Spin Period

The objectives of the FUNcube project are set out here.

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Spin Period

Postby g3vzv » Mon May 05, 2014 9:18 pm

The spin period of FUNcube-1 continues to change..Presently it is over 4 minutes so the dipole antennas on the spacecraft can be end on to your station very two minutes. At this point you will receive only very weak signals of course.

We will be very happy when we find out the reason for the spin period changes.

In the meantime, many thanks to Colin, Jim and Terry for keeping track of the data and providing this graph!

73
Graham
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Re: Spin Period

Postby ac2cz » Mon May 05, 2014 11:37 pm

This is very interesting. It looks like it is headed for another maximum and the period is 3-4 months. Of course it could just be a fairly random pattern at this point. Could it be a drawn out damping of the oscillation as the passive magnetic stabilization settles the spin into the earths magnetic field? Or is the spin related to the path that the satellite is taking through the magnetic field in some way.

Any way, very interesting. I clearly have no idea.

One question. Why use the panel temperature to measure the spin and not the sun sensors?

73
Chris
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Re: Spin Period

Postby wa8sme » Tue May 06, 2014 12:07 am

Chris,

I have found that when the rotation rate goes slower than about 2 minutes per revolution that the sun sensors are no longer a reliable indicator for detecting the rotation rate. If you think about the collection/reporting scheme of the sun sensors, it makes sense. It is related to Nyquest but also because the data is collected for one minute and not collected for one minute. Also when the rotation rate got really slow, on the order of 8.5 minutes per revolution, the bird in all likelihood does not complete one revolution while within range to collect the high resolution data directly unless you just happen to be lucky.

I have been tracking the rotation rate from the beginning and get the same result independently as graphed above. Today the rate was 5.33 minutes per revolution.

So far I have come up with three differently hypotheses as to what is going on. Of course this is purely a mind game, I doubt if the hypotheses will ever to be tested and it is just going to take more data to refine the speculation.

One observation is that the temperature stability and distribution (compared between illumination/shadowed) are somehow related to the rotation rate even with the same illumination duty cycle. This bird just keeps on giving.

Mark, WA8SME
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