The overheads on exposures are summarized in Table 10.1. All numbers are approximate and, for the observatory level overheads, rounded up to the nearest half minute. These overhead times are to be used (in conjunction with the actual exposure time and the Cycle 13 Phase I Proposal Instructions) to estimate the total time in orbits for NICMOS proposal time requests. After an HST proposal is accepted, the observer will be asked to submit a Phase II proposal to allow scheduling of the approved observations. At that time the observer will be presented with actual, up to date overheads by the scheduling software. Allowing sufficient time for overheads in the Phase I proposal is important; additional time to cover unplanned overhead will not be granted later.
Overheads can be subdivided into two main categories:
BRIGHTOBJ
mode is particularly burdensome, since this mode resets and reads each pixel, one pixel at a time.
DROP-TO-GYRO
) or re-acquire the guide stars (3 minute overhead per re-acquisition-note that this is not the 5-minute orbit re-acquisition) every time the telescope goes back to the target; with the first option the pointing uncertainty is about 1 milliarcsec/second due to telescope drift. The drop-to-gyro option can be adopted for background pointings, where telescope drift is not a concern.
Going From: |
Going To: |
||||
---|---|---|---|---|---|
Coronagraph |
NIC 1 |
Intermediate |
NIC 2 |
NIC 3 |
|
Coronagraph |
0 |
40 |
80 |
125 |
620 |
NIC 1 |
55 |
0 |
40 |
85 |
580 |
Intermediate |
95 |
40 |
0 |
45 |
540 |
NIC 2 |
150 |
95 |
55 |
0 |
285 |
NIC 3 |
645 |
590 |
550 |
285 |
0 |
Space Telescope Science Institute http://www.stsci.edu Voice: (410) 338-1082 help@stsci.edu |