Mid-Cycle programs provide an opportunity to obtain observations that could not have been proposed for at the last main cycle and cannot wait until the next main cycle, either because there are time constraints or there is exceptional scientific urgency. They are limited in both scope and in time request. Please pay careful attention the guidelines before submitting.

Dates and Deadlines

In Cycle 31, up to 300 orbits will be available for Mid-Cycle GO programs. Given the shorter-than-usual ten-month Cycle, there will be one Mid-Cycle review and the deadline will likely be shifted from the usual times. Mid-Cycle proposals may be submitted at any time to be reviewed at the next opportunity.

Mid-Cycle Important Dates:

• Deadline: Wednesday November 15, 2023 at 11:59pm EST
• Proposal Review: November 29, 2023 - January 5, 2024
• Notifications expected: Mid-January 2024

Mid-Cycle Criteria

Mid-cycle programs were initiated in Cycle 23 to provide the community with an opportunity to propose for in-cycle observations of recently-discovered, non-transient objects with high scientific urgency. As such, they complement Director’s Discretionary programs, which target unexpected transient phenomena and time-critical observations. (For more information about different proposing opportunities see Targets of Opportunity and Director's Discretionary Programs.)

Mid-cycle GO proposals must meet the following primary criteria:

1. Proposers must provide an explanation of why the proposal could not have been submitted in response to previous Calls for Proposals: for example, the target may have been identified subsequent to the most recent relevant proposal deadline. 
2. Proposers must provide a clear description of the compelling scientific urgency of these observations and why they should be executed in the present cycle.

Mid-cycle programs should address specific science questions. Pilot or preparatory studies are generally not appropriate for mid-cycle time, and should be deferred until the next main cycle.

Proposers can see the past HST Mid-Cycle Approved Programs.  This list is updated after the results of each Review have been made public.

Mid-Cycle Submissions

Dual Anonymous Peer Review

Mid-Cycle proposals must now be submitted and will be reviewed in an anonymous format. The review process is similar to that used in HST Anonymous Proposal Reviews, except the review of the team expertise will be done internally by the Science Policies Group. There is no need to submit a separate Team Expertise and Background statement.

Proposal Template and Characteristics

Proposals should be submitted via the Astronomer’s Proposal Tool (APT) as type GO, using the Mid-Cycle template for the pdf attachment. This is important as this template contains an extra mandatory section unique to mid-cycle programs. Proposals may be rejected for failing to comply with this requirement.

Proposers should use APT version 2021.5 or later. Upon completion of your mid-cycle submission, your program will be transferred to the STScI for processing. If you run into problems submitting a mid-cycle proposal, contact the STScI HST Help Desk https://hsthelp.stsci.edu for assistance.

Proposals for Mid-Cycle time must be sufficiently detailed for adequate evaluation, comparable with proposals submitted for the regular observing cycles as described in the current Call for Proposals.  Among other things,

• Both the proposed observations and the use of Mid-Cycle time must be justified explicitly,
• There must be an adequate description of how the proposed observations relate to the current state of knowledge,
• And the proposed observations must be described in sufficient detail to allow technical evaluation.

Mid-Cycle GO proposals will have the following characteristics:

• Proposals are limited to requesting no more than 15 orbits; 
• Observations should have minimal constraints to maximize scheduling flexibility – Target of Opportunity proposals may not be submitted as Mid-Cycle Proposals;
• Observations taken for accepted programs will have a proprietary period of no more than 3 months;
• Proposals may request only HST time - joint proposals are not permitted;
• Proposers may apply for all available instruments. Proposals must be compliant with the technical restrictions described in the most recent Call for Proposals;
• Page limits are the same as Regular GO Small proposals;
• Calibration proposals may not be submitted as Mid-Cycle Proposals.
• Archival (AR) programs may not be submitted for Mid-Cycle review.

Please also note that Mid-Cycle proposers may select any of the HST Special Initiatives for their proposal.

Mid-Cycle Review Process

Members of the STScI Science Policies Group will undertake an initial review of GO Mid-Cycle proposals to determine whether the proposals comply with the primary criteria. Proposals that do not meet those criteria will not be distributed for further review; the Principal Investigator will be informed of that decision, and is free to submit the proposal at the next standard cycle deadline. Re-submissions of previously-rejected proposals will be rejected automatically.

Mid-Cycle proposals will receive scientific review by members of the community who have contributed to recent HST TAC reviews. Each proposal will be distributed to four reviewers.

The STScI Science Policies Group will collect the reviews and rank order the proposals. The Director will make the final selection of proposals to be awarded time.

Mid-Cycle Evaluation Criteria

Reviewers are required to address the following issues:

1. The scientific merit of the proposed investigation and its potential contribution to the advancement of scientific knowledge – grade 1-5;
2. The program’s importance to astronomy in general – grade 1-5;
3. The scientific urgency of the observations and their suitability for a mid-cycle proposal – grade 1-5;
4. The program science goals can only be achieved by observations with Hubble Space Telescope – yes/no.

Grades are as follows:

1. - Excellent
2. - Very Good
3. - Good
4. - Fair
5. - Poor

Reviewers are also required to provide brief text feedback on the strengths and weaknesses of the proposal, and a rationale for their grades.