Posted: Tue, Aug 21, 2007, 7:32 AM ET (1132 GMT)
A valve implicated in a partial failure of an Atlas 5 rocket in June has been replaced in the engines of the upper stages of both the Atlas 5 and Delta 4. The hydrogen valve in the RL10 engine, used in the upper stages of both rockets, has been modified to prevent a freezeup experienced during an Atlas 5 launch of two NRO reconnaissance satellites in June. The valve allowed liquid hydrogen fuel to leak out, causing the RL10 engine to shutdown several seconds early, placing the satellites into a lower-than-planner orbit. The satellites have been gradually raising their orbits using their own thrusters. The redesigned valve has been incorporated into the engines for upcoming Atlas 5 and Delta 4 launches, with the first being an Atlas 5 launch of a next-generation military communications satellite in mid-September.

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