'Zombie' Satellite Returns To Life 98
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."
Does this mean (Score:2, Insightful)
So does Intelsat have to give the insurance money back now? Or does it take more than a year to process this kind of claim anyway?
Nice story submission! (Score:5, Insightful)
Seriously, three short lines which clearly convey the entire summary of the story, contains lots of links to both story and background, AND doesn't contain terrible typos! Also, geeky and interesting. This is what slashdot needs more of.
Re:Just like that? (Score:5, Insightful)
Not too long ago the norm was actually for transponders to simply be open.
Meaning if you had a means to send a signal to a particular frequency it would be easy to bounce from that transponder and relay back down. Now, if the NOC (or SOC really) caught an open transponder being used as a relay they would eventually shut it down if you were not paying for the air time.
This became a big deal during the initial war in Iraq as there were a good deal of hijack broadcasts spewing forth from across the sea. In response, they eventually began shutting down transponders until they were scheduled to be used. Either out of interest or trying to lock a particular bird I would find them at random times.
Somehow I doubt the mechanisms used on the old satellites were more obscurity then security to prevent updates.
Re:Traversing the sky? (Score:4, Insightful)
Corollary one: Any object in orbit around a body with mass has an external force applied to it.
Corollary two: Any object in the solar system is part of an n-body problem and has lots of external forces applied to it.
Re:Triaxiality (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.