Superbird A Rotation Axis Correction

Jim Varney (
Thu, 10 Oct 1996 19:48:44 -0700

Who checks the checker?

I found a pesky error in my vector calcs.  My independent calc is now in
very close agreement with Rob Matson's numbers.

It's a tedious exercise to subtract the sat-obs vector from
the obs-sun vector to arrive at the sun-sat vector.  Then you average
the components of the obs-sun and sun-sat vectors to get the solar panel
normals.  The axis is the vector that is normal to the panel normals.

What makes it tedious is that the RA and Dec's have to be transformed
into i,j,k vectors and back again.

I used my September 29 observation (0325 UT) and last night's observation 
(October 9 at 0340 UT). 

20040 89 41A Superbird A
09/29 0325   17h19m00s	-7d47.6m
10/09 0340   16h52m06s	-7d08.1m

09/29 0325   12h23.2m	-2.50d
10/09 0340   12h59.6m	-6.37d

Normal to solar panel
09/29 0325   8h 52.3m	+4d 23.8m
10/09 0340   8h 56.1m	+0d 47.5m

Rotation axis
R.A. 14h 57.0m, Dec 14d 47m

But correcting my error validates an earlier bit of guessing.  On 
October 1 I wrote:

>I think the axis is more or less in the plane of the orbit, and is pointing
>a little to the "left" of the sun

Which proves the maxim: If you give a monkey a keyboard, his keystrokes
will, by random chance, eventually result in a correct deduction about 
satellites... :)

Jim Varney       | 121^ 23' 54" W,  38^ 27' 28" N   |           Sacramento, CA
Member, SeeSat-L |           Elev. 31 ft.           |                         
Member, Sacramento Valley Astronomical Society      |