Page 36 - Apollo Moonships

34 On bOard apOllO mOOnships
S–IVB THIRD STAGE
The last stage of the Saturn V had a single J-2 engine fed by a 64 000 gallons fuel tank (liquid hydrogen, or LH2) and a 20 000 gallons oxidizer tank (liquid oxygen, or LOX) situated at the bottom of the propellant tank. The J-2 engine turned on at 114.5 miles of altitude and drove the Apollo spacecraft up to a parking orbit around the Earth located 155 miles above sea level. Once the astronauts were authorized to continue the mission, the S-IVB stage ignited again, accelerated at 25 000 mph, and sent the spaceships heading to the moon. The rocket engine was attached to the thrust structure, an inverted aluminum-alloy truncated cone that also provided fixation points to other components, such as the engine piping, wiring, and electrical and electronic panels. At the top of the S-IVB stage was the forward skirt assembly, which served as a mounting structure for the instrument unit, the nerve center of the Saturn V rocket (see page 25), and for other equipment. Another load- bearing component—the aft skirt—was located on the bottom of the stage and linked it with the interstage forward support ring and S-II stage.
SATURN V S–IVB STAGE AND INSTRUMENT UNIT CUTAWAY
1 J–2 engine (5)
2 Engine gimbal point
3 Helium bottles
4 Thrust structure
5 O2/H2 burner
6 Liquid oxygen (LOX) feed line 7 Non propulsive vent
8 Aft skirt
9 Ullage rocket motor
S–IVB STAGE SIZE
10 Bottom of LOX tank 11 LOX tank sump
12 Cruciform baffle
13 LOX tank ring baffles 14 LOX tank probe
Instrument Unit
Forward skirt
Propellant tank
1
9
8
5 10 7
6 11
2
12 4
3
14
13
59.3 feet
15 LOX tank bulkhead
16 LOX tank manhole cover 17 Internal insulation
18 LH2 tank ring baffles
Aft skirt
MAJOR STRUCTURAL COMPONENTS
J–2 engine
21.6 feet
5.20 feet
1 THRUST STRUCTURE
2 AFT SKIRT
7.0 feet