Dec. 9, 2004 — NASA's plan to send a robot to do an astronaut's job is too expensive, technically risky and too time-consuming to develop, said a scientific panel that investigated a NASA proposal to outfit the Hubble Space Telescope for several more years of scientific research.

The space agency backed away from plans to send shuttle astronauts to repair and upgrade the orbiting observatory following the February 2003 Columbia accident.

In the wake of a biting report about oversights that led to the accident, investigators recommended that NASA have in-orbit rescue capabilities or be able to house shuttle astronauts aboard the space station should their craft become too damaged for a safe return to Earth.

Opting to complete the space station as quickly as possible and retire the fleet, NASA managers decided to cancel the shuttle's final servicing call to Hubble to avoid having to tie up two shuttles for the mission (the second craft on standby as rescue vehicle), as the station's orbit is inaccessible from Hubble's location.

Public outcry over NASA's plans spurred the agency to come up with another option to save Hubble. Rather than send a shuttle crew, managers decided to explore developing a robot to fix critical systems and install new science gear.

A committee of the National Academy of Sciences, however, told Congress Wednesday that plan wasn't viable.

"It was clear the shuttle approach was a much-lower mission risk," said committee member Richard Truly, a former NASA administrator.

Further, the committee said in its 164-page report, using the shuttle to save Hubble would be worth the risk.

The panel determined that developing and flying a robot could cost more than $2 billion, about the price of Hubble itself and far more than the agency's planned replacement telescope, which is slated for launch in 2010.

Members also questioned whether the technology to develop a robotic repairman could be developed before Hubble suffers equipment breakdowns that will make it inoperable. Of particular concern are Hubble's gyroscopes, which keep the telescope properly positioned for celestial observations and its batteries.

Before the Columbia accident NASA also had planned to replace two science instruments aboard Hubble. The panel said some of the tasks may be too technically demanding for a robot to accomplish.

NASA is not bound by the panel'e recommendation, and will likely mull over the problem further before deciding what to do about Hubble.

But even if Hubble cannot be saved for scientific work, NASA must come up a plan to safely remove the 13-ton observatory from orbit to minimize the chance that it falls from space and crashes in a populated area. Heating from the sun expands Earth's atmosphere, gradually creating drag on the low-Earth orbiting spacecraft.

NASA had been using the shuttle to periodically boost the telescope's orbit. At the end of Hubble's mission, spacewalking astronauts were to attach a propulsion module so the telescope could be safely steered from orbit and plunge through the atmosphere over the ocean.

The panel determined having astronauts attach the propulsion module is a much safer bet than relying on a robot to do the job.