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.
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