SLS main to sport 4-engine setup

The main stage of NASA's Space Launch System being developed for deep space exploration will use four RD-25D space shuttle main engines. Engineers also considered three- and five-engine versions, Boeing officials said at the National Space Symposium in Colorado. After the RD-25D supply is used up, a throwaway version, the RD-25E, will be used. The main stage of SLS will be assembled at NASA's Michoud Assembly Facility in New Orleans using friction-stir welders, and probably will be built of aluminum lithium. The first unmanned SLS flight is scheduled for 2017, and the first flight carrying the Lockheed Martin developed Orion crew capsule is slated for 2021. (Source: Aviation Week, 04/18/12) The RD-25 engines will be tested at Stennis Space Center, Miss., which is also testing the J-2X that will be used in the second stage.