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33.2 RAPID Mode Observation Timing Uncertainties

Under certain circumstances, the start times of individual exposures in an FOS RAPID mode time series must be calculated by a special algorithm, which requires information available only from the engineering telemetry stream. The reason for this requirement is that the interval between individual groups in a RAPID (or rarely, ACCUM) mode sequence is not always constant

If absolute or relative start times of RAPID mode exposure sequences must be known to accuracies more precise than 0.125 seconds, then we recommend that RAPID mode observers contact the Help Desk (E-mail: help@stsci.edu) for help in determining the precise start times of the exposures.

FOS ISR 154 provides a detailed description of the causes of uncertainties in the start times of FOS exposures and provides many low-level details of FOS data taking

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