Moulton Lava

Moultonic Musings

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Location: New England, United States

Wednesday, February 15, 2006

Tracking SuitSat-1

Amateurs around the world have been tracking SuitSat-1 and reporting their reception of messages, telemetry, and slow-scan TV signals.

Part of the telemetry is the 'mission time' — the number of minutes since the gear was powered on prior to deployment.

Because of noise and signal fading, it's not always possible to hear all the digits in the telemetry. But the mission time should be predictable from UTC, once you work out the precise date and time the clock was started.

A few days ago, there were enough posted reports to do this, and to work out a convenient formula relating mission time to UTC.

I did this with the first three reports where the full telemetry of the mission time could be heard. My calculation of the 'epoch term' — the UTC corresponding to the startup time — should have been the same for all three reports, but they inexplicably differed by about 17 minutes.

Finally, one of the hams posted a comprehensive table with all his data for a week. I plugged them into a spreadsheet and applied my formula.

Lo and behold, the error between my calculated valued of mission time and the reported mission time was getting larger by the day. Was the clock aboard SuitSat-1 running slow?

I reworked, my formula, allowing for the possibility that the clock was running at a rate other than 1440 minutes per 24-hour day. Sure enough, I got a perfect straight line fit with the clock running at 1432.4 minutes per 24-hour day. SuitSat's onboard clock was apparently losing precisely 7.6 minutes a day.

The designer of the clock confirmed that it is indeed running slow, for reasons not yet diagnosed.

This peculiar discovery will give students one more activity to do while tracking SuitSat-1.


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