Path: utzoo!utgpu!water!watmath!clyde!bellcore!rutgers!cmcl2!husc6!mailrus!uwmcsd1!marque!studsys!jetzer
From: jetzer@studsys.mu.edu (jetzer)
Newsgroups: sci.space.shuttle
Subject: Re: TDRS-C means never having to say LOS?
Summary: almost
Message-ID: <247@studsys.mu.edu>
Date: 1 Oct 88 14:50:19 GMT
References: <6732@dasys1.UUCP>
Organization: Marquette University - Milwaukee, Wisconsin
Lines: 36

In article <6732@dasys1.UUCP>, tneff@dasys1.UUCP (Tom Neff) writes:
> I know the TDRS network is supposed to provide continuous communication
> with a lot of non-GEO satellites, and I also know that we get partial
> air-to-ground coverage on Shuttle flights right now from the one TDRS
> successfully deployed before STS-26.  As I write this, it appears Discovery
> is deploying TDRS-C nominally.  Assuming the IUS works and the second
> TDRS is parked and activated, will we henceforth have continuous downlink
> during Shuttle missions from now on?  Or will the "LOS Guam, AOS Hawaii
> in 6" game continue until we have three birds up there?

> Second question - the early diagrams had an equilateral triangle of
> TDRS coverage taking care of satellite and spacecraft comm.  But lately
> I hear that when TDRS-D is deployed, TDRS-A will be parked as a hot
> spare while C or D assumes its duties.  Are we still aiming for three
> live birds at some point, or are we resigned to antipodal coverage?

The October issue of Countdown magazine has an article about TDRS in it.
There is a diagram of the expected placement of TDRS-1 and TDRS-2 (called
TDRS-C until it's in orbit).

Imagine that there is a large square around the earth, with the earth at the
center.  The two TDRSs are at adjacent corners of the square.  Because of
this, there will still be "about 15 percent" of the shuttle's orbit will
be "in the shadow" and not covered by the TDRSs.

Two ground stations have already been closed, and six more will be closed
"once there are two fully operations TDRS satellites on orbit.  'Operational'
in this sense does not include TDRS-1."  So it does seems that TDRS-1 will be
a "hot spare" once TDRS-3 comes online.   TDRS-D was slated for launch during
STS-29 on January 19, 1989, but that date has apparently slipped.

No information concerning the relative locations of TDRS-D, -E, or -F was
given.
-- 
Mike Jetzer
"Hack first, ask questions later."