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Basically, the file is intended to include the necessary information (other than tables of effective area) for calculating exposures. So it has the position and attitude of the LAT for regularly-spaced time intervals (nominally 30 seconds, although shorter intervals are used when the LAT enters and exits the South Atlantic Anomaly). As currently planned, SAA entry and exit will correspond to the stop and start time for the data taking 'runs' in flight. For orbits that miss the SAA, a run stop/start will be issued when the LAT crosses the orbital plane heading north. The reason for the forced stop/start has to do with preventing some counters rolling over for very long runs. For these stop/starts, the interval between the entries may also be less than 30 s. For each of the intervals in an FT2 file the accumulated live time is also recorded.
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