Superbird axis

Rob Matson (
4 Oct 1996 15:40:31 -0800

                      Subject:                              Time:  14:23
  OFFICE MEMO         Superbird axis                        Date:  96/10/04

Okay, here's the rundown on Superbird A's rotation axis.  I used the midpoint
of each of Jim Varney's 3 measurements to come up with the following
coordinates for Superbird A:

9/29/96 3:25:50.55   -1.8098  -155.4626  35963.1km
10/3/96 3:31:31.54   -1.6478  -162.9827  35962.1km
10/4/96 3:32:59.25   -1.6078  -164.8627  35961.8km

Based on these values, the normal to the solar panel axis was
pointed in the following directions:

  Date    UTC Time       RA           Dec
-----------  ----------------   --------------    ----------
9/29/96 3:25:50.55  8h 52.6m   4d 26'
10/3/96 3:31:31.54  8h 38.8m   2d 55'
10/4/96 3:32:59.25  8h 35.4m   2d 33'

If you take the cross product of the first two vectors, you get a rotation
axis pointing to RA 2h 12.6m, Dec 65d 57'.  If instead you take the cross
product of the first and third vectors, you get an axis pointing to RA 2h
12.4m, Dec 66d 04'.  Pretty good consistency, indicating that the points are
fairly close to falling on a great circle.

Using this information, someone should be able to determine precisely what
times the sun will reflect off the panels and strike the earth.  --Rob