Page 52 - Apollo Moonships

50 On bOard apOllO mOOnships
SM SERVICE PROPULSION SYSTEM (SPS)
The SPS provided the thrust necessary to propel the Apollo mother ship and perform all major velocity changes (retrobraking, midcourse corrections, transearth injection, etc.). Using Aerozine 50 as fuel and nitrogen tetroxide (N2O4) as oxidizer,its single rocket engine—which could be restarted 36 times—
generated 20,500 pounds of force for a maximum of 12.5 minutes.
The thrustchamber engine was mounted in the center section of
the Service Module (SM) and had gimbal capabilities. The SPS
also included a propellant subsystem formed by two fuel
tanks (storage and sump), two oxidizer tanks (storage
and sump), and its correspondent feed lines. Other
major components were the pressurization
subsystem, equipped with two helium tanks;
a bipropellant valve assembly composed of
two gaseous nitrogen pressure vessels; a
thrust mount assembly; an engine injector;
and electrical heat.
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7 6
4 3
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SPS MAIN COMPONENTS
1 Extension nozzle
2 Service propulsion engine
3 Thrust chamber
4 Gimbal ring
5 Fuel sump tank outlet to engine
6 Fuel service connection
7 Fuel heat exchanger
8 Fuel fill point
9 Oxidizer sump tank outlet to engine
10 Oxidizer service
connection
11 Oxidizer heat exchanger
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1
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12 Oxidizer fill point
13 Aft heat shield
14 Fuel sump tank
15 Fuel storage tank
16 Helium tank
17 Oxidizer sump tank
18 Oxidizer storage tank
SM REACTION CONTROL SYSTEM
Used to control the three axes of rotation (pitch, yaw, and roll) in minor translation and orientation maneuvers, the
SM Reaction Control System (SM-RCS) consisted of 16 thrusters grouped in clusters or quads of four, placed every 90° apart around the periphery of the Service Module. The quads had a D-A clockwise designation, with Quad A being on SM Sector 6 (see page 49). Each quad contained its own fuel tanks and plumbing distribution system to operate independently. A number identified its associated reaction engines: thrusters 1 and 4 were used to control roll, while thrusters 3 and 4 controlled pitch and yaw movements. Each quad incorporated a bipropellant system formed by two tanks of nitrogen tetroxide as an oxidizer and two tanks of monomethylhydrazine (MMH) as fuel. Each quad also included a single spherical helium storage tank—gas used as a propellant pressurant agent during the thrusting periods— and other components such as valves, filters, and associated plumbing. The reaction engines could fire continuously,
but they were also able to generate short-thrust impulses for more accuracy in extremely tricky attitude alignment maneuvers. To prevent any malfunction contingency or
in order to save propellant, the SM was able to maintain complete three-axis rotational capability with only two adjacent quads operating.
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4
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5
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SM–RCS QUADS
1 Quad A
2 Quad B
3 Quad C
4 QuadD