HST Cycle 28 Director's Discretionary Time Submission

Up to 10% of the available HST observing time may be reserved for Director's Discretionary (DD) allocation. A DD proposal is appropriate when a truly unexpected transient phenomenon occurs or when developments since the last proposal cycle make a time-critical observation necessary. The pool of orbits for in-cycle DD proposals is limited and typical proposals are less than 5 orbits, although larger requests can be considered under exceptional circumstances.

Director's Discretionary Proposals might be appropriate for

  1. followup of newly-discovered unexpected transient phenomena, or when developments since the last proposal cycle make a time-critical observation necessary;
  2. or the timely follow-up of new discoveries that will provide a critical link in the understanding of the phenomena, particularly those important for planning future observations with major facilities. 
  3. Requests to reserve target of opportunity targets that have not yet been discovered are not appropriate for Director's Discretionary Proposals.

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.  

Please note: All scheduling requirements must be specified, including timing requirements that would require disruptive (< 3 week) or ultra-disruptive (< 2 day) turn-around times for activation. The limitation on each of these is described in HST Cycle 28 Observation Types and Special Requirements. Proposals that imply a time requirement, e.g., "as soon as possible", but do not specify a disruptive or ultra-disruptive activation time, will be returned.

DD proposals must now be submitted and will be reviewed in an anonymous format. The review process is similar to that used in HST Cycle 28 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 document.

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 Cycle 28 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.

Templates for the PDF attachment of the Scientific Justification can be found on the Current Cycle PDF Preparation page. Page limitations should follow the Page Limits for the PDF Attachment for proposals of the same-sized proposal category, as shown on HST Cycle 28 Guidelines and Checklist for Phase I Proposal Preparation

Upon completion of your DD submission, your program will be transferred to the STScI for processing by our DD team. If you run into problems submitting a DD Request, send mail to help@stsci.edu for investigation/resolution.

Please refer to the section on Director's Discretionary Time proposals in HST Cycle 28 Proposal Categories for policies regarding this type of proposal.

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 28. 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.


Summary of APT DD Required Items

Coverpage information
  • Title
  • Abstract
  • Category
  • Cycle
  • Primary orbits
  • Parallel orbits
  • Exclusive Access (Proprietary) Period. DD programs generally do not have an exclusive access period and must request and justify requests for one.
  • Scientific Category
  • Science Keywords
  • Justification PDF Attachment
Investigator information
  • Full address for PI and limited information for CoIs

Observation information (repeat for as many observations as required)

  • Target Name, Coordinates, Magnitude
  • Configuration
  • Science Mode
  • Spectral Elements
  • Total Orbits
  • Observation Flags
Proposal Justification Information (see also HST Cycle 28 Preparation of the PDF Attachment)
  • Rationale for DD time: Explain why DD time is required, i.e., why the proposal was not submitted to the most recent TAC, or why the proposal cannot wait until the next TAC for evaluation.
  • Scientific Justification: Provide a scientific justification to allow for the scientific evaluation.
  • Description of Observations: Provide a description of the proposed observations. Explain the amount of exposure time and number or orbits requested (e.g., number of objects, examples of exposure-time calculations and orbit estimations for some typical observations, etc.) Explicitly describe any non-standard calibration requirements and observations.
  • Scheduling Requirements: Provide specific scheduling requirements to allow for scheduling impact assessment. This includes required (or desired) execution windows, special orientation or background requirements, and time links or coordinations with HST or other observations. Include a brief justification of the scheduling constraint, especially if it will be under the 21-day non-disruptive window.