Paula Cleggett-Haleim Headquarters, Washington, D.C. March 18, 1992 (Phone: 202/453-1547) RELEASE: 92-39 NEW OPERATIONS FOR COMPTON GAMMA RAY OBSERVATORY Mission managers for NASA's Compton Gamma Ray Observatory are implementing a new operating procedure, because of a problem in the playback of recorded data. Science observations are continuing without significant loss of data. Scientific and spacecraft data will now be transmitted directly to the Tracking and Data Relay Satellite System (TDRSS) and then to a ground control center, without using tape recorders. Fortunately, the capability of TDRSS, using two of its spacecraft, will enable nearly full coverage of each Compton orbit. This procedure will be used while an investigation continues into the cause of the problem. Normally, the four science instruments onboard the observatory collect data, which are recorded onto one of two tape recorders (designated "A" and "B"). When a specified amount of data have been collected, typically about 3-hours worth, the recorded data are played back at high speed and transmitted to a ground control center using the TDRSS. The cycle of data collection, recording and transmission, with high speed playback, is then repeated. Since early in the mission, minor errors in the data recording and playback have been detected. As long as the rate remained low, however, the errors could be removed on the ground using computer processing. The errors were first detected in tape recorder A. Mission managers then decided to switch to tape recorder B, which was experiencing a lower rate of error. The error rate in B, however, increased in a short period of time and has reached the point where computer processing is slow and laborious. Therefore, managers decided to switch to the new operations mode. This new mode directly relays data to TDRSS without using recorders. -more- - 2 - Compton cannot be in constant communication with TDRSS, because of "viewing angles." Some data, therefore, will be lost. If the error rate in the recording/playback process does not significantly worsen, it may be possible to record and store data during that portion of the orbit when the Observatory is not in contact with TDRSS. Managers could then recover data that would otherwise be lost. It is anticipated that, when fully implemented, a data capture rate of 80 percent of the optimal level will be achieved. Although the new operating procedure will result in some inefficiency, the science goals of the mission still can be achieved through increased observing times. If the recorders are not used at all, the primary goal of the mission, to conduct an all-sky survey at gamma-ray wavelengths, will now be completed in late 1992, instead of this summer, as originally anticipated. The new procedures should have no effect on the length of the mission, which is designed for a minimum of 2 years. If the present problem can be identified and a corrective action implemented, the observatory may be restored to nominal operations. The specific cause of the errors is not known, but an investigative team has been formed at NASA's Goddard Space Flight Center (GSFC), Greenbelt, Md. The investigation will exam the tape recorders as well as on-board electronics, which prepares data for recording and playback in preparation for transmission to the ground. Compton Gamma Ray Observatory, the second of NASA's Great Observatories, was launched April 5, 1991, by the Space Shuttle Atlantis to study high-energy radiation from space. The spacecraft was developed and is managed and operated by GSFC for NASA's Office of Space Science and Applications, Washington, D.C. - end -