Thursday, February 25, 1999 Published at 12:05 GMT
Hubble in danger of shutdown
The space shuttle proved its worth with Hubble
Nasa may have to make an emergency repair mission to the Hubble Space Telescope.
Hubble is having problems with its gyroscopes. These are used for stability and for fine control when pointing the telescope at the astronomical objects.
If the problems worsen, Hubble may shut itself down, bringing a temporary halt to scientific observations.
Hubble needs three gyroscopes to work properly and it has lost two of its six. Another gyro "is sick and may go down in three months," Nasa's Dan Goldin told the US Congress.
If the telescope loses a fourth gyro, it will switch into an automatic "safe mode" until repairs are made, he said. A decision about a repair mission is expected no later than next week.
But although it appears to have sufficient gyroscope back-up, David S. Leckrone, senior project scientist for the telescope, said the observatory is already on the edge of shutting down.
Close to shut down
"If another gyro fails, we would not put the fourth gyro back into service," he said, meaning that the Hubble is really only one failure away from being shut down.
An earlier servicing mission to change cameras and other equipment was flown in 1997. The successful flight showed the worth of the space shuttle. A final servicing mission is planned for 2003.
Hubble was launched in 1990. Almost immediately it hit problems when astronomers realised that it was short-sighted - its 2.4-meter mirror had been ground to the wrong curvature.
A new set of optics was installed by astronauts in 1993 which corrected the problem. Since then, Hubble has produced the most stunning pictures ever taken of the cosmos.
Some of the objects it has imaged are more than 13 billion light years away, near the theoretical edge of the universe.
Hubble was designed to remain operational until 2010 with periodic servicing, although Nasa would like to launch a Next Generation Space Telescope in 2007.