Re: Why do we have LOS, when we have all these TDRSes?

On Thu, 14 Sep 2006 15:45:07 +0200, "Steen" <virker@xxxxxxxxxxxx>
wrote:

Just minutes ago, I heard Capcom mention that the ISS was going into an LOS,
and that they would resume their conversation, once they were out of the
LOS.

As far as I can see, there are 10 TDRS satellites distributed fairly evenly,
so that there should be no LOSes.

Why are they still talking about LOSes?

I think most of those TDRS are in semi-retirement. They generally use
two for Shuttle, designated TDRS-East and TDRS-West. Most of the
earlier satellites are being used in other roles. TDRS-1, up there
since '83, was last being used as a link to the South Pole research
stations, for example.

As for LOS, the Ku-band antennae still have to switch from pointing at
one TDRS to the next, which takes time to slew across the sky. Also,
there is a gap called the Zone of Exclusion 180 deg around the world
from the TDRS ground station at White Sands. Sometimes, NASA uses a
TDRS there (called TDRS-Z, which links to a ground station in
Australia, then up to one of the other TDRS) but not always.

Brian
.

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