HST Proposal Opportunities and Science Policies

Articles in this section comprise the traditional Call for Proposals.  These articles include information on observing and science policies, and details on the proposal submission process, including roadmaps.

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.

Current HST Proposal Opportunities


Release Notice: December 2, 2019

We are pleased to announce the Cycle 28 Call for Proposals for Hubble Space Telescope (HST) observations and funding for archival research programs.

Participation in this program is open to all categories of organizations, both domestic and foreign, including educational institutions, profit and nonprofit organizations, NASA Centers, and other Government agencies.

Cycle 28 will extend from October 1, 2020 to September 30, 2021. We will accept proposals for the following instruments: ACS, COS, FGS, STIS, and WFC3.

We anticipate allocating up to 2700 orbits in this cycle. See Hubble Space Telescope Call for Proposals for Cycle 28 for further details.  

This solicitation for proposals will be open through March 6, 2020 8:00 pm EST. The Astronomer's Proposal Tool (APT), which is required for Phase I Proposal Submission, will be made available for Cycle 28 Phase I use on December 31, 2019. Results of the selection will be announced by late May.

Questions can be addressed to the STScI HST Help Desk (https://hsthelp.stsci.edu or email help@stsci.edu).  We encourage the use of the new website where you can submit questions directly to the appropriate team of experts.

The Cycle 28 Call for Proposals

The Call for Proposals (CP) invites the astronomical community to propose for observing time on HST in a given cycle (nominally one year in duration). It summarizes the policies and procedures for proposing in that cycle of HST observing, including requests for research funding on archival HST data.  See Hubble Space Telescope Call for Proposals for Cycle 28 for more information.

The Hubble Space Telescope Primer for Cycle 28 provides an overview of the Hubble Space Telescope, with basic information about the telescope operations, instrument capabilities, and technical aspects of the proposal preparation process. 

Late Breaking News


  • Long-term GO proposals can be of any size category, Small, Medium, or Large. A typo did not include the Small category in this set. Further details are provided on HST Cycle 28 Proposal Categories.


  • STScI and NASA recognize that measures taken to address the coronavirus COVID-19 are affecting the resources available to some researchers. We will accept late proposals from scientists impacted directly by those issues. Late submissions must be accompanied by an appropriate justification (pending approval) by email to hubblereview@stsci.edu. These late submissions will be accepted until March 12, 2020. Contact the HST Help Desk for further details and assistance.


  • We have discovered and largely addressed a problem with MAST archival searches by coordinate in the period of 4 Dec 2019 to 26 Feb 2020, such that a significant fraction of HST observations were not found, instrument footprints were not properly displayed for the affected observations, and retrieved data had incorrect header astrometry. This problem is particularly important for potential HST observers currently performing duplication checks as part of the preparation of HST Phase I proposals (due on 6 Mar 2020). If you or your collaborators performed such searches in the affected timeframe, please resubmit your archival requests and duplication checks to the MAST archive. A small number of datasets (of order 1%) remain uncorrected and undiscoverable in searches using the newer MAST interface, and will remain so until after the Phase 1 deadline, but those data will appear in searches with the classic MAST interface.  We apologize for any adverse impact on your archival research and proposal preparations.


  • Some questions have arisen regarding the Hubble Tess Exoplanet Initiative (HTEI). The following statements are offered to clarify the nature of the initiative:
    • There is no pre-specified orbit allocation for HTEI programs. HTEI proposals will be reviewed by the Cycle 28 TAC and will be assessed along with all other Large and Treasury programs. The total orbit allocation to the TAC is 600 orbits.
    • HTEI programs are long-term programs (up to 3 cycles) that will allow the exoplanet community to maximize the science return from TESS by developing coherent, large-scale programs that can respond to new discoveries. Unlike most other programs, targets can be added after the program is approved. Since the aim is to benefit the broad community, the program must describe how community input will be taken into account in selecting new targets.
    • All data taken for HTEI programs will have no exclusive access period and will be available immediately to the community.
    • HTEI proposal must adhere to dual anonymous guidelines.
    • HTEI proposals are not the only avenue for TESS follow-up with HST. As usual, smaller-scale proposals will be reviewed by the panels in Cycle 28 and in subsequent cycles. Based on past precedents, priority will generally be assigned to accepted smaller programs in the event of duplications with HTEI programs.


  • Support Letters for Proposed Mission Support: Proposers for observations in support of NASA/ESA missions who intend to include mission support letters should email them separately to hubblereview@stsci.edu no later than March 13, 2020. The letters should not be added or included in the PDF attachment as they would not likely be compliant with the guidelines for the dual anonymous review. When necessary, the letters will be provided to the TAC panels in the Team Expertise and Background review.


  • The APT Proposal Tool was released on January 22, 2020.


  • Proposers who are eligible for NASA funding and intend to request funds for supporting resources, including support for ground-based observations, should make those intents clear in the scientific justifications of their Phase I proposals. The Financial Review Committee will not approve requests to cover costs for resources in budget proposals (from successful programs) that are not justified in the approved Phase I proposals.

See also HST Cycle 28 New and Important Features.

Science Justification Templates

Templates for HST Cycle 28 Proposal PDF attachments:

Note: the Word and LaTeX templates have intentionally different margins, to accommodate the same amount of text per page. See HST Cycle 28 Guidelines and Checklist for Phase I Proposal Preparation for information on page limits.

See HST Cycle 28 Preparation of the PDF Attachment for more information.

Download the PDF

Supporting Documents