Position Tagged Telecommands
Similar to time tagged commands are commands which are stored for execution until the spacecraft is at a specified position. These are most useful for earth observation satellites, which need start an observation over a specified point of the Earth's surface. The spacecraft, often in sun synchronous orbits, take a precisely repeating track over the earth. Observations which are taken from the same position may be compared using interferometry, if they are in close enough register.
The precise position required is sensed using GPS.
Once a position tagged command has been executed, it may be flagged for deletion or left to execute again when the spacecraft is once again over the same point.
Read more about this topic: On-Board Data Handling
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