re: Superbird problem gets mudd

Philip Chien (kc4yer@amsat.org)
Tue, 11 Feb 1997 23:43:12 -0500

"ROB MATSON" <ROBERT.D.MATSON@cpmx.saic.com> said:

>I think I have an answer which explains this.  Unfortunately, it completely
>changes the rotation axis calculation.
>
>First, some assumptions.  (1) There are two solar arrays.

Correct.  Superbird is (make that 'was') a three-axis stabilized satellite.
Box shaped main body with two flat solar 'wings'.  The wings extend from
the North and South sides of the satellite (up and down) and articulate on
one axis to follow the Sun.


>(2) The two arrays are not necessarily parallel to one another, nor to the
>satellite's axis of rotation.

In normal operation you'd expect the two arrays to work in tandem, since
the sun angle would be identical.  They are not physically attached, but
the solar array drive electronics would be designed to move the two arrays
simultaneously.

Of course the satellite's no longer in normal operation ...


>(3) The two arrays are essentially identical in terms of
>their dimensions and reflective properties.

Correct with a qualifier.  While the two arrays are basically identical,
(possible exception would be small solar sail flaps at the ends which would
be mirror images of each other) their front and back surfaces are very
different materials.

The 'front' is the normal dark-blue colored solar cells with a glass-like cover.

The 'back' (I'm guessing) would be flat black and designed as a radiative
surface.


>(4) The satellite's rotation period is approximately 23 1/2 seconds.

Well, in normal operation the roatation period would be once per day
(inertially) or zero (relative to the Earth's surface).  But - as I've
mentioned before - it's no longer in normal operation.  ;-)


I posted an URL for the Space Systems Loral site which includes an artist's
rendition of the standard Loral three-axis stabilized bus a while back.  If
you need it I can look up the old message.


>Sooner or later I'll get this damn bird figured out to the point that a new
>observer can see it!

Looking forward to it!  I'm intrigued enough that I may convince myself to
try to go search for it.


Philip Chien, KC4YER
Earth News - space writer and consultant
note new E-mail address - pchien@digital.net