GHRS Instrument Handbook
In Phase I you are trying to determine first of all if your observations are feasible with the GHRS. Feasibility means: Can I acquire the target?; Can I obtain a spectrum or image that will provide the information I need to address my science goals?; and Can that spectrum or image be obtained in a reasonable time?
The next section and Chapter 7 provide the information needed to understand GHRS target acquisitions. The previous chapter and chapter 8 provide information essential for judging whether or not the GHRS can obtain the observations you need. In particular, examine Table 8.1 on page 104, Table 8.3 on page 113, and Table 8.4 on page 113 to lay out your strategy of gratings to be used and central wavelengths, based on your science needs. Chapter 8 also provides the information you need to estimate exposure time.
On the presumption that your observations are feasible, you then want to estimate how much time will be needed. To do so you need to answer some questions:
- Is a standard acquisition adequate for my target, or will I need a real-time or early acquisition?
- Are standard calibrations adequate for my needs or will I need to ask for time for special ones?
- How long will my exposures take?
- How should exposures be divided into visits?
- What is the total time requirement in orbits?
The tools provided here and in the Phase I Proposal Instructions should be adequate for estimating the number of orbits a program will require in most cases. However, if you have a very complex program and have access to Phase II documentation for Cycle 5 and the RPS2 software, you may wish to use that software to produce a more detailed estimate of the orbits you may need.
The next chapter will discuss the details needed for your Phase II proposal. However, the distinction between Phase I and Phase II is somewhat arbitrary and we recommend that you read both chapters during both phases of your proposal writing.
Based on the previous chapter, you will have selected one or more modes of operation: IMAGE, ACCUM, or RAPID. In most cases observers want to get a spectrum that takes advantage of the GHRS' features, meaning ACCUM mode.
Further comments on observing strategy are given at the end of this chapter.