"Am I optimistic? Yes. Is it a done deal? No," said Ed Weiler, NASA associate administrator for space science.

Weiler said that in response to an agency request for information, 26 proposals have been submitted on ways the telescope could be serviced or de-orbited without the use of human crews.

The proposals have come "mostly from commercial companies," Weiler added. NASA had asked for ideas to identify what technologies might be available to use on a Hubble repair mission and what companies might be interested in participating in such an effort.

On Jan. 16, NASA Administrator Sean O'Keefe announced that the agency would no longer use the space shuttle fleet to service the telescope's ailing systems due to safety issues.

Following the Feb. 1, 2003, shuttle Columbia accident, the board investigating the disaster called for limiting shuttle flights to those where the crew of a damaged craft could take refuge aboard the International Space Station. Such contingencies would arise if a shuttle's crew lacked a specific onboard repair capability or if damages sustained during launch exceeded the crew's capacity to save the spacecraft.

A shuttle flight to service Hubble would not be able to fly on to the station in the event it was damaged and would have to rely exclusively on onboard repair capacity.

O'Keefe decided that because any Hubble mission would lack the space station refuge option, the increased risk to the crew outweighed the value of the Hubble.

Without the shuttle, there appeared to be no other way to conduct the repairs to the telescope, which confronted the astronomy community with the grim possibility the Hubble could die of malfunction years before before a replacement space telescope could be launched.

But that possibility has raised such a public outcry that O'Keefe relented slightly on his initial decision and agreed to 1) convene a special inquiry to evaluate the risks of and alternatives to a Hubble repair mission and 2) ask the aerospace industry for ideas on other ways to save, service or de-orbit the craft.

The National Academy of Sciences is studying both the decision to cancel the shuttle servicing mission and possible robotic flights to the telescope.

Weiler said even before the NAS study -- now set for summer -- is completed, the chances for a robotic rescue will be increasing. Failing a repair mission, he said, NASA is considering sending a robotic craft to take control of the telescope and send it into fiery atmospheric re-entry.

The 26 proposals included complete robotic mission scenarios as well as "pieces of missions," Weiler said. In a sense, any rescue or return mission is racing the clock, as Hubble's batteries slowly drain and the craft's critical gyroscopes -- used to aim and hold the telescope in position -- break down.

"They can last until the end of '07," Weiler said of the batteries. After that, failure of the power system would send the telescope out of control, making any robotic mission impossible.

Even the review by the national academies, due out this summer, might be too late.

"We need to be ready to get (a request for proposals) in June," Weiler said. "If we want a robotic mission in '07 or '08, we need to get contracts out this fall."

Weiler also said a two-month study of the Hubble issue is underway at the Goddard Spaceflight Center in Greenbelt, Md., as well as five or six other NASA facilities. That in-house review also is looking at robotic systems that could be flown to the telescope, he said.

Whatever is decided will be a tradeoff, Weiler suggested, between the cost of such a mission and the value of the years that could be added to Hubble's usefulness. He pointed out that no nation has ever conducted a purely robotic servicing of a spacecraft.

Crews aboard space shuttles conducted satellite rescues in 1984 and 1985, and tested a satellite refueling concept in October 1984. But the refueling technique was never used. Use of the shuttle as a servicing system for commercial and civil satellites was canceled following the January 1986 Challenger disaster.

Russia has conducted robotic docking of supply craft to the MIR and International Space Station, but cosmonauts and astronauts aboard always have been in final control of the tasks. Japan has tested a small robotic docking spacecraft, but has developed it into an operational system.

Thus, if NASA chooses a fully robotic mission to Hubble, it would become another first for U.S. space technology.

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