Regarding satellite positions

[mohanaprakash]

Dear All

My understanding on satellite position is at each longitude there will be only one satellite, but when i referred LyngSat - Lyngemark Satellite i found

Eurobird 1
Astra 2A
Astra 2B
Astra 2D

Are all at 28.2 deg East. Similarly some other satellites are also there.

Can some one clarify how this is done.

Thanks in advance.

Regards
Mohanaprakash T

 

[pedrogarcia]

Geostationery satellites have a longitude position (east west) and inclination position (north south). A drift occurs due to gravitational pull, solar radiation and cosmic "weather". This drift is allowed within a box measured from earth as no greater than 0.3 degrees. This represents a position of about 160 kilometers in each direction so you see it is easy to maintain a number of satellites at a single longitude position maintaining the same footprint on earth.

 

[geekt]

That would probably mean that a fractional degree in either direction, depending on the day, could give you a better signal.

 

[pendragon]

I believe most of the geostationary birds for North America are required to stay in a box +/- 0.05 degrees, and likely some are much better. As they drift around in this box, a fixed large antenna may see a fluctuating signal, so these are preferably aligned when the satellite is in the "center-of-the-box". Times for this are available on the Internet for many of the satellites.

In other terms, a box 0.1 degrees on a side at a geostationary altitude has a dimension of about 74 km or 44 miles. It's fairly straightforward to position several birds within such a box and keep them from colliding.

 

[pedrogarcia]

That would probably mean that a fractional degree in either direction, depending on the day, could give you a better signal.

Generally it would only be noticeable using a large dish to pick up a signal way outside the footprint.
Pendragon> yes the NA birds being closer together, may well have a tighter box, my understanding was the box was increased to preserve fuel and maintain a reserve to send birds to the graveyard orbit to decay.

 

[AcWxRadar]

Dear All

My understanding on satellite position is at each longitude there will be only one satellite, but when i referred LyngSat - Lyngemark Satellite i found

Eurobird 1
Astra 2A
Astra 2B
Astra 2D

Are all at 28.2 deg East. Similarly some other satellites are also there.

Can some one clarify how this is done.

Thanks in advance.

Regards
Mohanaprakash T

Mohanaprakash,

Some of those may actually be on the same "bird" or satellite - physically. You can have multiple antenna arrays (or multiple sats by name) on the same structure (i.e. C-band and Ku-band eminating from the same physical sat, but referred to with different names).

There can be more than one satellite at the same orbital slot (not precisely, but very close), if they are positioned correctly in their elevation. Obviously, they cannot occupy the same physical "space", but they can be close enough that your dish won't know the difference.

RADAR

 

[mohanaprakash]

Hi guys

Thanks for your replies, from the discussion my understanding is different satellites can be placed very closely (with fractional degree different), but when we look at from the earth, then all the satellite signals may received from same longitude position.


I am having one query is there is any limitation on number of transponders on a single satellite or it depends only on bandwidth, if there is any limitation, then can you please recommend any specification for this.


Thanks in advance
Mohanaprakash T

 

[turbosat]

The satellite is probably constructed to have a certain number of transponders specified by it's owner.
One place you might look would be the companies that own/operate satellite fleets, like SES (ses.com).
I'm sure there's physical limits to the number of tps due to the physical size of a satellite and its component parts.