Satspy graphical plots

Jason Hatton (
Thu, 26 Mar 1998 12:32:06 +0000

Eric Vondra wrote:
My mistake was looking for the pass
using the graphical plot from SatSpy. I'm not
sure how the program handles this type of pass--the ephemeris, listing
and Dec, matched but the graphical plot was way off.

& Tyler MacKenzie wrote:
I also used SatSpy to locate Superbird A in Hydra for its 03:33 UT peak;
the ephemerides had it nearly 120 DEGREES TO THE WEST! (RA 0h 9m 35s)
while the graphical display looked about right (I did manage to see
SuperbirdA's flashes = cool!).
        Does anyone know what is going on? 

	The trajectory of Satspy plots are calculated with respect to Alt -
Azimuth. This works fine for LEO satellites but when you have a pass
which can last several hours the position of the satellite will become
displaced significantly with respect to the stars. However, the
tabulated emphemerides should be correct. I had contacted the author of
Satspy (Dave Cappellucci) some time ago to see if there was any way of
plotting the satellite trajectory with respect to RA / Dec. Below are
his suggestions:

"Thanks for the suggestion. I think that it is a good idea and will add
to my list of features for future versions. 

In the meantime, there is a hidden feature in version 2.5 which allows
you to plot external ephemeris data on both the
RA/DEC plot and the Local Sky window. I added this feature when comet
Hale-Bopp was visible, but never finished
cleaning it up for official release. As such, I cannot guarantee that it
will work. To use this feature, hit Ctrl-E when the
Ra/Dec or Local Sky windows are top-most. You will be prompted to input
a file name. For demo purposes, use the file
named Hbeph.dat in your SatSpy directory. It is a text file formatted as
below. It shows the path of Hale-Bopp over much of
1996 and 1997. 

Date RA Declination Not used in V2.5 
------------ ------------ ------------
1996 Oct 2 17 29 44.05 -04 57 09.7 2.989 7.68 2.875 73.8 19.5 162 5.8 
1996 Oct 7 17 30 15.07 -04 42 42.1 3.009 6.60 2.816 69.3 19.4 130 5.8 

Note that everything after the Declination fields are not used. 

In future versions, I will probably add code to allow you to save a
Skytrace ephemeris in a format that
can be read using Ctrl-E. For now, unfortunately, you will need to
modify the format yourself."

Jason P Hatton
ETS Strasbourg
67065 Strasbourg Cedex

48.538N / 7.731E / 143m