Satgen 391 Operating on Oscar Ten by GM4IHJ 21 Sept 96 Oscar 10s recent return to operational status is very welcome indeed. That it will no doubt lapse back into a non operational mode before too long is highly likely. The following reports observations of Oscar 10 over several months and suggests why it is behaving as it is. Firstly Oscar 10 has no battery back up for its solar cells. When it goes into earth shadow it closes down completely in a few seconds. But even when it is clearly in full sunlight it often fails to achieve an operational state. In this non op mode several clues are obvious. Firstly its beacon signal is very weak , secondly its beacon signal is frequency modulated cycling between 50 and 100 Hz ( when not being accessed by improper users), about 6 times a minute, thirdly its signal strength is also cycling about 6 times each minute exactly in step with the FM cycle. Clearly though the satellite is in sunlight its solar panels are not face on to the sun. Indeed it is clear that the satellite is spinning or tumbling at about 2 rpm, and as it rotates its solar panels see a little sunlight at a poor angle for a few seconds, but pass out of sunlight 6 times a minute. That does not however, seem to be the full story. The cyclic change of signal strength also seems to have a component consequent on its antenna being eclipsed , as the satellite body gets between the antenna and the earth 6 times a minute. Every 3rd dip in signal strength takes the sig/noise right down to zero , suggesting that the satellite is actually tumbling around twice a minute but the 3 corners each cause a partial eclipse , thereby producing the 6 rpm shift in frequency and signal strength. All of which is pure supposition but seems to be the only way to account for what is happening. Every so often , ie in May of this year and now again in September the combination of change of satellite spin /tumble axis , and the changing position of the Sun, conspire to place the solar panels temporarily in almost full Sun light. The change in performance is then very marked . The cycling 0 to 10 dB sig/noise beacon , becomes a cycling 20 to 30 dBs sig/noise . The FMing disappears and the transponder is available for useful operation so long as the satellite stays out of earth shadow. This is the present state of affairs , with qsos on the sat being as good as they were back in 1983. It is stuck in mode B 435 up 145 down , and as mentioned the transponder appears almost as good as new. But the beacon is not doing anything but send out a steady carrier. Or at least that seemed to be the case, until a couple of days ago, when the beacon appeared to be sending keyclicks in short burst whenever the signal to noise ratio peaked. Clearly the transponder antennas are being shielded or partially eclipsed twice each minute, but even this feature is lost when the satellite is passing to this stations south at closest point of approach - a feature which is only to be expected if the problem is due to the antennas being shielded as it approaches stations and pulls away from them , but being relatively unobscured for the brief period as the satellite goes past the station. IHJ intends monitoring Oscar 10 regularly each week and will attempt to report changes in its operational parameters.