Lot\'s of good news about AO-40!

Discussion in 'Amateur Radio News' started by Guest, Feb 27, 2001.

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  1. Guest

    Guest Guest

    From AMSAT-DL's Homepage...



    The SEU (sensor electronic unit) is triggering the sun again after the end of eclipse on orbit #147.



    The telemetry channel #100 (analogue spin rate) is now showing a value of #49. This is the same value that it was showing on orbit #89 when we lost Sun Sensor triggering.



    Within a few orbits we should see that the Sun Sensor SS2 also starts triggering and this would allow us to obtain attitude information and re-start magnetorquing to spin-down the spacecraft.








    A week ago the 3-Axis sun sensors have been turned on and they seem to work nominally. It was planned to use the information from the 3-axis omni directional sun sensors to obtain the necessary reference information for a new algorithm to spin-down the spacecraft without the SEU. The new software code, which will be patched into the 20ms interrupt service, is almost ready for upload, but due to the premature return of the SEU data, this might no more be necessary.



    Analysis of the IHU temperature by DB2OS recently revealed, that the maximum sun angle, with the lowest temperatures, was much earlier than anticipated (see graphics below). The temperature of the IHU reached it's minimum exactly on 2001 February 01 with a temperature of about -8.4 °C. This is almost one month earlier than originally thought. There is no explanation at the moment, why this is premature.



    The spin rate of around 17.5 RPM did not changed in the last couple of weeks and whatever it caused to increase, it stopped. As soon as the SEU will deliver good sun sensor data, the magnetorquers will be used under the control of the IHU (integrated housekeeping unit) to reduce the spin, which will than make attitude changes easier. This will also improve the telemetry reception on S-band.



    The next milestone is to bring the spacecraft into a good orientation to fire the Arcjet with no electrical power and gaseous ammonia only. The test firing will be used to check the Arcjet control electronics and valves. Even without the Arcjet "burning", the thrust from the test firing will be enough to raise the perigee by about 100km.



    Several independent analysis (including the french space agency CNES) confirmed, that the current orbit will be stable for many years, i.e. more than the anticipated lifetime of the spacecraft.



    The test firing should give us additional safety margin and a better feeling. However, it is later planned to optimize the current orbit with a full running Arcjet. This is planned after testing of the 3-axis momentum wheels, which will be used to re-orient the the spacecraft during these maneuvers.



    While the spacecraft was in hibernation, the command stations were restless with preparations for the next activities, watching the spacecraft telemetry and health.



    AMSAT-DL expresses its thanks to Paul Willmott, VP9MU for his outstanding service in gathering and archiving the AO-40 telemetry from the different parts of the world. This is vital additional information for the command stations in their continuing effort to turn P3-D back into operation. Everyone should be encouraged to send captured telemetry (with P3T) to the AO40 telemetry archive at 'ao40-archive@amsat.org'



    After all, the spacecraft seems to be in very good shape, with no further damages or other problems detected. The power budget is very good and even during the maximum sun angle it was not necessary to reduce power consumption by turning off the S-band transmitter for parts of the orbit.



    This is indeed a good sign for the next activities.



    Stay tuned...



    Additional information can be found at the AO-40 web page.



    73s Peter, DB2OS - AMSAT-DL
     
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