[amsat-bb] Re: sirius orbit name?

Rick Mann rmann at latencyzero.com
Thu Feb 21 13:19:51 PST 2008

On Feb 21, 2008, at 10:29 AM, Jim Jerzycke wrote:

> The Sirius birds are in an "Inclined Orbit".
> It's explained more in the WikiPedia entry, about half
> way down the page.
> http://en.wikipedia.org/wiki/Sirius_radio

What I read says it's in a "geosynchronous highly elliptical" orbit.  
Strictly speaking, you can't have a truly geosynchronous orbit that's  
elliptical (it must be circular). It must also have an inclination of  

But: the inclined elliptical orbit causes the satellite to speed up  
relative to Earth's rotation during parts of its orbit, and slow down  
during others. This is what causes the East-West motion of the figure- 
eight. The inclination is what gives the North-South motion. The two  
are combined in such a way as to give a nice figure-eight pattern over  
the surface of the Earth.

The Wikipedia entry refers to this as a "Tundra Orbit":



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