Re: Fobos-Grunt: analysis of orbit evolution

Date: Tue Nov 22 2011 - 15:48:14 UTC

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    You can ignore aerodynamic lifting for satellites by all practical
    means. Furthermore, the orbit evaluation of Phobos Grunt can be
    explained convincingly by the mentioned thruster activity for attitude
    -----Original Message-----
    Date: Tue, 22 Nov 2011 15:45:55 +0100
    Subject: Re: Fobos-Grunt: analysis of orbit evolution
    From: Bill Bard <>
    To: George Roberts <>
    How about some aerodynamic lifting during perigee as a result of a fixed
    orientation then?
    On Nov 22, 2011, at 9:41 AM, "George Roberts" <> wrote:
    >> Is there a way to calculate kinetic energy of Phobos-Grunt vs time to
    >> 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
    > 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
    > have changed.  Energy other than drag.  More energy than expected from
    > "solar wind".  This suggests thrusters or a leak.  The best way to
    > 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
    > 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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