freed@nss.FIDONET.ORG (Bev Freed) (06/16/91)
14 June 1991 ESA Release #19 INVESTIGATION INTO OLYMPUS SATELLITE FAILURE STARTED The European Space Agency, ESA, has started an investigation into the origins of the loss, early on 29 May 191, of orbit and attitude control of its Olympus satellite. In parallel, ESA has succeeded in gaining additional evidence on the status of the spacecraft, thus improving the chances for recovering the mission in a few weeks. Olympus is an advanced telecommunications satellite featuring direct TV broadcasting, distance learning, various business networks and several other experimental payloads. As already reported, all services have been interrupted since the loss of control. The satellite rotates once every 90 seconds or so, and it is drifting eastwards at five degrees a day. Since Olympus continues to send short streams of telemetry data to Earth, more information on its attitude and the status of its subsystems has been obtained in the meantime. The telemetry data indicate in particular that, for the time being, the solar array is receiving rays from the Sun at a very oblique angle; in a few weeks this situation will improve, and it might then be possible to recharge the batteries and get commands into the satellite. Because of the present unfavorable orientation of the solar array, attempts to get commands into the satellite from NASA's high-power ground station at Robledo near Madrid (Spain) were unfortunately not successful. The Enquiry Board set up to investigate the cause of the failure met for the first time on 11 June 1991 under the chairmanship of professor Massimo Trella, ESA Inspector General. It reviewed in detail the events immediately before and after the loss of control of the satellite. For reasons that are still not known and are currently the subject of a technical investigation, the satellite ceased to point at the Earth at 0321 hours GMT and went into Emergency Sun Acquisition Mode, which is an on-board automatic safety procedure that is activated whenever the satellite loses the Earth reference signal. In recovering from the emergency to the normal mode, commands were sent to the satellite that did not conform to standard procedures. It appears that modifications to those procedures had been introduced in an attempt to have the satellite back in normal mode by 0900 h EST for the start of broadcasting operations, but instead a sequence of events was initiated that eventually led to the loss of control. However, another contributing factor was the technical status of the satellite: one solar array had not been active since January, and had the solar generator been fully operational, the spacecraft would most likely have recovered on its own. The team specially set up to lead activities to rescue the mission has started work, and has been analysing all the available data from the satellite and the conditions on board resulting from the abnormal attitude and power situation. At this time, it is believed that salvaging Olympus might be feasible. Detailed procedures are being agreed, and the actual recovery telecommands will be initiated in a few weeks, when solar illumination will have improved. --- Opus-CBCS 1.20.17 * Origin: NSS BBS - Ad Astra! (412)366-5208 *HST* (1:129/104.0) -- Bev Freed - via FidoNet node 1:129/104 UUCP: ...!pitt!nss!freed INTERNET: freed@nss.FIDONET.ORG