9.4 Acquisition Overheads

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-SIZE2); add times to move OSM1, OSM2, and the aperture, if necessary; add the overhead below for the correct SCAN-SIZE; and add 37 s for readout to estimate the total ACQ/SEARCH time.

Note that these overheads assume the standard (default) STEP-SIZE of 1.767". Overheads are slightly shorter for smaller STEP-SIZEs.

ACQ/IMAGE: Multiply the exposure time by 2 (since images are obtained before and after centering); add times to move OSM1, OSM2, and the aperture, if necessary; add 120 s for setup; and add 56 s for readout to estimate the total ACQ/IMAGE time.

ACQ/PEAKXD: For NUV, start with the exposure time; add times to move OSM1, OSM2, and the aperture, if necessary; add 86 s for setup; and add 37 s for readout to estimate the total ACQ/PEAKXD time. For FUV, use the timing outlined below for ACQ/PEAKD. The default FUV 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); add times to move OSM1, OSM2, and the aperture, if necessary; add the overhead below for the correct NUM-POS; and add 37 s for readout to estimate the total ACQ/PEAKD time. The numbers below assume the default STEP-SIZE for each NUM-POS as given in Table 8.3.

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.