Scan motor current is going up again, maybe it will fix?
this post was submitted on 13 Oct 2023
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Amateur Satellites
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Discussion about amateur reception and processing of data from artificial satellites, primarily through radio signals but data from internet resources is welcome too.
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This picture could use some resyncing in the middle.
Anyway, how do you know the scan motor current has gone up? Is there a digital signal besides the image?
The satellite is sending the sync pulse for the second channel twice in that middle bit, so the software fails to sync.
The scan motor current for this satellite is on this page under Telemetry/Scan Motor Current
There is a small digital signal (DSB) near this downlink that has some other sensors and telemetry.
There is also another digital signal (HRPT) at a much higher frequency (1.7GHz) that has all the sensors and also the raw data for this image. It requires a dish and tracking, but this satellite has a broken transmitter for that higher frequency, so it's much weaker. The artefacts look completely different in the raw digital image. An image from this sat on HRPT:
Wow. Where are the artefacts coming from? Why is the analog transmission still active if digital is also available?
Also, the vertical lines in your image look suspicious. Is this a result of your software interpolating lines?
The satellite has a malfunction. The imager scans the planet one line at a time and the motor that scans it is stuck, and causing the motor to spin too slow. I'm not sure on the specifics, but the onboard computer ends up sending broken data, resulting in the artefacts in this image and the analog version.
The analog transmission is there for compatibility with old ground stations. It's much easier to receive, so cheap ground stations can be set up in places that don't have the money for a dish and rotor setup. The last satellite with the analog transmission was launched in 2009, all US satellites since have been only digital, and even removed the HRPT and replaced it with a much higher rate, harder to recive downlink.
Russian satellites have a digital signal at the same lower frequency instead of the analog signal for the same reason, but it looks much better because it is digital.
The image is the data as it was sent by the satellite, the vertical lines are probably coming from the satellite computer getting confused by the stuck scan motor.
Oh. I thought the analog scanner and digital imager were separate, and didn't realize that the analog signal had been digitally processed already.