HST Cycle 27 Proposal Selection Procedures

This page describes the processes by which proposals are selected. HST programs are selected via competitive peer review in panels chosen for their relevant scientific expertise. The Telescope Allocation Committee makes their final recommendations to the STScI director, who determines the allocation of observing time.

How STScI Conducts the Proposal Review

HST programs are selected through competitive peer review. A broad range of scientists from the international astronomical community evaluates and ranks all submitted proposals, using a well-defined set of criteria and paying special attention to any potential conflicts of interest. The review panels and the Telescope Allocation Committee (TAC) offer their recommendations to the STScI Director. Based on these recommendations, the STScI Director makes the final allocation of observing time.

The Review Panels

The review panels will consider Small, Medium, and Calibration GOs, as well as Snapshot programs, and Regular, Calibration, and Theory AR proposals. Panelists are chosen based on their expertise in one or more of the areas under review by the panels. Each panel spans several scientific categories. In Cycle 27, we anticipate having 15 panels covering several scientific topics. We will have one panel for Solar System, two on Planets and Planet Formation, three on Stellar Physics, two on Stellar Populations and the ISM, two on Massive Black Holes and Their Host Galaxies, three on Galaxies and the IGM, and two on Cosmology. Each panel will have an orbit allocation according to proposal and orbit pressure. Each panel will be managed by a panel chair, and there will be one overall TAC chair overseeing the review process. Proposers should frame their scientific justification in terms appropriate for a panel with a broad range of astronomical expertise.

Note: Beginning in Cycle 26, the review panels will conduct a largely anonymous proposal review. It is important that submissions are sufficiently made anonymous to enable this type of review. Failure to do so may result in the disqualification of the submission. See HST Cycle 27 Anonymous Proposal Reviews for more information on what is required, and how it will be used in the Cycle 27 review.

The Telescope Allocation Committee (TAC)

The TAC will include the TAC chair, the 15 panel chairs, and the three at-large members to ensure broad expertise across the full range of scientific categories. The primary responsibility of the TAC is to review Large and Treasury GOs, and Legacy AR Proposals for scientific balance. The TAC will also consider particularly large requests of resources, including GO Calibrations, large SNAPs, or Pure Parallel programs. 

Selection Criteria

Evaluations of HST proposals are based on the following criteria.

Criteria for all Proposals

  • The scientific merit of the program and its potential contribution to the advancement of scientific knowledge;
  • The program’s importance to astronomy in general. This should be stated explicitly in the “Scientific Justification” section of the proposal;
  • The strength of the data analysis plan;
  • A demonstration that the unique capabilities of HST are required to achieve the science goals of the program.

Additional Criteria for all GO and SNAP Proposals

  • What is the rationale for selecting the type and number of targets? Reviewers will be instructed to recommend or reject proposals as they are and to refrain from orbit- or object trimming. Therefore, it is very important to justify strongly both the selection and the number of targets in your proposal, as well as the number of orbits requested.
  • Is there evidence that the project has already been pursued to the limits of ground-based and/or other space-based techniques?
  • What are the demands made on HST and STScI resources, including the requested number of orbits or targets, and the efficiency with which telescope time will be used?
  • Is the project technically feasible and what is the likelihood of success? Quantitative estimates of the expected results and the needed accuracy of the data must be provided.

Additional Criteria for Large GO, Treasury GO, and Legacy AR Proposals

  • Is there a plan to assemble a coherent database that will be adequate for addressing all of the purposes of the program?
  • Is there evidence that the observational database will be obtained in such a way that it will be useful also for purposes other than the immediate goals of the project?

Additional Criterion for SNAP Proposals

  • Willingness to waive part or all of the exclusive access period. While this is not the primary criterion for acceptance or rejection, it can provide additional benefit to any proposal and will be weighed by the reviewers as such.

Additional Criterion for Calibration Proposals

  • What is the long-term potential for enabling new types of scientific investigation with HST and what is the importance of these investigations?

Additional Criteria for Archival Research Proposals

  • What will be the improvement or addition of scientific knowledge with respect to the previous original use of the data? In particular, a strong justification must be given to reanalyze data if the new project has the same science goals as the original proposal.

  • What are the demands on STScI resources (including funding, technical assistance, feasibility of data requests, archiving and dissemination of products)?

  • Is there a well-developed analysis plan describing how the scientific objectives will be realized?

  • Will the project result in the addition of new information that can be linked to the Hubble Source Catalog (HSC)?

Additional Criteria for Treasury GO and Legacy AR Proposals

  • What scientific investigations will be enabled by the data products, and what is their importance?
  • What plans are there for timely dissemination of the data products to the community? High-level science products should be made available through the HST data archive or related channels.

Additional Criteria for Theory Proposals

  • What new types of investigations with HST or with data in the HST Data Archive will be enabled by the theoretical investigation, and what is their importance?
  • What plans are there for timely dissemination of the theoretical results, and possibly software or tools, to the community?


Next: HST Cycle 27 Guidelines and Checklist for Phase I Proposal Preparation


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