The Hubble Space Telescope Primer for Cycle 31

The HST Primer provides an introduction to the Hubble Space Telescope for Phase I proposers.

About This Document

The Hubble Space Telescope (HST) Primer for Cycle 31 is a companion document to the Hubble Space Telescope Call for Proposals for Cycle 31. It provides an overview of HST, with basic information about telescope operations, instrument capabilities, and technical aspects of the proposal preparation process. A thorough understanding of the material in this document is essential for the preparation of a competitive proposal. The Call for Proposals discusses the policies and procedures for submitting a Phase I proposal for HST observing or archival research. Technical documentation on the instruments are available in their respective handbooks, available on the HST Document overview site.

Late Breaking News

  • May 19, 2023:

    • There was a typo in the text regarding AR program guidelines. Please note, any HST data that you wish to analyze must reside (or be expected to reside) in the Archive, and be released from exclusive access rights by the start of Cycle 31 (December 1, 2023). This restriction does not apply to the ULLYSES datasets.
  • May 8, 2023:

    • There will be one Mid-Cycle opportunity in Cycle 31. The deadline for Mid-Cycle submissions will be Wednesday November 15, 2023 at 11:59pm. Notification of results are expected in mid-January 2024.
  • May 2, 2023:

    • Proposers submitting combined GO-Archival proposals should use the GO template, and include the Analysis Plan section.
  • May 1, 2023:

    • The ACS/SBC offers far-UV imaging with a low dark rate that historically varies from ~1E-5 to ~5E-5 cts/sec/pix during the course of a visit, as the detector temperature increases by ~10 degrees C for a visit spanning 5 orbits.  Recently, the dark rate has been elevated by a factor of ~2, even though the temperature profile has not changed.  This behavior is under investigation, but users considering the SBC for their observations should plan on shorter visits (1-2 orbits) to help mitigate this behavior, if it persists.

See also HST New and Important Features.

Proposing Calendar and Deadlines

  • Cycle 31 Phase I proposal deadline: Wednesday May 24, 2023 at 8:00pm EDT

  • Cycle 31 Peer Review: August 1-9, 2023

  • Cycle 31 Phase II proposal deadline: September 14, 2023

  • Cycle 31 Budget deadline: October 5, 2023 at 5:00pm EDT

  • Cycle 31 Mid-Cycle Deadline: Wednesday November 15, 2023 at 11:59pm EST

Where to Get Help

Submit questions to the HST Help Desk at See for additional tools and resources.

Who's Responsible

The HST Call for Proposals and related materials for Cycle 31 were edited by Laura Watkins and Molly Peeples. The Associate Director for Science, Neill Reid, and the Science Mission Office (SMO) at STScI are responsible for the oversight of the HST science program selection process. SMO members include Alessandra Aloisi (SMO Mission Head), Elena Sabbi (SMO Deputy Mission Head), Laura Watkins (SMO Deputy Mission Head), Claus Leitherer (Hubble Science Policies Lead), Molly Peeples (Hubble Science Policies Deputy Lead), Katey Alatalo, Christine Chen, Andrew Fruchter, Amaya Moro-Martin, Jamila Pegues, Linda Smith, and Technical Manager Brett Blacker.

Next: HST Primer: Resources, Tools, and Other Documentation