6.5 Constructing Your Program

Your final step is to fit all science exposures and overheads into the visibility period of each orbit for all your visits. The better you can pack your orbits, the more efficient your proposal will be. For particularly complex programs, the APT phase II orbit planner can be used for assessing the orbit layout. Please contact help@stsci.edu if you need assistance.

When placing the observations into orbits and visits, note that you cannot pause exposures across orbits. This means that if you have 20 minutes left in an orbit, you can insert only an exposure that takes 20 minutes or less (including overhead). If you wish to obtain a 30 minute exposure, then you can either put it all into the next orbit, or you can specify, for example, a 20 minute exposure at the end of the first orbit, and a second 10 minute exposure in the next orbit.

Table 6.14 shows, as an example, the layout of a visit with 2 orbits of spectroscopic observations that require a target acquisition, but no SAMs and no special calibration observations. For simplicity, overheads are shown to occur after each exposure; in reality some overheads occur before an exposure (e.g., a filter change) while others appear afterwards (e.g., read-out time).

More detailed examples for each of the SIs are given in Appendix A. Those examples are for common, simple uses of the instruments. For examples of more complicated uses and observing strategies, please consult the HST Instruments Handbooks (see Section 1.2).

Coordinated Parallel Observations

If you have a program with coordinated parallel observations (see Section 4.2.1 of the Call for Proposals), then it should be fairly straightforward to lay out the parallel observations into orbits and visits. The primary observations determine the orbit and visit structure, and the coordinated parallels should conform to the visit structure of the primary observations.