8.1 Overview

After you establish a set of scientific exposures, as well as any additional target acquisition or calibration exposures required for your program, you are ready to determine the total number of orbits to request. Generally, this straightforward exercise involves compiling the overheads for individual exposures, packing exposure plus overhead time into individual orbits, and tallying up the results to determine the total number of orbits needed. It may be an iterative process as you refine your exposures to better use the orbit visibility times.

The Call for Proposals includes instructions that provide information on the Observatory policies and practices with respect to orbit time requests. The HST Primer provides specific advice on orbit determination. Both can be found on the HST Proposal Opportunities and Science Policies web page. In this Chapter, we provide a summary of the ACS specific overheads, and give several examples that illustrate how to calculate your orbit requirements for a Phase I Proposal.

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ACS Instrument Handbook
- • Acknowledgments
- • Change Log
- • Chapter 1: Introduction
- Chapter 2: Considerations and Changes After SM4
  - • 2.1 SM4 Repair of ACS
  - • 2.2 Comparison of WFC and UVIS
  - • 2.3 Comparison of HRC and UVIS
  - • 2.4 Dithering Considerations
  - • 2.5 CTE Considerations
  - • 2.6 SBC Considerations
- Chapter 3: ACS Capabilities, Design and Operations
  - • 3.1 ACS Location in the HST Focal Plane
  - • 3.2 Instrument Capabilities
  - • 3.3 Instrument Design
  - • 3.4 Basic Instrument Operations
  - • 3.5 ACS Quick Reference Guide
- Chapter 4: Detector Performance
  - • 4.1 Overview
  - • 4.2 The CCDs
  - • 4.3 CCD Operations and Limitations
  - • 4.4 The SBC MAMA
  - • 4.5 SBC Operations and Limitations
  - • 4.6 SBC Bright-Object Limits
- Chapter 5: Imaging
- Chapter 6: Polarimetry, Coronagraphy, Prism and Grism Spectroscopy
  - • 6.1 Polarimetry
  - • 6.2 Coronagraphy
  - • 6.3 Grism and Prism Spectroscopy
- Chapter 7: Observing Techniques
  - • 7.1 Designing an ACS Observing Proposal
  - • 7.2 SBC Bright Object Protection
  - • 7.3 Operating Modes
  - • 7.4 Patterns and Dithering
  - • 7.5 A Road Map for Optimizing Observations
  - • 7.6 CCD Gain Selection
  - • 7.7 ACS Apertures
  - • 7.8 Specifying Orientation on the Sky
  - • 7.9 Parallel Observations
  - • 7.10 Pointing Stability for Moving Targets
- Chapter 8: Overheads and Orbit-Time Determination
  - • 8.1 Overview
  - • 8.2 ACS Exposure Overheads
  - • 8.3 Orbit Use Determination Examples
- Chapter 9: Exposure-Time Calculations
  - • 9.1 Overview
  - • 9.2 Determining Count Rates from Sensitivities
  - • 9.3 Computing Exposure Times
  - • 9.4 Detector and Sky Backgrounds
  - • 9.5 Extinction Correction
  - • 9.6 Exposure-Time Examples
  - • 9.7 Tabular Sky Backgrounds
- Chapter 10: Imaging Reference Material
  - • 10.1 Introduction
  - • 10.2 Using the Information in this Chapter
  - 10.3 Throughputs and Correction Tables
    - • WFC F435W
    - • WFC F475W
    - • WFC F502N
    - • WFC F550M
    - • WFC F555W
    - • WFC F606W
    - • WFC F625W
    - • WFC F658N
    - • WFC F660N
    - • WFC F775W
    - • WFC F814W
    - • WFC F850LP
    - • WFC G800L
    - • WFC CLEAR
    - • HRC F220W
    - • HRC F250W
    - • HRC F330W
    - • HRC F344N
    - • HRC F435W
    - • HRC F475W
    - • HRC F502N
    - • HRC F550M
    - • HRC F555W
    - • HRC F606W
    - • HRC F625W
    - • HRC F658N
    - • HRC F660N
    - • HRC F775W
    - • HRC F814W
    - • HRC F850LP
    - • HRC F892N
    - • HRC G800L
    - • HRC PR200L
    - • HRC CLEAR
    - • SBC F115LP
    - • SBC F122M
    - • SBC F125LP
    - • SBC F140LP
    - • SBC F150LP
    - • SBC F165LP
    - • SBC PR110L
    - • SBC PR130L
  - • 10.4 Geometric Distortion in ACS
- • Glossary

8.1 Overview

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