NASA needs to increase the size of its space-flying crew to meet the upcoming projects over the next five years, suggests a report.

Its astronauts have substantially reduced in recent years due to retirements or the end of the space shuttle programs.

The report says, In order to meet the minimum manifest requirements for the ISS, NASA's current 25% management reserve is too low and should be increased.

According to the National Research Council, United States does not currently have enough astronauts to meet the demand, as the American astronaut corps has steadily decreased as most of them retired after its shuttle program ended in July this year.

The report ,published by a non-profit organization, says: A significant amount of NASA astronauts have been reduced in recent years, from about 150 in 2000 to only 61 in 2011.

It currently has only 61 astronauts. To meet the demands of the International Space Station (ISS) crew requirement, NASA has to take significant steps to ensure that it maintains a highly trained corps for the upcoming programs.

A committee of 13 experts, including five astronauts, prepared this report for NASA.

The report says, Given the range of potential crew assignment constraints and uncertainty in future requirements, the astronaut corps appears to be sized below the minimum required.

The report also notes that the current plan for the size of the astronaut corps does not have the flexibility to accommodate commercial, exploration, and new mission development tasks, or unexpected increases in attrition.

It says that the currently projected minimum staffing target size for the active astronaut corps poses a risk to the US investment in human spaceflight capabilities.

NASA is undergoing an uncertain transformation. It should prepare for an uncertain future if it fails to increase the size of its space program crew, to at least meet the minimum needs in near future.