Sunday, 25 July 2010

Manoeuvring KeyHoles and the flashing Iridium 33 wreckage

July 2010 so far yielded a nice series of clear evenings, due to very warm, sunny weather (in most cases allowing observations in shorts and shirt). I observed on July 3, 4, 6, 12, 15, 16, 17 18, 19 and 22.

Two manoeuvring KeyHoles

Prime targets this month were the KH-12 KeyHoles USA 186 (05-042A) and USA 161 (01-044A). These both manoeuvred on the 14th of July, giving us observers a nice task of recovery and renewed tracking.

The manoeuvre of USA 186 (05-042A) was first noted by Pierre Neirinck in France. After some other observers missed it, he observed it being very late, but initially lost his reference points. Ted Molczan next created a number of search orbits, based on different presumed manoeuvre times. Next Alberto Rango and me again recovered the satellite (Alberto first while I still had daytime, then me on the next orbit, in deep twilight), in an orbit very close to one of Ted's search orbits.

Using pre-manoeuvre and post-manoevre orbits calculated by Ted Molczan from our observations, the manoeuvre occurred on July 14th at the ascending equator crossing at about 15:00 UTC, over Indonesia.

Next it turned out that another KH-12 Keyhole, USA 161 (01-044A) had also manoeuvred early on the 14th. Again, Pierre noted it first, observing it 12 minutes late on July 17th. Next Ted and a number of other observers joined the recovery (including me at some point). Using pre- and post-manoeuvre orbits calculated by Ted and Mike from our observations, the manoeuvre ocurred at the ascending equator crossing near 00:20 UTC, July 14th, near Hawaii.

The flashing behaviour of the Iridium 33 wreckage

On 10 February 2009, the American Iridium 33 (97-051C) telephone communication satellite and a defunct Russian satellite, Kosmos 2251, collided in space. A large number of debris pieces were spread over Low Earth Orbit (see here), and the main wreckages of the two objects kept orbiting, now wildly out of control.

The Iridium 33 wreckage (97-051C) made some fine passes last month, displaying the same kind of flashing behaviour due to tumbling that I also observed shortly after the collision in 2009 (see here, here and here). Some of these flashes are easy naked eye flashes, reaching mag. +0. The object interchanges bright flashes like these with (more numerous) fainter flashes in the +4 range.

I targetted the satellite wreckage several times this month to determine the flashing behaviour. In March 2009, it showed a period of 4.7 seconds. Analayses of the imagery of the past few nights, shows this has changed to about 3.1 seconds. Below is one of several images, taken on July 16th, showing a series of fainter and brighter flares:

click image to enlarge

Below are graphic representations of the flare positions (yellow dots) observed on consecutive nights (resp 16-17, 17-18, 18-19 and 22-23 July 2010). Please note: only flares happening during photographic exposures are shown here. There were more flares, but these happened while the camera wasn't open:

click maps to enlarge

(maps made using Heavensat)

An unusual flare was captured on July 17-18, consisting of a triple flare with flares within 0.5 seconds:

click image to enlarge

Other objects besides the KH-12 Keyholes USA 161 and USA 186, and the Iridium 33 wreckage observed last 3 weeks include:

- the geostationary objects Milstar 5, Mentor 2 and Mentor 4 (USA 202);
- the HEO objects USA 184, the USA 40 rk;
- the LEO objects Progress-M 04M, MSX, Lacrosse 5, the Lacrosse 5r, IGS 1B, the IGS 5r, USA 32, the NOSS 3-3 duo and the USA 144 decoy,;
- plus a large number of GEO and LEO strays.

I have yet to analyse the USA 144 decoy (99-028C) data from July 20 for a new tumble period determination.

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