Globalstar intrinsic magnitudes?

Ed Cannon (ecannon@mail.utexas.edu)
Mon, 12 Jul 1999 21:06:52 -0500

There have been questions in some quarters about why Globalstar
satellites, given that they are fairly small and in 1400 km 
orbits, are as bright as they sometimes are (+4 to +5).  

In Mike McCants' recent RCS file, which includes 20 Globalstars,
the average RCS of 19 of them is about 5 square meters.  (For
some reason #25651's RCS is 25, perhaps about equal to the area 
of the full face of the solar panels.  The RCS of #25649 in the 
file is 9.3.)

As best I can discover, each satellite is a box, with four 
rectangular sides and two trapezoidal sides (the "ends" of the 
box).  The earth-facing side is largest, at 152 cm wide.  They 
have two solar panels whose total span is 1075 cm.  This page:

 http://www.globalstar.com/tech/system/satellite.htm#Desc

has much of this information plus illustrations such as this:

 http://www.globalstar.com/img/system/satcon4.gif

The length of the earth-facing side and width of the solar 
panels is not clear but may be about 150 cm.

I don't know how much tolerance the satellites have in their 
attitude.

The only way that's fairly clear to me as to them being brighter
than might be expected is when they are between the Sun and the 
observer with the angle such that the observer gets a direct 
reflection from the earth-facing side.  

Ed Cannon - ecannon@mail.utexas.edu - Austin, Texas, USA