Space Telescope Science Institute  A.1 ACS A.3 NICMOS

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 6.2.2). 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 6.1). 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 6.8) 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
POS
1
per exposure, V<14
POS
2
per exposure, 14<V<15
TRANS
1
per target
TRANS
0.2
per scan
Instrument Setup
4
once every orbit
Instrument Shutdown
3
once every orbit

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.1 ACS A.3 NICMOS
Space Telescope Science Institute
http://www.stsci.edu
Voice: (410) 338-1082
help@stsci.edu