PHOBOS-GRUNT BEFORE REENTRY

Any use of one of these images other than strictly private must be subject to prior authorization from legault@astrophoto.fr

This video of Phobos-Grunt was taken from the Calern plateau Observatory (above Nice, French Riviera) on January 1st 2012, during a zenithal passage (culmination at 88.5 of altitude at 6:17:24 UTC, direction NNE). Distance to observer: 237 km. Speed: 7.75 km/s. Angular speed at culmination: 1.85/s (without tracking system, at the scale of the video the satellite would cross your screen in about 1/30s). Phobos-Grunt is out of control and its atmospheric reentry is currently scheduled for mid-January.

On the image and video below, thanks to the specific orientation of the telescope mount (calculated with www.calsky.com), the movement of the satellite during the whole passage remains strictly horizontal, from left to right. Around culmination of the satellite, the Sun is on the right side and the trajectory of Phobos-Grunt is directed toward the Sun (azimuth of the apparent orbit plane: 122 ESE; azimuth of the Sun: 114 ESE). The images show that Phobos-Grunt is moving backwards, with the solar panels deployed but not lightened by the Sun. There is no sign of tumbling, and a video taken 24 hours before (Dec 31st) shows the satellite in a similar orientation. According to experts, that corresponds to an orientation driven by aerodymanic forces: the heaviest parts (tanks) ahead and the parts subject to the highest atmospheric friction (the solar panels) backward. The image below is a stack of 30 raw frames, with 50% enlargement.

Instrument: Celestron EdgeHD 14 Schmidt-Cassegrain telescope (focal length of 7000mm) on automatic tracking system, as described on this page. Camera: Lumenera Skynyx L2-2 (12-bit files in fits format). Raw files are available on request.

This video sequence shows Phobos-Grunt in the original acquisition size, it begins at 6:16:41 and ends at 6:18:01 UTC, for 963 images (acquisition rate: 12 fps, processed video rate: 25 fps). A the beginning of the video Phobos-Grunt comes from West-North-West (direction opposite to the Sun), it is well illuminated and we mainly see the bottom of the main tank and the backside of the solar panels. At the end of the video it's going East-South-East, it's dimmer because backlit and we see the edge of the main tank and just the edge of the solar panels (the panels themselves are not lightened).


The observation site (4345'05"N, 655'26"E), with the twin Soirdete interferometer domes in the background and, on their left, the Moon-laser
telescope destined to measure the distance of the Moon thanks to reflectors left by Apollo missions. This observatory is 850 km from my home.


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