Report: NASA needs to keep more astronauts on hand

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, to fill crew slots aboard the International Space Station and help forge the way for exploration in the decades ahead.

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

But the National Research Council warns that may not be enough.

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 — five of them former astronauts — conducted the study.

NASA's current projected target size for the astronaut corps "poses a risk to the U.S. investment in human spaceflight capabilities," the report stated. It does not offer enough flexibility to accommodate sudden departures or other matters.

"Reducing the size too much can create shortages of key skills," the report said.

In this time of change and uncertainty, "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. "Making sure NASA maintains adequate training facilities is also essential to ensure a robust astronaut corps."

Because there's different medical requirements for spending six months on a space station, versus a week or two on a space shuttle, NASA needs extra astronauts on hand in case crew replacements are needed because of illness or disability. Besides those assigned to station missions, astronauts will be needed in Houston to help keep the space station running and deal with any emergencies, help develop future spacecraft, and interact with the public, noted the 102-page report.

NASA plans to periodically choose a small group of new astronauts, a good approach, the report said. The last group — consisting of nine — was selected in 2009.

Until U.S. companies start launching crews -- estimated to occur in three to five years -- NASA astronauts will continue to hitch rides on Russian Soyuz capsules launched from Kazakhstan. The Soyuz rockets are grounded and all crew flights to the space station are on hold because of last month's failed launch of space station cargo. The supply vessel crashed into Siberia.

NASA said the space station -- continuously inhabited for nearly 11 years -- will need to be abandoned temporarily if a new crew cannot be launched before the last of the six residents fly back to Earth in mid-November