Official Nasa Communication 92-117

Brian Dunbar Headquarters, Washington, D.C. July 20, 1992 (Phone: 202/453-1547) Jessie Katz Goddard Space Flight Center, Greenbelt, Md. (Phone: 301/286-5566) RELEASE: 92-117 NASA'S UPPER ATMOSPHERE RESEARCH SATELLITE RESUMES OPERATIONS NASA's Upper Atmosphere Research Satellite (UARS) has resumed full science operations following the resolution of problems with the satellite's solar array drive. "All 10 instruments are turned on and should be fully operational by late July 20," said John Donley, UARS Deputy Project Manager, NASA's Goddard Space Flight Center, Greenbelt, Md. Flight controllers placed UARS in a "safe mode" and turned off the instruments June 2 after observing the solar array drive was not operating smoothly and the solar array itself was not properly tracking the Sun. The team issued commands that repositioned the array to "high noon," allowing the array to receive maximum solar energy for one-half of each orbit. With the solar array parked, UARS had enough power in its "safe" mode to operate two instruments, the Cryogenic Limb Array Etalon Spectrometer (CLAES) and the Microwave Limb Sounder (MLS), which were turned on June 10 and June 14, respectively. The two instruments continued to obtain unprecedented data on levels of ozone and chemicals involved in ozone depletion in the upper atmosphere. In this condition, the spacecraft remained healthy while UARS

project officials ran extensive diagnostic tests and analyzed the problem. Working with a failure review team, project officials determined that a spring on the solar array's "A" side drive was not completely releasing from the shaft of the solar array. The condition was such that the redundant "B" side drive, which was otherwise operational, could not be used. However, based on a thorough review of the test data, project officials determined that engineers could operate the solar array using the "A" drive and allow all 10 instruments to perform normally. - more -2On July 8, the operations team began rotating the solar array. The array responded as expected, and the flight operations team began turning on several more of the instruments. This process was stopped, and the solar array parked once again on July 13 when UARS made its yaw maneuver, a normal turning of the spacecraft from front to back or back to front. This procedure takes place approximately every 36 days to adjust the viewing angle of the instruments relative to the Sun. The rotation was subsequently resumed in preparation for full operation. On July 14, the Halogen Occultation Experiment (HALOE) was turned on. On July 16, CLAES resumed operating, and by late July 20 all instruments were expected to be operating. UARS was launched Sept. 12, 1991, aboard the Space Shuttle Discovery. It is providing scientists with their first comprehensive data on the chemistry, dynamics and energetics of the Earth's upper atmosphere, focusing particularly on ozone depletion. UARS is the first major satellite element of NASA's Mission to Planet Earth, a coordinated, long-term program to study the Earth as a global environmental system. The UARS is managed and operated by Goddard Space Flight Center for NASA's Office of Space Science and Applications, Washington, D.C. - end -