9.1 Overview

Chapter 4 of this Handbook describes the procedures for designing a Phase I WFC3 observing proposal. Two of the steps involved in this process are estimating the exposure times needed to achieve your scientific goals, and then combining these individual exposures with their associated overheads to derive the number of spacecraft orbits that you will request in your Phase I proposal.

This chapter gives guidance on estimating exposure times. The following chapter, Chapter 10, then describes how to include the various overheads so as to determine the total number of spacecraft orbits needed for your program.

You should also refer to the HST Call for Proposals, which includes information on policies and practices with respect to orbit-time requests. The HST Primer provides specific advice on orbit determination. Below, we provide a summary of the WFC3 sensitivities and give several examples that illustrate how to calculate your exposure times for Phase I Proposals.