This page describes the exclusive access periods that are associated with various types of HST proposals, as well as the policies regarding duplication of existing data.

Data Rights

Depending on the category, observers may have exclusive access to their science data during an exclusive access period. For Very Small, Small, and Medium GO Proposals, this period is normally 6 months following the date on which the data are archived. At the end of the exclusive access period, the data become available for analysis by any interested scientist through the HST Archive.  

Submitters of Very Small, Small, and Medium GO Proposals who wish to request a shorter exclusive access period of 3 months, or who are willing to waive their exclusive access rights altogether, should specify this in the ‘Special Requirements’ section of the proposal. 

Data taken under the Treasury and Large Program categories will by default have no exclusive access period. All Roman Preparatory Science Initiative proposals will by default have no exclusive access period, regardless of size. Any request for non-zero exclusive access periods for programs in these categories must be justified in the ‘Special Requirements’ section of the proposal and will be subject to review by the TAC.

Policies and Procedures Regarding Duplications

Special policies apply to cases in which a proposed HST observation would duplicate another observation either already obtained or scheduled to be obtained.

Duplication Policies

An observation is a duplication of another observation if it is on the same astronomical target or field, with the same instrument, with a similar instrument mode, similar sensitivity, similar spectral resolution and similar spectral range. It is the responsibility of the proposers to check the proposed observations against the catalog of previously executed or accepted programs.

If any duplications exist, they must be identified in the ‘Observation Summary’ section of the proposal, and justified strongly in the ‘Justify Duplications' section of the proposal as meeting significantly different and compelling scientific objectives. 

Any unjustified duplications of previously executed or accepted observations that come to the attention of the peer reviewers and/or STScI could lead to rejection during or after the Phase I deliberations. Without an explicit Review Panel or TAC recommendation to retain duplicating exposures, they can be disallowed in Phase II. Specifically,

(1) Regular GO programs will have their orbit allocations reduced if genuine duplications are found.
(2) SNAP programs are allowed to substitute similar targets if duplications are found, provided the new targets match the original target selection criteria.
(3) Parallels are not considered in terms of duplications, so a prime observation will not be disallowed even if an accompanying parallel observation duplicates an existing observation

ACS and WFC3 Duplications of WFPC2, NICMOS or STIS imaging

ACS and WFC3 have imaging capabilities superior to WFPC2, NICMOS and STIS for many purposes (see the Scientific Instrument Comparisons section of the HST Primer). Nonetheless, proposers should note any duplications of previously approved or executed WFPC2, NICMOS, or STIS imaging exposures that lie in their fields, and justify why the new observations are required to achieve the scientific goals of the project. Proposers for WFC3 observations should note and justify any duplications of previous ACS observations.

How to Check for Duplications

To check for duplications among the observations that you wish to propose, please use the tools and links on the HST Proposal Support webpage at MAST. The following two options are available:

• The HST Duplication Checking Web Form
• The Planned and Archived Exposures Catalog (PAEC), which is available from the HST Catalogs webpage at MAST. This catalog contains summary information about exposures in ASCII format and can be browsed with any text editor. It is normally updated monthly, but will be kept fixed between the release of this Call for Proposals and the Phase I deadline.

Please make sure that you are either searching in the HST duplication table (automatic if you use the Duplication Checking Web Form) or the PAEC. Other archive tables, such as the science table or the ASCII format Archived Exposures Catalog (AEC) do not include exposures that have been approved but have not yet executed, and are therefore not suitable for a complete duplication check.

Next: HST Proposal Selection Procedures