This gyro situation is not expected to impact the upcoming servicing mission. In fact, anticipation that another gyro could fail was the primary reason that Hubble managers scheduled an early repair mission and split the third servicing mission activities into two flights: Servicing Mission-3A (Dec. 6, 1999) and Servicing Mission-3B (Mid-2001).

"This event underscores the wisdom of dividing the third HST Servicing Mission into two parts, with Servicing Mission 3A scheduled for December 1999 -- only 3 weeks of science data will be lost," said Dr. John Campbell, Hubble Space Telescope Program Manager at NASA's Goddard Space Flight Center, Greenbelt, MD.

The safe-hold mode has been thoroughly tested and used twice since Hubble's launch in 1990. The telescope is not at risk. This protective safe mode allows ground control of the telescope, but with only two gyros working, Hubble cannot be aimed with the precision necessary for scientific observations of the sky.

The safe mode does not require gyros, so even if another gyro should fail in the next few weeks, HST will remain safe, according to project managers. The aperture door has been closed to protect the optics, and the spacecraft is aligned to the sun to ensure adequate power is received by Hubble's solar panels.

Engineers are investigating the cause of the gyro loss. The gyro will be returned to ground after the upcoming servicing mission for in-depth analysis.

During Servicing Mission 3A, astronauts will replace all the gyroscopes, a fine guidance sensor, a transmitter, a spare solid- state recorder and a high-voltage/temperature kit for protecting batteries from overheating. Additionally, the crew will install an advanced computer.

Servicing Mission 3B will be conducted in 2001 to complete the third HST servicing mission activities.