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Answers Your Questions

From: Giles Harney, of Laurel, Md.
To: Sally Davis, flight director


Question: On the graphic that has a green cone that depicts the station and shuttle during the docking phase, what does it mean when the color of the station and text turns to red?

Answer: The graphics you refer to are run by a program called Visual Proximity Operations Program, or VPOP for short. It takes telemetry from the shuttle and displays the position of the orbiter with respect to an imaginary 8-degree cone protruding from the International Space Station. The graphic turns red to indicate a loss of telemetry, which happens occasionally when the orbiter's communications antennae can't see the Tracking and Data Relay Satellites. While we try to avoid these "loss of signal" periods during critical operations like rendezvous and docking, brief drop-outs are inevitable as the orbiter passes communications responsibilities from one TDRS satellite to another, or when the communications signal is blocked by orbiter structures, such as the tail.

Ray Bigonesse
Space Shuttle Rendezvous Officer


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Curator: Kim Dismukes | Responsible NASA Official: John Ira Petty | Updated: 12/01/2002
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