Pratt & Whitney is aiming its new RL50 upper-stage engine at future versions of the Boeing Delta IV and Lockheed Martin Atlas IV evolved expendable launch vehicles (EELVs) now under development.

The 50,800-65,000lb (226-289kN)-thrust liquid hydrogen-fuelled engine is being developed privately and is expected to be available in 2003. The RL50 is designed to fit the same physical envelope as that of P&W's RL10 cryogenic upper-stage engine, used in Atlas, Titans and new Delta IIIs, but has over twice the thrust.

Incorporating advances developed by the engine maker under the US Air Force's Integrated High-Payoff Rocket Propulsion Technology programme, the RL50 promises a specific impulse - a measure of rocket motor efficiency - of over 470s, compared to the RL10's 444-465s.

Source: Flight International