Hubble will remain in orbit as long as it can fulfill its duties, then be brought crashing back into Earth's atmosphere, with re-entry expected in 2011, officials said.

"It is a sad day that we have to announce this," John Grunsfeld, chief scientist for the National Aeronautics and Space Administration (NASA), said at a news conference late Friday.

"We will get as much life as we can out of the Hubble telescope, and we will continue to support research and analysis even after re-entry," he said.

NASA administrator Sean O'Keefe broke news of the "painful decision" to cancel the fifth servicing mission to Hubble to mission managers at the Goddard Space Flight Center in Greenbelt, Maryland on Friday.

Goals of the mission, scheduled for mid-2005, were to install a new wide field planetary camera and a supersensitive ultraviolet spectograph designed to observe new hot stars, quasi-stellar objects and the insterstellar medium.

But it would have required expensive shuttle safety updates that are not necessary for the shuttle's only other job, working on the International Space Station, Grunsfeld said.

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 seven astronauts on board.

"It was a question of looking at the risk elements involved to support the mission," Grunsfeld said.

Hubble depends on periodic service calls by spacewalking astronauts who upgrade its equipment and replace or repair its gyroscopes and batteries.

It was unclear how long the telescope would continue to function without the 2005 supply mission.

"It could die tomorrow, it could last to 2011," Dr Steven Beckwith, director of the Space Telescope Institute at Johns Hopkins University in Baltimore, Maryland, was quoted as saying in The New York Times.

NASA had no further trips to the Hubble planned until a final "close-out mission" in 2010.

Friday's announcement marked the first change to an existing NASA mission since President George W. Bush two days earlier announced new directions for the space program, saying he wants to send manned missions to the moon from 2015, and eventually to Mars and beyond.

But the space agency was allocated only an additional billion dollars over five years, in addition to its annual budget of 15.4 billion dollars, to work toward that goal.

The decision to stop servicing the Hubble devastated scientists, since the telescope has provided a wealth of information and stunning images of the universe since being dropped off in space in April 1990.

Among its achievements, Hubble has established the age of the Milky Way at between 13 and 14 billion years, helped gather evidence to support the Big Bang theory and provided the first convincing proof by an optical telescope of the existence of black holes.

"It was a tough and painful decision, but given where we are now in terms of the flight of the space shuttle and the context of the national space policy outlined by President Bush, it was a decision we had to make," said Glenn Mahone, a NASA spokesman.

NASA plans to put a new-generation orbital observatory, the James Webb Space Telescope, into orbit in 2009.

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