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Title: Satellites in our Sky (GMT June 24th 2003 2:21pm)

Credits: Philip Chi-Wing Fu, Andrew Hanson: Indiana University
         Priscilla Frisch: University of Chicago
         NASA Grant numbers: NAG5-8163, NAG5-11999
Program: Earthday

Explanation: 
  We have over a thousand satellites flying through the sky over our
heads; this brief animation, representing a user's interaction with
the Earthday graphics program, shows a large portion of these at a
selected time, and then zooms in for a closeup of the International
Space station (ISS).  All objects rendered in the images are
positioned at the same time (2:21pm 24th June (GMT)), and the scene
includes the satellites and the earth with daylight shading.  The
program's normal star and planet rendering capability is disabled to
avoid confusion with the satellites.
              
  In this animation, we start our journey looking at Africa in the
evening, then rotate our view to look at the United states at about
9:21am (Eastern Standard Time) in the afternoon.  To position these
satellites, we make use of the SGP4/SDP4 satellite tracking software
from NORAD for near-earth (period < 225 minutes) and deep-space
(period >= 225 minutes) satellites respectively.  Located 38,500km
above the Earth's surface (about 6 times the radius of the Earth), we
find the ring structure of geo-stationary (deep-space) satellites
rotating with the Earth.  In order to visualize satellite types, we
color-encode each satellite: Weather (blue), Communication (Yellow),
Scientific (Green), Navigation (Cyan), etc.  We thus see that most
geo-stationary satellites are communication satellites, and that there
are more satellites in the northern hemisphere than the southern.

  Moving in towards the Earth, we find another layer of near-earth
satellites, which are about 300km to 1500km from Earth's surface.
Finally, we move through this layer and zoom in to the ISS, which is
also a low orbit object around the Earth.  The ISS is at about 389km
over central United state at the chosen moment.  Corresponding scenes,
including real time animation of satellite motions, can be generated
for any given date under interactive user control.

Data sources: Earth Satellites:
   http://www.celestrak.com/NORAD/elements/
ISS space station model:
  http://spaceflight.nasa.gov/gallery/vrml/station/
  with modifications by John H. Huffman, Indiana University