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Answers Your Questions

From: Brandon Bennetzen, of Grand Island Nebraska
To: Bill Reeves, flight director for the planning team

Question: How does TDRS compare to ground stations around the world?

Answer: Hi Brandon. I will assume you want to know how the TDRS communications compares to ground station communications with the space shuttle. There's a big difference! The Tracking and Data Relay Satellite system can provide 100% coverage of the shuttle's orbit. Spacecraft Tracking and Data Network(STDN) and Space to Ground Link System (SGLS) ground stations cannot provide near the coverage. There are currently 10 ground stations that can provide communications coverage with the orbiter. They are Merritt Island (MIL-Florida), Wallops (WLP-East Coast), Dryden (DFR - California), Oakhangar (OTS - England), Diego Garcia (DGS - Indian Ocean), Vandenberg (VTS - California), Colorado (CTS), New Hampshire (NHS), Hawaii (HTS) and Guam (GTS). The ground stations can only provide communications to the orbiter when it passes over the site and the site is scheduled to support! It's fair to say that although the constellation of TDRS satellites can provide 100% coverage to the shuttle, typically there's a gap in coverage called the Zone of Exclusion (ZOE) that occurs over the Indian Ocean. During periods of high activity or critical activities, the communications coverage can be scheduled to close the gap. The only losses of communication that will occur when 100% coverage is desired, are the handovers between the TDRS's and attitudes of the shuttle that cause weak signals (ratty comm).

I hope this answers your question!

Laura Hoppe
Instrumentation and Communications Officer - Orbit 2 shift

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Curator: Kim Dismukes | Responsible NASA Official: John Ira Petty | Updated: 04/07/2002
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