NASA's Lunar Reconnaissance Orbiter (LRO) is now being planned May 20 aboard an Atlas V from Cape Canaveral Air Force Station. The moon mapper and a piggyback payload that will search for polar ice had been slated to fly on April 24, and then tentatively for May 7.
Launch of the mission must be timed to put both the orbiter and the LCROSS shepherd and impactor on a proper course to achieve its objectives. Launch opportunities come up about every two weeks, when the proper polar orbit to terminator juxtaposition can be achieved at lunar orbit insertion upon arrival.
NASA was forced to abandon an April 24 launch and launch opportunities between May 7 and May 9 when a planned May 9 launch of another Atlas V, with a military communications satellite slipped to March 13.
NASA had considered trying to launch LRO-LCROSS during the early May window but ultimately decided that Atlas turnaround operations would "make the schedule too tight."
NASA earlier this week set March 12 as a tentative launch date for shuttle Discovery's International Space Station assembly mission. But the agency has yet to officially book the date on the Air Force Eastern Range, which provides tracking, range safety, weather forecasting and launch scheduling services for all missions from Kennedy Space Center and Cape Canaveral Air Force Station.
The U.S. Air Force would have to agree to push back the March 13 Atlas V launch for Discovery to fly on March 12. It typically takes two days to reset range systems for the launch of different vehicles.