Don Savage/Jennifer McCarter
Headquarters, Washington, DC                     March 10, 1999
(Phone:  202/358-1547)

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

RELEASE:  99-38

NASA PLANS AN EARLY SERVICING MISSION
TO HUBBLE SPACE TELESCOPE 

     NASA will launch a Space Shuttle mission to the Hubble Space 
Telescope in October so astronauts can replace portions of the 
spacecraft's pointing system, which has begun to fail.

      Hubble is operating normally and continuing to conduct its 
scientific observations, but only three of its six gyroscopes -- 
which allow the telescope to point at stars, planets and other 
targets -- are working properly.  Two have failed and another is 
acting abnormally. If fewer than three gyroscopes are operating, 
Hubble cannot continue its science mission and automatically 
places itself in a protective "safe mode."

       "The Hubble Space Telescope is the crown jewel of NASA's 
space observatories, and we need to do everything within reason to 
maintain the scientific output of this national treasure," said 
Dr. Edward Weiler, Associate Administrator for the Office of Space 
Science, NASA Headquarters, Washington, DC.  "We appreciate the 
rapid response of the Space Shuttle community to this request."

       "When Hubble reached the point of having no back-up gyros, 
our flight rules said we must look at what we term a 'call-up 
mission' to correct the situation," said Dr. John H. Campbell, the 
telescope's Project Director at NASA's Goddard Space Flight 
Center, Greenbelt, MD.  "Since we are already involved in 
preparations for the scheduled third servicing mission next year, 
we essentially decided to divide the planned mission into two 
flights and reduce the workload on each." 

     A team of veteran astronauts had already begun training to 
install the new instruments and upgrade the telescope's systems.  
NASA astronauts Steven L. Smith, C. Michael Foale, John M. 
Grunsfeld and European Space Agency astronaut Claude Nicollier 
will perform the spacewalks on both servicing missions.  Smith is 
the payload commander for the missions, coordinating the 
astronauts' space-walking activities.  A flight crew for the 
servicing missions will be selected in the near future.

     In addition to replacing all six gyroscopes on the October 
flight, the crew will replace a guidance sensor and the 
spacecraft's computer.  The new computer will reduce the burden of 
flight software maintenance and significantly lower costs.  A 
voltage/temperature kit will be installed to protect spacecraft 
batteries from overcharging and overheating when the spacecraft 
goes into safe mode.  A new transmitter will replace a failed 
spare currently aboard the spacecraft, and a spare solid state 
recorder will be installed to allow efficient handling of high-
volume data.  Both missions will replace telescope insulation that 
has degraded.  The insulation is necessary to control the internal 
temperature on the Hubble.

       The later servicing mission will focus on installing the 
Advanced Camera for Surveys.  With its new imaging capabilities, 
this camera will be 10 times more powerful than the present Faint 
Object Camera.  New efficient rigid solar arrays will replace the 
existing solar arrays.  Astronauts also will install the Aft-
Shroud Cooling System.  This new system is designed to carry heat 
away from the scientific instruments and to allow the instruments 
to operate better at lower temperatures.  The cooling system 
allows multiple instruments to operate simultaneously, helping the 
science team maintain the program's high productivity.

       In addition, an advanced cooling system will be installed 
on the Near-Infrared Camera and Multiobject Spectrometer, which 
became dormant after its solid nitrogen coolant was exhausted in 
January 1999.

                              - end -

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