s imula te much of the de ta i l ed fue l - s losh and bend ing dynam ics , becau set h es e u s u a ll y we re s t u d ied s ep a ra t e l y in an a l l - an a lo g s i mu l a t io n . At t h e p r i m e L Mco n t r ac t o r f ac i li t y, t h i s o p e ra t i o n mean t an in te r rup t ion o f the miss ion-ver i f i ca t ions imula t ions and a t tendan t schedu l ing p ro b lem s . Bec ause the LM s im ula t io ns usua l lyw ere co nd u ct ed u s in g t h e s u b s y s t em h a rd w are , f l ig h t -a t ti tu d e t ab l e , and o t h e r i n t e r f ace

equipment , a large amount of id le t ime would be ex p ec t ed . Ho wev e r, i d l e t i me fo r t h i s. r e a s o n w a s n ot a m aj o r p ro b l em. So me an n oy i ng eq u i pmen t f a i l u r e s w e r e ex p e r i en ced ,b u t t h e s e r a t h e r i n f r eq u ent f a i l u r e s u s ua l ly w e r e fi x ed q u ick ly . T h e mo s t t r o u b l e s o m epiece of tes t equipment was t he p r o g r a m - a n a l y z e r c o n s o le t ha t s up p li e d t h e m e m o r y f o r

* the gu idance com puter . Th i s componen t , which w as used by all t h e s i m u l a t o r s w ithh a rd w are g u id ance co m p u t e r s , w as a f r e q u e n t s o u r c e of l o s t t i m e . B e c a u s e th e co n so l ew as d esi gn ed as a piece of labo rator y test eq u i p men t , man y fu n c t io n s o t h e r t h an t h em em o ry were p ro v id ed . A s p ro v en b y ex p e r i en ce , a s i m p l e r p ie c e of equ ipment tha ts e r v e d o nly as a memory un i t wou ld have been better.

10



However , in all cases, l a rg e , expens ive s imula t ion facilities w e r e b u il t at th ec o n t r a c t o r f a c il it y . T h i s p r a c t i c e is good ea r l y in th e p ro g ram b ecau s e t h e ap p ro p r i a t ec o n t r a c t o r p e r s o n n e l are ce r ta in to becom e d i rec t ly invo lved in the opera t ion . How-e v e r , if an unusua l ly long opera t iona l per iod is scheduled, as i n t h e A po llo P r o g r a m ,ma i n t a in i n g t h e co n t r ac t o r cap ab il i ty can b eco m e ex p en s i v e if t h e f ac i l i t y is r e q u i r e d o n lyd u r i n g s h o r t , i n f r eq u en t p e r i o d s . Po s s i b l y , a mo re eco n o m i ca l ap p ro ach t h a t s h o u ldbe g i ven co n s i d e ra t i o n wo u ld b e t o h av e t h e co n t r ac t o r p e r s o n n e l b u il d an d o p e ra t e t h es i m u l a t o r at s o m e p e r m a n e n t G o v e rn m e n t facility. L a t e r i n t h e p r o g r a m , t h e s i m u l a -t o r c ou ld be o p e r a t e d as r eq u i r ed by c i v i l s e rv i ce p e r s o n n e l .

The Role of Simulation

T h e i n t en d ed ro l e of t h e s i mu l a t i o n ac t iv i ty i n t h e o v e ra l l p ro g ram h as a m a j o reffect on p ro gr am implem enta t ion , cos t , and mode of opera t ion . E ar ly in the p ro gra m,t h e a s s u mp t i o n was mad e t h a t a m iss ion s imula t ion would be a f l ig h t co n s t r a i n t o n eachlaunch . Al though exp er ien ce showed tha t such was no t the case, in the 2 y e a r s t h ate l ap s ed b e fo re t h i s co n cep t w as ch an g ed, a co n s id e rab ly m o re amb i t i o u s and ex p en s i v e

p r o g r a m w a s b e i ng p r e p a r e d at t h e p r i m e CM co n t r ac t o r f ac i l i ty t o p ro v id e fu l ls imula t ion-suppor t capab i l i ty . To mi n i mi ze t h e r i s k of d e l ay in g a l aunch bec aus e ofs i m u l a t o r p r o b l e m s , tw o c o m p l e t e s i m u l a t o r s w e r e b e in g b u il t. T h e s i m u l a t o r s w e r es t a r t e d e a r l y t o mak e ce r t a i n th ey wou ld be r ead y , wi t h t h e r e s u l t th a t a cont inuousseries of chang es w as needed to " track" the evo lv ing spa cec raf t des ign . Wi th the sched-u l e s t h a t e x i s t e d at t h e t im e , it w as not ap paren t tha t one set of s u b s y s t em h a rd w arecould be mad e av a i l ab l e fo r s i mu l a t i o n b e fo re t h e first m iss ion and p rov id ing two setsw as out of the qu es t ion.

As ex p e r i en ce s ho wed, a l im i t e d n u m b e r of s i m p l e r s i m u l at io n s w e r e d e s ig n a t edas ce r t i f i c a t i o n test r e q u i r e m e n t s f o r t he su b s y s te m h a r d w a r e . T h e s e s i m u l a t i o n s w e r es ch ed u l ed t o be co mp l e t ed b e fo r e t h e first mi s s i o n o n wh i ch t h e p a r t i c u l a r s y s t e m or

fu n c ti o n w as t o b e u s ed . How ever , evident ly , lack of com plet ion of th es e tests f o r a n yrea s o n o t h e r t h an t ro u b l e wi t h t h e s y s t e m b e i n g t e s t ed wo u ld n o t co n s t r a i n t h e l au n ch ifall o t h e r t e s t i n g we re co mp l e ted s a t i s f ac t o r i l y . T h e s i tu a t i o n n ev e r ac t u a l l y a ro s e be-

c a u s e all r eq u i r ed s i mu l a t i o n s w e re co mp l e t ed in t i me ; h o wev er , t h e r ed u n d an t s i mu l a -t i o n ap p ro ach w as d i s co n ti n u ed .

L a t e r i n th e p r o g r a m , a r e q u ir e m e n t f o r a f o r m a l s o f tw a r e - v e ri f ic a t io n s i m u l a -t i o n wa s ad d ed and s ch ed u l ed t o be co mp l e t ed b e fo re e ach l au n ch . In m o s t cases, t h e s ead d i ti o n a l s i mu l a t i o n s a l s o we r e co mp l e t ed i n t i me , b u t s o me p lan ned ex cep t i o n s w e remad e wh en it b ec am e ev i d en t t h a t mee t i n g all sched u les would be imp oss ib le .

CO NCLUDI NG REMARKS

On t h e basis of the Apol lo exper ienc e , the fo l lowing recom me ndat ions are m a d ec o n c e r n i n g e n g i n e e r i n g s im u l a t io n f o r f u t u r e l a r g e p r o g r a m s .

1. E n g i n e e r i n g s i mu l a t i o n s ho u ld be recogn ized as a po ten t i a l ly l a rge , expens iveo p e ra t i o n an d , as such , g iven app ropr ia te a t ten t ion dur in g the in i t i a l con t rac t def in it ionan d n eg o t i a t i o n s so tha t wel l -def ined ba se- l ine p lans and co s t s are es t ab l i s h ed .

11



2 . The ro l e tha t s imula t ion is expec ted to have in the p ro gram shou ld be definedin enough spec if i c de ta i l s o tha t an appropr ia te s imula t ion p lan tha t is adequate bu t no tu n n eces s a r i l y e l ab o ra t e can be es t ab l i s h ed , If poss ib le , th i s shou ld be inc luded in ther e q u e s t f o r p r o p o s a l so tha t the in i t i a l p roposa l by the con t rac to r can be expec ted tocon ta in appropr ia te p lans and cos t s .

3 . Management of the s imulat ion act iv i ty should be d e l ega t ed i n s o me ap p ro p r i a t eway so tha t the ac t iv i ty wi l l rece ive adequate fu l l- t ime a t ten t ion .

4 . Prov i s ion shou ld be m a d e s o that any plan adopted can be suppor ted adequate lywi th th e r eq u i r ed s u b s y s t em h a rd wa re an d test equ ipment .

5 . Con siderat ion should be g i ven t o h avi n g l a rg e s i m u l a t o r s t h a t r eq u i r e s u b s y s -t em h a rd ware co n s t ru c t ed at Go v ern men t facilities. Co n t r ac t o r p e r s o n n e l wo u ld be

used as requ i red dur ing cons t ruc t ion and the in i t i a l pha ses of opera t ion , and c iv i l s e rv -ice personn el would be used later i n t h e p r o g r a m .

6 . Det ai led p l an ni ng fo r l a rg e s i m u l a t o r s s h ou ld be begun ear ly in th e p r o g r a m ,

bu t ac tu a l implementa t ion shou ld be delayed as long as poss ib le to avo id " t rack ing" andi n co rp o ra ti n g i n t e r i m ch an g es t o t h e s y s t em b e i ng s i mu l a t ed .

7. Detailed planning should be des igned to en su re the inc lusion of the re qu i re -men t s f o r s p ec i a l -p u rp o s e eq u ip men t fo r i n t e r f ace or s u b s y s t em s i mu l a t i o n , ex t e rn a ls cen e g en e ra t o r s , and th e p ro v i s io n s fo r data inpu t and ou tpu t, bec ause these req u i re -men t s can b eco me ex p en s i v e.

8 . At the beg inn ing of the p roposed p r ogr am , the de gre e of des i re d fo rm al i tya s s o c i a t ed wi t h t h e s i m u l a t o r o p e ra t i o n s h ou ld be d e t e r m i n e d s o t h a t p ro p e r p l an s canbe ma de. Conf igura tion con t ro l , documenta t ion , extra sets of hard -copy da ta , fo rmalt e s t - r ea d i n e s s r ev i ews , and an o ma ly r ep o r t i n g can co m p r i s e a g r e a t ly i n c r e a s e d w o r k -

load for suppor t personnel .

Manned Spacecraf t Ce n terNat iona l Aerona u t i cs and Space A dmin i s t ra t ion

Hous ton , Texas , January 4, 1972914-50-17-08-72

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