Re: STS Magnitude (1103)
Mike McCants (mike@comshare.com)
Tue, 14 Nov 1995 09:39:52 -0600
Jim Gorges asks:
>When using Quicksat to predict passes during STS missions, what are
>proper values for magnitude and dimensions to edit into QUICKSAT.MAG?
The "intrinsic magnitude" of the shuttle can be anything from 1.0
to -2,0 depending on its phase and orientation. I currently use
-0.5, but I observed STS 73 to be about 1.5 magnitudes brighter on
a favorable pass. On the other hand, if the shuttle is docked
"behind" Mir with Mir's solar panels shadowing them both and the
phase angle is not favorable, maybe 0.0 would be an appropriate
"intrinsic magnitude". But, QuickSat will ignore a 0 value, so
you must put in -0.1 or 0.1 as a non-zero value.
>Shuttle intrinsic magnitude values vary between missions.
The values that appear in the Quicksat.mag file are based on my
observations.
>Is this a function of how a particular
>mission is flown (vehicle attitude or orbit inclination, for example),
>or of each vehicle's physical characteristics, or some other factor?
Yes, vehicle attitude oftens affects the brightness. No, I don't think
the vehicle characteristics are different. The "other factor" is the
actual viewing conditions when I observed these missions. It's not
a sphere, so if I correct its observed magnitude to get an intrinsic
magnitude as though it were a sphere, ... Also, I have my memory of what
I have used in the past (-0.5), and that can bias my observations.
>Some previous STS data lines in QUICKSAT.MAG have dimensions (37.1 23.8
>17.1), other lines do not. Are these dimensions correct?
As to the dimensions, they are for reference purposes only.
The shuttle is a rather unusual shape :-), so sometimes Ted
puts in a "box" shape (37.1 23.8 17.1) and sometimes he puts
in a spherical shape (30.0, 0.0, 0.0). I am just copying his
dimensions.
Mike