Hubble Space Telescope Primer for Cycle 11

A.5 WFPC2

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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	6.2
Guide star re-acquisition	5	per orbit after first orbit	6.2
Exposure (CR-SPLIT)	5	per exposure (CR-SPLIT is default for >600s)	6.12
Exposure (no CR-SPLIT)	3	per exposure (no CR-SPLIT is default for <=600s)	6.12
Efficiency	1	per orbit	6.13
SAM of 1"	0.33	Small Angle Maneuver between positions in the pattern	6.14

 
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