HST New and Important Features

What's New for Cycle 33

The following are new policies, opportunities and features for proposers to consider this Cycle:

  • No Legacy Archival Programs in Cycle 33:
    • Owing to funding constraints, we do not anticipate being able to fund Legacy Archival programs at a level that will ensure their successful completion. As such, we will not be soliciting Legacy Archival programs in Cycle 33. We are actively seeking alternative solutions and may revisit this decision for future cycles as the funding landscape changes.
  • Observations with ACS/WFC and WFC3/IR:
    • Proposers should be aware that ACS/WFC and WFC3/IR are offered as shared risk and may receive minimal calibration and support in Cycle 33. The level of operational support in future cycles is contingent on the outcome of the 2025 Senior Review. Observations with those modes executing in Cycle 34 and beyond may be subject to termination. Where possible, proposers are encouraged to consider alternative instrumental modes, such as WFC3/UVIS and JWST, to achieve their science goals.
  • Reduced Gyro Mode (RGM): Hubble has transitioned to RGM. RGM provides the same quality of science data as three-gyro mode, but does impact overall scheduling opportunities. Therefore, as a result of this transition:
    • We remind proposers that all special requirements (such as timing and orientation constraints) not requested and justified in Phase I are implemented only under exceptional circumstances.  If this renders a science program infeasible, the program risks termination. Proposers are encouraged to minimize their observing constraints to improve schedulability.
    • Because of the South Atlantic Anomaly, there are times in the schedule when only targets north of +60deg in declination are observable. Therefore, in cases where multiple targets can satisfy the same science goals, proposers are encouraged to favor targets north of +60deg in declination to improve schedulability under RGM. While having such targets will not affect whether or not a proposal is selected, approved GO programs will likely benefit from earlier scheduling while SNAP programs will likely have a higher frequency of execution.
    • More information about RGM can be found at Reduced Gyro Mode Tips and Resources.
  • Special Initiatives:
    • STScI is introducing a new initiative for Long-Term Monitoring programs. These programs should aim to exploit HST's 30-plus year heritage of observations and/or the expectation for a 20-year lifetime for JWST. For more information, see HST Special Initiatives.
    • STScI is introducing a new initiative for Roman Preparatory Science programs. This initiative is designed to encourage observations with Hubble that complement and enhance the scientific impact of Roman Space Telescope observations, or that are essential to achieving critical science goals of future Roman programs. For more information, see HST Special Initiatives.
    • We will no longer offer the Fundamental Physics Initiative but will be continuing the UV Initiative. 
  • No Mid-Cycle calls:
    • We will not offer a Mid-Cycle Call in Cycle 33.
  • Discovery Director's Discretionary (DD) Programs:
    • Discovery DDs are a new class of DD program suitable for observations of compelling scientific urgency that significantly accelerate scientific discovery. These are a supplement to the traditional Time-Critical DD programs. For more information, see Director's Discretionary Time Submission.
  • No Large-Scale Structure panel:
    • There is no longer a separate review panel on Large-Scale Structure, though we still welcome and encourage proposals in this area. Please see information regarding Science Categories and Keywords for more information.
  • Use of Generative Artificial Intelligence Technology:
    • Proposers are discouraged from using GAI in constructing proposals. Any use of such tools should be described in the Team Expertise section of the proposal. For further information see the full Policy on Use of GAI Tools.
  • Funding for DD and Joint programs:
    • Due to the restricted level of NASA grant funding for HST proposals, no funding will be available for Cycle 33 DD programs or joint time awarded by partner observatories.

Important Features

The following are important features that proposers should keep in mind when crafting their proposals.

Policy

  • Special Requirements & Scheduling Constraints:
    • Phase I proposals must itemize and briefly justify the Special Requirements that will be implemented in Phase II, using the Phase I section designated for this purpose. This includes orientation constraints. Special Requirements and Scheduling Constraints not specified in Phase I are implemented only under exceptional circumstances. If this renders a science program infeasible, the program risks termination. All visit-level Special Requirements and exposure-level Special Requirements must be justified. See HST Preparation of the PDF Attachment for more information.
    • We encourage accepted programs to minimize scheduling constraints. STScI recognizes that some of the scheduling restrictions for successful programs may not be apparent to an observer using APT. Constraints may need to be relaxed to enable scheduling of the program. See HST Proposal Implementation and Execution for more information.
  • >6 Consecutive Orbit Blocks:
    • Programs requiring blocks of more than 6 consecutive orbits must be explicitly described and justified in the Special Requirements section of the Phase I proposal. See HST Proposal Implementation and Execution for more information.
    • If your observations require a string of more than 6 consecutive orbits, that string will execute at shared risk (i.e., it will not be eligible for repeat if impacted by observatory problems).  Please consider alternative observational approaches to achieve your science goals.
  • GO Program Completion Limit of N+1 Cycles:
    • STScI aims to complete approved observing programs in a timely manner to ensure that scientific impact is maximized. To formalize this aim, in Cycle 31, we introduced a policy that all GO programs must be completed in N+1 cycles under nominal operations, where N is the number of cycles requested in the Phase I submission. Most programs will be unaffected by this policy. For more information, see HST Proposal Implementation and Execution.

  • Observations of Transient Phenomena:

    • Proposers are reminded that Director’s Discretionary (DD) proposals are intended for follow-up transient phenomena whose occurrence is unexpected. Target of Opportunity (ToO) proposals are intended for observations of transient phenomena whose exact timing is unknown but whose occurrence is expected on a timescale of 1-3 years. As much as possible, we encourage ToO proposals through the regular Call for Proposal cycle over DD proposals for transient phenomena. For further guidance, see Targets of Opportunity and Director's Discretionary Programs.

    • Number of Target-of-Opportunity Activations in APT: For proposals containing Target-of-Opportunity observations, the procedure for specifying the number of Target-of-Opportunity activations within APT has changed.  The number of activations should now be specified within the APT Proposal Information form.  For more instructions, see the Number of Target-of-Opportunity Activations section.
    • Duplications of Carry-Over ToOs: In the case where ToO requests duplicate ToOs in programs from previous cycles, triggers from the previous-cycle ToOs have priority over the newly-proposed ToOs.  Proposers must identify and justify any requests for duplicate ToOs.  For more information, see Carry-Over ToOs. 
  • Future-Cycle Terminology and Policies:
    • In Cycle 32, the terminology for "Long-Term" proposals changed, and these proposals are now known as "Future-Cycle" proposals. The documentation was updated regarding 1) how future-cycle requests should be entered in APT and 2) the Target-of-Opportunity requests that are allowed for Future-Cycle Programs.  For more information, see Future-Cycle Proposals. Future-Cycle GO programs may only include non-disruptive ToOs for execution in future cycles.
  • Review Panel for High-Energy Transients:
    • In response to increased demand for follow-up of transient events, we introduced a new review panel to the Cycle 32 Telescope Allocation Committee. The High-Energy Transients panel reviews all Target of Opportunity (ToO) proposals related to Galactic or Extragalactic high-energy transient phenomena.
    • No change is required by proposers for how such proposals are submitted. The appropriate science category should be selected as usual, and all appropriate ToO flags should be selected. However, the introduction of a new panel changes the cross-section of reviewer expertise, and proposers may wish to be mindful of this when writing their proposals.
  • Extensions in cases of exceptional circumstances
    • In exceptional cases where there are extenuating circumstances beyond a proposer’s control, proposers may request a moderate extension to the deadline via the HST Helpdesk. Extensions must be requested before the deadline with appropriate justification. If possible, it will be helpful to submit a preliminary proposal before the deadline including the proposal title, investigators, number of orbits requested, and requested instruments. 

Opportunities

  • New Target of Opportunity Category (Flexible Thursdays):
    • In addition to the long-standing Target of Opportunity (ToO) categories, a new ToO category was introduced in Cycle 31, anticipating a larger sample of transient events for Hubble follow-up observations.  Once a month, the Hubble schedule now includes a Flexible Thursday (beginning at approximately 12:00 UT) with targets that can be rescheduled relatively easily, to accommodate the trigger of a ToO on the preceding Tuesday (fully detailed activation and Phase II submission by 10:00 UT). For more information, see HST Observation Types.
  • Hubble UV Legacy Library of Young Stars as Essential Standards (ULLYSES):
    • As of Cycle 32, all ULLYSES observations have been completed and multiple data releases were announced. The community is encouraged to consider submitting Cycle 33 proposals to supplement and complement the program. This includes Archival proposals to analyze all or a subset of the full ULLYSES datasets.
  • HST-TESS Exoplanet Initiative (HTEI):
    • The HTEI will continue in Cycle 33, designed to provide the community with an opportunity to submit future-cycle Treasury programs that capitalize on the exciting small exoplanet discoveries generated by the Transiting Exoplanet Survey Satellite. HTEI proposals should be identified as such in the proposal abstract. See Special Initiatives for further information.

Instrumentation

  • ACS Spectropolarimetry:
    • Imaging spectropolarimetry was introduced for ACS in Cycle 31. The ACS polarizers (Instrument Handbook Section 6.1) can be used in conjunction with the G800L grism (Instrument Handbook Section 6.3.1) to provide low spectral resolving power (R~100 @ 8000Å) imaging spectropolarimetry from ~5500Å – 8000Å. This mode was still being calibrated during Cycle 30. Therefore, prior to proposing, potential observers should contact the Help Desk to discuss their specific goals and the current status of the mode. Full descriptions of the polarimetry capabilities of the ACS can be found in the ACS Instrument Handbook, and details about reduction of the data are described in the ACS Data Handbook.
  • Hubble Advanced Spectroscopic Products:
    • The Hubble Advanced Spectral Products (HASP) initiative transforms the accessibility and utility of archival Hubble Space Telescope (HST) data by automating the coaddition and abutment of one-dimensional spectra from the Cosmic Origins Spectrograph (COS) and Space Telescope Imaging Spectrograph (STIS). HASP provides data products at both visit and program levels, covering all COS and STIS spectra, for each CENWAVE and grating. This service is regularly updated with the latest calibrations and new data from over 3200 programs and 64000 datasets. Additionally, HASP enables users to perform custom coadditions through interactive Jupyter Notebooks. For more details, visit the HASP webpage or Instrument Science Report.
  • COS2025:
    • Users preparing COS proposals are reminded that the COS2025 policies are still in effect. These policies consist of restrictions on the choice of detector segment and FP-POS positions for the G130M observing modes. Detailed information about the changes is available at the COS2025 policies page.
  • COS Lifetime Positions:
    • To extend the lifetime of the COS/FUV detector, spectra are recorded at multiple lifetime positions (LPs) along the cross-dispersion direction, depending on which setting is in use. Details are provided in Section 2.1 of the COS Instrument Handbook (IHB). The main consideration for users is that G160M exposures longer than approximately half an orbit use LP6, while shorter G160M exposures may use LP4 to reduce overheads, if requested in the Phase I proposal. For the conditions under which G160M may be used at LP4, see Section 9.5.1 of the IHB.
  • STIS Spatial Scanning:
    • Spatial scanning with the STIS CCD is an available-but-unsupported mode for obtaining high signal-to-noise ratio spectra of bright targets. A recent analysis of this mode (as reported in the September 2020 STAN) demonstrated that after de-trending, the white light flux measurements can achieve an rms scatter of only 30 ppm.
  • WFC3 Spatial Scanning:
    • Each orbit must have 6 minutes of visibility time under FGS control (i.e. 6 minutes without scanning) to allow for pointing control system updates.
  • WFC3 IR Grism Imaging:
    • Specify the direct image filter in the Phase I and use at least one direct image at the beginning and end of each orbit for optimum calibration, ideally close to the wavelength of the grism.
  • WFC3/UVIS Flash Level:
    • The ETC (rather than APT) provides the most accurate estimate of the image background levels.
  • WFC3 ORIENTs:
    • Any ORIENT restrictions should be included in the Phase I proposal, as these will affect schedulability.

Next: HST Proposal Checklist