karn@eagle.UUCP (06/21/83)
Things are definitely looking better up there. It is now believed that a combination of factors is causing the sun angle to improve at about 3 degrees per day; at this rate, the sun sensor should become operational only about a week from now. Average temperatures are also improving; the latest report from Tokyo is that the battery is bottoming out at about -3.9 C, when it had been considerably colder just a few days ago. I am doing some research to determine how long we can safely remain in our current orbit. While I do not yet have access to an analytical model for solar and lunar perturbations, we can take heart in the fact that the pieces from previous Ariane launches left in the transfer orbit are still up there. This even includes Ariane L-1, which was launched on 24 Dec 1979. The only effect on us will probably be a drop in apogee height due to perigee drag, which will have a noticeable effect on orbital period but isn't likely to be serious. Keep your fingers crossed; the patient is still in guarded condition, but the trends are all positive. Phil
karn@eagle.UUCP (06/22/83)
Things continue to improve more rapidly than expected aboard Amsat-Oscar-10. The sun angle is coming down so rapidly that the sun sensor pulses are expected back by Friday. Battery temperatures are now spending much of their time above 0 C. In addition, the combined effects of spin axis and orbit plane precession appear to be moving the spin axis toward the orientation it will need for the first motor firing! Once the sun pulses are back, it will then be possible to command the onboard computer to do spinup and attitude maneuvers for the first firing. The General Beacon is now on full time, since the solar array currents have come up enough to support it. Some initial ranging has been done, but not enough to well determine the orbit yet. We're continuing to use elements provided by NORAD last week but they seem to be slightly off. A special software routine was written to dwell on a single solar array in order to determine the spin rate - approximately 6.2 RPM and apparently INCREASING by itself. The current orbit has been analyzed and there is no need to worry over the short term (1 month) about orbit decay. In short, we seem to have "pulled a TDRS" (to coin a phrase); the satellite is surviving like a real cat, always landing on its feet. Phil Karn
karn@eagle.UUCP (06/25/83)
As expected, the sun sensors on AMSAT-OSCAR-10 are now beginning to function. Yesterday, initial data from the sensors indicated that the spin is very low, less than the 2 RPM lower limit at which the spin rate determination system will function properly. This spin rate was consistent with observed regular fades due to the side lobes of the off-pointed hi-gain antennas. It was also determined that the spacecraft is apparently spinning slowly BACKWARDS from the direction it should have been spun by the Ariane. This now points to an explanation in which the Ariane either did not give us the correct spin rate or did not spin us up at all. In any case, software has been loaded to spin up the satellite (in the "backwards" direction so as to avoid going through a zero spin rate) and should execute on the upcoming perigee pass about an hour from now. Spacecraft systems continue to function quite well, and there is now plenty of power from the solar arrays due to the improved sun angle. Here is a CW telemetry frame just copied from the 145.810 mhz general beacon: AMSAT OSCAR 10 at 03:30:00 UTC Orbit 19 MA 216/256 TLM: UBAT 14.5 V TBAT 4.9C Iarray 0.4A SA 0.2 dg Spin 2 RPM Satellite status: First motor firing and orbit change delayed to orbit 50 because orientation change required transponder off until then listen to this bulletin on the hour for latest news AMSAT OSCAR 10 HI HI Comments: Solar array current has not risen because there is already enough current for the spacecraft systems and the battery is fully charged; therefore the battery charge regulator has cut back the operating point of the solar arrays, reducing the generated current. The battery voltage is lower than it was during the first few days of the mission because the NiCds have a negative temperature coefficient; a fully charged battery has a higher open circuit voltage at lower temperatures. "MA 216/256" (MA = "Mean Anomaly") means that the satellite has completed 216/256 of its orbital period; perigee is defined as MA = 0, and apogee is 128. The SA (sun angle) and Spin figures are still wrong because of the very slow spin rate. Phil Karn, KA9Q/2
karn@eagle.UUCP (06/30/83)
This past evening, a second spin-up maneuver was performed successfully on AMSAT-OSCAR-10. The resulting spin rate is now measured as 18.68 RPM, although the CW telemetry is saying 26 RPM (the CW telemetry routine has a bad calibration formula in it, but hey, it's only software..!) The actual measurement was done with a chart recorder attached to the S-meter of a receiver. If you listen you will hear rapid, regular fading on the beacon. This is due to the fact that on two meters, the spacecraft isn't large enough to act as an ideal ground plane for the omni whip, resulting in three side lobes at certain look angles. During torquing maneuvers, the general beacon on 145.810 has been placed into the 20-minute-on, 40-minute-off cycle as a precautionary measure. Once it is verified that the sun angles are still OK (i.e., the spinup did the right thing), the beacon will probably be put back on full time operation. The next step is a precession of the spin axis northward to the proper firing attitude. This will probably take a few more days, so that if all goes well the first motor burn will be next week. Keep your fingers crossed (or, as the Germans say, hold onto your thumbs!) Phil