Re: How about 4?

Posted by Dale on Mar 12, 2002 at 09:28

Re: I tried 5 also (bobbapink)

The geosynchronous requirement isn’t the same as geostationary. A geostationary orbit (seeming to hover over a single point) requires an equatorial orbit. A geosynchronous orbit only requires an orbital period of 1 sidereal day. You can have a polar orbit that is also geosynchronous. But I think I see your point. You want to be a stickler for that geosynchronous (1 sidereal day) definition. I was allowing my satellites to orbit in a 24 hour period rather than a sidereal day which allows them to maintain position over the band.

But your question caused me to rethink it and it can be done with 4. But how to describe the orbits? Three doesn’t work because no matter what the instantaneous locations, you can envision a triangle that is either centered on a great circle or is to one side or the other. If it is to one side then the other side of the planet is not covered. If it is centered, then the “poles“ of the great circle are uncovered. But by placing 4 satellites in a pyramid shape then I think it can be arranged so that there is always a triangle covering one side and the forth satellite to cover the hole on the other side. Put them at the right altitude and they can meet the requirement that they all be in geosynchronous orbits though this is not required for the ability of universal communication.

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