Communications

I was wondering of anyone could give me a quick summary of how the ISS
communicates with Earth.
I know it has a Ku-Band and an S-band. What do each do? While trying to
research this, I read that video feeds use the Ku-band when it was
"online". Why is it ever offline? It is online only at certain times of
the day?

Dean

dean wrote in news:2006112212132050073-
robodean@gmailcom:

I was wondering of anyone could give me a quick summary of how the ISS
communicates with Earth.
I know it has a Ku-Band and an S-band. What do each do? While trying to
research this, I read that video feeds use the Ku-band when it was
"online". Why is it ever offline? It is online only at certain times of
the day?

Ku-band is high bandwidth, S-band is low bandwidth. S-band can do voice,
data, and limited (sequential still) video, while Ku band can do full
video.

The Ku antenna requires a direct line-of-sight to a TDRS satellite. Due to
the placement of the antenna on the Z1 truss and the temporary placement of
the P6 truss segment atop the Z1, the Ku line of sight to TDRS is blocked
part of the time.


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On 2006-11-22 20:36:22 -0500, "Jorge R. Frank" said:

TDRS satellite

So if it were not for the issues with the array's placement on the
truss, the ISS would have 100% contact with a TDRSS? I imagine yes as
both the TDRS satellites and the ISS are geosynchronus, then if they
woukd have line of sight, they always stay in line of sight, right?

Dean

dean wrote in
news:2006112309451675249-robodean@gmailcom:

On 2006-11-22 20:36:22 -0500, "Jorge R. Frank"
said:

TDRS satellite

So if it were not for the issues with the array's placement on the
truss, the ISS would have 100% contact with a TDRSS? I imagine yes as
both the TDRS satellites and the ISS are geosynchronus, then if they
woukd have line of sight, they always stay in line of sight, right?

Dean



A reasonably good source for basic information is the ISS evolution book
from Langley. Do a search to pick up volume two.
http://library-dspace.larc.nasa.gov/...dle/2002/11338

The TDRSS is in Clarke orbit, the ISS is in LEO. Therefore only the TDRSS
is geosynchrous. The ISS goes around the Earth approximately every 90
minutes. You are correct in it being a line of sight issue, caused as
much by obstructions as by limitations of the antenna pointing system.

Do some research, read some more, ask some questions.

"dean" wrote in message
news:2006112212132050073-robodean@gmailcom...
I was wondering of anyone could give me a quick summary of how the ISS
communicates with Earth.
I know it has a Ku-Band and an S-band. What do each do? While trying to
research this, I read that video feeds use the Ku-band when it was
"online". Why is it ever offline? It is online only at certain times of
the day?

Dean


OK. I am an expert on shuttle ascent and entry but no comm, so I may be
talking BS here. My understanding is the Ku communication is MUCH faster,
but requires an antenna point at the TDRS satellite. The S-band doesn't.

Danny Dot
www.mobbinggonemad.orb