6.1 How STScI Evaluates Submitted Proposals

HST Programs are selected through competitive peer review. A broad range of scientists from the international astronomical community evaluates all submitted proposals, using a well-defined set of criteria (see Section 6.2). They rank the proposals and offer their recommendations to the STScI Director. Based on these recommendations, the STScI Director makes the final allocation of observing time.

6.1.1 The Review Panels

Review Panels will consider Regular GO (fewer than 100 orbits; see Section 3.2.1), Survey GO (see Section 3.2.3), Calibration (see Section 3.2.4), SNAP (see Section 3.3), Regular AR (see Section 3.4.1), Calibration AR (see Section 3.4.3) and Theory (see Section 3.4.4) Proposals. Each Review Panel has an allocation of a specific number of orbits and a dollar amount; the Panel can recommend GO Proposals up to its orbit allocation, and Theory and AR Proposals up to the budgetary allocation. In order to encourage the acceptance of larger GO Proposals, a progressive orbit "subsidy" is allocated to the panels, with orbits in the subsidy coming from outside the direct panel allotment. The algorithm for this "subsidy" has the goal of creating an acceptance rate of Regular GO programs that is approximately independent of size. Survey programs will receive an additional subsidy, since those programs offer advantages in scheduling the telescope more efficiently.

The panel recommendations generally do not require further approval of the TAC (see 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 (100 orbits or more; see Section 3.2.2), Treasury GO Programs (see Section 3.2.6) or AR Legacy Proposals (see 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). For example, in Cycle 15 there were two panels dealing with Hot Stars, ISM and Circumstellar Medium; three panels dealing with Star Formation, Cool Stars and Stellar Populations; two panels dealing with Galaxies, AGN and Quasars; three panels dealing with Quasar Absorption Lines and Cosmology; and one panel dealing with the Solar System. The division of scientific categories over panels may be different in Cycle 16, but the breadth of the panels will remain the same. 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.

Given the breadth of the panels, proposers should frame their scientific justification in terms appropriate for a panel with a broad range of astronomical expertise.

6.1.2 The Telescope Allocation Committee (TAC)

As in previous years, the TAC will include the TAC chair and the panel chairs. In order to ensure broad expertise across the full scope of scientific categories, several at-large members will be added to the TAC in Cycle 16. The primary responsibility of the TAC is to review the Large GO Programs (100 orbits or more; see Section 3.2.2), including Large Survey programs (see Section 3.2.3), Treasury GO Programs (see Section 3.2.6), AR Legacy Proposals (see Section 3.4.2), and any other particularly large requests of resources (GO Calibration programs, SNAP, AR, Theory or Pure Parallel). The HST TAC is also the arbiter of any extraordinary or cross-panel issues.

6.1.3 The Joint HST-Spitzer Telescope Allocation Committee (Joint TAC)

Coordinated HST-Spitzer proposals will be reviewed by a special TAC that is comprised of members of both the HST and Spitzer TACs. The Joint TAC will meet in mid-March 2007, before the HST and Spitzer TAC meetings. This allows the Coordinated HST-Spitzer Proposals to be reviewed in conjunction with other Large Proposals submitted to both observatories. Comments on each proposal will be solicited from the relevant HST and Spitzer panels.