Celestia Forums

One might think geostationary satellites do not move with respect to Earth. Well, this is not right. I made shots of 2 satellites motion during 24 hours. Have a look in my gallery:


http://ennui.shatters.net/gallery/view_photo.php?set_albumName=Calculus&id=2_geostationary_satellites_2003_05_18_string

Tie-breaker:
Can anyone tell me what countries you can see in the background ?

So which satellites are these? And where did you get the orbital elements? I just want to make sure there's not some inaccuracy in Celestia causing the movement

--Chris

chris wrote:So which satellites are these? And where did you get the orbital elements? I just want to make sure there's not some inaccuracy in Celestia causing the movement :)

--Chris

From the left hand side, you have ITALSAT F2 and HOT BIRD 2
The orbital elements come from http://celestrak.com/NORAD/elements/
(provided by Thomas Guilpain)
I've checked several satellites (around 20) and I don't see any problem in Celestia. The satellite's movement is consistent with what I was expecting. Some have the famous 8 shape. Some have a large movement amplitude. Some are almost motionless. However, since I used the osculating elements of last july 2002, it is very unlikely that they are still the same in 2003. This is the reason why I did not mention their designation.
I also increased their radius to 15km to make them visible!
My intention was to show the 24 hours motion of the satellite's zenith on earth. Though possible with Celestia, it was too much time consuming, so I just found a far POV in sync with Earth and with a narrow FOV. The result is what you can see on the image and it gives a motion's shape close to the one expected.

Calculus wrote:Can anyone tell me what countries you can see in the background ?

Indonesia, Malaysia, Brunei, and Singapore.

(I checked by looking it up in an atlas, but I guessed right. Brunei is right on the edge, and part of Thailand is just out of the picture.)

Try this-- it's cool:

Get Thomas Guilpain's geostationary .ssc file off Bruckner's site and install it (there are multiple versions of the .ssc files in each ZIP archive, for different purposes; make sure you haven't got redundant ones installed at the same time or they will just suck cycles for no good reason-- the only .ssc you need is Geostationary_full.ssc). Then:

1. Turn off spacecraft labels
2. Turn off star rendering
3. Turn the magnitude limit to the dimmest setting
4. Sync orbit Earth
5. Zoom out until you can see the Clarke ring of comsats surrounding the Earth
6. Now speed up time.

You'll see a ring of satellites that stay pretty much still over the equator (the geostationary satellites), and another ghostly band of satellites that have inclined orbits and consequently bob north and south over the course of a day (geosynchronous but not geostationary satellites).

The thing I didn't expect is that the band of not-quite-stationary ones do not have randomly distributed orbital orientations; their ascending nodes, while not identical, are concentrated so that the band wobbles around the Earth like a hula hoop (seen from the Earth's frame of reference). If you follow Earth instead of sync-orbiting it, you'll see that the band has a definite fixed orientation tending toward the ecliptic plane. I wonder why that is?

Matt,
of course, you are right for the countries.

As for your questions, you'll find some basic information here:
http://www.celestrak.com/columns/v04n07/

And more detailed information about the 54 years cycle here:
http://members.aol.com/geostat2/geo2.htm
(But since Celestia uses only elliptical orbits, it can't simulate this phenomenon, yet!)

So the answer is that most of the non-geostationary satellites are the dead ones! And the shape of the geosynchronous band has to do with the forces pulling them off station once their fuel is gone.

Thanks for posting the links.