NASA is pushing back an internal date, by a year, to send astronauts into space on a replacement to the Space Shuttle, top managers said Monday.

The Constellation program, with its Ares 1 rocket and its Orion capsule for astronauts, is in development as the replacement to the Space Shuttle, which has its last flight scheduled in May or June of 2010. NASA has kept a March 2015 date as the official goal for returning astronauts to the International Space Station, but has now pushed back an aggressive internal date from September 2013 to September 2014. Eventually the rockets are supposed to return humans to the moon.

The Constellation program is depending on the retirement of the shuttle, which costs hundreds of millions of dollars per flight, to pay for the rapidly ramping up development of Ares and Orion.

But concerns over the 2009 federal budget are forcing NASA to be more cautious in its development timeline. Most expect that the US Congress, anticipating a new administration in January, will avoid passing a budget this fall and will instead pass a continuing resolution, which freezes spending at the previous year’s levels. That means NASA could be stuck at 2008 spending levels for the for six months of fiscal year 2009, according to Aviation Week and Space Technology, which scored an interview with NASA Administrator Mike Griffin.

The Associated Press also reported that a safety panel has concerns over the inclusion (or lack thereof) of backup safety systems in Constellation designs, though managers defended the designs as works in progress. The panel’s safety report can be found here.

Image credit: NASA/MSFC