3.8 Director's Discretionary (DD) Time Proposals

Up to 10% of the available HST observing time may be reserved for Director's Discretionary (DD) allocation. Scientists wishing to request DD time can do so at any time during the year, by using the APT. Instructions and updated information can be found on the DD Submission Web page.

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

Upon receipt of a DD proposal, the STScI Director will usually seek advice on the scientific merit and technical feasibility of the proposal from STScI staff and outside specialists. A proposal for DD time might be appropriate in cases where an unexpected transient phenomenon occurs or when developments since the last proposal cycle make a time-critical observation necessary.

Recognizing the limited lifetimes for major space facilities such as HST, Chandra and Spitzer, DD proposals for timely follow-up of new discoveries will also be considered even if the astrophysics of the phenomena do not require such rapid follow-up. In such cases, the proposers must demonstrate that the observations will provide a critical link in the understanding of the phenomena and that carrying them out quickly is particularly important for planning future observations with major facilities. They should then also indicate their plans for quickly making the scientific community aware of their discoveries, to enable subsequent wider community follow-up.

DD observations should not generally be requested if any of the following is true:

• The observations could plausibly have been proposed for in the most recent regular proposal Cycle, possibly as a Target-of-Opportunity proposal (see Section 4.1.2).
• The observations were proposed in a previous regular proposal Cycle, and were rejected.
• The proposed observations could wait until the next proposal Cycle with no significant reduction in the expected scientific return.

The primary criteria for acceptance of DD proposals are high scientific merit and a strong demonstration of the timeliness of the 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 his/her 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.

Subject to availability of funds from NASA, STScI will provide financial support for U.S. PIs and CoIs of approved DD programs. Details of the STScI Funding Policies (including the definition of the term 'U.S. Investigators') are outlined in Section 12.2. Please contact the STScI Grants Administration Office (see Appendix A.1) for more information about budget submissions for DD proposals using the Grants Management System.