Tank pressure control of the S-IC stage

To obtain a proper flow of propellants towards the five F-1 thust engines, the tank pressure has to be kept within a certain range of pressure values. These conditions are achieved by using a pressure relief system and a gas supply system. Pressure sensors monitor the tank pressure and will trigger the relief system and the gas supply system respectively, when the pressure has become too high or too low.
During the first stage boost phase, the heart of both systems is formed by the pressure control modules. These modules are linked to the pressure sensors and a network of valves. They make a proportional control of the tank pressure possible.
Prior lift-off, during pre-pressurization, the pressurization gas is supplied from separate regulated ground sources for each propellant tank.

The relief system is basically a vent system. Each propellant tanks has two vent valves.

Two modes of operation can be distinguished for the tank pressurization:

  1. Prior to lift-off
    The pressurization process is called pre-pressurization. Cold Helium gas is used as the pressurization gas and is supplied by the ground source equipment (GSE).
  2. During the the burn of the five F-1 engines of the S-IC stage
    During this phase of the flight when liquid Oxygen and RP-1 fuel is consumed by the F-1 engines, a high flow rate of pressurization gas is required to achieve the proper tank pressure. The cryogenic liquid Oxygen tank is pressurized with gaseous Oxygen which is obtained by tapping off a small fraction of the liquid Oxygen and routing it through heat exchangers which are mounted around each exhaust duct of the turbo pumps which feed the F-1 enigines. In order to pressurize the non cryogeninc fuel tank, hot Helium gas is used, which is obtained by routing cold Helium gas from storage bottles through the five heat exchangers. The He storage bottles are located inside the liquid Oxygen tank.
Mode 1
Mode 2

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Copyright 2005 by   Sander Panhuyzen
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