Surgery For A Sick Satellite

Press, Volume CIV, Issue 30879, 12 October 1965, Page 12

Surgery For A Sick Satellite

One year ago it seemed that the first Orbiting Geophysical Observatory satellite (OGO-l) was a write-off. It was safely enough in orbit but two of its 13 arms did not unfold and one of them obscured a sensor which had been intended to lock on to the horizon and control the stablisation system. With no possibility of stablisation, the spacecraft was officially classed as a failure. It seemed that when OGO’s batteries went dead for want of recharging from the solar cells its signals would cease and the biggest and most complex scientific satellite ever launched would be just another piece of space-junk. WORKED ON PLAN But the project scientists and managers at the OGO Control Centre still cherished their crippled spacecraft and did not relish the thought that years of effort was going down the drain. They went to work and developed a plan for retrieving as much data as possible from their satellite. Although OGO-l had begun to spin uncontrollably at about five revolutions a minute they were able to concoct a series of complicated commands which were radioed to the satellite for turning its solar paddles around to an angle where the cells would catch the most sunlight.

The next problem was to work out computet- programmes for extracting the effects of the spin from the scientific data transmitted by OGO-l. The 20 scientific experiments on board were all designed for operation on a stable satellite and the unwanted fluctuations introduced by the spin rate had to be removed to make the data meaningful. These problems were brilliantly solved and OGO-l has been functioning far better than anyone dared hope. During the last year OGO’s solar paddles were slewed 11 times to follow the sun’s seasonal drift. Each slewing operation required more than 400 separate commands within three hours. HOLD RECORD OGO-l holds the American space record for the number of commands it has obeyed—just a shade under 20,000 to date. OGO-l has now exceeded its designed life of one year, and 16 of its 20 experiments are still yielding valuable data on space phenomena. Already 16 scientific papers have been written on the results obtained. Had OGO-l functioned perfectly its scientific output would have been greater but the wonder is that anything

at all useful was obtained A N.A.S.A. official. Dr. John Naugle, said the OGO team had demonstrated that large spacecraft would work and that built into them was sufficient versatility to recover from a major disaster. Unless there is a postponement, the second Orbiting Geophysical Observatory will be launched from California on Thursday. The spacecraft, which weighs half a ton, will be placed in a highly elliptical polar orbit.