Despite progress in its effort to retire the space shuttle fleet, NASA is now unlikely to meet its initial September deadline, according to a government report released yesterday.

The 32-page report from NASA's Office of the Inspector General concludes that it will probably take NASA until the first or second quarter of 2011to complete the last of the four remaining shuttle flights. The report was released just prior to today's meeting of NASA directors at the Kennedy Space Center in Florida for a flight readiness review of the space shuttle Discovery 's scheduled April 5 launch of a mission to the International Space Station.

The Inspector General's report said that while the space agency continues efforts to complete the four remaining shuttle flights by September 30, fulfilling that plan is unlikely.

"Based on calculations by the Office of Inspector General, historical flight rates, and internal NASA evaluations, NASA is not likely to meet its September 2010 timetable, and it will most likely take until the second quarter of FY 2011 to complete the last of the planned Space Shuttle flights," the report noted.

According to the report, pushing as hard as possible to meet the September 30 deadline would cost up to $54 million for personnel overtime. The report also notes that extending the program beyond September would cost about $200 million a month.

NASA officials did not respond to a request for comment on the report.

Meanwhile, President Barack Obama's 2011 federal budget proposal, which was introduced in February, calls for eliminating NASA's plan to return humans to the moon by 2020, and turning the agency's attention to developing new engines, in-space fuel depots and robots that can venture into space.

The proposed budget plan calls for NASA to work with commercial aeronautics companies to design and build so-called space taxis that could take astronauts to the space station and eventually into outer space.

Obama plans to hold a summit meeting on his plans for NASA in April.