Phobos Grunt re-entry projections

From: Paul Salanitri (
Date: Fri Jan 06 2012 - 13:06:46 UTC

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    It seems that either the atmospheric density is lowering (due to solar flux
    etc) or orientation changing slightly to ease slightly the drag on the
    Phobos Grunt spacecraft.
    Using a (yet-another) numerical method for re-entry calculations, I'm
    currently seeing a 17-Jan-2012 01:00 UTC +/- 2 day re-entry window.
    Projection v Actual :
    Tracks with SatEvo for +/- 1 day :
    The buffeting and fluctuations in atmospheric density through solar flux
    can still cause dramatic changes in prediction at this stage.  Some recent
    short-peaks (spikes), simultaneously effecting many satellites, can drop
    altitudes (beyond its current rate of decay) by 100s of metres fairly
    It appears that around time of re-entry the Northern Hemisphere will have
    the visible passes in the evening (around 40degN) and the Southern
    Hemisphere will get morning passes (around 25degS)
    Paul S.
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