This page describes the process by which proposals go from being accepted to being implemented and executed, including technical reviews and scheduling, along with an overview of how to access the data once it has been observed by the telescope.

Notification

The review panels and the TAC will meet June 23 - July 3, 2025. Electronic notification of the outcome of the Phase I selection process are expected to be sent to all proposers in late July 2025.

Phase II Submission

Successful GO proposers must submit a Phase II proposal providing complete details of the proposed observations. Detailed instructions on the preparation of Phase II proposals are provided in the STScI Phase II documentation. Complete observational details must be provided by the Phase II submission deadline. Accurate target coordinates must also be supplied at this time, except for certain Targets of Opportunity or in other exceptional circumstances, provided that those circumstances were described clearly in the Phase I proposal.

Failure to submit a Phase II proposal by the required deadline will result in loss of the time allocation. Program changes after the Phase II deadline are allowed as described in the Policy Document for the Telescope Time Review Board (TTRB), available on the Web.

Proposers are not allowed to make changes to the list of investigators (PI and Co-Is) after acceptance of the Phase I proposal, unless permission is granted by the Hubble Science Policies Group – such requests should be submitted via the HST Help Desk and must be well-justified.

Program Coordinator and Contact Scientist Support 

Accepted observing programs are assigned a Program Coordinator (PC), whose role is to help the observer deliver a Phase II program that is syntactically correct and will schedule successfully on the telescope.

Certain types of programs (Large, Treasury, DD, ToO, moving-target, WFC3, or those using complicated observing strategies or require bright-object checking) will also be assigned a Contact Scientist (CS). The role of the CS is to provide advice on observing strategies, and to answer specific questions about instrument performance. Observers who are not automatically assigned a CS may request one. The CS is generally an Instrument Scientist involved in the calibration and characterization of the primary instrument used in the observer’s program. The role of the CS ceases at program execution. Please contact the STScI Help Desk for post-execution assistance.

Duplication Checking

Some computer-aided duplication checks are carried out in Phase II, in part by STScI and also by observers who wish to check whether any of their own observations are being duplicated. Any duplications found that were not justified explicitly in the Phase I proposal and recommended by the review panels or the TAC will be disallowed. No compensatory observing time will be allowed and the observing time will be removed from the allocation.

Technical Review

In Phase I STScI does not perform technical reviews for the majority of the submitted proposals. In Phase II a technical feasibility review is performed and special attention is given to observations/modes that may damage the instrument, are particularly complex, are recent/experimental, are human- and technical resource-intensive, or require the use of limited resources (such as ToO Programs). All technically challenging or infeasible observations are flagged. It is the responsibility of the PI to ensure that none of the observations violate bright-object constraints.

Proposal Scheduling

After the technical review, observations determined to be feasible are scheduled for execution. The scheduling process attempts to optimize the overall HST efficiency. STScI will not contemplate requests to advance or postpone the scheduling of individual programs based on other considerations, with the possible exception of compelling scientific arguments.

Program Completion Limit

STScI aims to complete approved observing programs in a timely manner to ensure that scientific impact is maximised. Under nominal operations, all GO programs must be completed in N+1 cycles, when N is the number of cycles requested in the Phase I submission. To ensure completion within N+1 cycles, observers are advised to be as flexible as possible within their timing constraints.

Proposers have the opportunity to request extension of the N+1 limit by 1 year once only (taking the limit to N+2 cycles). Requests should be submitted to the Telescope Time Review Board and must be scientifically justified. Further extensions will only be considered in exceptional circumstances, such as when observations are not possible due to a telescope safing event, or other deviation from nominal operations.

Long Consecutive-Orbit Blocks

Observers are strongly encouraged to craft their programs in blocks of 6 consecutive orbits or less. If your science requires more than 6 consecutive orbits scheduled continuously, the program will proceed under a shared risk between STScI and the observer. Specifically, if the planning & scheduling team can reasonably schedule your program in this manner, it will be attempted, but if there is a problem, any subsequent attempt must be done in a series of 6 orbits or less. In the Special Requirements section of your Phase I proposal, you must justify the use of a longer series of consecutive orbits, and explain the impact to your science goals if your observations cannot be scheduled in that manner, either on the 1st attempt or in the event of failure.

Unschedulable or Infeasible Programs

Proposers should be aware that after acceptance of a proposal, the actual execution of the observations may in some cases prove impossible. Possible reasons include:

• The accepted observation may be found to be infeasible or extremely difficult for technical reasons only after receipt of the Phase II information; ToO and time-critical observations can be particularly complex to plan and execute, and will be completed only to the extent that circumstances allow.
• The observing mode or instrument selected may not be operational.
• Suitable guide stars or scheduling opportunities may not exist.
• Programs requiring blocks of more than 6 consecutive orbits must be explicitly justified in the Phase I “Description of Observations” and will proceed under a shared risk between STScI and the observer.  If a program can be reasonably scheduled in this manner, it will be attempted, but if there is a problem, any subsequent attempt must be done in a series of 6 orbits or less.
• Programs with only one scheduling opportunity per year (i.e., falling in one of the weekly HST schedules) will proceed under a shared risk between STScI and the observer, and in the event of observation failure, any attempted repeat might not be granted without relaxed scheduling constraints.

Note: All HST observations are accepted with the understanding that there can be no guarantee that the data will actually be obtained.

The STScI Director reserves the right to disallow at any time any or all observations of an approved program if it is demonstrated that incorrect or incomplete information was provided in the Phase I proposal that may have significantly influenced the approval recommendation by the review panels or the TAC.

Access to Data Products

Data products are available from the HST Data Archive. Enhanced products for non-exclusive access observations may also be available from the Hubble Legacy Archive (HLA). Any processing or scientific analysis of the data beyond the standard pipeline calibrations performed by STScI is the responsibility of the observer.

Observers retrieve their data directly from the Data Archive through the MAST website. In order to retrieve exclusive access data from the Archive, proposal PIs and those designated by them must use their Single Sign-On (SSO) account. Proposers are encouraged to consult the current Archive Account web page to determine if they already have an SSO account, or see the SSO FAQ for further information. HST data normally become non-exclusive access six months after they are taken, though this depends on the proposal type.

The HST Data Handbook describes the data produced by the instruments. stenv has information about how to install the latest software to calibrate and analyze HST data.

• Observers with questions about the retrieval of their data should contact the Archive Help Desk.
• Observers with questions about the analysis and calibration of their data should contact the STScI Help Desk.

Archival Research Support

STScI provides limited assistance in the reduction and analysis of archived data. Although a Contact Scientist is not usually assigned to a funded AR Program, STScI will do so upon request. The CS will serve as a single point of contact to help resolve calibration issues. Proposers should plan to conduct the bulk of their archival research at their home institutions, and should request funds accordingly. Limited resources preclude extensive assistance in the reduction and analysis of data by non-funded archival researchers.

Archival projects utilizing the Hubble Source Catalog (HSC) will be assigned a contact scientist. Proposers interested in the viability of potential projects should contact HSC personnel via the archive help desk.

• Archival Researchers with questions about the retrieval of data should contact the Archive Help Desk.
• Archival Researchers with questions about the analysis and calibration of data should contact the STScI Help Desk.

NASA High-End Computing Program

NASA's High-End Computing (HEC) Program maintains a comprehensive set of resources and services for the agency's four Mission Directorates, the NASA Engineering and Safety Center, external collaborators, and the nation. By closely partnering with each Mission Directorate, the HEC Program addresses their specific resource requirements and user needs. Mission support includes ensuring reliable remote access for a user community spread broadly across NASA centers and partner organizations nationwide.

Successful HST proposers will be eligible to apply for NASA High-End Computing Time. More information on NASA HEC Program can be found on https://www.hec.nasa.gov.

Failed Observations

HST observations fail at a rate of a few percent. Some of these failures result from occasional guide stars that cannot be acquired, or from an instrument anomaly, or the telescope happening to be in a safe mode when a particular observation was scheduled. Such failures, which are obviously beyond the proposer’s control, can usually be scheduled for a repeat observation. When this is the case, the proposer receives a notice of the failure and information on obtaining a repeat observation.

A smaller fraction of failures do not have a clear cause, and may not be evident from our internal reviews of data quality. If you believe your observation has failed or is seriously degraded, then you may request a repeat for your program using the Hubble Observation Problem Report (HOPR) website available from the HST Program Information Page. The HOPR must be filed within 90 days after the observations are taken. In cases where the failure resulted from proposer error (e.g., incorrect target coordinates), a repeat will not be granted. In cases where the failure was a result of incorrect instrument performance, or incorrect information provided by STScI, a repeat is usually granted.

The policies that apply to failures and repeats are described in the Policy Document for the Telescope Time Review Board (TTRB). We wish to emphasize in particular: 

• Standard policy dictates that if observations are to be repeated, the degraded/failed observations will be made public.
• If an observer has obtained more than 90% of the planned observations and the missing data are not uniquely important, then a repeat is not normally granted.
• If a Pure Parallel exposure fails during execution it may be repeated with suitable justification and if a suitable parallel scheduling opportunity is available.
• Observations taken using Available-but-Unsupported modes that fail due to the use of the unsupported mode will not normally be repeated.
• Observations that are lost due to bright-object violations will not be repeated.
• Observations that have partially or completely missing data due to a failure to successfully retrieve the data from the spacecraft may be repeated with suitable justification. PIs must describe how their data have been affected.

Publication of HST Results

It is expected that the results of HST observations and Archival Research will be published in the scientific literature. All refereed publications based on HST data must carry the following footnote (with the first phrase in brackets included in the case of Archival Research):

“Based on observations made with the NASA/ESA Hubble Space Telescope, obtained [from the Data Archive] at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. These observations are associated with program # ____.”

If the research was supported by a grant from STScI, the publication should also carry the following acknowledgment at the end of the text:

“Support for program #____ was provided by NASA through a grant from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555.”

The relevant program ID should be entered in these phrases where indicated.

Dissemination of HST Results

We remind HST observers that they have a responsibility to share interesting results of their HST investigations with the public at large. The Office of Public Outreach (OPO) of STScI is available to help observers use their HST data for public information and education purposes (see Appendix A for contact information). Proposers can find guidelines and examples of these activities on the OPO webpage that discusses Scientist Resources.

NASA's policy is to distribute all news fairly and equitably, giving wide access to scientific findings, and enabling their broad impact. Both STScI and NASA can provide considerable resources to support the creation and distribution of press releases, and investigators are strongly encouraged to make use of those resources. The STScI Public Outreach news officers should be made aware of potentially newsworthy science results by principal investigators before the acceptance of HST publications, with sufficient time for consideration of a news release. STScI will only undertake a press release if the results are not circulated prematurely on social media or through an uncoordinated release from another entity.

Next: HST Grant Funding and Budget Submissions