Mar. 9, 1999 Ground controllers are slowly gaining control of NASA's Wide-Field Infrared Explorer (WIRE), but the entire supply of frozen hydrogen needed to cool its primary scientific instrument has been released into space, ending the scientific mission of the spacecraft.
"We are very disappointed at the loss of WIRE's science program," said Dr. Ed Weiler, NASA's Associate Administrator for Space Science at NASA Headquarters, Washington, DC. "We are establishing a formal anomaly investigation board to find out what happened, which will help us to plan future missions. I'm confident that many of the scientific goals can be accomplished by upcoming missions such as the Space Infrared Telescope Facility, so it will be science delayed rather than science lost."
Spacecraft controllers believe the primary telescope cover was released about three days earlier than planned. As a result sunlight began to fall on the instrument's cryostat, a container of frozen hydrogen designed to cool the instrument. The hydrogen then warmed up and vented into space at a much higher rate than it was designed to do, causing the spacecraft to spin. Controllers do not know what specifically caused the cover to be released.
WIRE's primary instrument is a 30-centimeter aperture (12.5-inch) Cassegrain telescope enclosed inside a solid hydrogen cryostat. The cryostat was designed to cool the telescope's inner workings to minus-430 degrees F -- cold enough so that the telescope's own heat emissions would not mask the infrared light that it is trying to detect in space.
By early Saturday, the spacecraft's rate of spin had stabilized at about 60 revolutions per minute, giving controllers hope they could start the painstaking process of regaining control of the 563-pound spacecraft. On Saturday, ground controllers developed and uploaded a new computer program to WIRE that began imparting small, countering forces using the satellite's onboard magnetic attitude control system to gently slow the spacecraft's spin.
Controllers have been successfully using this approach to slowly regain control of the spacecraft and reduce the spin rate approximately 3 degrees per second per orbit. WIRE is now rotating about 250 degrees per second. The objective is to reduce the spin rate sufficiently that the onboard system will take over and provide full attitude control. Controllers are hopeful this will be accomplished by the end of this week.
"The spacecraft was never designed to be controlled in this manner," said Jim Watzin, Small Explorer Project Manager, "so it's slow, tedious work. I'm confident by week's end we will have WIRE in a stable configuration, available for any analysis deemed appropriate."
WIRE was launched March 4 at 9:57 p.m. EST from Vandenberg Air Force Base, CA. When the spacecraft made its second pass over one of the WIRE tracking stations, ground controllers determined that WIRE was spinning instead of maintaining a stable position in orbit, and temperatures for the cryostat and the instrument were warmer than expected.
After the anomaly investigation board completes its work with WIRE, engineers plan to use the spacecraft as an engineering testbed to evaluate advanced attitude control systems, communications, and data handling and operations.
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