The National Aeronautics and Space Administration announced mid-January it was canceling the telescope's next servicing mission, scheduled for 2006, by shuttle astronauts.

NASA cited safety concerns and also budget problems for its decision that effectively condemns the Hubble to an early demise.

The telescope will remain in orbit as long as it can fulfill its duties, then be brought crashing back into Earth's atmosphere.

While a service mission would have allowed the Hubble to keep going beyond 2010, it could now stop working as early as 2007.

"We are dealing with a level of risk that's higher than on" the International Space Station (ISS), O'Keefe told journalists Thursday, to explain what he earlier described as the "painful decision."

The next mission to the Hubble would have required expensive shuttle safety updates that are not necessary on the ISS, the shuttle's only other job, NASA's chief scientist John Grunsfeld said late last week.

The updates were deemed necessary following the loss of the space shuttle Columbia, which disintegrated upon re-entry into the Earth's atmosphere in February 2003, killing all seven astronauts on board.

NASA's decision has provoked criticism among researchers and at Congress.

O'Keefe said Thursday that he was asking retired admiral Hal Gehman his view on NASA's decision in response to Democratic Senator Barbara Mikulski's request that he reconsider.

"I've asked admiral Gehman for his view -- not his judgment, not his analysis -- just his view," O'Keefe said, offering little hope, however, that he intends to go back on the decision.

NASA's announcement that it was dropping the Hubble came just days after President George W. Bush announced an ambitious space program to take US space travel back to the Moon to prepare the way for later missions to Mars.

SPACE.WIRE