karn@eagle.UUCP (06/18/83)
Here is a summary status report from Jan King, W3GEY, Phase 3-B project manager, along with Phil Karn, KA9Q and John DuBois, W1HDX, who are at the primary US command station for Amsat-Oscar-10. On the first pass visible from the European command station in Marburg (orbit #1), Karl Meinzer, DJ4ZC, determined for the first time that we had the bad sun angle problem. At that time, solar array current was about 100 ma; Karl increased it to approximately 280 ma by adjusting the operating point of the solar arrays. At that time, there were already many pieces of information all indicating that the antenna side of the spacecraft was pointing very near the sun: the low solar array current, the large temperature gradient between the top and bottom surfaces, the +Z axis sensor reading very high, and no sun pulses from the side-arm sun sensors, which have a limit of +- 45 degrees. At all times, the command links have been 100% solid. PSK telemetry quality has been improving due to both a "learning curve" in the various stations equipped to receive this signal, and a change to the high gain antenna which was commanded yesterday during orbit 4 [the spacecraft called this orbit 3 because it numbers from zero]. Due to the high sun angle (estimated to be near 70 degrees), average spacecraft temperatures are running very cold. Various readings at apogee are: Nitrogen Tetroxide tank: -4C UDMH tank: -7C (the UDMH tank is nearer the cold bottom) Top battery: -9C Bottom battery: -17C Bottom surface: -29C During perigee, heating effects due to the albedo (reflectivity) of the earth are being observed. These increase the battery temperature to -4 to -5C with some lag due to thermal inertia. Total solar array current has increased by about 95 ma between orbits 1 and 4 indicate that the sun angle is improving. We believe that the sun angle is improving due to two favorable effects: 1. The motion of the sun, which is increasing in right ascension (celestial longitude) as the earth moves around the sun. 2. A northward precession of the spacecraft spin axis due to slight drag effects on the spacecraft during perigee passages. Since the spacecraft is rotating clockwise as viewed from the rear, with the kick motor pointing almost straight at the center of the earth at perigee, the east-to-west drag force on the large engine bell results in a net south-to-north precession which increases the declination (celestial latitude) of the spin axis. These two effects are at approximately right angles to each other, and are estimated to be about 1 to 1.5 degrees per day each. This should result in a net improvement in sun angle of about 1.8 degrees per day, and the increases observed so far in solar array current are consistent with this value. The memory error counter (the onboard computer has a 16K memory with Hamming error-correction circuitry) is counting approximately 4 errors per orbit, two during each pass through the Van Allen radiation belts. This is less than had been expected. The error correction circuitry is working perfectly and so is the onboard computer. Signal strength from the GB (power about 2 watts) are now quite good. The EB (engineering beacon) signal is fantastic, but so is the power drain when it is own. This beacon may be switched on between 10 and 15 minutes past the hour; if you hear the GB suddenly switch off before 20 minutes past the hour, look around for the EB. The regular fade pattern on the beacon is due to "spin modulation" from the hi-gain antenna. We would like to measure the precise interval between fades as a means of determining if the spin rate is slowly decreasing; we would like to gather readings from other stations to help with this. Simply write down the seconds reading from your clock at each fade null over a one or two minute interval, and then go back and compute the average inter-fade interval. We observed an average of 8.9 seconds during the 6/18 04:00 UT transmission and would like any accurate measurements for transmissions either before or after that time. At this time, we have still not been able to obtain any indication from ESA as to our separation attitude from the launcher; we DO now know, however, that the ECS-1 spacecraft did receive their correct attitude. Keep those telemetry reports coming. We've had to take time off to get sleep (!) so numbers during the late night (east coast USA time), as well as for passes not visible over the eastern US, are especially helpful. Keep your fingers crossed. We're confident that we'll get out of this mess, but it will take time and careful planning. The best set of orbital elements I have been able to obtain from the Millstone Hill L-band deep space radar site about 10 miles from here are as follows: Satellite: oscar-10 Epoch time: 83168.36000000 Fri Jun 17 08:38:24 1983 UTC Inclination: 8.5900 deg RA of node: 249.1010 deg Eccentricity: 0.7290171 Arg of perigee: 178.4960 deg Mean anomaly: 343.1210 deg Mean motion: 2.29630240 rev/day Decay rate: 8.1e-06 rev/day^2 Epoch rev: 3 Semi major axis: 24274.330 km Anom period: 627.095107 min Apogee: 35592.587 km Perigee: 199.784 km Millstone has not been able to positively identify the various separate pieces of this launch except for the spent third stage of the Ariane which is now quite some distance away. Therefore, these elements could actually be those for ECS-1, although predictions based on these elements have been pretty accurate. It is now clear that we achieved a lower apogee than had been initially indicated, which is why first AOS over the USA came early on Thursday evening. This also explains why the "mean anomaly" counter in the telemetry, which counts off regularly-spaced 1/256 period time increments over each orbit, was running "slow". Yesterday evening, this count was commanded to step forward 20 counts, but since the rate has not yet been changed it will continue to "lose time". 73, Phil Karn, KA9Q/1