What's New for Cycle 34

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

• No Legacy Archival Programs in Cycle 34:
  
  • We are not soliciting Legacy Archival programs in Cycle 34 due to funding constraints. We may revisit this decision in future cycles as the funding landscape evolves.
    
    

• New Habitable Worlds Observatory (HWO) Precursor Science Initiative:
  • STScI is introducing a new Habitable Worlds Observatory Precursor Science (HPS) initiative, aimed at encouraging observations with HST that will help guide HWO's science cases and early development. For more information, see HST Special Initiatives.
     
• New Hubble-Roman Science Initiative:
  • The Hubble-Roman Science (HRS) initiative is designed to encourage observations with HST that complement and enhance the scientific impact of Roman Space Telescope observations, or that are essential to achieving critical science goals of Roman programs. For more information, see HST Special Initiatives.
     
• Rocky Worlds Director's Dirscretionary (DD) Time Program:
  • The Rocky Worlds DD Team has selected the final set of M dwarf exoplanet targets for observation. The current sample of exoplanets targets can be found on the Rocky World's DD Time page. The community is encouraged to consider complementary or supplementary GO programs or associated AR Theory programs.
     
• Observations with ACS/WFC and WFC3/IR:
  • Proposers should be aware that ACS/WFC and WFC3/IR may be offered as shared risk and receive minimal calibration and support in Cycle 34. The level of operational support in future cycles is contingent on NASA budgets for FY27 and beyond. Where possible, proposers are encouraged to consider alternative instrumental modes, such as WFC3/UVIS and JWST, to achieve their science goals.
     
• Use of Generative Artificial Intelligence (GAI) technology:
  • Proposers are not prohibited from the use of Generative Artificial Intelligence (GAI) tools, such as ChatGPT. However, following NASA policy, the proposal must acknowledge content that is not the creative product of the proposal team. Thus, any material contained in the proposal that is derived from GAI must be described and cited, e.g., the name of the program, version number, the date and time, and a short statement on how the GAI was used. This information must be included with the References and does not count against the page limits. Failure to disclose the use of GAI will result in disqualification. For further information, see the full Policy on the use of GAI tools.
     
• GO Program Completion Limit of N+2 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 within a certain number of cycles. For Cycle 34, this is within N+2 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.
     
• Strict Deadline:
  • The proposal deadline is Thursday, April 16, 2026 at 8:00pm EDT. Unlike previous cycles, the APT portal will close and will not accept any submissions or re-submissions after this time. STScI encourages proposers to submit their proposals "early and often". 
  • The policy regarding extensions remains the same: 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 Help Desk before the deadline with appropriate justification.  More details can be found here.
    
    

• APT Support:
  • Starting with Cycle 34, APT will only support operating systems that are still supported by their vendor. For more details and specifics about which operating systems are supported, see the APT installation pages.
    
    

• COS Instrument Handbook Update:
  • An updated version of the COS Instrument Handbook will be released in January 2026. Users preparing Cycle 34 proposals should refer to the COS IHB v17.1 for current reference information and check the COS webpage and upcoming STANs for the latest updates once the new version becomes available.
    
    

• COS Potential Addition of G140L at LP11:
  • Depending on ongoing analysis and investigations, the G140L grating may be offered at Lifetime Position 11 (LP11) during Cycle 34. Proposers interested in this mode should consult the COS webpage and future STANs for the most up-to-date information prior to submission.

Important Features

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

Policy

• New Page Limits since Cycle 33:
  • Page limits were reduced substantially (in most cases halved) relative to Cycle 32. See the HST Preparation of the PDF Attachment for more information.
     
• No Mid-Cycle Calls:
  • We are no longer offering mid-cycle calls. There is a new opportunity for Discovery Director's Discretionary Time proposals, starting in Cycle 32.
     
• Funding for DD and Joint programs:
  • Proposers may still apply for DD and Joint programs, however due to the restricted level of NASA grant funding for HST proposals, no funding will be available for Cycle 34 DD programs or joint time awarded by partner observatories.
     
• 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.
     

• >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.
     
• Observations of Transient Phenomena:
  • Target of Opportunity vs Director's Discretionary Proposals:
    • 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.
       
  • ToOs in Future-Cycle Programs:
    • Future-Cycle GO programs may only include non-disruptive ToOs for execution in future cycles.
       
• 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

• Long-Term Monitoring (LTM) Initiative:
  • In Cycle 33, STScI introduced 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.
     
• 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.
     
• 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.
     
• NASA High-End Computing (HEC) Time:
  • Successful HST proposers will be eligible to apply for NASA HEC Time. See HST General Information, Resources, Documentation, and Tools. More information on NASA HEC Program can be found on https://www.hec.nasa.gov.
     
• Hubble Data on AWS:
  • All non-exclusive access data for current Hubble instruments (ACS, COS, STIS, WFC3, FGS) have been made available as part of the Amazon Web Services (AWS) public dataset program. Proposers may request to make use of this dataset under the Archival Cloud Computing Studies category.

Instrumentation

• ACS Advice for Planning Observations:
  • New analysis of the impacts of degraded CTE on extended sources in WFC imaging provides several recommendations for proposers. New measurements of SBC background levels are also available. More information on these and other considerations for proposers can be found in the  Advice for Planning ACS Observations document.
     
• 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.
     
• ACS/SBC Background:
  • Analysis of historical ACS/SBC data have shown that airglow is usually significantly fainter than what was previously predicted by the ETC, meaning far shorter integration times are necessary for background-limited observations in F115LP, F122M, F125LP, and F140LP. ETC version 34.1 provides the option to use an empirical background model that incorporates this change; see ACS ISR 2025-04 and the ETC users guide backgrounds page for details.
     
• COS Usage Policies:
  • Users preparing COS proposals are reminded of three policies that are designed to minimize FUV detector degradation. The first policy, COS2025 consists of restrictions on the choice of detector segment and FP-POS positions for G130M. The second policy restricts exposure times for targets to not exceed the maximum allowable signal-to-noise (S/N) for a given mode and number of FP-POS positions. More details are found in the July 2024 COS STAN, The third policy restricts users to using less than 2% of detector lifetime at an LP for an observing program and requires PIs to estimate their detector usage. More details are found in the March 2025 COS STAN.
  • 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). Starting in Cycle 34, G130M observations will experience more overheads due to the placement of G130M at LP7, while G160M observations will experience less overheads at LP10. In some cases this will mean that G130M observers using the 1055, 1096, or 1222 CENWAVEs may consider requesting and justifying programs with fewer than 4 FP-POS. See July 2025 COS STAN for more details.
     
• 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.
     
• Hubble Spectroscopic Legacy Archive:
  • Proposers will be able to access the newly updated Hubble Spectroscopic Legacy Archive (HSLA) for high-level data products of COS and STIS spectra intended to accelerate the scientific use of existing spectroscopic data. This archive contains “science grade” co-added spectra of all usable public data, combining exposures for each target from across visits, programs, and cycles and “quick-look” spectra that join all gratings observed for a given target. More details are available at the HSLA website.
     
• STIS Coronagraphy Notebook:
  • A new notebook to help with planning coronagraphic observations is available, the New Coronagraphic Observation Feasibility Tool, see STIS January 2025 STAN for more information.
     
• STIS Flux Recalibration:
  • The STIS instrument team has been working to update their flux calibration and zeropoints.  For more details, see the STIS flux recalibration webpage and STIS June 2025 STAN.
     
• 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. See STIS IHB Chapter 12.12 Spatial Scans with the STIS CCD for more details.
     
• WFC3/UVIS Flash Level:
  • When using the ETC , include your estimated postflash values to obtain the correct S/N values for your observations. More details can be found in the HST Primer and WFC3 Instrument Handbook.

Next: HST Proposal Checklist