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Satellite Tracking

Tyneside, UK
2017 Aug 19
Saturday, Day 231

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Tracking Compass 2

Compass 2 was launched 2006 May 26 by Shtil (RSM-54) missile from the submarine Ekaterinberg, submerged in the Barents Sea. It achieved orbit at 402 x 493 kilometres, 93.5 minutes, 78.9 degrees inclination.

IZMIRAN, (the Pushkov Institute of Terrestrial Magnetism, Ionosphere and Radiowave Propagation), operator of the satellite, gave 137 MHz and 1.7 GHz as telemetry and command/control frequencies and 150/400 MHz for the Mayak beacon. The latter would be switched on some time after achieving orbit.

In the event, the 137 MHz transmitter appears to have come on immediately (possibly automatically) but the 1.7 GHz transmitter is not operating. First signals were reported by Maik Hermenau of Germany and later confirmed by Barney Hamlin in the US. They gave 137.285 MHz as the frequency - signals were strong and coming in short bursts. Grady Whitney in the US subsequently reported reception at 137.415 MHz. It became clear, and has been confirmed by IZMIRAN, that the nominal frequency is 137.35 MHz. The transmissions reported sidebands at +/- 65 kHz.

Transmission was probably intended to be continuous. Soon after launch, rumours started to circulate that the satellite was in trouble. IZMIRAN eventually confirmed them, saying that Compass 2 is not responding to commands and that the transmission carries no data.

Signal Structure

The bursts of signal in groups have no immediately-obvious pattern. Mike Kenny of Australia confirms that transmissions at the centre frequency and on the sidebands occur simultaneously.

Below is a trace recorded by Richard Flagg in Hawaii. It shows the bursts coming in groups with the strength varying and obvious 'missing' ones. Hawaii observations tend to show 4/5 pulses to a group while observations over Europe sometimes show as few as three.

Hawaii Observation

Richard confirms IZMIRAN's assertion that no data is being received by showing the typical content of a signal burst as a repetitive chain of pulses at a transmission rate of 60 Hz.

The burst nature of the transmission may be due to the satellite rotating and the onboard systems reacting to varying output from the solar panels. There is a measurable pattern in addition to the 3-5 burst groups. Observations from Lincoln, UK over three days show consistency in the timing of signal bursts:

Burst Pattern

This alignment may be due to the local geometry between the satellite spin axis and the sun on the section of orbit under observation. If so, a run of readings elsewhere else on the globe might produce a different pattern.

The gap between the end of one burst and the beginning of the next varies between 10.1 and 79.9 seconds. There are lots of readings near the minimum level and several around 79 seconds so they may represent limits. Maybe 10.1 seconds is the fastest the battery can be charged to a level that gives sufficient output to trigger the transmitter. How long the transmitter stays on could be due to a combination of battery drain plus output from the panels.

There is a visible drift to the right in the plot. Some of the peaks at the left from revs 60 and 61 are not visible on revs 91 and 92. Conversely, new ones have appeared on the right to replace them.

As Sven Grahn has pointed out, Compass 2 was launched into orbit at a time of day to ensure continuous sunlight. From June 9, the satellite will start to experience increasingly-long eclipses. The effect on the signals is not predictable.
Copyright © Robert Christy, all rights reserved
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