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Appendix A:
Orbit Calculation Examples 

In this appendix...
A.1 ACS / 47 
A.2 FGS / 49 
A.3 NICMOS / 51 
A.4 WFPC2 / 52

Chapter 5 described the construction of an observing program and the calculation of the total orbit request for a Phase I proposal. As an illustration, this appendix contains some simple example orbit calculations for each of the science instruments (SIs) offered in Cycle 16.

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 53 minutes of visibility time per orbit (see Table 5.1). 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 [min.]
Notes
ACS/WFC
IMAGING
F606W
4
8.3
Pattern (see Section 4.4) with an offset of 25" between positions
ACS/HRC
IMAGING
F814W
2
5
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 [min.]
Notes
see
Table
Guide star acquisition
6
First orbit in new visit
5.2
Guide star re-acquisition
6
Per orbit after first orbit
5.2
WFC exposure (first)
4
First exposure in a series of identical exposures
5.4
WFC exposure (not first)
2.5
Per exposure after the first exposure in a series
5.4
HRC exposure (first)
2.5
First exposure in a series of identical exposures
5.4
HRC exposure (not first)
1
Per exposure after the first exposure in a series
5.4
SAM of 25"
0.67
Small Angle Maneuver between positions in the pattern
5.13
Table A.3:ACS Example: Orbit Planning
Activity
Duration [min.]
Elapsed Time [min.]
Orbit 1
 
 
Guide star acquisition
6
6
WFC/F606W Exp Time
4x8.3
39.2
WFC/F606W Overhead
4+(3x2.5)+(3x0.67)
52.7
Unused time
0.3
53
Orbit 2
 
 
Guide star re-acquisition
6
6
HRC/F814W Exp Time
2x5
16
HRC/F814W Overhead
2.5+1
19.5
HRC/F606W Exp Time
2x6
31.5
HRC/F606W Overhead
2.5+1
35
HRC/F435W Exp Time
2x7
49
HRC/F435W Overhead
2.5+1
52.5
Unused time
0.5
53

A.2 FGS

Suppose that you wish to use the FGS to observe a binary star named Binary01, as well as five reference stars ref1,......,ref5. All stars are in the same FGS field of view, and can therefore be observed in one and the same visit (see Section 5.2.2). Stars ref4 and ref5 have magnitude V=14.6, and all the other targets have 13.0<V<14.0. The targets have a declination of +42 degrees, so that there are 53 minutes of visibility time per orbit (see Table 5.1). To enable the removal of drift and jitter in the post observation analysis of the data, the binary is observed in POS mode several times (twice in our example) and the reference stars are each observed twice. Your desired exposures are listed in Table A.4, and the associated overheads are listed in Table A.5. In Table A.6 you can see how this fits into a total of 1 orbit.

Table A.4:FGS Example: Planned Exposures
Config
Mode
Spectral Element
Number of Exp
Time per Exp [min.]
Notes
FGS
POS
F583W
8
0.2
2 exposures of target Binary01, and 2 exposures for each of the targets ref1, ref2, and ref3
FGS
POS
F583W
4
0.7
2 exposures for each of the targets ref4 and ref5
FGS
TRANS
F583W
1
13.3
20 scans of 40 sec each (see Table 5.8) for Binary01
Table A.5:FGS Example: Incurred Overheads
Overhead
Overhead
Time [min.]
Notes
see Table
Guide star acquisition
6
First orbit in new visit
5.2
POS
1
per exposure, V<14
5.6
POS
2
per exposure, 14<V<15
5.6
TRANS
1
per target
5.6
TRANS
0.2
per scan
5.6
Instrument Setup
4
once every orbit
5.7
Instrument Shutdown
3
once every orbit
5.7
Table A.6:FGS Example: Orbit Planning
Activity
Duration [min.]
Elapsed Time [min.]
Orbit 1
 
 
Guide star acquisition
6
6
Instrument Setup
4
10
Binary01/POS mode Exp Time
0.2
10.2
Binary01/POS mode Overhead
1
11.2
ref1/POS mode Exp Time
0.2
11.4
ref1/POS mode Overhead
1
12.4
ref2/POS mode Exp Time
0.2
12.6
ref2/POS mode Overhead
1
13.6
ref3/POS mode Exp Time
0.2
13.8
ref3/POS mode Overhead
1
14.8
ref4/POS mode Exp Time
0.7
15.5
ref4/POS mode Overhead
2
17.5
ref5/POS mode Exp Time
0.7
18.2
ref5/POS mode Overhead
2
20.2
Binary01/POS mode Exp Time
0.2
20.4
Binary01/POS mode Overhead
1
21.4
ref1/POS mode Exp Time
0.2
21.6
ref1/POS mode Overhead
1
22.6
ref2/POS mode Exp Time
0.2
22.8
ref2/POS mode Overhead
1
23.8
ref3/POS mode Exp Time
0.2
24.0
ref3/POS mode Overhead
1
25.0
ref4/POS mode Exp Time
0.7
25.7
ref4/POS mode Overhead
2
27.7
ref5/POS mode Exp Time
0.7
28.4
ref5/POS mode Overhead
2
30.4
Binary01/POS mode Exp Time
0.2
30.6
Binary01/POS mode Overhead
1
31.6
Binary01/TRANS mode Exp Time
13.3
44.9
Binary01/TRANS mode Overhead
1+(20x0.2)
49.9
Instrument Shutdown
3
52.9
Unused
0.1
53.0

A.3 NICMOS

Suppose that you wish to use the NICMOS to observe a target at a declination of -50 degrees, so that there are 54 minutes of visibility time per orbit (see Table 5.1). Your desired exposures are listed in Table A.7, and the associated overheads are listed in Table A.8. In Table A.9 you can see how the observations fit into a total of 1 orbit.

Table A.7:NICMOS Example: Planned Exposures
Config
Mode
Spectral
Element
Number of Exp
Time per Exp [min.]
Notes
NIC2
IMAGING
F110W
4
2.2
Pattern (see Section 4.4) of MULTIACCUM exposures with an offset of 1" between dither positions
NIC2
IMAGING
F160W
4
4
Pattern (see Section 4.4) of MULTIACCUM exposures with an offset of 1" between dither positions
 
NIC2
IMAGING
F222M
4
4
Pattern (see Section 4.4) of MULTIACCUM exposures with an offset of 1" between dither positions
Table A.8:NICMOS Example: Incurred Overheads
Overhead
Overhead Time [min.]
Notes
see Table
Guide star acquisition
6
First orbit in new visit
5.2
MULTIACCUM exposure
0.07
 
5.9
Instrument Setup
0.3
Beginning of each orbit
5.10
Filter change
0.3
 
5.10
SAM of 1"
0.33
Small Angle Maneuver between positions in the pattern
5.13
Table A.9:NICMOS Example: Orbit Planning
Activity
Duration [min.]
Elapsed Time [min.]
Orbit 1
 
 
Guide star acquisition
6
6
Instrument Setup
0.3
6.3
F110W Exp Time
2.2
8.5
F160W Exp Time
4
12.5
F222M Exp Time
4
16.5
Overhead
(3x0.07) + (2x0.3) + (1x0.33)
17.6
F110W Exp Time
2.2
19.8
F160W Exp Time
4
23.8
F222M Exp Time
4
27.8
Overhead
(3x0.07) + (3x0.3) + (1x0.33)
29.3
F110W Exp Time
2.2
31.5
F160W Exp Time
4
35.5
F222M Exp Time
4
39.5
Overhead
(3x0.07) + (3x0.3) + (1x0.33)
40.9
F110W Exp Time
2.2
43.1
F160W Exp Time
4
47.1
F222M Exp Time
4
51.1
Overhead
(3x0.07) + (3x0.3) + (1x0.33)
52.6
Unused
1.4
54

A.4 WFPC2

Suppose that you wish to use the WFPC2 to observe a target at a declination of -45 degrees, so that there are 53 minutes of visibility time per orbit (see Table 5.1). Your desired exposures are listed in Table A.10 and the associated overheads are listed in Table A.11. In Table A.12 you can see how the observations fit into a total of 3 orbits.

Table A.10:WFPC2 Example: Planned Exposures
Config
Mode
Spectral
Element
Num of Exp
Time per Exp [min.]
Notes
WFPC2
IMAGING
F814W
1
40
CR-SPLIT
WFPC2
IMAGING
F450W
1
40
CR-SPLIT
WFPC2
IMAGING
F555W
4
8
Pattern (see Section 4.4 ) with an offset of 1" between positions
Table A.11:WFPC2 Example: Incurred Overheads
Overhead
Overhead Time [min.]
Notes
see Table
Guide star acquisition
6
first orbit in new visit
5.2
Guide star re-acquisition
6
per orbit after first orbit
5.2
Exposure (CR-SPLIT)
5
per exposure (CR-SPLIT is default for >600s)
5.11
Exposure (no CR-SPLIT)
3
per exposure (no CR-SPLIT is default for <=600s)
5.11
Efficiency
1
per orbit
5.12
SAM of 1"
0.33
Small Angle Maneuver between positions in the pattern
5.13
Table A.12:WFPC2 Example: Orbit Planning
Activity
Duration [min.]
Elapsed Time [min.]
Orbit 1
 
 
Guide star acquisition
6
6
F814W Exp Time
40
46
F814W Overhead
5
51
Efficiency Overhead
1
52
Unused
1
53
Orbit 2
 
 
Guide star re-acquisition
6
6
F450W Exp Time
40
46
F450W Overhead
5
51
Efficiency Overhead
1
52
Unused
1
53
Orbit 3
 
 
Guide star re-acquisition
6
6
F555W Exp Time
4x8
38
F555W Overhead
(4x3)+(3x0.33)
52
Efficiency Overhead
1
53
Unused
0
53
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