CAPE CANAVERAL, Fla. — They risked their lives for the Hubble Space Telescope and did so gladly.

Now, many of the astronauts who worked on Hubble hundreds of miles above Earth are dismayed, bewildered or both by NASA's decision to pull the plug on the mighty observatory.

"I just think it's a huge, huge mistake," says Greg Harbaugh, who performed Hubble repairs during a pair of spacewalks in 1997. "It is probably the greatest instrument or tool for astronomical and astrophysical research since Galileo invented the telescope, and I think it is a tragedy that we would consider not keeping the Hubble alive and operational as long as possible."

Though the decision is not absolute, there appears to be little chance NASA administrator Sean O'Keefe will change his mind about a Hubble servicing mission, deeming it too risky to astronauts in the wake of Columbia.

That would mean a premature death for the 14-year-old observatory whose latest snapshot — revealed last week — showed the deepest-ever view of the universe, a mishmash of galaxies dating almost all the way back to creation.

Tom Akers, part of the spacewalking team that restored Hubble's eyesight in 1993, also favors another mission.

"I definitely think that's an asset that we shouldn't throw away," says Akers, who teaches college math in Missouri. "That's my position and they know it."

NASA has been fending off heavy criticism ever since O'Keefe decided in January to cancel the last servicing, set for 2006.

Last week, at congressional urging, O'Keefe agreed to ask the National Academy of Sciences to study the issue from all perspectives, including using robots to install new cameras or augment battery power.

But he does not expect to reconsider sending up astronauts despite the outcry.

An Internet petition has collected thousands of names, O'Keefe's e-mail system is clogged with complaints, members of Congress are demanding reviews by independent groups, and the chief Columbia accident investigator is urging a public-policy debate on the Hubble gains versus shuttle risks.

Even John Glenn has weighed in, telling President Bush's commission on moon and Mars travel that another servicing mission is necessary "to get every year's value out of that thing."

The canceled servicing mission would have been the Hubble's fifth and would have equipped it with two state-of-the-art science instruments already built and worth a combined $176 million, as well as fresh batteries and gyroscopes. The work by spacewalkers would have kept Hubble humming until 2011 or 2012.

Without intervention, Hubble will probably take its last picture in 2007 or 2008. O'Keefe says he does not see how NASA could launch a servicing mission before then without shirking the recommendations of the Columbia Accident Investigation Board.

As an alternative, engineers are trying to figure out how to prolong the telescope's life with robotic help.

NASA is quick to point out that when Hubble was launched, 15 years of service were promised, a goal that will be met next spring. The space telescope has helped scientists gauge the age and size of the universe and confirmed the existence of black holes.

Regardless of Hubble's merit, O'Keefe says he cannot let astronauts fly to the telescope and risk being stuck there if their shuttle is damaged by foam or other launch debris.

There's no way a stranded shuttle crew could get from Hubble to the international space station in an entirely different orbit.

The NASA chief insists his decision is rooted in safety, and he's recruited the agency's chief scientist, John Grunsfeld, a two-time Hubble space repairman, to help defend his decision.

Yet eyebrows were raised given the timing of the announcement: It came two days after President Bush unveiled a plan to complete the space station and retire the shuttle by 2010, and to send astronauts back to the moon by 2020.

Glenn worries the Columbia accident may be making NASA gun-shy.

Harbaugh, now director of the Florida Air Museum, says he felt no more danger flying to Hubble than anywhere else in space. There is little difference, he says, "in risk between launching to Hubble and launching to station and just launching period."

Astronomers would be at a loss if Hubble is abandoned and its powerful replacement, the James Webb Space Telescope, is lost in a rocket explosion or has crippling design flaws. That's why so many would rather wait to decommission Hubble until Webb is launched, now set for 2011.

While NASA's Chandra X-ray Observatory and Spitzer Space Telescope see the universe in X-ray and infrared, respectively, Hubble observes visible light and peeks into the ultraviolet and near-infrared. Webb will focus on the infrared and outdo Hubble with a mirror more than double its size.

Astronauts — Hubble repairmen included, who say they would do it again — like to point out that a ship is safe in the harbor, but that's not what ships are built for.

Says Bruce McCandless, who helped deliver Hubble to orbit and now works in industry: "John Paul Jones is also reported to have said, 'Give me a fast ship for I intend to sail in harm's way.' He wasn't going to sit in the harbor, either."