Ascent Propulsion Subsystem
The Ascent Propulsion Subsystem uses a fixed, constant-thrust rocket engine. The system includes the associated ambient helium pressurization and propellant supply components. The engine develops 3,500 pounds of thrust in vacuum, sufficient to launch the Ascent Stage from the lunar surface and place it in orbit. Two main propellant tanks are used: one for fuel, the other for oxidizer. The tanks are installed on either side of the Ascent Stage structure. The propellant supply sections in this subsystem also provide for fuel and oxidizer interconnect to the Reaction Control Subsystem as a propellant supply for the latter during select mission phases. The fuel is a 50/50 mixture of hydrazine and unsymmetrical dimethyl hydrazine. The oxidizer is nitrogen tetroxide. These propellants constitute a hypergolic system, that is, engine ignition results when the propellants come in contact with each other.