Hubble Space Telescope Primer for Cycle 11

A.1 ACS

---

Suppose that you wish to use the ACS to observe a target at a declination of +35 degrees, so that there are 54 minutes of visibility time per orbit (see Table 6.1). Your desired exposures are listed in Table A.1, and the associated overheads are listed in Table A.2. In Table A.3 you can see how the observations fit into a total of 2 orbits.

Table A.1: ACS Example: Planned Exposures

Config	Mode	Spectral Element	Number of Exp	Time per Exp [m]	Notes
ACS/WFC	IMAGING	F606W	4	8.5	Pattern (see Section 5.4) with an offset of 25" between positions
ACS/HRC	IMAGING	F814W	2	6	CR-SPLIT
ACS/HRC	IMAGING	F606W	2	6	CR-SPLIT
ACS/HRC	IMAGING	F435W	2	7	CR-SPLIT

 
Table A.2: ACS 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
WFC exposure (first)	4	First exposure in a series of identical exposures	6.4
WFC exposure (not first)	2.5	Per exposure after the first exposure in a series	6.4
HRC exposure (first)	2.5	First exposure in a series of identical exposures	6.4
HRC exposure (not first)	1	Per exposure after the first exposure in a series	6.4
SAM of 25"	0.5	Small Angle Maneuver between positions in the pattern	6.14

 
Table A.3: ACS Example: Orbit Planning

Activity	Duration [m]	Elapsed Time [m]
Orbit 1
Guide star acquisition	6	6
WFC/F606W Exp Time	4x8.5	40
WFC/F606W Overhead	4+(3x2.5)+(3x0.5)	53
Unused time	1	54
Orbit 2
Guide star re-acquisition	5	5
HRC/F814W Exp Time	2x6	17
HRC/F814W Overhead	2.5+1	20.5
HRC/F606W Exp Time	2x6	32.5
HRC/F606W Overhead	2.5+1	36
HRC/F435W Exp Time	2x7	50
HRC/F435W Overhead	2.5+1	53.5
Unused time	0.5	54