Crossing Phobos 2.0

We received an update from Robert Guilanya, flight dynamics lead for ExoMars/TGO, earlier today. He provided a short explanation of the Phobos orbit crossing that happened, for the first times, at 14:30 UTC and 20:00 UTC.

The crossing of the TGO orbit by the other Mars satellites is a normal situation that we monitor. During the last two weeks, we have been controlling the progress of the aerobraking campaign such that at the time Phobos crosses the TGO orbit, TGO is as far away as possible.

For today’s orbit, see below a series of plot that shows the Phobos orbit (blue line) and the TGO orbit (black line). The red dot shows Phobos’ position, and the black dot, TGO’s position.

To give you some numbers with the orbit of today:

1. Today at 06:44 UTC Phobos crossed the TGO orbit
   

   Phobos orbit & TGO trajectory 06:44 UTC 16 Nov 2017 Credit: ESA/R. Guilanya

2. 259 min later, TGO crossed Phobos orbit, at 11:03Z
   

   Phobos orbit & TGO trajectory 11:03 UTC 16 Nov 2017 Credit: ESA/R. Guilanya

3. 200 min later, Phobos crossed again the TGO orbit, at 14:23Z
   

   Phobos orbit & TGO trajectory 14:23 UTC 16 Nov 2017 Credit: ESA/R. Guilanya

As you can see, both satellites (Phobos, too, is a ‘satellite’) had a large phase difference at the time they were crossing the orbits.