STScI especially seeks proposals that fall into one of several "Special Initiatives," described below. These initiatives highlight the unique science capabilities possessed by HST.

Ultraviolet Initiative

Ultraviolet GO Proposals

In recognition of the unique UV capabilities of Hubble and the finite lifetime of the mission, the UV Initiative will continue in Cycle 33. The initiative highlights programs that use the UV capabilities of Hubble and, in so doing, aims to increase the share of primary GO observing time dedicated to UV observations. A description of past programs is available on the HST UV Initiative Programs webpage.

No extra time is made available for UV Initiative proposals, and no additional weight is given in grading. However, setting the UV Initiative flag serves to highlight the unique science enabled by Hubble’s UV capabilities during the review. Proposals must still justify why Hubble is required to achieve the program's science goals, as described under the HST Proposal Selection Procedures. UV proposals recommended for acceptance must meet the usual requirement of high scientific quality set for all successful Hubble proposals. Very Small, Small, Medium, Large, and Treasury GO Proposals can benefit from the UV Initiative, in Cycle 33, as can Archival Proposals. Two conditions must be met for a GO Proposal to be eligible:

• The proposal must use the UV capabilities of Hubble. The eligible instrument modes (with central wavelength <3200 Angstroms) are ACS/SBC imaging (all filters), COS (all modes), STIS/MAMA spectroscopy and imaging (all gratings and filters), STIS/CCD spectroscopy (UV gratings only), and WFC3/UVIS imaging (UV filters F200LP, F300X, F218W, F225W, F275W, FQ232N, FQ243N, and F280N), and WFC3/UVIS G280 grism spectroscopy.
• The UV observations must be essential to the proposed science investigation. This condition will automatically be met for proposals requesting UV observations only. For proposals requesting both UV and optical/IR observations, the scientific necessity for the UV observations must be carefully justified in the Scientific Justification of the proposal.

Proposers are particularly encouraged to consider programs that will lay the groundwork for the Habitable Worlds Observatory, NASA's next UVO flagship mission.

Proposers must check the UV Initiative box in APT to identify whether their proposal qualifies for the benefit based on the above criteria.

Ultraviolet Archival Proposals

The UV Initiative also extends to Archival Proposals. STScI will ask the review panels and the TAC to give particular consideration to UV-specific archival proposals in the review process, provided they lead to UV high level data products and tools for the Hubble archive, and enable broader use of those datasets by the community, or (in the case of Theory Proposals) provide new models or theories to aid in the interpretation of UV HST data.

For Archival Programs that propose the joint analysis of UV and optical/IR datasets, the UV datasets must be essential to the scientific investigation for the UV Initiative benefit to apply. In this case, the proposers should carefully justify the importance of the UV component of their program in the Scientific Justification of the proposal.

AR proposers should check the "UV Initiative" box in APT to identify their proposal as eligible for the benefit.

Long-Term Monitoring (LTM) Initiative

Time-domain astronomy was highlighted as a key priority in the Astro2020 Decadal Survey. While much attention focuses on short-term transients, Hubble’s longevity provides an opportunity for investigations on substantially longer timescales, both with Hubble data alone and as a precursor to JWST follow-up through its 20-year lifetime. With that in mind, STScI constituted a Working Group to explore options for how HST can better support science in this area. The Working Group’s report highlights a number of areas where HST can make significant contributions. Consequently, STScI is inaugurating the LTM Initiative.

The community are encouraged to submit proposals that:

• Capitalize on past HST observations by providing late-epoch observations that are designed to probe long-term astrometric, photometric and/or spectroscopic variations.
• Propose first-epoch observation to lay the foundation for future time-domain work with either HST or JWST. The TAC will be instructed to assess the science impact of the full program, not just the current cycle observations. Proposers may submit joint HST-JWST proposals that request either or both HST and JWST observations in current and future cycles.
• Request observations beyond the 3-cycle limit for Future Cycle programs. Proposers must specify the required cadence of observations in the Special Requirements section of the proposal.

LTM programs will be regularly monitored to ensure appropriate progress, but if approved, they will not need be subject to TAC review for future observations.

Proposers much check the LTM Initiative box in APT to identify whether their proposal qualifies for this initiative.

No extra time is made available for LTM Initiative proposals, and no additional weight is given in grading. However, setting the LTM flag serves to highlight Hubble's longevity and its importance for time-domain astronomy during the review. Proposals must still justify why Hubble is required to achieve the program's science goals, as described under the HST Proposal Selection Procedures. LTM proposals recommended for acceptance must meet the usual requirement of high scientific quality set for all successful Hubble proposals.

Roman Preparatory Science (RPS) Initiative

The Nancy Grace Roman Space Telescope (Roman) will launch by May 2027, with a first call for proposals in Fall 2025. Roman will provide wide-field survey data including imaging and slitless spectroscopy spanning the wavelength range 0.5 to 2.3 microns.
 
The RPS Initiative is designed to encourage observations with Hubble that complement and enhance the scientific impact of Roman observations, or that are essential to achieving critical science goals of future Roman programs.
 
RPS Initiative proposals should comply with the following guidelines:

• Proposers must check the “Roman Preparatory Science” box in APT to be included in this initiative.
• Proposers should use the Special Requirements section to describe the connection with specific Roman observations.
• If the Hubble observations are critical to the success of the future Roman program, the science goals of the full program should be described in the Scientific Justification, including an explanation as to why Hubble observations are deemed essential to achieve those goals.
• By default, RPS proposal data will not have an Exclusive Access Period (EAP, a default of zero months). A non-zero EAP may be requested, and should be justified in the Special Requirement section. 

The connection between the proposed Hubble and Roman observations will be considered as part of the review process. Where the Hubble observations are deemed essential to achieving the overall science goals, the proposal will be assessed based on the science expectations for the full program including both the Hubble and Roman observations. Requests for non-zero EAP data will also be assessed by the TAC.
 
No extra time will be made available for RPS Initiative proposals, and no additional weight will be given in grading. However, setting the RPS flag serves to highlight Hubble's broad impact and its importance for future science with Roman during the review. Proposals must still justify why Hubble is required to achieve the program's science goals, as described under the HST Proposal Selection Procedures. RPS Initiative proposals recommended for acceptance must meet the usual requirement of high scientific quality set for all successful Hubble proposals.

HST-TESS Exoplanet Initiative

NASA’s Transiting Exoplanet Survey Satellite has discovered a wide range of planetary systems, notably small exoplanets (mini-Neptunes and super-Earths) around nearby stars.  The HST-TESS Advisory Committee was constituted by the STScI Director to provide guidance on optimal strategies for maximizing the scientific return from HST observations of TESS exoplanet targets. Following extensive consultation with the community, the HST-TESS AC final report highlights the vital role that HST can play in characterizing small exoplanets and identifying high priority targets for subsequent JWST observations.

Specifically, the committee noted that to maximize the science return, it is crucial that TESS targets have well determined periods and masses. Proceeding in a linear fashion, however, will lead to significant delays in obtaining follow-up HST observations of sufficient systems. Moreover, working on a target-by-target, proposal-by-proposal basis is unlikely to optimally sample the exoplanet population. Based on those considerations, the Space Telescope Users Committee has recommended the HST-TESS Exoplanet Initiative (HTEI) to provide the community with an opportunity to propose for observations of a well-characterized, representative sample.

Exoplanet Initiative proposals should

• Focus on mini-Neptunes and super-Earths
• Be sufficiently comprehensive in scope to address demographic questions
• Characterize the atmospheric properties as a function of size and equilibrium temperature
• Lay the foundations for subsequent observations with JWST

HST-TESS Exoplanet Initiative programs are Treasury programs and must meet the requirements for those programs. They are anticipated as long period (multi-cycle) programs that can capitalize quickly on the ongoing characterization of TESS exoplanet discoveries. The HST-TESS AC also recommended strong community participation in these programs, particularly with regard to target selection.

All HTEI exoplanet targets must have reliable mass determinations. Since an appropriately characterized sample of TESS targets is not available at the present time, HTEI proposals should identify specific targets that could be observed in Cycle 33 but may list generic targets for future cycles. The proposal must specify the quantitative criteria (such as mass, density and separation) that will be used to define the full sample. In addition, the proposals must describe appropriate mechanisms for building community consensus on how new targets will be added in future cycles.

HTEI programs will be assessed by the TAC along with other Large and Treasury programs. There is no specific orbit allocation for this initiative.

HTEI proposals must conform with the dual anonymous guidelines.

Next: HST Observation Types