About this Article

STScI recently completed the proposal review and telescope allocation process for Hubble Cycle 32. As for Cycle 31, this was a hybrid review comprised of External panels that were fully asynchronous, Discussion panels that met virtually, and an Executive Committee met in person in Baltimore. As always, we were impressed by the extremely high quality of the proposals, the compelling science, and the dedication, commitment and integrity of all those involved in the process, both as reviewers and behind the scenes.

There were a number of items of note during the submission and review period. In summary:

• We solicited Multi-Cycle Treasury (MCT) programs, requesting at least 350 orbits to enable science requiring time requests that cannot be accommodated through the regular time allocation process.
• NASA implemented an Operational Paradigm Change Review (OPCR) for Hubble.
• Near the end of the review, Hubble transitioned to Reduced Gyro Mode (RGM).
• We introduced a new High-Energy Transients panel to review Target of Opportunity (ToO) proposals for high-energy phenomena.

These are discussed in more detail below.

Here we summarize the review process and the results from the Hubble Cycle 32 proposal review, and discuss upcoming changes for Cycle 33 and beyond.

Proposal Submissions

The Cycle 32 Call for Proposals (CfP) was released on December 3, 2023, announcing observing opportunities with Hubble’s current instrumentation—the Advanced Camera for Surveys (ACS), the Cosmic Origins Spectrograph (COS), the Fine Guidance Sensors (FGS), the Space Telescope Imaging Spectrograph (STIS), and the Wide Field Camera 3 (WFC3)—and opportunities to request funding for theoretical and archival research. The CfP also announced a special opportunity to propose MCT programs.

A number of special initiatives from previous years were continued to encourage proposals in special-interest areas, including: Ultraviolet (UV) Initiative proposals, Transiting Exoplanet Survey Satellite (TESS) coordinated proposals, Archival Cloud Computation Studies proposals, Fundamental Physics proposals, Mission Support proposals, Calibration proposals, and UV Legacy Library of Young Stars as Essential Standards (ULLYSES) proposals. As in previous cycles, it was possible to request joint time on JWST, Chandra, XMM-Newton, and on NOIRLab and NRAO facilities, alongside HST observations (except for MCT programs).

The Phase I deadline was on March 26, 2024. Extensions were possible for those with last-minute emergencies. We received 1 request for a deferred deadline for 1 proposal; the request was approved.

At the deadline, we received a total of 937 proposals. Of these, 2 proposals were withdrawn, and 5 proposals were disqualified for failing policy or anonymity violations. This left a total of 930 proposals reviewed:

• 9 MCT programs requesting a total of 5,271 orbits;
• 769 General Observer (GO) programs, requesting a total of 17,520 orbits;
• 33 Snapshot (SNAP) programs, requesting 4,112 targets;
• 128 Archival Research (AR) programs, of which 41 were in the Theory category.

These proposals included investigators from 44 US states and territories, and investigators from 51 countries.

Not including the MCTs, this leaves us with a total of 921 compliant proposals submitted, requesting 17,520 prime orbits, a reduction of approximately 5% in both proposals and orbits compared to Cycle 31, which was itself approximately 12% lower than previous cycles. We attribute this reduction to the availability of JWST opportunities and proposal fatigue in the community. The effort required in preparing MCT proposals may also have contributed to the reduction in other programs this Cycle.

Proposal Review

Approximately 40% of the proposals were sent for External review by 215 reviewers from all over the world, separated by subject area. This included SNAP programs requesting fewer than 250 targets, regular AR and Theory programs (except for Solar System), and Small GO programs with fewer than 16 orbits (for Exoplanets, Galaxies, Stellar Physics, Stellar Populations). This process was conducted through April and May.

The remaining proposals were reviewed by 100 reviewers in Discussion panels separated by subject area (remaining Small and Medium GOs for all panels, and also AR, Theory and SNAP proposals for Solar System), and an Executive Committee (EC) of 18 members who reviewed the MCT, Large GO, Treasury GO, and AR Legacy proposals. The virtual Discussion panel meetings took place in May, and the in-person EC meeting took place in June.

Discussion panelists spanned from Eastern Europe to Hawaii. To accommodate the wide range of time zones, the Discussion panel meetings ran across four 6-hour days to allow plenty of time for comprehensive discussions and for writing feedback during the review.

We continue to strive for impartiality and fairness in the HST review process. Conflicts of interest for each reviewer were identified, including competing proposals, mentorship relationships, family members, and close collaborations. Panelists were not permitted to review, grade, or discuss proposals for which they were conflicted. As with most NASA programs, this was a Dual-Anonymous review.

A total of 16 proposals were flagged for compliance issues, of which 5 were judged to be severe violations and were disqualified from the review, and 11 were judged to be minor violations and were reviewed but issued warnings for future cycles. The nature of the compliance issues included:

• 11 proposals that were non-compliant or only in marginal compliance with our Dual-Anonymous Peer Review (DAPR) guidelines (3 disqualifications, 8 warnings);
• 3 proposals that were found to violate our font size requirements (1 disqualification, 2 warnings);
• 1 proposal that used an incorrect template resulting in missing information (1 warning);
• 1 proposal that was incomplete (1 disqualification).

Together, the reviewers and panelists provided recommendations to the Director, who approved 138 regular GO and SNAP proposals totalling 2,835 awarded orbits, and 2 MCT proposals for a total of 1,247 orbits across the next 3 cycles. Programs will start executing at the beginning of Cycle 32 on November 15, 2024. Notifications were sent on July 8, 2024.

Operational Paradigm Change Review

NASA is conducting a review of Hubble operations with a view to reducing costs. The review is driven by financial pressures within the overall NASA Astrophysics Budget, not by any deficiencies in Hubble science or operational performance.

Due to the OPCR, the amount of grant funding available for Cycle 32 remains uncertain. For this reason, no AR programs have been approved at this time. Decisions will be made regarding AR programs when we receive guidance from NASA regarding the OPCR outcomes and final budget. That timescale is uncertain. Notifications were sent to AR proposers to inform them of this situation. All AR proposers were sent the same notification; receipt of a notification does not imply that a program will be accepted if funding is favourable.

The OPCR was in progress during the Cycle 32 TAC meeting and the TAC were instructed to review proposals based on pre-OPCR Hubble capabilities. STScI has not yet received formal guidance from NASA, but more information on the potential impacts of the OPCR  can be found at the Operational Paradigm Change Review HDox page, including information about what the Hubble budget covers, the guiding criteria we followed when preparing for the OPCR, the likely outcomes of the OPCR, and frequently asked questions. This page will be updated as we learn more.

Reduced Gyro Mode

On June 4, NASA announced that Hubble has transitioned to RGM. This announcement came after the proposal discussions had concluded, and did not impact the panelist review of proposals. Neither did it impact the relevance and enormous value of the work of the reviewers; we ask the TAC panelists to assess the scientific merit of each proposal, and deliver a scientific ranking of the proposals in their panel, and this need is unchanged under RGM.

This announcement and transition did impact our usual post-review wrap up process. Following the review and before notifications are released, STScI typically assesses the approved Large and Treasury GO programs to ensure they are observable and schedulable, as far as can be determined from the Phase I information. For Cycle 32, STScI performed checks on every approved GO and SNAP program to check for feasibility under RGM, flagging each as possible (spanning from no changes required to implement to likely very challenging to implement) or impossible. At this stage, just 3 programs were identified as being impossible under RGM and were ultimately rejected. The rest were approved, pending successful Phase II submissions and additional feasibility reviews. In all cases, the final program must achieve the science goals described in the original proposal under the RGM observing constraints. The need for these extra reviews impacted our notification timeline significantly.

STScI is currently very busy transitioning programs from Cycle 31 and earlier to RGM. Due to the late notifications to the community, the effort required to transition existing programs to RGM, and the additional effort required to ensure approved Cycle 32 programs are feasible under RGM: the Cycle 32 Phase II deadline has moved to Friday August 16, 2024, and the Cycle 32 start date has moved to November 15, 2024.

The transition to Reduced Gyro Mode operations will take time and may require multiple iterations on individual programs. Now and in future, the fewer constraints a program has, the easier it will be to schedule. We greatly appreciate the cooperation and patience of all PIs as we transition the Cycle 31 science program and build the Cycle 32 science program for Hubble.

 Initial guidance on RGM best practices is provided at the Reduced Gyro Mode Implementation HDox page; this guidance will be updated as we learn more about Hubble’s performance.

Multi-Cycle Treasury Programs

MCT Programs were introduced with the successful completion of Hubble’s Servicing Mission 4 to establish a lasting legacy for Hubble. The primary aim is to provide an opportunity for the community to address high-impact scientific questions that require very large time requests that cannot be accommodated within the standard time allocation process. As Treasury programs, they are also required to provide enhanced data products or software tools for the scientific community, with the impact and scope of the products or tools commensurate with their extensive time request. In line with their legacy nature, there is no Exclusive Access Period on MCT program data.

An MCT opportunity was previously offered in 2009, which resulted in 3 extremely successful programs.  MCT Programs were solicited for the second time as part of the Cycle 32 Call for Proposals. The call stated that up to 1,500 orbits would be made available for these programs (250 GO orbits and 250 DD orbits per cycle for Cycles 32-34). Proposals were required to request a minimum of 350 orbits and were allowed to request up to the maximum pool available.

We received 9 MCT proposals, requesting a total of 5,271 orbits. Individual proposals ranged in size from 420 orbits to 811 orbits, and spanned several science areas, including Exoplanets and Exoplanet Formation, Stellar Populations and the Interstellar Medium, Galaxies, and the Intergalactic Medium and Circumgalactic Medium. MCT proposals were reviewed by the EC alongside regular Large GO, Treasury GO, and Legacy AR programs. After a round of preliminary grading, the lowest-ranked 40% of EC proposals were triaged from the review. 8 of the 9 MCT proposals passed the triage step and were discussed in the panel meeting.

To be selected, MCT programs had to first rank competitively against standard EC programs. After comprehensive discussions and a second round of grading, the EC determined that 5 MCT programs passed this bar and were eligible for acceptance. Together these programs requested a total of 3,258 orbits, far exceeding the MCT orbit pool available. The two highest-ranked MCT programs were accepted, for a total of 1,267 orbits. This represents a success rate by orbits of 24% and by proposals of 22% for the MCTs.

The successful MCT programs are:

• “CLUTCH: The COSMOS Legacy UV-Optical Treasury Campaign with Hubble” (PI Kartaltepe) and
• “STELa: Survey of Transiting Exoplanets in Lyman-alpha” (PIs Loyd & Vissapragada).

We do not anticipate offering MCT programs annually. Given the successful response to this call, we may consider opportunities for future cycles.

Approved Science Programs

As previously discussed, decisions for AR programs are still pending. As such, this section focuses only on the statistics for submitted and approved GO and SNAP programs.

Overall, 793 GO and SNAP programs were reviewed. Of these, 138 proposals were approved. This includes 128 GO programs for a total of 2,835 orbits (104 Small for 1,258 orbits, 18 Medium for 875 orbits, 6 Large & Treasury for 702 orbits), 10 Snapshot programs for 1,156 targets.

The approved GO and SNAP programs included 70 UV Initiative programs, 5 Fundamental Physics programs, 1 ULLYSES program, and 4 Mission Support programs. In addition, 2 joint HST-Chandra programs, 4 joint HST-JWST programs, 3 joint HST-NOIRLab programs, 2 joint HST-NRAO programs, and 3 joint HST-XMM-Newton programs were approved.

The approved programs included 69 ToO activations: 2 ultra-rapid activations of < 2 days, 5 disruptive activations of 2-21 days, 45 non-disruptive activations of more than 21 days, and 17 Flexible Thursday activations. We typically approve only 1 ultra-rapid ToO activation per cycle. However, following recommendations from the TAC, we accepted two in this cycle: one ultra-rapid ToO with a high probability of activation, and one ultra-rapid ToO with a very low chance of activation but a very high science impact.

View a list of the Cycle 32 approved GO and SNAP programs.

The overall success rate for Cycle 32 proposals was 17.4%, compared to 16.7% from Cycle 31. PIs from ESA member countries led 30% of the accepted Cycle 32 programs (compared to 17% in Cycle 31). Additional statistics are provided in Table 1.

*Multi-Cycle Treasury Programs not included 
AR decisions pending, not included in statistics

Once again, WFC3 was the most-awarded instrument, with 38% of the allocated time. A further 24% was allocated for STIS, 23% was allocated for ACS, and the remaining 15% was allocated for COS. Overall, 62% of the allocated observations are for imaging and 38% are for spectroscopy. A further breakdown of observing modes is given in Table 2. The success rate for the proposals under the UV Initiative was 40% by proposal (70 of 315 GOs, 0 of 0 SNAPs).

Multi-Cycle Treasury Programs not included

One major shift we have seen since the introduction of Dual Anonymous Peer Review (DAPR) is the increased success of first-time PIs. In Cycle 32, 29% of PIs are first-time PIs (38 of 129 unique PIs). This continues the trend we have seen since the introduction of DAPR (around 30%), and in stark contrast to earlier cycles (around 5%), which did not.

The Cycle 32 proposal / orbit distribution per science category is as follows:

• 15.2% / 17.3% for Exoplanets and Planet Formation (relative to 13.2% / 13.3% submitted),
• 15.9% / 17.2% for Galaxies (20.1% / 22.4% submitted),
• 6.5% / 10.2% for Intergalactic Medium and Circumgalactic Medium (4.2% / 8.0% submitted),
• 2.2% / 1.2% for Large-Scale Structure (3.3% / 2.6% submitted),
• 11.6% / 3.3% for Solar System (8.2% / 4.5% submitted),
• 28.3% / 21.4% for Stellar Physics (27.7% / 20.4% submitted),
• 7.2% / 16.6% for Stellar Populations (12.1% / 16.7% submitted),
• and 13.0% / 12.9% for Supermassive Black Holes (11.2% / 12.1% submitted).

High-Energy Transients Panel

Following feedback from previous TAC members and the STUC, in Cycle 32, we introduced a new High-Energy Transients panel. The purpose of this panel was to review ToO programs related to high-energy transient phenomena (including, but not limited to, supernovae, kilonovae, gravitational waves, fast radio bursts, gamma ray burst, and tidal disruption events). Other classes of ToOs remained in their topical panels, including Solar System, microlensing, and AGN ToOs. No changes were required at submission; all ToO programs were assessed after submission and assigned to the appropriate panel based on their science topic. Overall, 59 ToO programs were submitted, of which 49 were reviewed by the Transients panel and 10 remained in their topical panels.

The reasons for introducing a new panel were three-fold: 1) Ultra-disruptive, Disruptive, and FlexDay ToO activations are limited each cycle, and this requires a lot of cross-panel discussions to manage. The high-energy transient science topics tend to have most of the limited activation classes, so the extra panel makes it easier to have those discussions. 2) Panelists in these high-energy transient areas have told us that they feel better able to review transient proposals in other broad science areas than they do non-transient proposals within their broad science area. 3) When these kinds of proposals are reviewed against other proposals in their broader science area, panelists are concerned that less urgent proposals are not competitive with the urgent ToOs. We have not observed this to be true in practice, but the concern is nevertheless real.

The feedback we received from the Chair and panelists of the Transients panel was uniformly positive. The Chair and many panelists had served on previous TACs, and all reported this was an improvement. We also found that it was easier to manage discussions of activation limits. We plan to continue to this panel in future cycles.

Mid-Cycle Opportunities

Due to the anticipated budget decrease and OPCR outcomes, there will be no Mid-Cycle opportunity in Cycle 32 or any future cycles.

Cycle 33 Plans

We anticipate that the Cycle 33 Call for Proposals will be released in mid-December 2024 and that the Cycle 33 Phase I deadline will be on Thursday April 10, 2025.

Following strong feedback from the HST and JWST TACs and User Committees, we anticipate major changes to the page limits in the Cycle 33 review. Proposals will be limited to N+1 pages, where:

• Small GOs, regular ARs, regular SNAPs: N=4,
• Medium GOs: N=5,
• Large GOs, Treasury GOs, Legacy ARs: N=6.

The main N pages will contain the Science Justification and the Description of Observations or Analysis Plan, as appropriate. The additional +1 page will be dedicated to justifying any special requirements, such as duplications, coordinated observations, joint time, orient constraints etc.

Programs that do not comply with the new page limits will be disqualified. If you plan to resubmit previously unsuccessful proposals, it may take you time to revise your proposal to comply with these new guidelines and we suggest you plan accordingly.

Due to the change in dates for Cycle 32 due to the RGM transition, Cycle 33 will run November 1, 2025 through October 31, 2026. We anticipate that these shifted cycle dates (November-October) will persist through future cycles.

Get Involved

STScI runs two TACs each year, one for HST (typically in the April-June timeframe) and one for JWST (typically in the November-February timeframe). We know that they require a lot of work from the community, and that you have many other commitments and demands on your time. We very much appreciate all who consider our invitations to serve. We cannot run these reviews without your expertise and your support, and we are so incredibly grateful for the time and energy committed by so many to making these reviews a success.

Anyone interested in serving on a TAC panel, either as a Discussion panelist or an External panelist, can fill out the HST Review Volunteer Form and/or the JWST Review Volunteer Form to be considered. Typically, postdocs with at least two years of experience, and those more senior are eligible, but in exceptional cases, more junior researchers could be considered.

Acknowledgements

We are extremely grateful to everyone who was involved in this process at any stage. It takes an enormous amount of time and energy from a huge number of people to see the review through from start to finish.

First and foremost, we thank the Hubble TAC Chair, Panel Chairs, Panel Vice Chairs, At-Large members, Discussion panelists, and External panelists for their service on the Hubble Cycle 32 TAC.

View a list of the Cycle 32 panelists.

The overall TAC process was managed by Claus Leitherer and Laura Watkins. The TAC logistics were coordinated by Aleksandra Hamanowicz. In addition, numerous STScI personnel supported the successful completion of the review process:

Technical Manager: Aleksandra Hamanowicz received, organized, and distributed the proposals, oversaw the proposal database, and announced the results. Amber Armstrong and Brett Blacker provided additional technical support.

Hubble Science Policies Group: Andy Fruchter, Nimish Hathi, Claus Leitherer, Amanda Pagul, Molly Peeples, Elena Sabbi, Matthew Siebert, and Laura Watkins were responsible for panelist selection, assigning proposals for review based on expertise while avoiding conflicts of interest, managing the panels, and coordinating and processing the reviews. Alessandra Aloisi, Jamila Pegues, Neill Reid, and Marc Postman assisted with policy coordination, and oversight before and during the panel meeting.

Event Planning and Administrative Support: Darlene Spencer (Lead), Melody Easton, Sherita Hanna, Marleen Palacios Calderon, Victory Ramnarine, Holly Reedy (ESA), Shemiah Smith

Spirit Tool Support: Doug Paul, Maria Bertch, Matej Bludsky, Jeff Bucklew, Aasif Chanandin, Alex Framarini, Craig Hollinshead, Kyla Miller, Lauretta Nagel

 AV Support: Thomas Marufu, Kevin Flinn, Gary Gilbert

 IT Support: the IT Services Division team

 Facilities: Raven Baxter, Brad Bukowsky, B Few, Rob Franklin, Tiffany Lallo, Trevor Thompson, Mike Venturella, Richard Washington, Gee Williams

 Office of Public Outreach: Pam Jeffries

 Panel Support: David Coulter, Rosa Diaz, Calum Hawcroft, Shelly Meyett, Sapna Mishra, Adarsh Ranjan, Tony Roman, Tricia Royle, Eduardo Vitral

 Instrument and Telescope Support: Annalisa Calamida, Joleen Carlberg, Marco Chiaberge, Leo dos Santos, Travis Fischer, Joel Green, Norman Grogin, Svea Hernandez, TalaWanda Monroe, Marc Rafelski

 Reduced Gyro Mode Checks: Jay Anderson, Sylvia Baggett, John Debes, Travis Fischer, Alex Fullerton, Joel Green, Nimish Hathi, Christian Johnson, John MacKenty, TalaWanda Monroe, Lou Strolger

 Planning and Scheduling Support: Brigette Hesman, William Januszewski, Bill Workman, Kristen Wymer

 ESA Observers: Chris Evans

 HSTMO Observers: Tom Brown, Helmut Jenkner, John MacKenty, Julia Roman-Duval

GSFC Observers: Ken Carpenter, Andrew Ptak, Jennifer Wiseman

External Panelists from Past Cycles

We have previously made public the names of Discussion panelists from previous cycles, but not External panelists. We would like to do so now. We are extremely grateful to all Externals panelists who have served since we first created External panels in Cycle 28, many of whom have served for two, or even three cycles.

View a list of the Cycles 28-31 External panelists.