Slashdot Mirror

← Back to Stories (view on slashdot.org)

'Zombie' Satellite Returns To Life

Posted by Soulskill on from the it's-a-trick,-run dept.

realperseus writes "The American telecommunications satellite Galaxy 15 has been brought under control after spending most of the year traversing the sky and wreaking havoc upon its neighbors. The satellite is currently at 98.5 degrees west longitude (from 133 west). An emergency patch was successfully uploaded, ensuring that the conditions which caused it to 'go rogue' will not occur again. Once diagnosis and testing have been completed, Intelsat plans to move the satellite back to 133 west."

5 of 98 comments (clear)

  1. 133 west by circletimessquare · · Score: 5, Funny

    aka 133t status

    --
    intellectual property law is philosophically incoherent. it is your moral duty to ignore it or sabotage it
  2. Nuke it from the ground by Stele · · Score: 5, Funny

    It's the only way to be sure.

  3. Amsat-OSCAR 7 by Gordonjcp · · Score: 5, Interesting

    It's worth comparing it with the venerable AO-7 satellite, which was launched in 1974 and eventually "died" when its battery failed dead short in 1981. A little over ten years later, the failed battery failed again, this time going *open* circuit and allowing the satellite to run entirely off its solar panels. So, while the satellite is illuminated by the Sun it works fairly reliably. You need to keep the power down, because it has a linear transponder so the more power you put in the more comes out - until you exceed the tiny amount produced by the solar cells. It works, though, and people communicate across the world on it every day.

  4. Triaxiality by mangu · · Score: 5, Informative

    Except for two stable points at 75 and 255 degrees east longitude, any geostationary satellite suffers an East-West (or West-East) perturbation due to the earth not being a perfect sphere. This is called "triaxiality" by experts in the field.

    The result is that without correcting maneuvers the satellite longitudinal position oscillates around those two stable points, even if the orbit is exactly at the geostationary altitude.

    1. Re:Triaxiality by mangu · · Score: 5, Insightful

      I have worked with geostationary satellite control for over twenty years, so I know a bit about this. The masses on the earth aren't distributed evenly, the higher density of the rock in some parts pull the satellite to the east or the west.

      You are right in that the perturbation caused by the moon is several orders of magnitude larger than the one caused by this slight longitudinal asymmetry. It's only for satellites that are either in geostationary orbit or in 12 hour period orbits that this effect becomes significant.

      For other orbits the pull in one direction is compensated by a pull in the opposite direction when the satellite comes around the earth. For geostationary orbits, however, the perturbation is always in the same direction, because the satellite is always in the same position with respect to the mass asymmetry, so the effect adds up in time.

      Typically a geostationary satellite needs correcting East-West maneuvers every couple of weeks or so. These maneuvers consume about 10% of the total fuel budget for station keeping, inclination maneuvers consume the other 90%. This goes to show how stronger the perturbations caused by the sun, moon, and earth's ellipsoid shape, which cause the inclination of the orbit to increase, are compared to the triaxial density asymmetry.