SATURN S-IV SPACECRAFT SYSTEM T. J. Gordon1
Douglas Aircraft Company, I n c . , Santa Monica, C a l i f . ABSTRACT
Vehicle stages operating in a space environment require the addition of new subsystems. The most important of these sys- tems that must be considered are: l ) attitude s t a b i l i z a t i o n in space, 2) zero g propellant storage, 3) space environmental protection, and k) checkout in o r b i t . Such operational r e - quirements have influenced the design of the S-IVB. The mis- sion considerations for this vehicle involve the functioning of the S-IVB f o r hours or days in space a f t e r separation from the lower stages. Some of the potential missions for the S-IVB are Earth o r b i t tanking, and an escape mission requiring a parking o r b i t . The S-IV vehicle program i s now w e l l into the development stage. I t incorporates many of the S-IVB de- sign features. The S-IV w i l l be f i r e d immediately a f t e r S - I cutoff, without o r b i t a l storage or coasting in space. After placing i t s payload in i t s o r b i t a l or escape f l i g h t path, the expended S-TV w i l l be l e f t as a derelict coasting in space.
Ultimately d e r e l i c t stages in space may be banded together to form the nucleus of a space station or as a space labora- tory. Douglas A i r c r a f t Company has i n i t i a t e d construction of a l a r g e scale space chamber to be used in qualifying l a r g e subsystems. The evolution of vehicles into spacecraft repre- sents one of the major design challenges facing the aerospace industry today.
INTRODUCmON
In the past, there has been a f a i r l y c l e a r dividing l i n e between booster vehicles and their payloads. Boosters were b u i l t by t i n benders, payloads by s c i e n t i s t s . The old concept was that of a scientific payload, boosted into orbit by a
Presented at the ARS Lunar Missions Meeting. Cleveland, Ohio, July 17-19, 1962.
IChief Saturn Systems Engineer.
T. J. GORDON
piece of "hardware/1 Today's mission concepts are merging these two areas: the vehicle itself may be the payload. This concept arises from two considerations. First, in certain mis- sions the vehicle must perform in space prior to placing the payload into its mission trajectory; for example, an escape mission involving an Earth parking orbit. Second, the termi- nal stage of a booster achieves orbital velocity in an Earth orbit boost mission or escape velocity in an escape mission.
These expended stages can, if properly prepared, perform mis- sions in themselves. These concepts require a merger of
booster vehicle performance requirements to payload reliability and environmental criteria. They produce far-roaming stages designed to store their propellants in space for long periods of time; they are also designed to provide their impulsive addition to the mission energy profile after many days in orbit, as well as to function in the atmosphere of some other planet. For example, the S-IV and S-IVB vehicles may be con- sidered payloads in themselves.
An analysis of the trajectories involved in launching toward a particular point in space shows that the launch time require- ments are more relaxed if launching is accomplished from an Earth orbit rather than from Earth itself. This effect is shown for a lunar mission in Fig. l(see Ref. 1 ) . Depicted here is the launch window experienced by launching toward the moon from a 300-naut mile orbit rather than from the surface of Earth.
During the cycle shown, there are six periods in which a launch is possible. Each of these launch windows is of several hours duration. However, at only one particular time for each orbit within the window can the launch occur. The country's first lunar missions were conducted using a three stage Thor vehicle, boosted into a direct escape trajectory. Because of the nar- row launch window, launch time was restricted to a period of 20 min. Even this length of time required readjustment of guidance parameters, as time varied in the 20-min interval.
In those days, countdowns were somewhat uncertain, and the fact that the launch window was hit on every attempt is still regarded as somewhat coincidental. Because R&D countdowns can introduce substantial uncertainties in launch time, many cur- rent escape missions involve parking orbits. This greatly extends the Earth launch time window. In this type of mission, the final stage of the space vehicle will be placed, together with its payload, into a low Earth orbit. During orbit, pre- cise trajectory information and launch time will be computed, and, at the proper time, the stage will be fired. This oper- ation requires that new systems be added to the vehicle's terminal stage. It is interesting to review how these sys- tems affect the S-IVB design.
1 A t t i t u d e s t a b i l i z a t i o n i n space. A t t i t u d e o r i e n t a t i o n may be d i c t a t e d by payload p e c u l i a r i t i e s , heat t r a n s f e r con-
s i d e r a t i o n s , or the n e c e s s i t y f o r o r i e n t a t i o n p r i o r t o i g n i - t i o n . I n the lunar o r b i t rendezvous mode, the S-IVB w i l l be r e q u i r e d t o provide a t t i t u d e s t a b i l i z a t i o n t o the Apollo/LOR v e h i c l e during Earth parking o r b i t . A f t e r r e s t a r t , the stage must continue t o provide a t t i t u d e s t a b i l i z a t i o n f o r the A p o l l o turn-around maneuver. I t i s expected that a t t i t u d e c o n t r o l w i l l be provided by e x t e r n a l l y mounted storable p r o p e l l a n t a u x i l i a r y rocket engines.
2 Zero g p r o p e l l a n t s t o r a g e . Questions a r i s e p e r t a i n i n g t o cryogenic venting techniques under zero g conditions when the p o s i t i o n o f the f l u i d s i n the tanks i s not known. In the f r e e coasting p o r t i o n of the S-IVB s f l i g h t , i t i s a n t i c i p a t e d that tank venting w i l l be r e q u i r e d . Two techniques under con- s i d e r a t i o n are c e n t r i f u g a l f l u i d separators which permit only the gas t o be vented from the tank, or u l l a g e rockets which provide a small forward a c c e l e r a t i o n t o s e t t l e the f l u i d s t o the r e a r of the tank j u s t p r i o r t o a venting o p e r a t i o n .
3 P r o t e c t i o n against the space environment. This includes micrometeoroid impact, thermal environment, solar r a d i a t i o n , e t c . Depending on t h e mission and the time the v e h i c l e must function i n space, these considerations may become major de-
sign points f o r the v e h i c l e .
k Requirement f o r checkout in o r b i t . In the lunar o r b i t rendezvous mode, the S-IVB w i l l coast with the payload i n Earth o r b i t p r i o r t o i n j e c t i o n i n t o a trans-lunar t r a j e c t o r y . The astronaut or the ground s t a t i o n must have knowledge of proper v e h i c l e functioning b e f o r e f i r i n g . I n e f f e c t , t h i s n e c e s s i t a t e s a countdown i n o r b i t . Real time presentation of
c r i t i c a l parameters associated with stage readiness t o f i r e w i l l be r e q u i r e d . S i m i l a r l y , c e r t a i n n a v i g a t i o n information must be transmitted t o the astronauts p r i o r t o t r a n s f e r from o r b i t a l t o escape t r a j e c t o r y . For example, the stage must be r e - o r i e n t e d i n t o the proper a t t i t u d e i n space p r i o r t o i g n i - t i o n so that the thrust v e c t o r i s applied i n the c o r r e c t d i r e c t i o n . Information on p o i n t i n g the stage could be t r a n s - mitted from the ground t o the astronauts during the Earth
o r b i t coast phase.
The S-IVB stage i s the t h i r d stage o f the Saturn C-5 v e h i c l e . This stage i s c u r r e n t l y being designed t o include p r o v i s i o n s for operation i n space. Two modes of operation f o r t h i s v e h i c l e are shown i n F i g . 2 .
T. J. GORDON
1 Earth o r b i t tanking mode. Here the S-IVB and A p o l l o stages are placed i n t o low Earth o r b i t . The S-IVB then ren- dezvous with a p r e v i o u s l y o r b i t e d tank and r e c e i v e s a l l or a p o r t i o n of i t s p r o p e l l a n t s i n o r b i t . A f t e r being f i l l e d , i t boosts the A p o l l o stages t o escape v e l o c i t y . Stay time in o r b i t f o r t h i s sort of mission i s on the order of s e v e r a l days.
During t h i s time, the S-IVB must provide a t t i t u d e c o n t r o l , be checked out, accept the tanker, and add i t s v e l o c i t y t o the mission p r o f i l e .
2 S-IVB may be used i n an escape mission that requires a parking o r b i t . I n t h i s mission, the S-IVB i s tanked p r i o r t o l i f t o f f and burns a p o r t i o n of i t s p r o p e l l a n t s t o place the A p o l l o and lunar excursion module i n t o Earth o r b i t . A f t e r an o r b i t a l coasting phase, the engine i s r e - i g n i t e d t o impart e s - cape v e l o c i t y t o the payload. I d e a l l y , i n a p e r f e c t l y executed mission, storage time i n o r b i t could be as short as one-half o r b i t . However, i f mission u n c e r t a i n t i e s develop, the stage may be required t o store i t s p r o p e l l a n t s i n o r b i t f o r much longer t i m e s .
To accomplish these two missions, the S-IVB stage i s pow- ered by l i q u i d oxygen and l i q u i d hydrogen and employs a s i n g l e Rocketdyne J-2 engine. I t i s constructed almost e n t i r e l y of welded 201VT-6 aluminum, using techniques proven i n the Thor and S-IV programs. The hydrogen tank i s i n t e r n a l l y insulated and the common bulkhead separatfing the hydrogen and oxygen tanks employs a bonded F i b e r g l a s honeycomb that permits the upper and lower surface t o work together as an i n t e g r a t e d struc- ture while e f f e c t i v e l y s e a l i n g each tank i n t o a c l o s e d con- t a i n e r . These o p e r a t i o n a l requirements n e c e s s i t a t e new sub- systems such as engine r e s t a r t , e x t e r n a l thermal and m i c r o - meteoroid p r o t e c t i o n , and e x t e r n a l storable a t t i t u d e c o n t r o l
system propulsive u n i t s . These are considered as f a c t o r y i n s t a l l e d k i t s or o p t i o n a l equipment, which can be added or removed as the mission d i c t a t e s .
The S-IV program precedes the S-IVB. This v e h i c l e c a r r i e s roughly h a l f the p r o p e l l a n t of S-IVB and w i l l be flown as the second stage of C - l i n 19^3· Many of the features t o be employed in S-IVB e x i s t in the S-IV c o n f i g u r a t i o n . This stage i s also hydrogen/oxygen powered, i n t e r n a l l y insulated, and constructed of 201^T-6 aluminum. This program i s progressing w e l l . F i g . 3 shows the six-engine f i r i n g program i n progress at Sacramento. An i n t e r e s t i n g feature i s the use of the e j e c t o r - d i f f u s e r system v i s i b l e i n the foreground of t h i s f i g u r e . This system i s employed t o lower the pressure at the e x i t plane of the P r a t t & Whitney engines t o avoid n o z z l e
The missions assigned to this stage are of the bang-bang variety. That is, the S-IV will be fired immediately after S-I cutoff, without orbital storage or coasting in space. How then does the S-IV qualify as a "spacecraft system"? After adding its energy to the mission and placing the payload in its orbital or escape flight path, the expended S-IV will be left as a derelict coasting in space. Can this mass be used?
It will be recalled that an Atlas/Score was launched in December 1958. The stage carried a transmitter broadcasting President Eisenhower1 s Christmas greetings to the world.
(Here was an expended stage performing a post-injection mis- sion. ) The same type of application can be made using the large, expended stages of future spacecraft. For example, one might even consider using an expended S-IV, as Wernher von Braun has suggested, as a space way station where lost travellers of the future may find refuge, as a first aid station, and as an S.O.S. beacon. In another application, the expended stage could well serve as a spacious space laboratory, unmanned in early flights. In conjunction with an Apollo, Mercury, or Gemini capsule boosted to orbit with the stage, later labora- tory missions could be manned as shown in Fig. k. Ultimately, perhaps the derelict stages in space can be banded together to form the nucleus of a space station.
These advanced applications of final stages may require qualification and checkout in a simulated space environment.
Today, NASA payloads are subjected to rigorous operational tests in simulated space environments. Since the vehicles themselves can be considered, in a sense, the payloads in future applications, more extensive space qualification of complete vehicle subsystems may be required. Anticipating this marriage of vehicle technology with payload environ- mental requirements, Douglas has recently initiated construc- tion of a large scale space chamber (Fig. 5) to be used in qualifying large subsystems. This chamber will accept an entire engine section of an S-IVB and apply pressures as low as 1 0t o r r , simultaneously with simulated solar radiation and vibration. The facility and other environmental qualifi- cation tools will be used extensively in S-IVB. The evolution of stages into spacecraft represents one of the major design challenges facing the aerospace industry today.
REFERENCE
1 Vought Astronautics, Orbital Launch Operations Report
#00.26, Contract NAS8-853, l6 January 1962.
T. J. GORDON
• H B F R O M O R B I T ι I F R O M E A R T H
" i
1
fl I ι i l l
0 10 20 30 4 0 50 60 D A Y S
Fig. 1 Hours During Which a Lunar Launch is Possible (Booster Capability Beyond Nominal Performance = 250 ft/sec)
Fig. 2 S-IVB Stage of Saturn C-5 Vehicle Shoving Provisions for Operation in Space.
F i g . 3 Saturn S-IVB Stage S i x Engine F i r i n g Program i n Progress at Sacramento, C a l i f o r n i a
T. J. GORDON
S - I V S P H E R E
Fig, h Saturn S-IV Stage Intermediate Orbit Manned Space Station
Fig. 5 Douglas Large Scale Space Chamber to be Used in Qualifying Large Subsystems
