HST Proposal Submission Policies

An overview of the policies regarding HST proposals, including deadlines, funding eligibility, and the definitions of the roles of principal investigator and co-investigator.

The Proposal Process: Phase I and Phase II

STScI manages the review of HST proposals in two phases. In Phase I, proposers submit a scientific justification and observation summary for peer review. The review panels and the Telescope Allocation Committee (TAC) recommend a list of proposals to the STScI Director for preliminary approval and implementation (see HST Proposal Selection Procedures). This Call for Proposals focuses on Phase I policies and procedures. Separate documentation is available for Phase II.

In Phase II, investigators with approved Phase I proposals must provide complete details of the observations in their proposed observing program. This allows STScI to conduct a technical feasibility review, and to schedule and obtain the actual observations. Programs are not approved fully until after submission of an acceptable Phase II program.

Eligible investigators who request funding must submit detailed budgets (see HST Grant Funding and Budget Submissions).

Proposal Deadlines

Cycle 31 has the following deadlines:

  • Phase I proposals are due Wednesday May 24, 2023 at 8:00pm EDT
  • Phase II proposals are due September 14, 2023
  • Budget proposals are due October 5, 2023 at 5:00pm EDT

Who May Submit 

Scientists of any nationality or affiliation may submit an HST proposal. Endorsement signatures are not required for Phase I observing proposals (unless required by the regulations of the proposing institution).

Principal Investigator and Co-Investigators

Each proposal must have a Principal Investigator (PI), who is responsible for the scientific conduct of the project. A Co-PI option is also available, allowing two or more proposers to share the scientific responsibility of the project. Any other individuals who are actively involved in the proposal should be listed as Co-Investigators (Co-Is). The proposal itself may be submitted through APT by either the PI or a Co-I.

Proposals by non-U.S. PIs that have one or more U.S. Co-Is must designate one of the U.S. Co-Is as the Administrative PI (Admin PI). This person will have overall oversight and responsibility for the budget submissions of the U.S. Co-Is in Phase II (see Grant Funding for funding eligibility requirements). All proposals have the option of designating a Contact Co-I, who will serve as the contact person for that proposal. The PI remains responsible for oversight of the proposal.

All proposals are reviewed without regard to the nationalities or affiliations of the investigators.

ESA Scientists

An agreement between NASA and ESA states that a minimum of 15% of HST observing time (on average over the lifetime of the HST project) will be allocated to scientists from ESA member states. It is anticipated that this requirement will continue to be satisfied via the normal selection process, as it has been in previous cycles. ESA scientists will be identified automatically by APT based on the institution selected.

Student PIs

Observing proposals from student PIs will be considered. 

Institutional Endorsement

STScI does not require the signature of an Authorizing Official (AO) on GO/AR Proposals in Phase I. However, some institutions do require AO approval of all submitted proposals. It is the responsibility of each PI to follow all applicable institutional policies concerning the submission of proposals.


Subject to availability of funds from NASA, STScI will provide financial support for U.S. PIs and Co-Is of approved Cycle 31 programs. Budgets are not due in Phase I, but are required by the budget submission deadline from successful proposers. Details of the STScI Funding Policies are outlined in HST Grant Funding and Budget Submissions.

NASA’s Science Mission Directorate has restructured its education program, and as a result STScI no longer solicits Education/Public Outreach (E/PO) proposals. We will keep the HST Cycle E/PO community informed of future opportunities should they become available.

ESA does not fund HST research programs. Therefore, successful ESA member-state proposers should seek any necessary resources from their respective home institutions or national funding agencies.

Proposal Confidentiality

Proposals submitted to STScI will be kept confidential to the extent allowed by the review process described in HST Proposal Selection Procedures. For accepted proposals, the scientific justification section of the proposal remains confidential, but other sections become publicly accessible, including PI and Co-I names, project titles, abstracts, description of observations, special scheduling requirements, and details of all targets and exposures. Phase II programs submitted for approved proposals become publicly accessible in their entirety.

Next: HST Proposal Categories