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AO-85 Extended Safe Mode: Discussion

Discussion in 'Satellite and Space Communications' started by K3RLD, Dec 4, 2018.

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  1. K3RLD

    K3RLD Ham Member QRZ Page

    Anybody know what is going on? Is this purely a power issue? Last pass over my FoxTelem station produced 4 DUV decodes (very good for my station during safe mode beaconing), and the satnogs capture shows a strong signal.
  2. WD9EWK

    WD9EWK Ham Member QRZ Page

    It appears that AMSAT is concerned about the battery voltage on AO-85. The batteries are showing a low voltage of 2.82 volts.

    The Fox-1 satellites use 3 NiCad cells, and NiCad cells are normally 1.2 volts each. A reading of 2.82 volts could mean the voltage for each cell dropped below 1 volt, or maybe one cell has a problem. I haven't seen anything official to explain the low-voltage situation, nor have I seen anything as to when AO-85 will return to service. I did see someone comment about AO-85's onboard temperature reaching 85°C, which wouldn't be good for the NiCad cells.

    IIRC AO-85 had been in a period of full illumination from the Sun, before the current period where AO-85 has significant periods of eclipse during its orbits.

    Hopefully AMSAT will be able to analyze the telemetry from AO-85, to figure out what to do next. They are busy now, after Fox-1Cliff's launch yesterday.

    K3RLD likes this.
  3. K3RLD

    K3RLD Ham Member QRZ Page

    Ok, so that is what I understood, too (the battery voltage issue - didn't realize it could be related to the temp, though).
  4. WD9EWK

    WD9EWK Ham Member QRZ Page

    Going further back into the memory... I think a similar issue with temperature is what started to degrade the batteries on AO-51. AO-51 had a similar period of full illumination, but it didn't have the MPPT monitoring the battery charging. In the case of AO-51, there were more options to cycle the batteries - AO-51 had two UHF downlinks, and an S-band downlink. Two the 3 could be turned on, and those transmitted all the time when turned on. Even with more options to consume power and keep the batteries from being overcharged, it appeared that the batteries started to fail during 2011, to the point that AO-51 went silent late that year.
    K3RLD likes this.
  5. N8HM

    N8HM Premium Subscriber QRZ Page

    AO-85 does not have an MPPT. The board wasn't finished in time and it has a simpler charging circuit than the rest of the Foxes that does not prevent overcharging of the batteries. I have noticed the battery performance diminishing quite a bit since the January period of full sunlight where temperatures reached 85 celsius. Pumping power into one or more of those cells while at that temperature seems to have done some damage.
    W5PFG likes this.
  6. WD9EWK

    WD9EWK Ham Member QRZ Page

    You're right, I forgot about the lack of an MPPT on AO-85. In that case, it may be - unfortunately - following what happened to AO-51 in 2011. :( Hopefully the situation with AO-85 can be managed, and brought back into service.
    WE4B and W5PFG like this.
  7. W5PFG

    W5PFG Premium Subscriber QRZ Page

    Probably need a real space man to go up there and swap out the batteries. Would take one heck of a catcher's mitt!
    WE4B and VE2HEW like this.
  8. K3RLD

    K3RLD Ham Member QRZ Page

    Looks like KO4MA will be putting Fox-1A back into transponder mode soon, with some operational requests from users. Good news (from the AMSAT mailing list).
    WE4B likes this.
  9. WD9EWK

    WD9EWK Ham Member QRZ Page

    I think the quote was "requests for operators". One was mentioned - not using the satellite when it is in eclipse. That makes sense, given the concerns over the batteries.

    WE4B likes this.
  10. K3RLD

    K3RLD Ham Member QRZ Page

    Yeah, my wording is terrible. Made it sound like users had asked HIM to do some stuff. Quite the opposite, as you pointed out.
    WE4B likes this.

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