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Hubble Space Telescope
Proposing Overview

Cycle 27 Announcement

STScI solicits proposals for HST Observing, Archival & Theoretical Research. Full details are made available through two documents, the Call for Proposals and the HST Primer.

The Cycle 27 Call for Proposals and the Cycle 27 HST Primer.

Cycle 27 Announcement

Proposing Calendar

January 14, 2019
This Call is provisional pending final approval by NASA
Cycle 27 Call for Proposals

February 1, 2019
APT Cycle 27 Phase I Release

April 5, 2019
Cycle 27 Phase I Proposal Deadline

June 9-14, 2019
Cycle 27 Peer Review

July 1, 2019
Cycle 27 Phase I Notifications

July 26, 2019
HST Cycle 27 Phase II Proposal Deadline

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 funding research on archival HST data. It also provides an overview of HST's expected capabilities for that observing cycle, including information about the telescope and the available scientific instruments.

For more information on the current proposing cycle see the Cycle 27 Announcement Page.

Phase I: Writing and Submitting a Proposal for HST Observing Time

A Phase I proposal provides:

  • A summary of the observing program.
  • The scientific justifications for the program.
  • A list of targets with their celestial coordinates.
  • The instrument(s) to be used with desired modes, filters, and dispersers.
  • An estimate of the number of spacecraft orbits needed to accomplish the observing program (a means to calculate this number is provided in the Phase I instructions).

Proposers should consult all relevant technical documentation about the capabilities and sensitivities of the instrument(s) to be used in their programs and should discuss the requirements of their observing programs with appropriate STScI experts. Contacts are provided via the STScI HelpDesk at To avoid duplication conflicts proposers also should consult up-to-date exposure catalogs, available on-line at the STScI Web site.

Completion of Phase I: The TAC Review of Phase I Submissions

A Telescope Allocation Committee (TAC), organized by the Space Telescope Science Institute (STScI), reviews and evaluates the submitted Phase I proposals. The TAC recommends a list of programs to the STScI Director for preliminary approval and implementation. Upon final approval by the Director, a successful proposal enters into the Phase II stage of proposal preparation.

Phase II: Providing the Observing Details

Following a favorable TAC review and approval by the director, proposers must provide the details required by the ground system to schedule HST and obtain their observations.

Observers are assigned two points of contact at STScI: a Program Coordinator (PC) and a Contact Scientist (CS). The PC helps the observer to deliver a Phase II proposal which is syntactically correct and will schedule successfully on the telescope. The CS provides advice on observing strategies to meet the scientific objectives of the program, answers questions about instrument performance, and can provide technical help in the data analysis phase of the observing program. The CS is an Instrument Scientist involved in the calibration and characterization of the primary instrument used in the observer's program.

Programs are not considered fully accepted until the following items have been completed:

  • An error-free Phase II proposal has been submitted.
  • Duplication checks against similar exposures in previous and current HST programs have been performed and any conflicts have been resolved.
  • All technical feasibility reviews (such as bright object checking, special requirements, etc.) have been completed and approved.

Release Documents

    The Call for Proposals describes the policies and procedures for submitting a HST Phase I proposal. Go to the CP.

    The Primer provides an introductory overview of the Hubble Space Telescope and explains how to calculate the appropriate number of orbits for an observing proposal. Go to the Primer.

    Science Justification Templates for Cycle 27 HST Phase I

  • Full Set of HST Documentation

HST Phase I Roadmap

    The Roadmap is a step-by-step guide to proposing and submitting an HST proposal. Download APT here.

DD Time

Up to 10% of the available HST observing time may be reserved for Director's Discretionary (DD) allocation.

Mid-Cycle Proposals

Up to 200 orbits per cycle will be available for Mid-Cycle GO programs. Mid-Cycle programs were initiated in Cycle 23 to provide the community with an opportunity to propose for in-cycle observations of recently-discovered, non-variable objects. As such, they complement Director’s Discretionary programs, which target unexpected transient phenomena and time-critical observations..

Special Programs from Past Cycles

Status of Current and Past Programs:

Past Proposal Opportunities