NASA needs to keep more astronauts on staff than planned, a new report revealed.

NASA's astronaut corps peaked at 149 in 2000. It's now down to 60. NASA projects it will need a minimum of 55 to 60 astronauts over the next five years.

Many astronauts have retired or quit with this year's end of the space shuttle program. But a robust corps still is needed, the report noted.

The new report, by the National Research Council, states that NASA's models for predicting its astronaut staffing needs in the near future do not fully account for unexpected personnel changes like retirements and medical leave.

Last year, NASA asked the council to look at the role and size of the astronaut corps during this transition time. A committee of 13 experts conducted the study. Five of them were former astronauts.

It's even more important that the talent level, diversity and capabilities of the astronaut office be sustained, Joseph Rothenberg, a former senior NASA official who helped lead the committee, said in a statement.

NASA's space station astronauts face a daunting training regime that has been streamlined in recent years, but still includes years of preparation for the typical six-month stays on the orbiting laboratory, the report states.

Station crews must be well-versed with the station's American-built hardware as well as equipment from NASA's Russian, European, Japanese and Canadian partners. Space Station training requires astronauts to spend time abroad in Russia and Europe to prepare for their missions

In addition there are space station spacewalk repairs to train for, software systems to learn and docking procedures for the international fleet of robotic and crewed spaceships that visit the orbiting lab.

NASA's nine newest astronauts joined the space agency's ranks in 2009 and have been training to fly on space station missions ever since.

The class includes six men and three women who have been training to fly on Russia's Soyuz spacecraft and NASA's new deep space capsule, which is expected to be used for the trip to an asteroid called for by President Barack Obama.