Geosyncronous satellites not directly over equator

[Padeye]

I went to the fascinating NASA J-Track page, http://liftoff.msfc.nasa.gov/realtime/jtrack/3d/JTrack3D.html after linking from MSNBC’s article about the new possible natural satellite. I found all the familiar C-band satellites but curiously found a few of them with orbits distinctly skewed from the equator such as MORELOS 2, SOLIDARIDAD1 and SATCOM 5. What’s the deal here? I’m pretty sure I’ve tuned in the some of those birds but wouldn’t a tilted orbit reqluire ground dish to be constantly moving over the course of a day?

[SmackFu]

Solidaridad 1 is dead. The control processor and backup failed.

I think the other 2 are retired and no longer in use.

[Squink]

From Bad Astronomy:

The broader class of geosynchronous orbits can have the orbits tilted a bit to the plane of the Equator. In other words, sometimes the satellite is a bit north of the Equator, sometimes a bit south (but never very far from the Equator; the orbit cannot be tilted too much or else the satellite will wander off target). To someone on Earth, a satellite in geosynchronous orbit will stay at the same longitude (east-west) direction in the sky, but will move north and south over the orbit.

[Chronos]

If it’s not directly over the equator, then yes, the position relative to the Earth will shift some over the course of an orbit. But it’ll keep the same average position, and if you don’t need to be too precise, then you’ll still be ablee to find it.

There will be both latitudinal and longitudinal motion, by the way, in a sort of figure 8, but the north-south motion will be much greater.

[David_Simmons]

*Originally posted by Padeye *
**I went to the fascinating NASA J-Track page, http://liftoff.msfc.nasa.gov/realtime/jtrack/3d/JTrack3D.html after linking from MSNBC’s article about the new possible natural satellite. I found all the familiar C-band satellites but curiously found a few of them with orbits distinctly skewed from the equator such as MORELOS 2, SOLIDARIDAD1 and SATCOM 5. What’s the deal here? I’m pretty sure I’ve tuned in the some of those birds but wouldn’t a tilted orbit reqluire ground dish to be constantly moving over the course of a day? **

The directive gain of the receiver antenna is such that sufficient signal is received even if the satellite isn’t precisely centered in the main antenna lobe. Minor wandering around doesn’t matter as long as the average position stays constant. I believe that it is necessary to nudge the satellite around some in order to position it so that the distance from earth gives a 24 hour orbit to an accuracy sufficient that the thing stands still on average.

[Padeye]

I do know the difference between geosyncronous and geostationary. Still I wouldn’t think a dead geostationary bird would so easily go into such a tilted orbit on its own.

[RM_Mentock]

The link that squink included from the Bad Astronomy pages also discusses the Molniya orbits, highly elliptical orbits in which the satellite is in nearly geosynchronous position for a while, then it zooms down close to the Earth and then back up. Such satellites can “hover” over any point on Earth, no matter what the latitude.

[partly_warmer]

Left-click and hold on that 3D JTrack, and the viewpoint swivels. Then it’s clear many of those satellites are not directly above the equator.

Two other reasons for this being so:

• A poor placement of the satellite which wasn’t worth wasting fuel to correct.

• A old satellite purposely bumped out of the orbit used by functioning satellites. They leave a bit of fuel at the end of a geosynchronous satellite’s life to do this, since there are only a certain number of “slots” – believe it or not – and they don’t want a non-functioning satellite anywhere near the ones that are under control. Maybe it’s not a problem now, but one could imagine what a mess it would be in 100 years…

[Padeye]

Okay, using satcom5 as an example it’s orbit is inclined from the equator but it crosses the correct path for geostationary satellites twice a day. That’s potentially far worse than if it remained in position.

I wonder when we’re going to have to develop a satellite catcher 'droid to capture lost comm satellites and either bring them back to be captured for repair or push them well outside geosync orbit.