What is Director's Discretionary Time (DDT)

Five percent of the available Spitzer observing time is allocated by the SSC Director as Director's Discretionary Time (DDT), and is intended to facilitate observations that address emerging scientific topics or areas missed in the proposal review process. Investigators wishing to request DDT can do so at any time during the year, by using the DDT submission template and procedures described here. Requests for DDT must be submitted electronically to the SSC Director.

The inaugural DDT program was the First Look Survey (FLS), which provided an early and representative sample of reliable infrared data. A portion of the Director's DDT is allocated to observations made by the Spitzer Fellows.

The primary utilization of additional DDT programs is in support of community-proposed requests that are based on exceptional, time-critical observing opportunities that cannot be accommodated with the regular cycle of Calls for Proposals. Other DDT usages include innovative observations that extend the scientific capabilities of Spitzer, and extraordinary events and opportunities that necessitate -- in the view of the SSC Director -- observations to be obtained with Spitzer for the benefit of the astronomical community. The final cryogenic cycle of observations has been selected for Cycle-5. More observations than we expect to execute were selected, due to the uncertainty in the cryogen depletion date. For Cycle-5 58.7 hours of Director's Discretionary Time was allocated through the normal TAC process for high-risk/high-gain GO programs that had a very high science ranking.

In previous cycles, adding DDT programs to the schedule merely delayed the execution of previously selected science. In Cycle-5 a delay in execution could translate into observations never being executed, given the uncertainty in the cryogen end date. DDT proposals for Cycle-5 must be extremely compelling science and must include a description of the long-term legacy value of the observations for the Spitzer mission. In other words, proposers must explain why in the future (e.g., over the next decade or so) it will be important for these observations to exist.

All Cycle-5 observations were assigned scheduling priorities. Priority 1 and 2 observations are currently in the scheduling pool. 2200 hours of priority 3 observations are on-hold until the pool becomes depleted of priority 1 and 2 AORs. Since the Cycle-5 selections were announced, DDT proposals are being submitted at a rate far exceeding the previous one. To handle this increased influx we will be invoking the following:

1. The SSC will determine if the proposal falls in the category of urgent, new science that could not possibly have been submitted for Cycle-5. These proposals will be handled through the normal DDT review process and, if accepted, will be given scheduling priority 1.
2. Proposals that do not meet the urgent and new criteria will be put on-hold and evaluated as a group on a quarterly basis (July, October, January). Proposals accepted in this category will nominally be assigned priority 3, unless a specific recommendation is made during the review process for higher or lower scheduling priority.

1. a strong scientific justification;
2. a description of the long-term legacy value of the program;
3. completed Astronomical Observation Requests (AORs), if possible;
4. a justification for why the request was not submitted during the Cycle-5 Call for Proposals.

Recognizing the limited lifetimes for major space astronomy facilities, such as the Hubble Space Telescope, the Chandra X-ray Observatory and Spitzer, DDT proposals for rapid follow-up of new discoveries will also be considered. In such cases, the proposing investigator 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.

A request for DDT observations is predicated on the assumption that the proposed observations are urgent, and that the observations will be of interest to the broad scientific community. Therefore, data validation periods for DDT observations will be no more than three months, at which point the data will enter the public domain. The SSC Director reserves the right to make all raw and calibrated data publicly available immediately as a condition for approving a DDT request, particularly where the data involve an unexpected Target of Opportunity.

Any science data analysis funding awarded to successful DDT proposers is determined using the same formula utilized for funding the current GO cycle.

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