Barry45RPM

I am a member of a Forum (www.Radio-Info.com) run by and for people in the Radio Buisness. Following is an exchange between 2 engineers explaining Sirius' Satellites to each other. I supply it for the general info it provides...

Comparison between Sirius "birds" and XM's.
« on: Yesterday at 12:55:25 pm » Quote

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.

"Quote from: AZJoe on Today at 12:21:08 am
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 America, then speed up on their southern hemisphere route, and return 8 hrs later to the 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.

And the Response...

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!

So I guess "They're working on it..."

xraymd

Hmmm, that's pretty cool. For some reason I thought the Sirius satellites were geosyncronous. Guess not. Wonder if they launch the new one in 2008 or wait for the planned merger to be worked out.

benzmodz

The signal strength doesnt exactly "shutdown" - the uplink does a handover to the nearest satellite available.

Only satellites in the "clarke belt" are stationary. It was named after Arthur C. Clarke who predicted and calculated the distance from Earth with respect to escape velocity. The reason it can not be used is because of the northern customers.

Once a satellite goes over the horizon it doesnt actually speed up or switch off. It loses its uplink and goes into a southern orbit which crosses more meridians in a short time than it does when it is in the northern orbit. It is really a pattern at a constant speed but on Earth it seems to vary greatly.

I can only assume that there are 3 orbits and the Earth rotates to face 2 of 3 satellites at any one time.

www.lyngsat.com has details on every broadcasting satellite in service. I can only assume that XM uses 1200 repeaters because they are running a longer-life satellite at lower power / closer to the Earth. When Sirius runs out of energy by running at the higher power level (wears out faster) then it will cost a whole lot more to operate the business and replace all three "birds".

The merger with XM gives Sirius more coverage with lower cost. It is cheaper to offer XM 2 billion for bandwidth and network rights than it is to replace 3 satellites. Naturally that can never happen without combined resources.

I dont think I would want to be Sirius if the merger falls over.

AndrewAZ

Sirius is screwed if the merger does not happen, like the early XM1 and XM2 satellites the 3 Sirius birds suffer from power defects and can not operate at full power. XM fixed this by launching XM3 and XM4 in the end of last year and XM1 and XM2 are now orbital spares.. I dont support the merger since I view both companies as mismanaged and the merger is only being done to save their asses and will end up causing poor service for users.

mbnj

They are both screwed if the merger does not go through. Both companies will be financially challenged, mostly by overpaying for talent and because satellite is not a great solution once you get home. Amazingly, this is an industry that is a duopoly and having a single competitor is too much to survive! If they do combine fasten your seatbelt, they will try to pull the price lever and content may walk over reduced pay upon renewal (talent). They will look to mobile video as a new revenue stream as well.

jimm

WOW! I’m glad to get the geosyncronous straighten out.

I haven’t been able to think about anything else.

jimm

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starbrite

Amen to that !