Hubble Space Telescope Call for Proposals for Cycle 27

STScI solicits proposals for HST Observing, Archival, and Theoretical Research. The full details are made available through two documents, the Call for Proposals, and the HST Primer. Downloadable PDF collections of these articles are provided as a courtesy, made available and updated when feasible. The online documentation is the authority, and will be updated with the latest information.

Late Breaking News


  • Two important reminders:
    • Proposers are reminded that the HST proposal review follows a Dual Anonymous system, and proposals must conform with the guidelines presented in the Call for Proposals. Reviewers are asked to flag non-compliant proposals, and excessive violations can (and have) resulted in proposals being disqualified from consideration. Proposers will receive a limited number of warnings for minor infringements.
    • All proposers must indicate whether any of their observations will require orientation constraints. Detailed orientations need not be specified at this time, but the specific observations affected must be identified, with an appropriate justification, in the “Special Requirements” section of the proposal. As endorsed by the STUC, the goal is to minimize unnecessary scheduling constraints on HST observations. Proposers who fail to identify and justify orientation constraints in the Phase I proposal will generally require approval by the TTRB to add any constraints in Phase II.


  • Joint Program proposers do not need to specify whether they were recently awarded time for similar or related observations with the coordinating facility. The HST Cycle 27 Preparation of the PDF Attachment instructions have been updated.

See also HST Cycle 27 New and Important Features


We invite scientists to participate in Cycle 27 of the Hubble Space Telescope (HST). The telescope and its instruments were built under the auspices of the National Aeronautics and Space Administration (NASA) and the European Space Agency (ESA). Management of HST’s scientific program is carried out by the Space Telescope Science Institute (STScI). We anticipate allocating up to 3400 orbits in this cycle, including 1700 orbits for Small Programs, 700 for Medium Programs, and 1000 for Large and Treasury Programs. An additional 1000 Snapshot observations and 500 Pure-Parallel observations may be allocated. Abstracts of previously accepted programs can be found on the HST proposal catalogs webpage.

This document establishes the goals, requirements, and policies for General Observer (GO) and Archival Research (AR) programs in Cycle 27. The table of contents for the web version of this document is on the right side of the page, and links there can take you to any page from any other page (click the arrow to expand the entire table of contents under "Hubble Space Telescope Call for Proposals for Cycle 27"). The links at the top of each page correspond to sections within that given page.

Proposing Calendar and Deadlines

Phase I proposal deadline is April 5, 2019 at 8:00pm EDT

The Cycle 27 Peer Review is scheduled for June 2019

The Phase II proposal deadline is July 25, 2019

The Budget submission deadline is August 8, 2019

The 1st Cycle 27 Mid-Cycle deadline is September 27, 2019 with a 2nd Cycle 27 Mid-Cycle deadline scheduled for January 2020.

Notification of the outcome of the Phase I selection process will be sent to all proposers in late June.

What's New for Cycle 27

See HST Cycle 27 New and Important Features

Where to Get Help

Who's Responsible

The HST Call for Proposals and related materials for Cycle 27 were edited by Louis-Gregory Strolger. The Associate Directory for Science, Neill Reid, and the Science Mission Office at STScI are responsible for the oversight of the HST science program selection process, whose members include Alessandra Aloisi (Head of Science Mission Office), Claus Leitherer (Head of Science Policies Group), Katey Alatalo, Christine Chen, Andrew Fruchter, Amaya Moro-Martin, Molly Peeples, Louis-Gregory Strolger, and Technical Manager Brett Blacker.

Next: HST Cycle 27 New and Important Features