NEAR glint location errors

Gene Heyler SRM (
Mon, 12 Jan 1998 09:08:45 -0500

Considering the NEAR glint experiment on the night of Jan 22/23:

There are four solar panels on the spacecraft, each with its own independent
deployment mechanism, and all nominally deployed with their normals in same
direction. If one considers independent errors in the final deployed positions
of each, then there would actually be four spots cast on the earth, each in
slightly different location, but hopefully still somewhat overlapping. The
animation assumes the spots are all perfectly overlapping.

So the actual spot size could be somewhat (up to 4 times) larger than shown,
and irregular in shape,  however any spreading would of course decrease the
observed magnitude. If your ground location is close to, but not inside one of
the areas shown on the animation, DO NOT GIVE UP HOPE. There is a great chance
the spot will be larger than shown.

An additional error would be the misalignment of the mechanical coordinate
system with the guidance coordinate system defined by the onboard star camera.
These were nominally aligned with great precision on the ground, however the
stress of launch, the gravity free environment, and especially the thermal
gradients across the spacecraft (the solar panels are on the hot side, the star
camera is on the cold side) could have caused a deviation in the star camera
pointing. This would cause a single constant bias in the location of all the
spots cast on the ground.

Gene A. Heyler          Ph:    410-792-6000 x 8664  
JHU/APL                 Fax:   410-792-6670 
Bldg 4 Rm 140           Email:				
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