The U.S. space agency, NASA, is under strong public, political, and scientific pressure to extend the life of the Hubble Space Telescope. The observatory has returned amazing astronomical discoveries in the past 12 years, but is degrading in orbit. As a result, NASA is considering using space robots to extend the observatory's life. At the same time, there is still a lot of support for the human touch.

Astronauts have repaired and upgraded the Hubble telescope four times since 1993. A fifth trip next year would have replaced its batteries and stabilizing gyroscopes and added two new instruments to keep it running until a successor is launched in 2011. But NASA decided in January to forgo the visit. Without a mission, it estimates the Hubble's batteries and gyroscopes might fail by 2007.

After the loss of the shuttle Columbia last year, the agency argues that sending another shuttle crew to the Hubble entails risks it is not willing to take. It says that when shuttles return to flight with safety modifications sometime next year, it would dispatch them only to complete construction of the international space station.

But a strong public outcry against that decision has caused NASA to investigate the Hubble repair potential after all.

?We at NASA are committed to extending the life of the telescope for as long as possible, and those efforts are under way as we speak," said NASA's chief of space flight Bill Readdy. "We are already investigating methodologies to allow us to preserve battery life and gyro[scope] life.?

Such procedures would be accomplished by ground controllers. These include transmitting new operating software to Hubble computers and turning off instruments when not in use instead of keeping them powered all the time.

In addition, NASA administrator Sean O'Keefe has asked the aerospace industry to submit proposals on how robots could perform maintenance. The agency's head of space science, Ed Weiler, says Mr. O'Keefe's request does not commit NASA to the robotic option, but is needed to get the design process started if he decides to go that way.

?The administrator has made a decision that it's worth pursuing and keeping our options open. I'm also convinced of that because I've seen some of these robots actually working on Hubble mockups and pulling out bolts and screws - actual hardware,? Mr. Weiler said.

Mr. Weiler spoke to an independent panel of experts whom NASA has asked to review repair choices. They are examining whether a robotic or human repair mission would be better. But administrator O'Keefe's recent public comments and request for robotic designs indicate that he has already made up his mind ahead of their deliberations. An aide to the House of Representatives committee that oversees NASA, David Goldston, says the astronaut option is apparently closed.

?NASA has made it clear that they are moving forward in certain ways now separate from the schedule this panel is on,? Mr. Goldston said. ?The administrator has already made it clear that he doesn't see any conclusion that would lead him to send a human mission to the Hubble.?

NASA says a shuttle could not fly to the telescope and still comply with new safety measures recommended after the Columbia disaster. The recommendations include having a safe haven such as the international space station nearby if the shuttle is irreparably damaged. The telescope could not provide such a retreat.

But the chairman of the independent investigation panel that made the safety recommendations, Harold Gehman, says a shuttle visit to the Hubble would not be significantly less safe than one to the station. He says most of the risk of spaceflight occurs at launch and re-entry, no matter what the target.

?The difference between going to the space station or going to the Hubble is probably not much,? he said. ?Going to the international space station helps you out a handful of [a few] percentage points. It's not a big deal. It doesn't overwhelmingly change the equation.?

Although a robotic repair of the Hubble telescope might be feasible, several former astronauts have sent a petition to President Bush endorsing a human mission. They argue that machines would be able to accomplish only a portion of the necessary maintenance and astronauts could better deal with unanticipated technical problems.