Path: utzoo!utgpu!water!watmath!clyde!att!osu-cis!tut.cis.ohio-state.edu!mailrus!ames!ll-xn!husc6!rice!titan!phil
From: phil@titan.rice.edu (William LeFebvre)
Newsgroups: sci.space.shuttle
Subject: Re: TDRS-C means never having to say LOS?
Message-ID: <1934@kalliope.rice.edu>
Date: 30 Sep 88 15:33:04 GMT
References: <6732@dasys1.UUCP>
Sender: usenet@rice.edu
Reply-To: phil@Rice.edu (William LeFebvre)
Organization: Rice University, Houston
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NASA has been officially saying that two operational TDRSs get about 85%
coverage of shuttle flights.  It depends partly on the inclination of the
orbit.  I understand that the figure is closer to 90%.  Part of the
problem is the "South Atlantic Anomaly":  an area of magnetic disturbance
that makes communication difficult.  But with two TDRS satellites, LOS
will be greatly reduced and almost eliminated.  The flight controllers
take this as a mixed blessing:  they usually take their bathroom breaks
during LOS.

The configuration NASA is shooting for is to have C and D fully
operational on opposite sides of the globe and have A lingering around as
a spare.  Three satellites are not needed for full coverage.  And I think
that using a configuration of three in a triangle will not get any
additional coverage that two opposing ones would not get.  That is my
limited and basic understanding.

			William LeFebvre
			Department of Computer Science
			Rice University
			<phil@Rice.edu>