Director's Discretionary (DD) programs provide an opportunity to obtain observations that could not have been proposed for at the last main cycle and cannot wait until the next main cycle, either because there are time constraints or there is exceptional scientific urgency. They are limited in both scope and in time request. Scientists wishing to request DD time can do so at any time during the year, by using APT. Please pay careful attention to the guidelines before submitting.

Overview of DD Programs

Up to 10% of the available HST observing time may be reserved for DD allocation. The pool of orbits for in-cycle DD proposals is limited and typical proposals are very small, although larger requests can be considered under exceptional circumstances.

There are two types of DD proposals – Time-Critical and Discovery – whose characteristics are described below.

Time-Critical DD Proposals

Time-Critical DD proposals are suitable for observations that could not have been requested in a previous observing cycle and cannot wait for the next standard observing cycle.  Examples of potentially appropriate Time-Critical DD time requests include:

• Follow-up of newly-discovered, truly unexpected transient phenomena;
• When developments since the last proposal cycle make a time-critical observation necessary. 

Examples of observations that are not suitable for Time-Critical DD time requests include:

• Observations that could plausibly have been proposed in the most recent regular proposal cycle, possibly as a target of opportunity proposal;
• Observations that were proposed in a recent regular proposal cycle, and were rejected;
• Observations that could wait until the next proposal cycle with no significant reduction in the expected scientific return.

Time-Critical DD proposals should be small, typically no more than 5 orbits in size. Proposals requesting significantly more than 5 orbits are generally better suited for the standard observing cycle and its TAC review process.

Discovery DD Proposals

Discovery DD proposals are suitable for observations of compelling scientific urgency that significantly accelerate scientific discovery. Proposers should indicate their plans for quickly making the scientific community aware of their discoveries, to enable subsequent wider community follow-up.

Examples of potentially appropriate Discovery DD time requests include:

• The timely follow-up of new discoveries that provide a critical link in the understanding of phenomena that would have significant impact on the broader field, particularly those important for planning future observations with major facilities;
• Small-scale pilot or test observations that would have an extraordinary impact on the broader field if they were successful.

Examples of observations that are not suitable for Discovery DD time requests include:

• Observations that are a subset of larger observing programs planned for future cycles; 
• Observations that are requested to prepare for more/follow-up observations in future cycles;
• Observations that were proposed in a recent regular proposal cycle, and were rejected, and for which the available information and/or observations have not substantially changed;
• Observations that do not have significantly compelling scientific urgency, and would therefore be more appropriately evaluated by the TAC review process during a standard observing cycle.

Discovery DD time proposals should be small, typically no more than 10 orbits in size. Unless the science is highly compelling, proposals requesting significantly more than 10 orbits are generally better suited for the standard observing cycle and its TAC review process.

Joint DD Proposals

Joint JWST-HST DD proposals are permitted. All joint JWST-HST proposals should be submitted through the JWST DD Process using the JWST Astronomer's Proposal Tool.

Joint DD proposals with other facilities are not permitted.

Exclusive Access Period (EAP)

Observations obtained as part of a DD Program generally do not have an EAP, and are made available immediately to the astronomical community. However, DD proposers may request and justify EAPs in their proposals.

Target-of-Opportunity Observations

Requests to reserve target-of-opportunity targets that have not yet been discovered are not appropriate for DD Proposals.

Requests for Rapid Observations

Weekly HST Command Loads are uplinked to the telescope on Sunday evenings; for nominal operations, the observing schedule is determined eleven days in advance of the uplink date. Although it is technically feasible to interrupt the schedule and initiate observations of a new target, short-notice interruptions place severe demands on the planning and scheduling process, decreasing overall observing efficiency and delaying other programs. Hence, requests for DD time must be submitted at least two months before the date of the requested observations, if possible. Requests for shorter turn-around times must be exceedingly well justified. In the case that a DD Program with a turn-around time of less than one month is accepted, the PI or their designee is required to be reachable by STScI personnel on a 24 hour basis between the submission and the implementation of the program, for Phase II preparation. Please see the Review and Implementation of Target of Opportunity and Director's Discretionary Time Observations for further details.

DD Proposal Submissions

Dual Anonymous Peer Review

DD proposals must be submitted and will be reviewed in an anonymous format. The review process is similar to that used in HST Anonymous Proposal Reviews, except the review of the team expertise will be done internally by the Science Policies Group. There is no need to submit a separate Team Expertise and Background statement.

Proposal Preparation

Proposers wishing to request Director's Discretionary (DD) time should first check the Real-time list of all Approved DD Programs. This list is updated nightly.

Proposers should use the Astronomer's Proposal Tool (APT) to submit their DD programs. To download and install APT, go to the APT page. For help on using APT to prepare and submit a Phase I program, go to the HST Phase I Proposal Roadmap. You will be providing the "Coverpage" information via the APT tool and you will attach your scientific justification and observation description as a PDF attachment to your submission. More detailed information is included below as well as in the Phase I Roadmap.

If you run into problems submitting a DD Request, send please contact the helpdesk for investigation and resolution.

Please refer to the section on Director's Discretionary Time proposals in HST Proposal Categories for policies regarding this type of proposal.

Proposal Template and Page Limits

Proposals should be submitted via APT as type DD, using the DD template for the pdf attachment. This is important as this template contains an extra mandatory section unique to DD programs. Proposals may be rejected for failing to comply with this requirement.

Page limitations should follow the Page Limits for the PDF Attachment for proposals of the same-sized proposal category, as shown on HST Guidelines and Checklist for Phase I Proposal Preparation. Please note that Cycle 32 DD programs must use the new Cycle 33 page limits. Proposals exceeding the proposals risk being rejected.

Proposal Review

Upon receipt of a DD submission, the STScI Director will usually seek advice on the scientific merit and technical feasibility of the proposal from STScI staff and external specialists.

To begin, your program will be transferred to the STScI Science Policies Group for processing by our DD team. The DD team undertake an initial review of any DD proposal to determine whether it complies with the primary criteria. Proposals that do not meet those criteria will not be distributed for further review; the Principal Investigator will be informed of that decision, and is free to submit the proposal at the next standard cycle deadline. Re-submissions of previously-rejected proposals will be rejected automatically.

DD proposals passing this initial review are sent out for scientific review by members of the community who have contributed to recent HST TAC reviews. Each proposal will receive four reviews. The primary criteria for acceptance of DD Proposals are high scientific merit and a strong demonstration of the timeliness of the observations. Proposals must make an appropriately compelling science case.

Proposals for DD time must be sufficiently detailed for adequate evaluation. The required level of detail is the same as for proposals submitted for the regular observing cycles, as described in the current Hubble Space Telescope Call for Proposals for Cycle 33. Among other things,

• both the proposed observations and the use of DD time must be explicitly justified, 
• there must be an adequate description of how the proposed observations relate to the current state of knowledge, 
• and the proposed observations must be described in sufficient detail to allow technical evaluation.

The DD team collects the reviews and presents a summary to the Director. The Director makes the final decision regarding whether a proposal is awarded time.

Proposal Resubmission

Proposers may not re-submit a DD proposal unless they have explicit guidance from STScI.

APT Requirements for DD Programs