The S-IVB stage (500 series)

The powerful J-2 engine is prominent in this photograph of a Saturn V Third Stage (S-IVB) resting on a transporter in the Manufacturing Facility at Marshall Space Flight Center in Huntsville, Alabama.

credit to NASA

General information

The S-IVB stage used liquid hydrogen and liquid oxygen as propellants. The use of hydrogen and oxygen as high performance propellants was condidered essential for the upper stages of the three stage Saturn V to obtain an efficient thrust to mass ratio. Early calculations on the launch vehicle design showed that if propellants were to be used with less performance, it would have imposed an unacceptable design constraint on the Apollo payload or the required launch vehicle itself would have become so huge that it would have had a large financial impact on the Apollo program.

The S-IVB stage was an uprated version of the S-IV. The designation S-IV has its roots in an initial design for a four stage moon rocket. The design called for a three stage rocket eventually. The S-IV stage with its six cryogenic RL-10 engines became used as a second stage for the Saturn I booster. But as soon as the requirements for the third stage of the Saturn V stack came into view, it became clear that it was not necessary to design a new stage, the S-IV with moderate modification would do the job quite well.

The slightly larger S-IVB had a single cryogenic J-2 engine which would provide about 104 Ton of thrust. On the contrary, the S-IV with its six cryogenic RL-10 engines had a total thrust of about 37 Ton. The S-IVB was produced in two versions: the 200 series which was used as a second stage for the Saturn IB booster and the 500 series which was used as a third stage for the Saturn V booster. The S-IVB 500 would have the important ability to restart the J-2 engine in space, which was essential to leave an Earth parking orbit on a trajectory to the Moon. This manoeuvre became known as Trans Lunar Injection (TLI). This parking orbit was an important mission requirement, it not only provided the opportunity to have a two hours go / no go check on the spacecraft, but it also provided the necessary flexibilty in the mission parameters, the launch window was one of them.


S-IVB stage main parts

From top down:
  1. The forward skirt
  2. The fuel tank and the liquid oxygen tank with their common bulkhead
  3. The aft skirt
  4. A conical shaped thrust structure
  5. One J-2 engine
  6. The interstage, a conical shaped connecting ring between the S-IVB and the S-II stage


Characteristics

  1. Height      : 14.49 meter
    Diameter  : 6.51 meter
    Mass empty stage           : 11.28 Ton
    Mass of propellants        : 106.61 Ton
    Mass of loaded stage      : 117.89 Ton
    Amount of fuel:
    Liquid Oxygen   : 86.88 Ton, 76 569 litres (Mass dens. LOx: 1.137 kg/ltr)
    Liquid Hydrogen : 19.73 Ton, 242 808 litres (Mass dens. LH2: 0.070 kg/ltr).
  2. Typical flight profile
    • First burn at an altitude of 160 km for 150 sec. to go into a 190 km high Parking orbit;
      velocity: 7 390 m/sec (22.5 Mach) (relative to Earth)
    • Second burn for 358 sec. for Trans Lunar Injection; velocity: 10 800 m/sec (33.0 Mach) (relative to space)
  3. J-2 engine:
    J-2 engine thrust : 104 Tons (metric)
    Height of J-2 engine : 3.38 meter
    Diameter of J-2 engine : 2.07 meter
    Mass of J-2 engine : 1.58 Ton
    Combustion pressure inside an J-2 chamber : 53 bar
    Combustion chamber diameter probably around 0.47 meter.
    Fuel consumption rate per J-2 engine : 0.23 Ton/sec.
    Specific Impulse at ground level : 440 sec.
  4. Manufacturer of the J-2 engines: Pratt & Whitney (initially)
    North American Aviation, Rocket dyne Division (eventually)
    Manufacturer of the S-IVB stage: Douglas Airplane Co.

This picture shows the flight path of the SA-503 (Apollo 8) during ascent. The J-2 of the S-IVB stage was ignited at about 8½ min. into the flight at an altitude of 160 km. This burn took about 2½ min. and brought the S-IVB with the Apollo spacecraft on top into a 185 km high parking orbit.

Apollo 8 ground track during Ascent, Earth Parking Orbit,
Trans Lunar Injection Burn and Trans Lunar Coast

This picture shows the ground track of the SA-503 (Apollo 8) during the first 3 hours into the flight: from lift-off until Trans Lunar Injection.
The S-IVB provided thrust at two moments:
A first 2½ min burn, which was the last burn in the boost phase and was meant to obtain a parking orbit around Earth.
And a second 5 minutes burn 2 hours and 50 min. into the flight for trans lunar injection.
After the Apollo spacecraft had been separated from the S-IVB stage, the S-IVB was sent into an orbit around the Sun.

Plan View S-IVB stage Forward section, Looking down

 
The S-IVB 500 stage

From top to bottom: the forward skirt, the combined oxygen & hydrogen tank, the aft skirt, the conical shaped thrust structure and the J-2 engine

Plan View S-IVB stage Aft section, Looking up

 



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Copyright 2005 by   Sander Panhuyzen
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