Space Telescope Science Institute  A.4 STIS Appendix B: Archival Instruments

A.5 WFPC2

Suppose that you wish to use the WFPC2 to observe a target at a declination of -45 degrees, so that there are 55 minutes of visibility time per orbit (see Table 6.1). Your desired exposures are listed in Table A.13 and the associated overheads are listed in Table A.14. In Table A.15 you can see how the observations fit into a total of 3 orbits.


Table A.13: WFPC2 Example: Planned Exposures
Config
Mode
Spectral
Element
Num of Exp
Time per Exp [m]
Notes
WFPC2
IMAGING
F814W
1
40
CR-SPLIT
WFPC2
IMAGING
F450W
1
43
CR-SPLIT
WFPC2
IMAGING
F555W
4
9
Pattern (see Section 5.4 ) with an offset of 1" between positions

Table A.14: WFPC2 Example: Incurred Overheads
Overhead
Overhead Time [m]
Notes
see Table
Guide star acquisition
6
first orbit in new visit
Guide star re-acquisition
5
per orbit after first orbit
Exposure (CR-SPLIT)
5
per exposure (CR-SPLIT is default for >600s)
Exposure (no CR-SPLIT)
3
per exposure (no CR-SPLIT is default for <=600s)
Efficiency
1
per orbit
SAM of 1"
0.33
Small Angle Maneuver between positions in the pattern

Table A.15: WFPC2 Example: Orbit Planning
Activity
Duration [m]
Elapsed Time [m]
Orbit 1


Guide star acquisition
6
6
F814W Exp Time
40
46
F814W Overhead
5
51
Efficiency Overhead
1
52
Unused
3
55
Orbit 2


Guide star re-acquisition
5
5
F450W Exp Time
43
48
F450W Overhead
5
53
Efficiency Overhead
1
54
Unused
1
55
Orbit 3


Guide star re-acquisition
5
5
F555W Exp Time
4x9
41
F555W Overhead
(4x3)+(3x0.33)
54
Efficiency Overhead
1
55
A.4 STIS Appendix B: Archival Instruments
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