Re: Fobos-Grunt: analysis of orbit evolution

From: rkresken@t-online.de
Date: Tue Nov 22 2011 - 15:48:14 UTC

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    Bill,
    
    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
    control.
    
    Rainer
    
    
    -----Original Message-----
    Date: Tue, 22 Nov 2011 15:45:55 +0100
    Subject: Re: Fobos-Grunt: analysis of orbit evolution
    From: Bill Bard <wbard@wb-web.org>
    To: George Roberts <gr@gr5.org>
    
    How about some aerodynamic lifting during perigee as a result of a fixed
    orientation then?
    
    Bill
    
    On Nov 22, 2011, at 9:41 AM, "George Roberts" <gr@gr5.org> wrote:
    
    >> 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
    > http://gr5.org
    > 
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