Space Telescope Science Institute   8.3.2 Sample Orbit Calculation 2:  8.3.4 Sample Orbit Calculation 4:

8.3.3 Sample Orbit Calculation 3:


This example demonstrates the orbit calculation for a coronagraphic observation. We want to obtain coronagraphic images of a star in two filters, F250W and F606W. The ETC has shown that the exposure times adequate for our scientific goals are 5 minutes. in F606W and 30 minutes. in F250W. From the orbit visibility table (see the HST Primer) we find that at the target declination of 15º the target visibility time is 52 minutes. With CR-SPLIT=2, we thus have to accommodate in that period 35 minutes. of four science exposures grouped in two series. The orbit calculation goes like this:


Table 8.5: Orbit calculation for example 3.
Action
Time (minutes)
Explanation
Orbit 1
Initial guide-star acquisition
6
Needed at start of observation of a new target
Target acquisition
3.5 +(2 ×0.1) = 3.7
Point-source acquisition on target
HRC overhead for the first exposures in the series
×2.5 = 5
Includes filter change, camera set-up, and readout
HRC overhead for the subsequent exposures in the series
×1 = 2
Includes readout
Science exposures in F606W
×2.5 = 5

Science exposures in F250W
×15 = 30

Total time for science exposures
35

Total used time in the orbit
~52

The derived total used time in the orbit shows that our target can indeed be imaged in the selected filters in one orbit. Since there remains 3 minutes of unused time, we can adjust our exposure times to make full use of the available time.


 8.3.2 Sample Orbit Calculation 2:  8.3.4 Sample Orbit Calculation 4:
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