Satgen339  Satellite Software Pt6    by GM4IHJ             23 September 95
 
COMPUTER MAPS continued. As suggested in previous bulletins , rather than
centre a great circle map on your station , it makes good sense if you
have a fast computer ( 486/pentium ) to centre the great circle on the
satellite and make the maximum radius of the great circle equal to the
footprint radius of the satellite . This way your computer can keep pace
with satellite tracking giving you a new map every 1 or 2 minutes, whilst
keeping you right up to date as to just what other stations are in the
satellite footprint and therefore might be available for communication.
This type of display can be very useful for the Phase 3 satellites AO10
and AO13, with their very large footprint when at apogee. It also has the
benefit of alerting you as the footprint shrinks as the satellite
approaches its perigee orbital low point.

A variation of the great circle footprint approach is the 3D or hemisphere
map. But please be aware that to be truly 3D , or , "The view from space
map ", as it is sometimes called , it cannot project a true view from
space and maintain an even distance scale from centre to circumference.
True 3D maps have enormous change of distance scale from centre to edge ,
with the geography at the edge being grossly crowded up and looking quite
unusual. Most of us are not use to the view from space , and its scale
changes can be confusing.

Changing the picture entirely there are several kinds of map ( or perhaps
display might be a better word ), which suit certain kinds of operation
such as EME Moonbounce , satellite visual tracking , satellite control,
and some specialised experimental formats.

The moon bouncer wants to know where the moon is in the sky . He can get
this from a simple mercator earth map showing the sub lunar point on the
earths surface , and a printout of lunar azimuth and elevation bearing.
This mercator can also show the edges of the lunar footprint to tell the
operator who else may be bouncing off the moon, and it can indicate local
time to alert the operator to the longitude belt where the world will be
awake and, the complementary belt of longitude where the inhabitants will
mostly be asleep. But the moon bouncer has other problems such as Sky
noise near the moon , and to answer this problem he is perhaps best served
by a map of the sky , preferably using a 3D type projection of half a
hemisphere, and displaying the sky noise contours with particular
reference to natural noise maker such as the Crab Nebula, the supernova
remnant Cassiopeia A, and the colliding galaxies in Cygnus.

In a different field of operation , the 3D sky map is very useful for
visual tracking of sunlight reflecting satellites across the predawn or
evening sky. This map can have simple azimuth and elevation contours
marked on it, or in the deluxe version it has the stars mapped out on it
so that the operator can follow the sat amongst the stars. This is a vital
aid if you go looking for the really small satellites such as Uosat and
Pacsat. You can put a red colour map on your laptop and sit outdoors with
your telescope or binoculars and sooner or later see all 43 or so extant
amateur satellites going by, if you have the time and the heated suit, (
plus a brace of sharp eyed young assistants , if available ).