The Hubble Space Telescope Primer for Cycle 34
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 34 is a companion document to the Hubble Space Telescope Call for Proposals for Cycle 34. 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
April 6, 2026:
APT Submission Portal Closure: Proposers are reminded that the APT submission portal will close at the submission deadline of April 16, 2026 at 8pm. Late submissions or resubmissions will not be accepted. In exceptional circumstances, proposers requiring an extension should make a request via the Help Desk before the deadline.
DD Submission Downtime: The APT submission portal will be closed from April 16, 2026 at 8pm until April 17, 2026 at 12pm. During the closure period it will not be possible to submit HST Director’s Discretionary (DD) proposals. Please plan accordingly.
- April 1, 2026:
- Reminder: ACS/WFC and WFC3/IR are available: ACS/WFC and WFC3/IR are anticipated to remain available and fully supported in Cycle 34. While the Call for Proposals notes that these modes “may be offered as shared risk” in future cycles, “shared risk” does not mean the instruments would be unavailable or poorly calibrated. Proposers with science goals best served by ACS/WFC or WFC3/IR are encouraged to propose for these modes in Cycle 34. More details can be found in the ACS February STAN and the WFC3 March STAN.
- February 26, 2026:
- There is a new requirement for Joint HST-NRAO proposals. Within one week of the HST Cycle 34 proposal deadline, the PI must fill out the following NRAO short form, consisting of highlevel metadata.
- February 19, 2026:
- LaTeX templates updated to ensure the PDF attachment document is Letter size. Overleaf now uses a European LaTeX distribution which produces documents in A4 size by default. Make sure to use the most recent version of the PDF attachment templates. Using an older template could cause the proposal to be disqualified.
- January 26, 2026:
- Starting in Cycle 34, single guide star (1GS) guiding will become the default for ACS/WFC and WFC3 observations with exposure times < 1001s in visits with length of 1 or 2 orbits (not including moving targets or spatial scans). There will be an opportunity to opt-out of 1GS with a strong scientific justification after Phase II notifications are sent out. Further information about 1GS is available in WFC3 ISR 2025-07.
- January 16, 2026:
- Word templates updated: Make sure to use the most recent version of the PDF attachment templates. Using an older template could cause the proposal to be disqualified.
- December 18, 2025:
- APT Released: APT version 2025.7.2 is now available. Any HST proposals started in earlier APT versions should now be edited and submitted in this version.
See also HST New and Important Features.
Proposing Calendar and Deadlines
Cycle 34 Phase I proposal deadline: Thursday, April 16, 2026 at 8:00pm EDT
Cycle 34 Peer Review: June 22 - July 1, 2026
Cycle 34 Phase II proposal deadline: anticipated August 13, 2026 at 5:00pm EDT
Cycle 34 Budget deadline: end-August 2026, for planning purposes only
Where to Get Help
Submit questions to the HST Help Desk at http://hsthelp.stsci.edu. See http://www.stsci.edu/hst/ for additional tools and resources.
Who's Responsible
The HST Call for Proposals and related materials for Cycle 34 were edited by Amy Jones. The Associate Director for Science, Mercedes López-Morales, and the Science Policy Division (SPD) at STScI are responsible for the oversight of the HST science program selection process. SPD members include Laura Watkins (SPD Head), Claus Leitherer (Hubble Science Policy Lead), Molly Peeples (Cross-Mission Policy Scientist), Daniel D'Orazio, Rebecca Levy, Joshua Lothringer, Amaya Moro-Martín, Nikolay Nikolov, Lou Strolger, and Technical Manager Aleksandra Hamanowicz. Neill Reid (Multi-Mission Project Scientist) participates in an advisory capacity.