Space Telescope Science Institute   8.3.4 Sample Orbit Calculation 4: Chapter 9:  Exposure-Time Calculations

8.3.5 Sample Orbit Calculation 5:


This example illustrates the orbit calculation for a simple 30 minutes WFC grism spectroscopic observation broken down by CR-SPLIT=2 into a series of two exposures.

Table 8.7: Orbit calculation for example 5.
Action
Time (minutes)
Explanation
Orbit 1
Initial guide-star acquisition
6
Needed at start of observation of a new target
Predefined imaging exposure for grism spectroscopy
7
Needed to co-locate the targets and their spectra in the FOV
WFC overhead for the first science exposure in the series
4.0
Includes filter change, camera set-up, and readout
WFC overhead for the subsequent science exposure in the series
2.5
Includes readout
Two science exposures
×15.0 = 30

Total science exposure time
30.0

Total used time in the orbit
49.5

Unlike similar imaging exposures, here we have to take into account an additional imaging exposure before the sequence of spectroscopic exposures, which takes 10 minutes. off the available orbit time.


 8.3.4 Sample Orbit Calculation 4: Chapter 9:  Exposure-Time Calculations
Space Telescope Science Institute
http://www.stsci.edu
Voice: (410) 338-1082
help@stsci.edu