Thierry Legault wrote: > hello, and happy new year 2012, to all members of the list! > > This were a special new year's day morning for me, since I was at the > edge of the French Riviera Observatory to take the last passage of > Phobos-Grunt over France, after weeks of bad weather. > > The video with all available shooting details is on this page: > http://legault.perso.sfr.fr/phobos-grunt.html > > There is no sign of tumbling, and a video taken 24 hours before in > close conditions shows PG in a similar orientation. The unexpected > thing that I realized when I looked carefully at the video is that PG > is moving backwards, with its solar panels deployed but at the > opposite of the Sun. It's not surprising that it had no energy to communicate! Thierry, congratulations on obtaining an excellent result, on a most challenging object. As you pointed out, F-G does appear to be oriented with the main propulsion module forward into the direction of travel. I suspect this behaviour may be similar to that of a shuttlecock: the nearly full fuel tanks at the main propulsion module end of the spacecraft are analogous to the cork of a shuttlecock; the solar arrays at the opposite end are analogous to the feathers. Here is a thesis, "Passive Attitude Stabilization For Small Satellites", by Samir Ahmed Rawashdeh, based on using precisely this phenomenon to provide attitude control for a cubesat: http://uknowledge.uky.edu/cgi/viewcontent.cgi?article=1628&context=gradschool_theses See Fig. 4-1 on pg. 40 (p. 53 of the pdf), and also Fig. 4-2 on the following page. Then look at the results of the attitude simulation, in Fig. 7 on pg. 47. On the previous page, the author states: "Figure 4-7 shows the time response of the simulation. The angle relative to the velocity vector is plotted in blue, and the angle relative to the nadir vector is in green. It appears that the satellite begins to track the velocity vector within 3 hours. The plot of the angle to nadir also shows the satellite lining up with the velocity vector 90 degrees from the nadir vector (for a circular orbit)." I believe there is sufficient detail in your imagery, as well as in the documentation of the time and location of the observations, to support analysis with the aid of 3D visualization software, to get a better idea of the exact orientation of F-G with the respect to the velocity vector. Ted Molczan _______________________________________________ Seesat-l mailing list http://mailman.satobs.org/mailman/listinfo/seesat-l
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