Re: Fobos-Grunt: analysis of orbit evolution

From: George Roberts (
Date: Tue Nov 22 2011 - 14:41:33 UTC

  • Next message: Bill Bard: "Re: Fobos-Grunt: analysis of orbit evolution"

    >Is there a way to calculate kinetic energy of Phobos-Grunt vs time to see 
    >if energy has
    >been added to the system (thrusters, leak) or if it's just been 
    >redistributed (circularization)?
    The middle part of Ted's graph shows that the orbit is decaying overall.  In 
    other words the orbit has less potential and less overall energy (but more 
    kinetic - this is the nature of lower orbits).
    However, even though it has decreasing energy mostly due to drag, it takes a 
    significant amount of energy to change PG's orbit in the way it seems to 
    have changed.  Energy other than drag.  More energy than expected from 
    "solar wind".  This suggests thrusters or a leak.  The best way to explain 
    the anomaly to me is that PG is maintaining an orientation such that it is 
    always pointed to the same star as it orbits the earth and it is constantly 
    thrusting towards that star.  This would explain the increase of one half of 
    the orbit and excessive decrease of the other half.
    - George Roberts
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