Tuesday, 24 November 2009

Altering tumbling period of the USA 144/Misty-2 decoy (1999-028C)

In August I used a series of photographs to determine the tumbling period of 99-028C, the enigmatic USA 144/Misty-2 "Decoy" (see here).

As the tumbling period of this object is known to alter, I am repeating the experiment. I still need some additional nights to construct a full curve: but the partial curve obtained from the November 19 observations (6 images) already shows a clear change compared to August:

click diagram to enlarge

The sinusoid is for a period of 62 seconds, which compares well to a very similar period visually determined by Ted the same night. It is nice to see the two results coming out so similar.

Back in August the period was 71 seconds. A change of 9 seconds in 3 months time.

In the diagram above, the greyed data points are data from when the trail was very close to both edges of the FOV. Their absolute levels have suffered from lens vignetting, so I scaled them to show that the trend of these points at least is similar to the trend of the period determined from the other four images. The black data points are raw, unaltered data from the latter images.

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