Monday, September 21, 2015

The slow, changing tumble of the USA 144 (Misty 2) decoy

The USA 144 Decoy (1999-028C)
(click image to enlarge)

Yesterday evening I did some observations on the two evening KH-11 Keyholes (USA 186 and USA 245). Following that, I targeted the USA 144 decoy (1999-028C), an enigmatic object from the launch of the stealth satellite Misty 2 in 1999.

Three classified objects and one unclassified: the USA 144 Decoy, NOSS 3-4 A & C,
and an old rocket booster with CAMEO attached
(click image to enlarge)

At left in the image above is a double trail of the classified NOSS 3-4 duo (2007-027 A & C). In the middle is an old Delta 1 rocket booster (78-098B) with CAMEO on top, an earth magnetosphere experiment from 1978. At right, the shortest trail, is the enigmatic classified object we call the USA 144 Decoy.

I have written about this enigmatic object before. It is a bright object in a high 2665 x 3155 km orbit originating from the Misty 2 Stealth satellite launch in 1999.

(click image to enlarge)

From a study of its orbital behaviour, Ted Molczan found that the orbital decay of this object is notably influenced by Solar Radiation Pressure (SRP). This suggests an object that is very "light" relative to its size, i.e. an object with a large area-to-mass ratio. This does not fit a normal payload, so we suspect that this relatively bright object might have been a decoy to attract attention away from the real, stealth payload.

The USA 144 Decoy is slowly tumbling, resulting in a clear brightness variation. Ted already noted that the period of this variation changes over time, sometimes increasing, sometimes decreasing. This is in line with the tumbling behaviour of other known objects subject to SRP (like fragments of the PAGEOS balloon satellites).

click diagram to enlarge

I took a series of images between 20:19:42 UT and 20:26:12 UT (20 Sep 2015) documenting the brightness variability. The curve fits a peak-to-peak period of about 50.5 ± 0.5 seconds (see diagram above). There is clearly much variation in amplitude peak-to-peak.

The period found, is shorter than the periods found during my earlier determinations in 2009 and 2010, a summary of which is given below:

20 Sep 2015:    50.5 seconds (this post)
5 Sep 2010:     60 seconds   (see here)
20 Jul 2010:    61 seconds   (see here)
2-9 Mar 2010:   88 seconds   (unpublished)
19 Nov 2009:    62 seconds   (see here)
25-27 Aug 2009: 71 seconds   (see here)

This variation of the period over time is in line with expectations for an SRP-influenced object like this.

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