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Cosmic Origins SpectrographInstrument Handbookfor Cycle 22 > Chapter 9: Scheduling Observations > 9.4 Acquisition Overheads

9.4
The various target-acquisition procedures are described in detail in Chapter 8. The exposure overheads associated with each are given below:
ACQ/SEARCH: Add 20 s to the exposure time and multiply by the number of dwell points. Add the grating-change overheads from Table 9.3 and Table 9.4. Even SCAN-SIZE values (2 or 4) trigger an additional overhead because of the telescope motion required to displace the aperture by half of a STEP-SIZE in both the dispersion and cross-dispersion directions, so that the overall pattern remains centered on the initial pointing.
ACQ/IMAGE: The associated overhead is 120 s plus twice the specified exposure time; this includes both the OSM1 and OSM2 movements and the overhead adjustment discussed in Section 9.6. The exposure time is doubled because, after HST is slewed to center the target, a confirmation image is obtained. Dumping the two images to memory requires an additional 58 s.
ACQ/PEAKXD: The overhead is 70 s (NUV) or 80 s (FUV) plus exposure time. Add the grating-change overhead from Table 9.3 and Table 9.4.
ACQ/PEAKD: Add 20 s to the exposure time and multiply by the number of dwell points. Add the grating-change overhead from Table 9.3 and Table 9.4. Add 39 s for memory readout.

Cosmic Origins SpectrographInstrument Handbookfor Cycle 22 > Chapter 9: Scheduling Observations > 9.4 Acquisition Overheads

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