Comparison between Sirius "birds" and XM's.

[pqgeorge]

How high up (in miles) are the Sirius satellites and what kind of orbit to they use between the three satellites they use? Am I correct in assuming that XM's "birds" are geo-syncronous at 22,500 miles up in Earth orbit? I know that Sirius birds recycle every few hours once they lose their radio horizon. Any explanation would be great ! Thanks.

 

[AZJoe]

Sirius uses 3 Loral FS1300 sats, in a unique elliptical orbit, sort of a figure 8 shape, the sats appear higher in the sky than XM's, thus having better northern and southern limits reach than XM. Sirius also says it is why they have far fewer repeaters than XM (120 vs 1200). The Sirius birds spend 16 hrs approx over North American, then speed up on their southern hemisphere route, and return 8 hrs later to nthe northern hemisphere. Thus 2 birds are above North America at all times. There are plans to add a geostationary satellite in 2008 to complement the others. I believe they are about 30,000 miles out in space from Earth.

 

[pqgeorge]

Sirius uses 3 Loral FS1300 sats, in a unique elliptical orbit, sort of a figure 8 shape, the sats appear higher in the sky than XM's, thus having better northern and southern limits reach than XM. Sirius also says it is why they have far fewer repeaters than XM (120 vs 1200). The Sirius birds spend 16 hrs approx over North American, then speed up on their southern hemisphere route, and return 8 hrs later to nthe northern hemisphere. Thus 2 birds are above North America at all times. There are plans to add a geostationary satellite in 2008 to complement the others. I believe they are about 30,000 miles out in space from Earth.

Thanks for the info. It's amazing how, on the ground, the Sirius birds "look" almost stationary for hours at a time, when in fact they are moving toward/and away from the Earth at an enormous velocity. I have actually heard a "handover" when one satellite is shutdown and another bird takes its' place. It's about 5-10 seconds when the satellite goes silent and then the other one fires up. You can see the signal strength increase when the other bird takes over. You can actually semi-predict when the handover is going to take place as the "bar graph" is less than 3 bars in a unobstructed path to the bird, they are going to switch it over soon. In sure the geostationary bird will fill in the little drop points, so prevalent when the trees are in full bloom. In the winter, no problem. Thanks again!