About this Article

STScI recently completed the proposal review and time allocation process for Hubble Cycle 31. This was a hybrid review: the topical panels met virtually, as they have since Cycle 28, and the Executive Committee met in person, for the first time since Cycle 27. There were no major changes in the review process. Once again, 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.

As a reminder, to avoid clashes between HST Cycle 31 activities and JWST Cycle 2 activities, HST Cycle 30 was extended by 2 months (through to 30 November 2023), and so HST Cycle 31 was shortened accordingly to be just 10 months long (December 1, 2023 through September 30, 2024), and the orbit allocation for the cycle reflects the shorter cycle length. HST Cycle 32 will return to the usual 12-month length.

Here we summarize the review process and the results from the Hubble Cycle 31 proposal review.

Proposal Submissions

The Cycle 31 Call for Proposals (CP) was released on March 1, 2023, announcing observing opportunities with HST’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). The CP also announced opportunities to request funding for theoretical and archival research.

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, as part of the HST proposal it was possible to request time on Chandra, XMM-Newton, and on NOIRLab and NRAO facilities. Newly available was the opportunity to request joint time on JWST.

The Phase I deadline was on May 24, 2023. Extensions were possible for those with last-minute emergencies. We received 1 request for a deferred deadline for 1 proposal; the request was approved and the proposal was submitted by the deferred deadline.

All told, we received a total of 965 proposals requesting a total of 18,653 orbits. Of these, 12 proposals were disqualified for failing policy or anonymity violations. This left a total of 953 proposals reviewed—785 in the General Observer category, 42 in the Snapshot category, 87 in the Archival Research and Archival Legacy categories, and 39 in the Theory category—requesting a total of 18,438 orbits. These proposals included investigators from 47 US states and territories, and investigators from 51 countries.

The Virtual Panel Meeting

Approximately half of the proposals were sent for external review by 216 reviewers from all over the world; this included Small GO programs with fewer than 16 orbits, regular Archival and Theory programs, and Snapshot programs. This process was conducted through June and July. The remaining proposals were reviewed by 91 reviewers in discussion panels separated by subject area (remaining Small and Medium GOs), and an Executive Committee (EC) of 19 members who reviewed the Large, Treasury and Legacy proposals. The review meeting took place in August. The panel meetings were again fully virtual, whereby all panelists, STScI staff, and observers joined the meeting remotely, following the review for HST Cycles 28-30 and the JWST Cycles 1-2. For the first time since HST Cycle 27, the EC met in person at STScI.

As for previous virtual meetings, the biggest challenge we faced was scheduling across many time zones as we had panelists spanning from Eastern Europe to Hawaii. Following feedback from panelists in last review, we extended the panel meetings to run across four 6-hour days (previously the meetings were three days) to allow more time for 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 24 proposals were flagged as non-compliant with our Dual-Anonymous Peer Review (DAPR) guidelines. 12 of these were judged to be severe violations and were disqualified. The remaining 12 were judged to be minor and were issued warnings for future cycles. Many violations occurred when proposers mistakenly uploaded the wrong proposal file via APT – in some cases, proposers had additional pages at the end of their proposal that they forgot to remove before submission, and in other cases, the proposers uploaded the APT version of the PDF, resulting in two sets of cover pages. We strongly encourage proposers to check the submitted version of their proposals to avoid such violations in future.

Together, the reviewers and panelists provided recommendations to the Director, who approved 159 proposals totaling 2,611 awarded orbits, which will start executing at the beginning of Cycle 31 in December. Notifications were sent on August 18, 2023.

Approved Science Program

A total of 953 compliant proposals were submitted, requesting 18,438 prime orbits, a reduction of approximately 12% reduction in both proposals and orbits compared to recent cycles. We attribute this reduction to the availability of JWST opportunities, the shorter cycle length, and proposal fatigue in the community.

If these, 159 proposals were approved for a total of 2,611 orbits. This includes 122 General Observer programs (104 Small for 1454 orbits, 12 Medium for 476 orbits, 6 Large & Treasury for 681 orbits), 7 Snapshot programs for 906 targets, 4 Archival Legacy programs, 21 Archival Research programs, and 5 Theory programs. These included 56 UV Initiative programs, 1 Cloud Computing program, 1 Fundamental Physics program, 1 ULLYSES program, and 4 Mission Support programs. In addition, 1 joint HST-Chandra program, 7 joint HST-JWST programs, 1 joint HST-NOIRLab program, 1 joint HST-NRAO program, and 2 joint HST-XMM-Newton programs were approved.

Cycle 31 introduced a new Target of Opportunity (ToO) class called Flexible Thursday ToOs: 3 Flexible Thursday ToOs proposals were submitted, and 1 was approved. Overall, the approved programs included 36 ToO activations: 8 disruptive activations of 2-21 days, 21 non-disruptive activations of more than 21 days, and 7 Flexible Thursday activations. No Ultra-Rapid (<2 day) activations were approved.

View a list of the Cycle 31 Proposals. 

The overall success rate for Cycle 31 proposals was 16.7%, compared to 19.4% from Cycle 30. PIs from ESA member countries led 17% of the accepted Cycle 31 programs (compared to 29% in Cycle 30). Additional statistics are provided in Table 1.

ESA Statistics for GO/Snapshot only

Once again, WFC3 was the most-awarded instrument, with 47.1% of the allocated time. A further 20.0% was allocated for STIS, 17.1% of the allocated time was for ACS, and the remaining 15.8% was for COS. Overall, 66% of the allocated observations are for imaging and 34% 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 35% by proposal (10 out of 30 for archival research and 46 out of 122 for GO).

Summary of requested instruments and observing modes for approved programs.

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 31, 28% of PIs are first-time PIs (41 of 147 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 31 orbit / proposal distribution per science category is as follows:

• 12.7% / 11.9% for Exoplanets and Planet Formation (relative to 15.2% / 13.5% submitted),
• 26.7% / 24.5% for Galaxies (28.2% / 22.6% submitted),
• 7.8% / 4.4% for Intergalactic Medium and Circumgalactic Medium (9.6% / 5.4% submitted),
• 3.7% / 4.4% for Large-Scale Structure (3.9% / 4.1% submitted),
• 6.7% / 7.5% for Solar System (2.9% / 6.1% submitted),
• 22.9% / 22.6% for Stellar Physics (18.6% / 24.3% submitted),
• 11.2% / 15.1% for Stellar Populations (13.4% / 13.4% submitted),
• and 8.2% / 9.4% for Supermassive Black Holes (8.3% / 10.6% submitted).

Cycle 31 Mid-Cycle Opportunity and the Cycle 32 Review

Owing to the two-month shortening of Cycle 31, there is only one Mid-Cycle opportunity in Cycle 31. Up to 300 orbits will be available in Cycle 31 for Mid-Cycle GO programs targeting recently discovered, non-transient objects. The Cycle 31 Mid-Cycle deadline is Wednesday November 15, 2023.

We anticipate that the Cycle 32 Call for Proposals will be released on Wednesday December 13, 2023 and that the Cycle 32 Phase I deadline will be on Tuesday March 26, 2024.

We further anticipate soliciting Multi-Cycle Treasury proposals as part of the Cycle 32 Call. More details can be found in this newsletter article. 

Get Involved

This is the second of 3 TACs STScI is running in a 14-month period (JWST Cycle 2 in January-April 2023, HST Cycle 31 in May-August 2023, and JWST Cycle 3 in November 2023-February 2024). We know that we have asked and will continue ask more service of the community than in a typical year, 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.

This has been an especially packed time. Moving forwards, TAC process for our observatories should be a little more spaced out. We anticipate that JWST reviews will have proposal deadlines in late October with reviews late January – early February, and HST will return to its recent normal of proposal deadlines in late March with reviews in early June.

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. Even in a normal year, it takes an enormous amount of time and energy from a huge number of people to see the review through from start to finish. To do so given the additional burdens, challenges and compounded stresses as the world comes back from a global pandemic is truly remarkable.

First and foremost, we thank all of the Hubble TAC Chair, Panel Chairs, Panel Vice Chairs, At-Large members, virtual panelists, and external panelists for their service on the Hubble Cycle 31 TAC. View a list of the Cycle 31 panelists.

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

Technical Manager: Brett Blacker received, organized, and distributed the proposals, oversaw the proposal database, and announced the results.

Science Policies Group: Andy Fruchter, Claus Leitherer, Molly Peeples and Laura Watkins were responsible for selecting virtual panelists and external panelists, assigning proposals for review based on expertise while avoiding conflicts of interest, and coordinating and processing external reviews. Katey Alatalo, Alessandra Aloisi, Christine Chen, Amaya Moro-Martín, Jamila Pegues, Neill Reid, Elena Sabbi, and Linda Smith assisted with policy coordination, and oversight before and during the panel meeting.

Administrative Support: Shemiah Smith (Lead), Sherita Hanna, Holly Reedy (ESA), Darlene Spencer

Spirit Tool Support: Doug Paul, Maria Bertch, Jeff Bucklew, Alex Framarini, Craig Hollinshead, Lauretta Nagel

AV Support: Thomas Marufu, Kevin Flinn, Gary Gilbert

 IT Support: Reena DeBerry and the IT Services Division team

 Facilities: Raven Baxter, Andre DeShazo, Rob Franklin, B Few, Tiffany Lallo, Mike Venturella, Gee Williams

 Office of Public Outreach: Pam Jeffries

 Panel Support: Gagandeep Anand, Chris Clark, Calum Hawcroft, Bhavin Joshi, Shelly Meyett, Amanda Pagul, Justin Pierel, Wilson Joy Skipper 

 Levelers: Francie Cashman, Chris Clark, Marjorie Decleir, Amelie Gressier, Beena Meena, Justin Pierel, Melissa Shahbandeh, Matt Siebert

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

 Planning and Scheduling Support: David Adler, 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, Mike Garcia, Andrew Ptak, Jennifer Wiseman