Orbital Focus - International Spaceflight Facts and Figures
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Tyneside, UK
2024 Feb 28
Wednesday, Day 59

Curated by:

Initial Observations

Omid was launched late in the day 2009 February 2 UTC. Information on its transmission frequency began to circulate and on February 3, I made arrangements to monitor likely times during the day to see what turned up.

After some blank passes, I picked up Omid on rev 14 when its transmitter switched on shortly after 18:38 UTC. The plot below is a scan of the signal from that pass.

Omid First Signals

The start is sharply defined, as the signal switched on, and the multiple bands of signal show up well - note that not all are of the same strength. This is "Mode 1". To the ear, this signal is a 1 kHz tone. It carries no data.

The 'Reverse-S' shaped curvature of the lines is due to the Doppler effect. On the plot, time runs horizontally - increasing towards the right. The vertical scale is frequency and the units are Hz.

Sven Grahn of Sweden logged signals on this pass too.

Second Pass - Rev 15

The next pass, on rev 15 - starting shortly after 20:11, was also visible from the UK but the signal was different. Here, the pass was observed as transmitting from horizon to horizon, and the structure of the sidebands is different from the previous rev. This signal carries data and is referred to as "Mode 2".
Omid Rev 15

In both cases, the track was taking Omid away from the UK towards Iran, although the second time, the subsequent track did not pass within direct reach of Iran.

Observations from South Africa

On February 4, Greg Roberts observed signals on revs 24 and 25. As with the UK observations, the satellite passed by and then headed along a ground track that took it across Iran. In Greg's case it was northwards up the east coast of the African continent. Greg observed the same patterns of signal as seen from Europe. First, there was a pass displaying the Mode 1 transmission format, and then it was followed by a pass in Mode 2 format.

Fill In

The obvious question is whether the transmission is continuous around the whole circuit of the Earth between the pair of transmissions. In the case of the morning transmission observed from South Africa by Greg Roberts, the answer is plainly "No".

By good fortune, a fourth observer is located on the island group of Hawaii in mid-Pacific. Richard Flagg's location is such that Omid passed over him between the passes observed from South Africa. A check showed no transmissions present. This indicates that Omid was switched on near South Africa, headed towrds Iran and was switched off sometime before reaching Hawaii. It was then switched on again before it reappeared over South Africa. After passing over Iran again, it was switched off before reaching Hawaii.
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