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GEMINI: MFRCURY EIISERIENCE APPLIED

By Jerome B. Hammack and Walt er J. Kapryan

NASA - Manned Spacecraft Center

INTRODUCTION

I t i s t h e i n t e n t of t h i s paper t o show how th e Gemini program has

attempted t o draw upon and pr o f i t from Mercury exp erience.

The Gemini P ro je c t has evolved a s a NASA space program with i t s

prime mission of providing a f l ex ib le space system t h a t w i l l enable

us t o ga in prof ic iency i n manned space f l i g h t and t o develop new

techniques fo r advanced f l ig h ts , in cluding rendezvous. To achieve

t h e s e o b j e c t i v e s , we must have a space vehicl e with su bs ta nt ia l l y

gr ea t er cap abi l i t y than the Mercury spacecraf t . This increased capa-

b i l i t y w i l l include provisions for two men, in st ea d of one, as i n th e

Mercury sp ac ec ra ft and f o r space missions of up t o two weeks' du rati on.

I t i s t he i n t e n t o f t he Gemini P ro j ec t t o bu i l d upon t h e experience

gained from Mercury so tha t most of th e en er gi es of th e new program can

be devoted t o th e solu t ion of the problems as soc ia ted wi th achieving

i t s primary mission object ives and no t have t o f i g h t i t s way through a

swelter of old problems.

4DESCRIPTION OF GEMINI

The Gemini f l i g h t program i s shown i n fi g ur e 1. The f i r s t f l i g h ti s a b a l l i s t i c s u b - or b it al q u a l i fi c a ti o n f l i g h t .

planned f or manned f l i g h t s t o begin w i t h t he second f l i gh t .I t i s p r e s e n t l y

Rendezvous



2

The Gemini launch vehicle i s a modified Titan I1 which repre-

se nt s a second-generation ve hi cle evolved from the Ti tan I . Theprimary modificat ions for t h e GLV are the incorpora t ion of a

redundant f l i g h t con tro l system and th e add i t ion of a Malfunct ion

Detect ion System (IDS) for pi lot safety.

I

The ta rg e t vehic le i s a mo dif ied Agena-D. The prim ary mo di fi -

ca t i ons t o t h e Pgena a re t he i ncorporat i on of a m u l ti p le r e s t a r t

system, th e addi t ion of a secondary propulsion system, and a command

and con t ro l sys tem th a t i s compat ible wi th the spacecraf t .

The Agena launch vehicle i s th e Atlas standard space launch vehic le .

This vehic le i s a re fi n ed Atlas-D and i s planned a s a "work-horse''

vehic le f o r many space pr o je ct s.

d

EXAMPLES OF APPLIED MERCURY EXPERIENCE

The authors have se le ct ed four are as t o i l l u s t r a t e how Mercury

experience influenced Gemini. These ar ea s are; in te gr at io n of man

in to system, design, checkout, and launch vehi cle in te gr at io n. There

fol lows a discussion of each area.

In te gr at io n of Man In to System

The f i r s t example of appl ying Mercury exp erien ce t o Gemini i s

t h e i n t e g r a t i o n of man in to the fl i g h t system. Since th e Mercury

program was America's f i r s t manned space venture, i t s design con-

s t r a i n t s were i n some ways more restrict ive than those of the Gemini

program. F ir st , s in ce w e had never bef or e put man i n t o space, it

was necessary t o develop a veh icle t h a t could and would oper atethrough a l l phases of fl ight completely independently of man. This



change in flow ch ar ac te ri st ic s of a valve i n the environmental con-

t r o l system caused pre ss ur e-s ui t temperatures t o reach un'comforkablelev e ls , b u t sys temat ic and eff ec t ive adjustment of t h e c o n t r o l v a l veby the p i l o t corre cted th e overtemperature. Had t h e p i l o t b een

u na bl e t o e x e r c i s e t h i s c o n tr o l, the f l i g h t would have been terminated

much e a r l i e r than was planned. Other examples could b e ci te d b ut

thes e should be su ff ic ie nt t o make the point .

To s t a te t h a t man i n space has proven himself in Mercury does not

imply t h a t t he r e a re no t s t i l l many many unknowns i n t h e a rea of human

fac tor s i n space f l ig ht . However, the re i s now concr ete evidence th a tman can m a te r i a l l y improve chances of mission su cce ss. I n Gemini, man

t h e r e f o r e i s being int eg rat ed i nt o much of systems operat ion. T h i s

approach enables use of s imp lified ci rc ui t r y , minimizat ion of auto-

mat ic equipment, and si nc e man i s t o he heavi ly r e l ie d on, more w i l l

be learned w i t h regard t o man's capabi l i t i es in space than would be

the case i f he were only requi red t o play a pass ive r ol e dur ing the

course of a mission.

Design

The Gemini program has drawn heavily upon Mercury experience i nt h e design of th e space craft . There fol lows a discu ssion of th re e

m ajor sy stems t o i l l u s t r a t e t h i s f a c t .

Landing System. - Considerable ef f o r t was expended t o develop a

su i ta bl e landing sys tem f o r Mercury.

of th e Mercury sp ac ec ra ft were performed pr ima rily t o develop th e

landing system.

from high-flying cargo air pla ne s w i t h var ious parachute conf igura t ions .

I n f a c t , t h e f i r s t f l i g h t t e s t s

These t e s t s involved dropping boi le r pla te capsules

Due t o vigorous i n -house e f fo r t s with in t he NASA as w e l l a s

extens ive e f fo r t by the cont rac tor , a re l i ab le landing system was



4

,A paraglider development program i s be ing d i l i ge n t ly pursued by

t h e NASA t o pr ov id e t h e c a p a b i l i t y of land landings on prepared s i t e s .A t y p i ca l pa rag l ide r conf igura ti on i l l us t r a t i n g t he dep loyment sequence

i s shown a s f ig ur e 6.maneuver, t o avoid l o c a l obs tr uc ti on s and land i n much th e same manner

a s with an airplan e. Use of a paragl ider w i l l e l imina te the need for a

landing bag a s was used on Mercury.

With the para gl id er , t h e p i l o t w i l l be a b l e t o

S ince t he pa rag l id e r i s a new development, a parachute landing

system si mi lar t o t he Mercury system i s being developed for interim

use un t i l t he pa rag l ide r sys tem i s q u a l i f i e d ( s e e f i g u r e 7 ) .t he spacec ra f t i s suspended i n such a manner a s t o provide reduced

landing impact loads. When th e spa ce cra ft en te rs th e water i n th e

manner shown, th e on se t g r a t e i s g re at ly reduced. The parachute

u t i l i ze d f o r t h i s system evolved from Mercury experience. I t i s an

84 f t . diameter version of th e r i ng -s a i l chute used on the Mercury

capsule.

However,

E le ct ri ca l power system. - The Gemini sp acec raf t u t i l i z e s f u e l

ce l l s a s t he major source of e l ec t r i ca l power d ur in g o r b i t i n g f l i g h t .

This i s because of th e extensive l oad requirements for both the long

duration and rendezvous missions. A system of s i l v e r z in c b a t t e r i e s

s im i la r t o those used i n Mercury w i l l supply e l ec t r ic a l power dur ing

reent ry, pos t l anding and for emergency opera t ion dur ing orbi t . A l l

squibs and pyrotechnics, th e high t ra ns ie nt vol tage devices, w i l l be

powered by an independent dual zin c-bat tery supply si mi lar t o th a t used

for r e e n t r y .

re l ays and timers malfunctioned a s a r e s u l t of the occurrence of hight r a n s i e n t v o l t a g e s or " g l i t c h e s . " A completely independent isolated

squib bus such a s i s bein g d esig ned i n to Gemini sho uld minimize, i f n o t

e l imina te , th e "gl i tch " problem.

.J

During t h e Mercury program upon a number of occasions

A ra d i a to r has been provided f or f u e l ce l l cool ing and t o supply



5

contaminat ion, therefore, i s an eve r-p res ent problem. Furthermore,

design considera tions di c ta ted the use of fl ar ed tubing. The use off l a r ed tubing has posed a con s tant l eakage thr ea t .

Control of th e Gemini sp ac ec ra ft i s achieved by means of t he Orb i t

Attitude and Maneuvering System whi l e i n o r b i t and by means of t h e

Reentry Control System during retrog rad e and re en tr y. Both systems

ut i l i z e hype rgo l ic p rop e l l an t s . The fu e l i s monomethyl hyd razene, and

the oxidizer i s ni t rogen t e t rox ide .

Hypergolic prop el lan ts were se lec t ed pr imari ly due t o th e i r higherFurthermore, with hypergol ics th er e i s not t he eve r -pe c i f ic impulse.

present danger of explosive decomposi t ion that i s a t t e n d a n t w i t h t h e

use of a peroxide system.

t h e use of hypergol ics rather than hydrogen peroxide i s on the order of

700 pounds. S t a in l e s s s t e e l t ub ing w i l l be used throughout the system

which should minimize "p as siv at io n" problems.

brazed system t o minimize leakage. Squib con tr ol le d diaphragm type

iso la t io n va lves have been incorpora ted ju s t sh or t ly downstream of th e

pressure and prope l lan t sup pl ie s t o f ur th er minimi,ze leakage. A s e r i e sof two to t en-mic ron f i l t e r s w i l l be used throughout the AGE and the

a i rborne system t o minimize the p os s i bi l i ty of contaminant s re s t r i c t i ng

in j e c tor o r i f i c e s . Although t h i s co nt r ol system repr es en ts a more

advanced st at e- of -t he -a rt system than Mercury, we f e e l t h a t th e major

tro ubl e ar ea s experienced by Mercury a r e being minimized i n th e Gemini

design.

The payload savin g ach ieved by Gemini thro ugh

The system w i l l b e an a l l

./However, i t i s w e l l known t h a t hype rgo li c p ro pe l l an t s a re ex t remely

toxic and must be handled w i t h g r e a t c a r e . A t th i s t ime, though th ere i s

not much experience t o use a s a guide i n handling hypergol ics, ad di t i on al

experience i s being ga ined da i ly as f or example i n the T i tan I1 and Agenaprograms.



7

F ac i l i t i e s wi thin which t o checkout th e Mercury spa cecr af t a t the

launch s i t e were woeful ly inadequate i n th e e ar ly phases of Mercury.The lack of proper AGE was a l so a handicap . These problems, we f e e l ,

ar e being circumvented i n our planning for not only Gemini but future

space programs as w e l l . Construction of f a c i l i t i e s on Merri t t I s l a n d

i n sup port of b oth Gemini and Apollo has alr ead y begun. I t i s n o t t o

be impli ed t h a t t he r e w i l l be no problems i n t h i s area; however,

r e l a t i v e t o Mercury, cons idera bly more planning and implementation

w i l l be achieved much e a r l i e r i n th e program. There w i l l be an

Operat ions and Checkout Building wherein the master t e s t s ta t i on s w i l l

be ins ta l led and where in mo s t of the modular and inte gra ted te s t s w i l lbe performed.

hy per go lic and cryogen ic systems. New a l t i t u d e chambers w i l l b e a v a i l -

ab le f o r manned and unmanned sim ula tio ns i n a space environment. A

radar range w i l l b e b u i l t for radar boresight and al ignment checks

and -for performing mated Gemini/Agena RF and func t iona l compat ibi l i ty

t e s t s , a n d so on. I n a number of ins tances , f a c i l i t i e s f o r t h e

performance of s im i la r t as ks i n Mercury were not av a i l ab le un t i l we l l

a f te r th e beginning of the o per a t io na l phase of the program.

A L i q u i d T e s t f a c i l i t y w i l l b e p r ov id ed f o r t e s t i n g of

d



a

J

Launch Vehicle Integration

The last area to be discussed which has profited from Mercury

experience is the area of launch vehicle/spacecraft integration.It was apparent early in the Mercury program that the launch vehicleand spacecraft must be regarded as a composite vehicle in the critical

powered portion of the flight. Therefore, compatibility criteria wasdefined early in the program.understanding of the structural carry-through loads of the combined

vehicle was also recognized during the Mercury program. In Gemini,therefore, a great deal of emphasis is being placed upon interface

loads criteria. The influence of cutouts, discontinuities andprotruberances in the spacecraft is being thoroughly analyzed. Designof the forward-skirt portion of the launch vehicle is taking these

effects into consideration. A combined spacecraft adapter and boosterforward section test is being conducted so that detailed knowledge of

resultant stresses are known.

The need for a thorough study and

The same detailed attention paid the design, fabrication andcheckout of the Mercury launch vehicle as outlined in reference 2

will be paid the Gemini launch vehicle.assembly area will be exclusively devoted to the assembly, integra-tion, and factory checkout of the launch vehicle; therefore, thewhole effort at Martin/Baltimore will be directed towards producing

man-rated vehicles.

personally visited the General Dynamics/Astronautics plant to inspect

Mercury procedures.monitor the more significant tests conducted at Martin/Baltimore.

as on Mercury there will be engineering reviews, roll-out inspectionsan d acceptance reviews by NASA/SSD and Aerospace. The same conceptwill be applied at the Cape during checkout.

The Martin/Baltimore

The weapon system Titan I1 is provided at Martin/

li Denver. The technical teams of the Martin/Baltimore plant have

Teams of NASA/SSD and Aerospace engineers willA l so ,



BIBLIOGW€K

-/

1.

2.

3 .

4.

5.

6.

7.

Bland, W i l l i a m M. , J r . and B e r r y , Charles A. , L t . Col., USAF X ,

"Project Mercury Experiences" - Astronautics and Aerospace

Engineering, February 1963, Vol. 1, No. 1.

"Resul ts of the Third United S ta te s Manned Orb i ta l Space Fl ig ht ,"

Oct. 3, 1962, NASA SP-12, Su pt. Doc., U.S. Government P r in ti n g

Office, Washington, D.C.

"Resul ts of th e Second United S ta te s Manned Or bi ta l Space Fl ig ht ,"

May 24, 1962, NASA SP-6, S up t. Doc., U.S. Government P r i n t i n g

Office, Washington, D.C.

"Results of th e F i r s t United S ta te s Manned Orb i ta l Space Fl i gh t ,"

Feb. 20, 1962, Sup t. Doc., U.S. Government P r in ti n g Of fic e,

Washington, D. C .

"Re sul ts of th e Second U.S. Manned Suborbital Space Flight,"

J u l y 2l, 1961, Su pt. Doc., U.S. Government P r in ti n g Of fic e,

Washington, D.C.

"Proceedings of a Conference on Re su lts of t he F i r s t U.S. Manned

Su bo rb ita l Space F li g h t, " Supt. Doc., U.S. Government Pr in ti n g Offi ce,

Washington, D.C.

Hammack, Jerome B. and Heberlig, Jack C . , "The Mercury-Redstone Program,"

American Rocket Soc ie ty P r e p r in t No. 2236-61 (New York, N.Y. ) , Oct. 9-15,1961.

REFERENCES



IGHT

IGHT

IGHTS

FLIGHTS

1

2

3

5

UNMANNED BALLISTIC

QUALIFICATION

MANNED QUALIF ICATION

& 4 -

THRU

LONG DURATION

12 - RENDEZVOUS

Figure 1.-Gemini flight program.



Fi,we 2 . - Gemini spacecraf t .



~

Figure 6. Gemini spacecraft ana paraglider



i.

Figure 7. GerLni spacecraft and parachute lafiding systeen.

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