Senaste uppdatering angende batteriproblemen:
Initial attempts today at recovering the S2 beacon on AO-40 have so far not been successful. However, these will be repeated many more times from multiple locations in the days ahead. We have a good fix on ALON/ALAT and we are spinning at 3.5 RPM, so we have quite a few days/weeks before the squints become problematic due to the mystery effect. Currently, the mystery effect is working for us to improve solar angle. Attempts will also be made in the next few days to bring the K-Tx on line and search for its signal. The command team has a series of simple machine code commands that, if heard, should activate transmitters, switch receivers, switch batteries, etc. without having to load the flight software into the IHU-1.
By way of review, the command team had been watching the main battery for a number of months and noting that its behavior, while not alarming, was not fully as expected. In particular, there were voltage fluctuations with
spin under relatively light power loads. When panels 1-6 received sunlight their 1/2 complement of solar cells would often lead to a voltage dip, which would pop back up when the fully arrayed panels were in the sunlight. This suggested that perhaps one cell in the 20 cell main battery
might be weakening. On Sunday, we noted that the battery was not maintaining its set voltage and this led to the safety software shutting off the passbands. Some minor adjustments were made to the solar array voltage offsets and this helped some, but we stayed in passband off mode to
study the matter further. It appears that at this time we may have acquired a second bad or shorted cell, though we are analyzing this further. During eclipse on orbit 1487, at approximately 1930 utc on 2004-01-26 the battery voltage hit the extreme low voltage trigger. This caused safety resets of the battery and solar array set points and the
auxiliary battery was tied in to the main battery. This all appears to have happened benignly, and when I got AOS at MA=8, about an hour and a half later on the following orbit, I noted that the extreme low voltage flag had been set ,as well as the other changes noted. Voltages on both
batteries at this time were similar to other post-Sunday values, as were the charge currents. At this voltage level, the auxiliary battery was considerably undercharged. We appeared to be in a stable, though not fully nominal mode, and I was in the process of noting the status of things to the command team to decide on the next course of action when, at 00:39:59 utc the battery voltage suddenly dropped from its post-Sunday level of 25.5
to 26.5 volts, down to 18 volts. This was accompanied by an expected increase in charge current. The safety software shut off the S2 Tx at the next MA change, and I brought it back up manually twice, noting that the voltage was relatively stable at about 14 volts with heavy charge
current. After letting things sit for a few minutes, a third attempt to start the S2 Tx was not successful.
Our current best understanding is that we suffered a catastrophic failure of the main battery which is clamping the buss voltage at a low level. Accordingly, we have been concentrating our efforts on trying to connect the auxiliary battery to the main buss and disconnect the main
battery, placing it on trickle charge for further analysis. If we can manage just 10 volts on the main buss to activate the IHU-1 we should be able to accomplish this with the simple machine codes noted above, and the
voltages should come up to levels where the S2 will function.
If you examine the telemetry during this time, 10 minutes after the low-voltage event , the temperature of heat pipe 4 + X + Y takes a 34.2 deg.C apparent increase in temperature over a span of 14 seconds (1 block interval), and continues to rapidly increase almost to the top of the
scale. Given the timing of this change, 10 minutes after the low-voltage event , its rapidity, the thermal inertia of the large, circumferential heat pipes, etc… it is difficult to believe that this is real. Most importantly, this heat pipe sensor sits in a benign area at the apex of panels 1 and 6, near the high-gain end of the spacecraft. There are no batteries or BCR s in this region, only the controller for the liquid rocket motor (which was powered off!), and the L1 receiver, which shows no accompanying change in temperature. All of the BCR s and batteries are much closer to heat pipes 1 and 2 at the omni end of the spacecraft. Therefore, this may represent a failure of the software/hardware due to low voltage, rather than a real temperature increase. However, this will be studied further. No other telemetry anomalies have been noted but we continue to look.
–W4SM for the AO-40 Command Team
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