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 Telescope Allocation Committee (TAC) comprises sub-discipline review panels and the Executive Committee (EC), which offer their recommendations to the STScI Director. Based on these recommendations, the STScI Director makes the final allocation of observing time.

The Review Panels

Dependent on their size, proposals in Cycle 33 will be reviewed either by external panelists or by discussion-based review panels.

The Cycle 33 discussion-based (i.e., face-to-face) review will comprise eight topical panels, one each for solar system astronomy, exoplanets and exoplanet formation, stellar physics and stellar types, stellar populations (and the ISM), galaxies, the circumgalactic medium and intergalactic medium, supermassive black holes and active galaxies, and high-energy transients. Panelists are chosen based on their expertise in one or more of the areas under review by the panels. With three exceptions, the discussion-based panels will assess and grade Small GO proposals and Medium GO proposals; the exceptions are the High-Energy Transients panel, which will review Target of Opportunity proposals for high-energy phenomena, regardless of size, and the Circumgalactic and Intergalactic Medium and Solar System panels, where the number of proposals is not sufficient for a split review. Additionally, the discussion-based panel for Supermassive Black Holes will also assess the Very Small proposals (up to 15 orbits). Each panel will be managed by a panel chair and a vice chair (except for Solar System, which has no vice chair), and there will be one overall TAC chair overseeing the review process. 

The remaining Very Small GO proposals (up to 15 orbits) and SNAP proposals will be distributed for external review. Those proposals will be assessed by five experts who will grade on an absolute scale against the primary criteria: scientific merit within the field, broader importance for astronomy & the strength of the data analysis plan; HST’s unique capabilities must also be required to achieve the scientific goals. Each external panelist will receive a limited number of proposals. The proposals will be grouped by subject area; information regarding the proposals likely to be recommended to the Director for acceptance will be provided to the chair of the appropriate face-to-face panel prior to the meeting to allow them to identify potential conflicts with the proposals reviewed by the panel.

Note: The review panels will conduct an anonymous proposal review, with the exception of a team expertise review after ranking occurs. 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 Anonymous Proposal Reviews for more information on what is required, and how it will be used in the Cycle 33 review.

The Executive Committee (EC)

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

Selection Criteria

Primary Criteria for All Proposals

Evaluations of HST proposals are based on the following three primary criteria. Each criterion is given a separate grade, then the grades are combined with equal weight. Reviewers will be instructed to evaluate these criteria based on what is written in the proposal.

(A) In-field Impact:

• The scientific merit of the program within its immediate sub-field, and its contribution to advancement of knowledge.
• The immediate sub-field of the proposal is the niche area of the program, not the whole broad science area (e.g. Trans-Neptunian Objects, not Solar System Astronomy).
• Proposals should address how the proposed program will improve understanding of the objects, classes of object, or specialist topics under study, and why the work is relevant and timely.

(B) Out-of-field Impact:

• The program’s impact outside of its immediate sub-field.
• A proposal does not have to impact all of astronomy. The out-of-field impacts could be in other sub-fields within the broader science area of the proposal, or in other broad science areas (e.g. in the case of a TNO proposal, this could be solar system formation or planet formation in general, among others).
• Proposals should discuss implications for other fields or sub-fields, and their breadth, significance, and timeliness.

(C) Suitability & Feasibility:

• The suitability of HST observations or datasets, or relevance to HST science. The necessity of special requirements. The feasibility of the science program.
• Proposals should demonstrate that the capabilities of HST are required to achieve the scientific goals, or demonstrate the relevance of the work to HST science. Technical issues will be adjudicated by STScI instrument scientists.
• Proposals should include a clear observing or analysis plan that demonstrates a clear path to science. Proposals should justify time requests and any special requirements, including duplications or joint observatory time.

Additional criteria exist as well, depending on the Proposal Category, as listed below. Letters in parentheses indicate the affected Primary Criteria.

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. (C)
• Is there evidence that the project has already been pursued to the limits of ground-based and/or other space-based techniques? (C)
• 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? (C)
• 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. (C)

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 Large GO and Treasury GO Proposals

• Is there a plan to assemble a coherent database that will be adequate for addressing all of the purposes of the program? (C)

• 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? (A,B)

Additional Criteria for Treasury GO Proposals

• What scientific investigations will be enabled by the data products, and what is their importance? (A,B)
• 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. (C)

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. (A,B)

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? (A,B)

Next: HST Guidelines and Checklist for Phase I Proposal Preparation