From: utzoo!decvax!cca!cobb@NBS-VMS@sri-unix
Newsgroups: net.space
Title: Dial-A-Shuttle
Article-I.D.: sri-unix.2065
Posted: Tue Jul 13 09:27:53 1982
Received: Fri Jul 16 02:05:04 1982


   The reason you don't hear all that much on the Dial-A-Shuttle
number is that Houston and the Shuttle can only talk to one another
when the shuttle is over a ground station, which doesn't happen all that
often.  The Shuttle is in such a low orbit that the horizon is only
a few hundred miles, and it's moving so fast that it covers that
distance fairly quickly.  Twenty minutes talking to the same ground
station is a long pass.  You have to know when the shuttle is over
a ground station in order to get anything out of the phone number
besides the recording.  Unfortunately, the ground stations are pretty
randomly scattered, and the shuttle doesn't cover the same ones on
successive orbits because the Earth rotates under it.  In order to
predict ground station passes, you need either:
   - a fairly sophisticated orbital trajectory program, or
   - a copy of NASA's flight plan, which has (among other goodies) a
map of the shuttle's ground track, including markers indicating which
ground stations are in communication with the shuttle at what times.
Once you correct for the difference between planned and actual liftoff
times, the map is very accurate.  The flight plan is included in the
Shuttle Mission Press Kit (at least it was in the one for STS-3), so
pester your friendly neighborhood newspaperman.

   Second topic:  The article I read said that AT&T had collected
$1.2 million dollars on that number during the last mission.  That's
not peanuts!  That's quite a few percent of the cost of the mission.
What are the chances of NASA collecting some royalties here?  After all,
they're \providing/ the signal; Ma Bell is just moving it around.

  Even if NASA can't get any of the money directly, that sure shows
that there's a helluva lot of popular support out there for the space
program.  Probably more than most congressmen realize...

				Stewart

PS - Does anyone have a program for calculating ground tracks/ground
station coverage?  Can anyone provide pointers to the appropriate
algorithms?  (Supposedly they fly an HP-41 calculator on the Shuttle
that's programmed to display upcoming ground stations, so it can't
be that hard.)