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 (see Section 6.2) and paying special attention to any potential conflicts of interest. The review panels offer their recommendations to the STScI Director. Based on these recommendations, the STScI Director makes the final allocation of observing time.
The review panels will consider Small GO (up to 34 orbits; Section 3.2.1), Medium GO (35-74 orbits;
Section 3.2.2), Calibration GO (
Section 3.2.4), Snapshot (
Section 3.3), Regular AR (
Section 3.4.1), Calibration AR (
Section 3.4.3) and Theory (
Section 3.4.4) proposals. Each review panel has an allocation of a specific number of orbits; the panel can recommend Small GO Proposals up to its orbit allocation. Medium GO proposals will be ranked side-by-side with the Small proposals, but the panels will not be charged for them; instead, the Medium proposals above the scientific cutoff line in each panel (as defined by the Small proposals) will proceed to the TAC, where they will be evaluated alongside highly ranked Medium proposals from the other panels. The panel recommendations generally do not require further approval of the TAC (
Section 6.1.2), and scientific balance will be determined within each panel rather than by the TAC. The panels do not adjudicate Large GO Programs (75 orbits or more; see
Section 3.2.3), Treasury GO Programs (
Section 3.2.6) or AR Legacy Proposals (
Section 3.4.2), but they will send comments on those proposals to the TAC for their consideration.
Panelists are chosen based on their expertise in one or more of the areas under review by the panel. Each panel spans several scientific categories (as defined in Section 8.8). In Cycle 21, we anticipate having two panels dealing with
Planets (including the Solar System, exoplanets, planet formation, and debris disks); three panels dealing with
Stars (of any temperature, in any evolutionary state, and including nearby star formation and Galactic ISM); two panels dealing with
Stellar Populations; three panels dealing with
Galaxies (including unresolved stellar populations, ISM in external galaxies, galaxy morphology, and galaxy evolution); two panels dealing with
AGN and IGM (including quasar absorption lines); and two panels dealing with
Cosmology (including large-scale structure, gravitational lensing, and galaxy groups and clusters). Within a panel, proposals are assigned to individual expert reviewers based on the keywords given in the proposal (see
Section 8.9). These keywords should therefore be chosen with care.
The TAC will include the TAC chair, the fourteen panel chairs, and 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 GO Programs (75 orbits or more; see Section 3.2.3), Treasury GO Programs (
Section 3.2.6), AR Legacy Proposals (
Section 3.4.2), and any other particularly large requests of resources (GO Calibration programs, SNAP, AR, Theory, or Pure Parallel). The TAC will also consider the panel recommendations concerning the Medium Programs (35-74 orbits, see
Section 3.2.2), will rank accepted Pure Parallel programs, and will be the arbiter of any extraordinary or cross-panel issues.
