A.4 STIS Example

STIS is used to observe a target at a declination of +15° degrees according to an observing strategy outlined in Table A.13.

•	For a target at declination of +15°, there are 54 minutes of visibility time per orbit (see Table 6.1).

•	The associated overheads for those types of observations are listed in Table A.14.

Therefore, a preliminary observing strategy can be created by the user to fit the observations in two orbits, as shown in Table A.15.

Table A.13: STIS Example: Planned Exposures

Config	Mode	Spectral element	Number of exposures	Time per exposures (minutes)	Notes
STIS/CCD	ACQ			0.1	Target acquisition
STIS/CCD	ACQ/PEAK			1	Peakup acquisition (necessary because of use of 0.1" wide slit for subsequent spectra)
STIS/CCD	IMAGING	F28X50OII	2	2
STIS/NUV	IMAGING	F25QTZ	1	21
STIS/NUV	SPECTROSCOPIC	G230L	1	13	with 52X0.1 slit
STIS/FUV	SPECTROSCOPIC	G140L	1	20	with 52X0.1 slit

Table A.14: STIS Example: Incurred Overheads¹

Overhead	Overhead time (minutes)	Notes	see Table
Guide star acquisition	6	First orbit in new visit	6.2
Guide star re-acquisition	4	Per orbit after first orbit	6.2
ACQ	6	Target acquisition	6.3
ACQ/PEAK	6	Peakup target acquisition	6.3
CCD imaging (first)	5	First exposure in a series of identical exposures	6.9
CCD imaging (not first)	1	Per exposure after the first exposure in a series	6.9
MAMA imaging	5	First exposure	6.9
MAMA spectroscopy	8	Only 1 minute if there is no change from first exposure. Add 4 minutes (6 minutes for modes G140M and G230M) for each exposure time interval that exceeds 2300 seconds at the same grating position.	6.9

Table A.15: STIS Example: Orbit Planning

Activity	Duration (minutes)	Elapsed time (minutes)
Orbit 1
Guide star acquisition	6	6
ACQ	6	12
ACQ/PEAK	6	18
F28X50OII Exp Time	2x2	22
F28X50OII Overhead	5+1	28
F25QTZ Exp Time	21	49
F25QTZ Overhead	5	54
Unused	0	54
Orbit 2
Guide star re-acquisition	4	4
G230L Exp Time	13	17
G230L Overhead	8	25
G140L Exp Time	20	45
G140L Overhead	8	53
Unused	1	54

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1

These overheads are for budgeting purposes. The actual overhead incurred depends upon the particular spectral element selected since the overhead to move the grating is position-dependent and the time for an auto-wavecal is mode-dependent. Additional efficiencies, such as executing auto-wavecals during guide star re-acquisitions or occultation, that may be realized from fine-tuning of the actual exposures (but cannot be assumed a priori), are not included.