|astronautix.com||Delta 3 - 2|
The upgraded cryogenic second-stage Pratt & Whitney RL10B-2 engine is based on the 30-year heritage of the reliable RL10 engine. It incorporates an extendable exit cone for increased specific impulse (Isp) and payload capability. The basic engine and turbo pump are unchanged relative to the RL10. The engine gimbal system uses electromechanical actuators that increase reliability while reducing both cost and weight. The propulsion system and attitude control system (ACS) utilize flight-proven off-the-shelf components. The second-stage propulsion system produces a thrust of 24,750 lb with a total propellant load of 37,090 lb, providing a total burn time of approxi-mately 700 sec. Missions requiring more than one restart are accommodated by adding an extra helium bottle for the additional tank repressurization. Propellants are managed during coast by directing hydrogen boiloff through aft facing thrusters to provide settling thrust. Propellant tank pressurization during burn is accomplished using hydrogen bleed from the engine for the LH2 tank and helium for the LO2 tank. After spacecraft separation, the stage is safed by dumping propellants followed by venting of the tanks.