Apollo Command Module RCS Fuel Tank

An engineering test unit from Bell Aerospace in 1965. It provided Monomethylhydrazine (MMH) fuel to the spacecraft’s twelve Rocketdyne SE-8 Reaction Control System (RCS) engines used for attitude control. A similar tank was used to store the oxidizer (N204 ) which was combined and ignited upon contact with the MMH. This is a hypergolic fuel system which does not require any separate ignition system.

Titanium MMH tank, with various valve connections (diagram below). Helium pressurizing gas pushed against flexible bladders in the fuel and oxidizer tanks to force the weightless propellants out of the tanks.

From the Spaceaholic post on the oxidizer tank (the compliment to this tank): “The tank incorporates an integral bladder for positive expulsion. Positive expulsion systems were necessary to provide continuous propellant flow to the engines regardless of vehicle position, environmental and dynamic forces, or zero gravity conditions where the propellant tended to float in the tank and cling to the tank wall instead of flowing naturally toward the tank outlet.

Propellant is contained within the bladder. A pressurizing port is provided on the tank shell and a propellant outlet port and liquid bleed tube are incorporated in the diffuser assembly. The propellant is loaded into the bladder through the propellant outlet port. When the bladder is full, helium, supplied by another onboard Command Module tank, was applied to the pressuring port of the tank to pressurize the area between the tank shell and the outside of the bladder. The pressurizing gas caused the bladder to collapse around a diffuser tube (which runs from the propellant outlet down through the center of the tank) and the propellant was expelled through the outlet port.”

The metal tag reads (from photo below):
TANK MMH POSITIVE EXPULSION
Manufactured 6-2-65
Contract NAS9-150 (indicates Apollo CSM)
NAA (North American Aviation) Control Number: ME282-0007-0001
Serial Number 8
Max Working Pressure: 360 PSIG
Proof Pressure: 480 PSIG
Burst Pressure: 540 PSIG

An artifact from the Future Ventures’ 🚀 Space Collection.