Donald Savage
Headquarters, Washington, DC
(Phone: 202/358-1547)

Nancy Neal
Goddard Space Flight Center, Greenbelt, MD
(Phone: 301/286-0039)

RELEASE: 99-136


NASA’s Hubble Space Telescope was placed into a safe hold at
approximately 8:30 a.m. EST Saturday morning when gyroscope #1
ceased operation. With only two operational gyros remaining, the
science program will be suspended until completion of Servicing
Mission 3A, currently scheduled for launch aboard Space Shuttle
Discovery on Dec. 6, 1999.

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.

Additional information on the mission and Hubble is available

– end –