A question about geostationary satellites

[Captain Jack]

A quick one really. With geostationary satellites, it seems like you cannot receive them if you're in the extreme polar regions, such as the Arctic or Antarctica.. or even somewhere like north Greenland. This is because even the highest satellite in the sky for those places would be below the horizon.

How does satellite communication work there? I guess they have to use satellites in other orbits...

 

[Llew]

There's the polar orbiting satellites that are used for instance by the Norwegian Troll Research station in Antarctica -

-http://www.spacecentre.no/?module=Articles;action=Article.publicShow;ID=50922

 

[Analoguesat]

The science stations very close to the pole often use heavily inclined satellites , although this of course limits transmission times to the periods when the bird is above the pole.

One of the Boeing spinner craft was retired not too long ago after nearly 30 years service - its latter years spent inclined providing coms to the south pole base.

 

[Captain Jack]

Very interesting! Thanks guys.

 

[BlindFaith]

simple answer, they don't use satellites in geostationary orbit

 

[Tsiklon]

Of relevance - Molniya orbit
_http://en.wikipedia.org/wiki/Molniya_orbit

 

[BM300]

All the geostationary satelltes are located on the equator.
How easy is it to see the equator from that location? and does it cover the area in question, is what matters.

 

[davidcmadrid]

Sort of related :

Engineers on Sunday intentionally crashed a Russian Express communications satellite stranded in space by an August rocket mishap, declaring the mission a total loss despite efforts by a start-up company to purchase the craft to serve the Antarctic research community

spaceflightnow.com/news/n1203/25expressam4/

 

[Huevos]

One of the Boeing spinner craft was retired not too long ago after nearly 30 years service - its latter years spent inclined providing coms to the south pole base.

It must have been inclined intentionally otherwise it still wouldn't be inclined enough. To get above the horizon at all it would need to be inclined more than 10º. Natural inclination is 0.85º per year. And natural inclination never passes 15º. So could only work between the horizon and 5º above, before inclination started to drift back in the opposite direction.

 

[Captain Jack]

So does that mean that satellites can essentially work forever with inclination of 15 degrees?

 

[Huevos]

No. Once it gets to 15 degrees it starts to decrease again at 0.85 degrees per year until it is back to 0 degrees inclination, and so the cycle continues.

 

[Captain Jack]

Oh OK. So, even then, it can stay in operation forever, right? As long as it can be tracked...

 

[Huevos]

Oh OK. So, even then, it can stay in operation forever, right?

No, because there is a requirement that all geo-sats keep enough fuel on board to send them into graveyard orbit. So once that level is reached they must be decommissioned.

 

[Captain Jack]

But you said that this inclination is natural; i.e. no fuel used up in this case - or am I misunderstanding this part?

 

[Huevos]

Yes, but you still need fuel for east/west station-keeping even if inclination is uncorrected.

 

[Captain Jack]

Ahh, I see! I would have thought that this would naturally stay there due to it being in geostationary orbit but looks like you still need to do station-keeping.

 

[PaulR]

Doesn't a satellite naturally tend to a figure-of-eight movement without correction?

 

[Captain Jack]

From what I understand, this only applies to north/south variation (i.e. inclination)

 

[Channel Hopper]

The 'figure of eight' is a two dimensional representation of what the satellite is doing, relative to the ground.

In reality it is not keeping in altitude, or inclination, and is not only more difficult to track from the ground, but if the fuel gets too low, or there is a communicaiton malfunction, then this craft could move orbital slots and and jeopardise other satellites.

Many of the more popular spots (above Europe for example) have a number of satellites occupying a specific location (Astra 1, 2 and Hotbird for example) and these are kept within around 100kms of each other so the small dish on the ground doesn't see any change in their position.

In reality there is a lot of free space between each of the different craft - imagine the probablility of two large buses at 50 miles apart hitting each other if one loses a driver - but nevertheless the very real possibility of debris being thrown about in all directions and passing through the space of other satellites, for all eternity, is an option than nobody really wants.

http://video.techbriefs.com/video/CleanSpace-One-a-Swiss-satellit;TBTV-Most-Recent