COS Instrument Handbook for Cycle 25
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Cosmic Origins SpectrographInstrument Handbook for Cycle 25 > Chapter 9: Scheduling Observations > 9.4 Acquisition Overheads

9.4
The various target-acquisition procedures are described in detail in Chapter 8. The approximate total exposure plus associated overheads are given for each procedure below:
ACQ/SEARCH: Multiply the exposure time by the number of dwell points (SCAN-SIZE^2) and add the overhead below to estimate the total ACQ/SEARCH time. These overheads include all OSM and aperture overheads.
Note that these overheads assume the standard (default) STEP-SIZE of 1.767". Overheads are slightly shorter for smaller STEP-SIZEs.
ACQ/IMAGE: The associated overhead depends on the choice of MIRROR and are 297s for MIRRORA, and 335s for MIRRORB; this include all OSM and most aperture overheads, and a 56s memory readout. If the aperture used is the BOA, add 5s in additional overhead. To estimate the total ACQ/IMAGE time add twice the exposure time to the overhead. The exposure time is doubled because, after HST slews to center the target, a confirmation image is obtained.
ACQ/PEAKXD: The overhead is 84s for NUV, and 105s for FUV observations taken before Cycle 25. Add this overhead to the exposure time to estimate the total ACQ/PEAKXD time. For Cycle 25 FUV ACQ/PEAKXDs, use the timing outlined for ACQ/PEAKD. The default Cycle 25 ACQ/PEAKXD configuration uses NUM-POS=3 and STEP-SIZE=1.3.
ACQ/PEAKD: Multiply the exposure time by the number of dwell points (NUM-POS) and add the
NUM-POS specific overheads listed below. The numbers below assume the default STEP-SIZE for each NUM-POS as given in Table 8.3. Add 37s for memory readout.
Note that the above estimates assume that all TA steps were taken with the same grating and cenwave or mirror configuration. If a change of configuration is used, add the appropriate overheads from Table 9.3 and Table 9.4.

Cosmic Origins SpectrographInstrument Handbook for Cycle 25 > Chapter 9: Scheduling Observations > 9.4 Acquisition Overheads

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