Cosmic Origins Spectrograph Instrument Handbook for Cycle 17

9.2 Generic Observatory Overhead

---

The first time that you acquire an object you must include overhead for the HST guide-star acquisition (6 minutes)

In all subsequent orbits of the same visit you must include the overhead for the guide-star reacquisition (also 6 minutes); if you are observing an object in the Continuous Viewing Zone (CVZ), then no guide-star re-aquisitions are required.

You must allocate additional time for each deliberate movement of the telescope; e.g., if you are performing a target acquisition exposure on a nearby object and then offsetting to your target, or if you are taking a series of exposures in which you move the target on the detector (POS-TARG), you must allow time for the telescope moves (time varies depending on size of the slew - see Table 9.1).

Table 9.1:

Table 9.2:
 

Action	Overhead type	Time needed
Guide star acquisition	Initial acquisition	6 min
	Re-acquisition	6 min per orbit
Spacecraft movements	Offset motion > 10 arcsec (1.5 arcmin max)	60 sec
	Offset > 1 arcsec up to 10	30 sec
	Offset < 1 arcsec	20 sec

Generic Observatory Overhead Times