I have been asked whether a marked dot captured by the geostationary Earth monitoring satellite GOES 13 could have been Phobos-Grount during reenter into atmosphere. To investigate the satellite image (Figure 1),  I have used my 3D tracking software to generate the view of Earth and Phobos as would have been captured from the GOES 13 satellite at 17.45 UTC (15 January 2012). The result of the simulation is shown in Figure 2 (on the right, below): Phobos is visible close to the southern hemisphere. Eventually, to relate the two images I superimposed the whole picture taken from the satellite, after the adjustment of the scale distortions, with the simulation. The result of the superimposition is shown in Figure 4: the simulated view perfectly matches the photo taken from the satellite, however, the actual Phobos position is very far from the suspected dot, which represents, therefore, just clouds. 

*Note. The current uncertainty of the re-enter time is still too large to identify the geographical region of reenter, however, it is already possible to estimate the bands around the planet that may be involved according to the available predictions. As the re-enter time approaches these bands may shift; click on the last column of the previous table to see them.

I received information (from a non official source) on the attitude control suggesting that PhG might be designed to control only one axis in Earth orbit. I don't know if this is the case, however, one-axis control could explain the changes in brightness that have been recently observed, leaving the satellite free of "tumbling" even if it is pointing towards the Sun. Therefore, I studied all the reported flares supposing that the attitude control is operative and PhG maintains its longitudinal axis pointed towards the Sun. For each of them I oriented PhG towards the Sun computing surface tilt and angle that satisfy the observation (see the picture below for an explanation of these values). The results are very interesting: five of ten reported flares would be generated by the same surface with tilt of 55 +- 1 degrees (which could be one of the solar panels not fully deployed). The other five flares would be generated by a second surfaces with tilt of 65 +- 2 degrees. If these results will be supported by new observations they can prove that PhG is still keeping itself oriented towards the Sun with accuracy better than 1-2 degrees. The following tables collect all the analyzed flares with the resulting angles.

High resolution photos taken by Ralf Vandebergh on November 29 and December 28 may help to identify the flaring surfaces and orientation. (Click here to see these photos)

Let us consider two flares: the oldest one and the first one reported in class 1 (generated by the surface titled 55 degrees). The oldest observation is dated 2 December whilst the last one 10 December, thus, more than one week later. Let us now suppose that on the 2nd of December the satellite was correctly oriented towards the Sun (declination -21.9 deg. and right ascension  256.5 deg) but since then the satellite stopped changing its axis and maintained this orientation up to December 10 when Brad Young observed the flare. In this case, the surface tilt to satisfy Brad's observation should have been of  41.1 degrees, which is a completely different value for class 1 (or, if you want to keep the surface at 55 degrees the flare should have been observed at 00:05:48, which is 20 seconds earlier).

November, 25

It is not clear whether the space-craft still keeps itselft oriented to the sun or not. It is not clear also what happened on November 21 when the perigee ceased to rise and the spacecraft began to behave like a passive satellite. Among the possible causes one might simply think that batteries discharged. In such low earth orbit the power available from the solar panels is only 60% since the spacecraft is often in Earth shadow. Despite on Mars the available power is also of about 50% due to the greater distance from the Sun with respect to the Earth distance, this might not be foreseen for the early stage of the mission. In that case I would focus the attention on December 13 and December 14 when, due to the orbit precession, the spacecraft will be constantly sunlit.

November, 13

To see the spacecraft trajectory in your sky follow these simple steps:

1) Double click on the map at your location to set your coordinates. Zoom in the map as much as possible to increase the accuracy.
2) Click on the button "Predict Passes" to generate the list of visible passes from your location.
3) Click in the "Rise Time" column for each visible pass. The program will show you the satellite position at the beginning of the pass.
4) Click on the "Draw Sky Chart" button to see the satellite track in your sky.
5) Change the time with the keys s or m (lower case) to increase the time by 1 second or 1 minute (upper case decreases).

See the value of magnitude in the program panel for knowing as bright the satellite will be.Visibility depends on your sky conditions, however, for values less than 4  the satellite is usually visible with the naked-eye. Greater values require binoculars (up to mag. 8 or more) or telescope.

To see where the spacecraft is in real time click on the "Real Time Tracking" button

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Фобос Грунт - Наблюдение