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Hubble Space Telescope Primer for Cycle 22 > Chapter 6: Orbit Calculation for a Phase I Proposal > 6.3 The Orbital Visibility Period

6.3 The Orbital Visibility Period
The orbital visibility period is the amount of unocculted time per orbit during which observations of a given target can be made. Table 6.1 gives the visibility period for fixed targets of given declination, for moving targets (assumed to be near the ecliptic plane), and for cases in which the special requirements CVZ (Section 2.2.1), LOW SKY (Section 8.16.12 of the Call for Proposals), and SHADOW (Section 8.16.12 of the Call for Proposals) are used.
The listed orbital visibility for the CVZ (96 minutes, i.e., the entire HST orbit) assumes that there are no SAA intersections in these orbits (see Section 2.2.2). This is the orbital visibility that should be used for planning CVZ observations, unless the proposer knows that he or she may have to observe in orbits that are SAA-impacted. In the latter case, the visibility time is approximately 70 minutes per orbit. Note that CVZ orbital visibility should not be requested if there are special background emission or timing requirements (see Section 2.2.1).
Also included in Table 6.1 are orbital visibilities suitable for use in Large Programs (see Section 3.2.2 of the Call for Proposals). Proposers submitting Large Programs should consult the Large Program Scheduling User Information Report which can be found on the HST Documents page (linked from the Cycle 22 Announcement webpage). This document contains a discussion of the issues surrounding Large Program scheduling.
Table 6.1: Orbital Visibility in Three-Gyro Mode.
Orbital Visibility Period for Pure Parallel Observations
For Pure Parallel observations (see Section 4.2.2 of the Call for Proposals), proposers may not know the prime target declinations. One of the following two options should be used for planning observations:
Map out the desired exposures (plus overheads) in an orbit for any legal orbital visibility period (54 to 61 minutes). If this method is selected, note that longer total exposure times typically have fewer scheduling opportunities.

Hubble Space Telescope Primer for Cycle 22 > Chapter 6: Orbit Calculation for a Phase I Proposal > 6.3 The Orbital Visibility Period

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