Hubble Shuts Eyes After Fourth Gyroscope Fails

The stream of science data from the Hubble Space Telescope stopped last weekend after the fourth of the instrument's six gyroscopes failed. The $2 billion telescope will remain in a "safe mode" until astronauts arrive next month for a scheduled service mission to the orbiting spacecraft. Even if all goes well, however, agency officials say it will take another month to get the telescope back on line.

The gyroscopes, which keep the telescope pointed properly, have bedeviled NASA engineers since the Hubble's launch in 1990. Four have been replaced on previous shuttle missions. But the devices have continued to fail, and because Hubble needs three working gyros to make observations, the latest failure, on 13 November, caused NASA to suspend all scientific operations. The shuttle was slated to rendezvous with Hubble in October to replace all six gyros and conduct other maintenance tasks, but problems with the Discovery shuttle have delayed the mission. Space agency officials are eager to meet the 6 December launch date because some of the software for the Hubble servicing mission is not Y2K compliant.

Space science chief Ed Weiler says that the delay poses no danger to Hubble. And because a servicing mission is imminent, "The timing [of the gyro failure] is not so bad," Weiler notes. "We have to just sit and wait." The shutdown interrupted researchers' plans to examine the turbulent upper atmosphere of Jupiter and Saturn's rings and put on hold the search for binary brown dwarfs and a survey of galaxies with high redshifts, according to officials at the Space Telescope Science Institute in Baltimore, which oversees the Hubble's science program. The research will be rescheduled, they added.

On the servicing mission, the shuttle crew will install replacement gyros modified to make them more reliable. The crew will make a total of four space walks--replacing a host of other equipment besides the gyros--before returning to Earth. The mission should keep Hubble operating through 2003.