This page describes the sections required to be present in the PDF attachment, including templates, page limits, and sections. This attachment is written as a standalone file using STScI provided templates, and is uploaded through APT.

You are responsible for ensuring that your PDF upload does not include extraneous material (such as extra cover pages, team expertise statements, and backup material). Extraneous material that causes the proposal to exceed the page limits or violate requirements of Dual Anonymous Peer Review will lead to disqualification of the proposal without review.

Templates

Templates for HST Cycle 34 Proposal PDF attachments:

Note: the Word and LaTeX templates have intentionally different margins, to accommodate the same amount of text per page. See 'Page Limits' below for information on page limits.

As described in Guidelines and Checklist for Phase I, a Phase I proposal consists of a completed APT proposal form and an attached PDF file. The present page describes the items that must be addressed in the attached PDF file. Template files (above) are available in LaTeX and Microsoft Word for the creation of the PDF file. Your PDF Attachment should obey the page limits given in the next section, 'Page Limits'. 

Changes to the template formatting (including but not limited to font size, figure caption size, margins, line spacing, kerning, etc) will result in the proposal being disqualified. Changing the font style is strongly discouraged and may result in disqualification. Proposers may remove section headings that are not required or necessary for their proposals; section headings for required or necessary sections must remain (as formatted) in the proposal template.

The entire PDF attachment must be anonymized, in accordance with the guidelines specified in HST Anonymous Proposal Reviews. Phase I proposals must itemize and briefly justify the special requirements that will be implemented in Phase II, using the Phase I section designated for this purpose. 

Page Limits

The bulk of the PDF attachment should comprise of the "Scientific Justification" and the "Description of Observations" (for all GO, SNAP, DD programs) and/or "Analysis Plan" (for all AR and Calibration programs).

• Four (4) pages are allocated for the Very Small GO, Small GO, Snapshot, and Regular AR proposals
• Five (5) pages are allocated for Very Small GO+AR, Small GO+AR, Medium GO, and Medium GO+AR proposals
• Six (6) pages are allocated for Large GO, Large GO+AR, and Treasury GO proposals

One additional page is available for all of the following sections combined (if required): Special Requirements, Justify Duplications, and Coordinated Observations (including Joint Programs).  Please see below and/or HST Proposal Categories to determine whether any of these sections are required for your proposal.

Proposals which include additional GO flags or AR flags should consult the relevant sections of the HST Proposal Categories for guidance on determining the size category and hence page limits.

In relation to these page limits, note the following:

• Proposals that exceed the page limits will be subject to disqualification in the review process.
• Your PDF attachment must be prepared using the templates provided above.  Do not change the format of any of the templates provided by STScI, including by not limited to the font sizes, margins, line spacing ,etc. Proposals that change the formatting of the templates will be disqualified.
• There are no limits on the numbers of figures and tables in the PDF attachment, and they may be interspersed in the text. However, the total page limit must be observed.
• References should be listed at the end of the proposal and do not count against the page limits. There are no restrictions on how references should be formatted.
• All proposals must include a Scientific Justification. GO proposals must also include a Description of Observations. AR proposals must include an Analysis Plan; Analysis Plans for GO-AR proposals are optional. Headings may be deleted if they are not required and relevant for your proposal. See our template files for further details.
• While there are no specific page limits on the scientific justification, the strongest proposals will have a balance between scientific justification and the other required sections (such as the Description of Observations or the Analysis Plan) so that reviewers can accurately assess the merits and feasibility of a proposal using the selection criteria.

Table: Page Limits

¹ For Calibration GO, Joint HST-Chandra, Joint HST-JWST, Joint HST-XMM-Newton, Joint HST-NOIRLab, Joint HST-TESS, and Joint HST-NRAO Proposals, users should determine whether their proposal is Very Small, Small, Medium or Large based on the HST orbit request, and use the appropriate page limits. DD proposals are also required to follow these guidelines.

² Required sections include "Scientific Justification", "Description of Observations" and/or "Analysis Plan".  Please see below to determine whether your proposal requires a Description of Observations and/or Analysis Plan. References should be listed at the end of the proposal and do not count against the page limits.

³ The One (1) additional page is available only for the following sections (if they are needed): Special Requirements, Justify Duplications, and Coordinated Observations (including Joint Programs). Combined, these sections may take no more than 1 page and must not include text or supporting materials (e.g., figure, tables) from the required sections (Scientific Justification, Description of Observations, Analysis Plan).

Sections of the PDF Attachment

There are no specific page limits on the length of each section, however the total length of your PDF attachment must obey the page limit requirements given above.

For a checklist of items to complete when writing your HST proposal, see HST Proposal Checklist and HST Guidelines and Checklist for Phase I Proposal Preparation.

Scientific Justification

(This item is required for all proposals)

 This section should present a balanced discussion of background information, the program’s goals, its significance to astronomy in general, and its importance for the specific sub-field of astronomy it addresses. The proposal should address the selection criteria listed on the HST Proposal Selection Procedures.

Depending on the type of proposal, the following items should also be included:

• GO Treasury and Pure Parallel Proposals should address the value to the astronomical community of the data products that will be generated by the program.
• Proposals using ACS/WFC, WFC3/UVIS, or WFC3/IR for undithered imaging must explain why this strategy is needed for the scientific objectives; dithering is required to eliminate hot pixels and other detector artifacts that may compromise the archival value of the data.
• ACS/SBC, COS, and STIS/MAMA proposers must address the safety of their targets and fields with respect to the appropriate count rate limits of the photon-counting detectors (see Chapter 5 of the Primer and the COS, STIS, or ACS Instrument Handbooks).
• SNAP Proposals should provide a complete description of the target sample and address that as a SNAP only a fraction of the targets will likely be observed.
• AR Proposals should describe how the project improves upon or adds to the previous use of the data.
  • AR Theory Proposals should include a description of the scientific investigation that will be enabled by the successful completion of the program, and their relevance to HST.
  • AR Data Science Software Proposals should describe how the software packages that will be developed are relevant to and necessary for the reduction or interpretation of HST data.
• Calibration Proposals should describe what science will be enabled by the successful completion of the program, and how the currently supported core capabilities, their calibrations, and the existing pipeline or data reduction software are insufficient to meet the requirements of this type of science.

Description of the Observations 

(This item is required for all for GO and SNAP Proposals)

This section of the PDF file should be used to provide a short description of the proposed observations. It should explain the amount of exposure time and number of orbits requested (e.g., number of objects, examples of exposure-time calculations and orbit estimates for some typical observations). It should summarize your target acquisition strategies and durations where relevant. For CVZ targets, state the number of CVZ opportunities available in the cycle (use the Visit Planner to determine this number).

Discuss and justify any non-standard calibration requirements. You should estimate the number of orbits required for these special calibrations, and include them in the Observation Summary.

Depending on the type of proposal, the following items should also be included:

• Future-Cycle Proposals should provide summary information for the entire program, with a cycle-by-cycle breakdown of the requested orbits.  See the Future-Cycle Proposals section of the HST Proposal Categories page for more important instructions on how to enter future-cycle observations into APT.
• Treasury Proposals should discuss the data products that will be made available to the community, the method of dissemination, and a realistic time line. It is a requirement of Treasury Programs that data products be delivered to STScI in suitable digital formats for further dissemination via the HST Data Archive or related channels. Any required technical support from STScI and associated costs should be described in detail.
• Investigators submitting Large or Treasury Proposals should discuss how they have designed their program with regard to schedulability.
• Proposers of programs with timing constraints and timing relationships between observations should describe those constraints, including allowable flexibility.
• Proposers of programs containing large blocks of orbits at constrained orientation angles, such as mosaics and surveys, should describe those constraints and allowable flexibility.
• For ACS/WFC proposals, if proposers choose not to dither between exposures (e.g., using CR-SPLIT), that choice must be justified. Dithering between exposures mitigates the effects of hot pixels, cosmetic defects, and cosmic rays in combined images, and can improve sampling of the point-spread function. See Section 2.5 in the ACS IHB for more information.
• Calibration Proposals should present a detailed justification of how they will achieve the goals of the program, and if applicable, a description of the conditions under which these goals will be achieved.
• Calibration Proposals should discuss what documentation, and data products and/or software will be made available to STScI to support future observing programs.
• Bright object protection information sufficient to establish the safety of any proposed measurements which utilize instruments subject to health and safety concerns. Programs that do not contain this information may be subject to cancellation.

Analysis Plan

(This item is required only for all AR Proposals, Theory Proposals, GO Calibration Proposals, and is optional for Combined GO-Archival Proposals.)

All AR and GO Calibration Proposals should provide a detailed data analysis plan and describe the datasets that will be analyzed. The plan should include a brief summary of the likely scale of the proposed program, including the number of personnel and associated work effort while still following the HST Anonymous Proposal Review (DAPR) guidelines. Do not provide details like the career stages of the team as this would violate DAPR. AR funding becomes available within 30 days of receipt of the grant PI notification letter. 

Theory Proposals should discuss the types of HST data that will benefit from the proposed investigation, and references to specific data sets in the HST Data Archive should be given where possible. They should also describe how the results of the theoretical investigation will be made available to the astronomical community, and on what timescale the results are expected.

Calibration Proposals should discuss what documentation, and data products and/or software will be made available to STScI to support future observing programs. Proposers should explain how their programs complement ongoing calibration efforts by the instrument groups. They must contact the relevant groups 14 days before the deadline to ensure that efforts are not duplicated.

For Combined GO-Archival Proposals, this information may be included as part of the Description of Observations, or as a separate Analysis Plan.

Special Requirements, including Scheduling Requirements

(This item only applies to GO and SNAP proposals.)

Special requirements include:

• For Target-of-Opportunity (ToO) observations, estimate the probability of occurrence during The page 2026-01-12_13-21-15_.Hubble Space Telescope Call for Proposals for Cycle 34 v34 was not found  -- Please check/update the page name used in the MultiExcerpt-Include macro, specify whether future-cycle status is requested, identify whether the ToOs are disruptive or non-disruptive, and state clearly how soon HST must begin observing after the formal activation.
• CVZ observations.
• Time-critical observations.
• Early acquisition observations.
• Coordinated Parallel observations.
• Target Acquisitions that use 'Save Offset' and 'Use Offset'
• Scheduling of STIS/MAMA and STIS/CCD observations (other than target acquisitions) in the same visit.
• Requests for expedited data access.
• Other special scheduling requirements (e.g., requests for non-SAA impacted observations, roll-angle constraints, SHADOW, LOW SKY, etc.).
• Other special requirements (e.g. PCS MODE, GUID TOL, DROP TO GYRO, CVZ, ON-HOLD, ORIENT (ORIENT TO, ORIENT FROM, SAME ORIENT), AFTER, BEFORE, BETWEEN, GROUP WITHIN, SEQ WITHIN, PERIOD, VISIBILITY INTERVAL CORON, SEQ-NON-INT)
• Observing bright targets with COS with exposure times that exceed the maximum achievable SNR in an orbit due to fixed pattern noise for a given Grating/FP-POS comibnation (link to HST obs types section/Restrictions on COS observations.)
• For observations in support of another NASA mission, proposers should identify the mission, describe how the HST observations complement the core mission science and indicate whether any coordination is required.
• Explicitly describe and justify any scheduling requirements requiring more than 6 consecutive orbits to be scheduled together. For more information see HST Proposal Implementation and Execution.
• Successful HST proposers will be eligible to apply for NASA High-End Computing (HEC) Time. If you intend to apply for HEC time, please request it here.

If applicable, discuss the need for a non-default proprietary period request.

Coordinated Observations

(This item only applies to GO Proposals.)

If you have plans for conducting coordinated observations with other facilities that affect the HST scheduling, please describe them here (examples are coordinated or simultaneous observations with other spacecraft or ground-based observatories). Describe how those observations will affect the scheduling.

If you have plans for supporting observations that do not affect HST scheduling, then do not describe them here. If they improve your science case, then describe them in the ‘Scientific Justification’ section of the proposal.

Joint HST-Chandra Observations

Proposers requesting joint HST-Chandra observations must provide a full and comprehensive technical justification for the Chandra portion of their program. This justification must include:

• the choice of instrument (and grating, if used),
• the requested exposure time, justification for the exposure time, target count rate(s) and assumptions made in its determination,
• information on whether the observations are time-critical; indicate whether the observations must be coordinated in a way that affects the scheduling (of either Chandra or HST observations),
• the exposure mode and chip selection (ACIS) or instrument configuration (HRC),
• information about nearby bright sources that may lie in the field of view,
• a demonstration that telemetry limits will not be violated,
• a description of how pile-up effects will be minimized (ACIS only).

Proposers should note the current restrictions on observing time as a function of pitch angle of the satellite. Refer to the Chandra Proposers’ Observatory Guide for detailed information. Proposers should check the pitch angles of their targets and be sure that any constraints they request do not render the proposed observation infeasible.

The following list on considerations will help a proposer determine the feasibility of their Chandra observations:

1. Chandra estimates the difficulty of observing a given target as Resource Cost (RC). Every non-TOO proposal requesting joint Chandra time should use the RC calculator (https://cxc.harvard.edu/toolkit/rccalc.jsp) to determine the RC value for their observation configuration, which includes target coordinates, instrument set-up, and any constraints required to achieve the science, including coordination with joint facilities. The proposer should provide the total RC for their requested observations in the body of the science justification. Nominal RC values are 1.6 RC units per kilosecond, factors well above this should be carefully justified. Please read the “Resource Cost” section in the Chandra Call for Proposals (CfP) for detailed information.
2. The amount of Chandra exposure time available for High Ecliptic Latitude (HEL) targets with |b_Ecliptic| > 55deg is limited. Very long exposures for HEL targets will incur a higher RC and targets may be rejected for exceeding Cycle-wide HEL time limits.  When proposing HEL targets, a proposer must explicitly note the requested amount of Chandra HEL time in the body of your science justification. Refer to section on HEL targets in the Chandra Call for Proposals (CfP) for detailed information.
3. Observations with the High Resolution Camera (HRC) will be split based on operational limits that restrict observing to 14.5 ks segments with a minimum 30 ks buffer between subsequent HRC observations. Refer to section on HRC in the Chandra Call for Proposals (CfP) for detailed information.
4. The proposers must verify that Chandra will be able to acquire suitable star fields for a given target using the Star Checker tool (https://cxc.cfa.harvard.edu/toolkit/starchecker.jsp).

Technical documentation about Chandra is available from the Chandra X-ray Center (CXC) webpage, which also provides access to the Chandra Help Desk. The primary document is the Proposer’s Observatory Guide, available from the Chandra Proposal Information webpage. Full specification of approved observations will be requested during the Chandra Cycle 28 period when detailed feasibility checks will be made.

Proposers requesting joint HST-Chandra observations must specify whether they were awarded Chandra time in a previous Chandra or HST cycle for closely-related observations in the "Team Expertise" section of the proposal. In this section, proposers must also specify whether the team has submitted a proposal requesting similar observations (HST and/or Chandra) in response to any other proposal call.

Joint HST-JWST Observations

JWST Scientific and Technical Justification for Joint Programs

Proposers requesting joint HST-JWST observations must provide a JWST Scientific and Technical Justification to allow the HST Time Allocation Committee to evaluate the proposed JWST observations. The JWST Scientific and Technical Justification needs to describe the following aspects:            

• Description of how the observations contribute to the goals described in the scientific justification and quantitative estimates of the accuracy required to achieve key science goals. The JWST ETC generally provides sufficient information to determine the necessary exposure time.
• Justification of the selection of instruments, modes, exposure times, and any constraints.
• Special Observational Requirements (if any): Justify any special scheduling requirements on timing or orientation, including time-critical observations.
• Justification of Coordinated Parallels (if any): Proposals that include coordinated parallel observations should provide a scientific justification for and description of the parallel observations. It should be clearly indicated whether the parallel observations are essential to the interpretation of the primary observations or the science program as a whole, or whether they address partly or completely unrelated issues. The parallel observations are subject to scientific review, and can be rejected even if the primary observations are approved.
• Justification of Duplications (if any): as detailed in the JWST Duplicate Observations Policy. Any duplicate observations must be explicitly justified.

Observers should account for observatory and instrument overheads in their time request. The observations may also be visualized in Aladin to verify target coverage and any issues with bright stars or extended emission in the field of view. The requested JWST observations will be held to the same technical standards as they are for JWST proposals.

Submission of APT file and PDF attachment with an Extended JWST Scientific and Technical Justification for Joint Programs

Proposers must provide STScI with an APT file that provides a full description of the proposed JWST observations. This is to allow STScI staff to conduct a technical review. This is required for all submitted joint proposals. The APT file and associated technical information must be submitted no later than four weeks after the HST proposal deadline has passed. PIs will be contacted to remind them to send this information along with instructions on how to submit it. The information is as follows:

• The APT file with the detailed observations. The proposal must have the same Title and Abstract as in the Partner Observatory proposal, adding the Partner Observatory ID to the Abstract so it can be matched to the Partner Observatory program. Proposers should make sure that they the mark the APT coversheet using the menu that expand out corresponding to "Coordinated telescopes", providing all the requested information.  Starting in JWST Cycle 4, APT has a new flag on the same line as the proposal Category: when JWST is secondary, you are prompted to identify the primary observatory (HST) and provide the HST proposal ID. 
• A PDF attachment with an Extended JWST Scientific and Technical Justification for Joint Programs (found on Submission Process for Joint JWST Proposals where the Partner Observatory is Prime). The latter should be provided using the template provided on Submission Process for Joint JWST Proposals where the Partner Observatory is Prime.  This text expands upon the information included in the HST proposal and is required for the technical review. Proposers should not attach the entire HST proposal to their submission, only the PDF attachment and the Extended JWST Scientific and Technical Justification for Joint Program

Further information regarding the submission process for joint JWST proposals where the partner observatory is prime may be found here. Technical documentation about JWST is available online.

Joint HST-NOIRLab Observations

Proposers requesting joint HST-NOIRLab observations must provide a full and comprehensive scientific and technical justification for the NOIRLab portion of their program, including:

• the telescope(s) and instrument(s) on which time is requested,
• the requested observing time per telescope/instrument, a specification of the number of nights for each semester during which time will be required, a breakdown into dark, grey and bright time, and an explanation of how the required exposure time was estimated, including information on filters, gratings, and observing conditions,
• information on whether the observations are time-critical, and whether the observations must be coordinated in a way that affects the scheduling (of either the NOIRLab or the HST observations),
• a description of any special scheduling or implementation requirements (e.g., optimum and acceptable dates).

Successful proposers will be required to provide this information in a NOIRLab Phase I proposal submitted through the standard NOIRLab process by the nominal deadline of October 2, 2026 for semester 2027A. For Gemini proposals, a Gemini PIT proposal must be submitted. For all other telescopes, the standard NOIRLab Time Allocation proposal form must be submitted. Detailed information for Gemini and other telescopes can be found in the NOIRLab Call for Proposals. Proposals not received by the deadline may not be scheduled for NOIRLab time. Successful proposers who receive time on Gemini Observatory will also have to prepare a Phase II proposal that includes a more detailed description of each observation. Submission instructions will be forthcoming following notification of the results of the HST review.

Technical documentation about the NOIRLab facilities is available from the NOIRLab webpage. Questions may be directed to the NOIRLab Proposal Help Desk by e-mail to proposal-help@noirlab.edu. NOIRLab will perform feasibility checks on any approved proposals.

Joint HST-NRAO Observations

Proposers requesting joint HST-NRAO observations must provide:

• the choice of NRAO telescope(s) (VLA, VLBA and/or GBT), and
• the total estimated NRAO observing time in hours.

NRAO plans to make up to 3% of VLA, VLBA, and GBT observing time available for this opportunity with a maximum of 5% in any array configuration and including an 18-month period close to the HST The page 2026-01-12_13-21-15_.Hubble Space Telescope Call for Proposals for Cycle 34 v34 was not found  -- Please check/update the page name used in the MultiExcerpt-Include macro such that all VLA configurations are available. A VLA configuration schedule is published at:

• https://science.nrao.edu/facilities/vla/proposing/configpropdeadlines

Detailed technical information concerning the NRAO telescopes can be found at:

• http://science.nrao.edu/facilities/vla
• http://science.nrao.edu/facilities/vlba
• https://greenbankobservatory.org/science/gbt-observers/

For the VLA, joint proposals may only use capabilities defined as “general observing” in the NRAO VLA Call for Proposals, released in July 2025. Technical questions about proposing or observing for NRAO telescopes (whose answers are not found in the above links) should be posted to the NRAO helpdesk.

If approved for NRAO time, successful PIs will be contacted by the NRAO Scheduling Officers (schedsoc@nrao.edu for the VLA/VLBA and gbtime@nrao.edu for the GBT). The successful PIs for GBT projects will be responsible for organizing the project's information in the GBT Dynamic Scheduling Software and for carrying out their GBT observations. For the VLA and VLBA, the PIs will be responsible for submitting scheduling blocks to the telescopes' dynamic queues. Projects requiring simultaneous HST-NRAO observations will be performed on fixed dates. In conjunction with HST, the NRAO Scheduling Officers will inform the PIs of those dates and times, and the PIs will be responsible for submitting scheduling blocks two weeks prior to the observations.

Joint HST-TESS Observations

Proposers requesting joint HST-TESS observations must provide a full and comprehensive technical justification for the TESS portion of their program, including:

• the suitability of using TESS survey data products,
• a justification for the selection and number of targets,
• and justification that the 120-second or 20-second cadence will sufficiently meet their science goals.

Technical information on the TESS General Investigator (GI) Program is available on the TESS GI website. 

Joint HST/XMM-Newton Observations

Proposers requesting joint HST/XMM-Newton observations must provide a full and comprehensive technical justification for the XMM-Newton portion of their program, including

• the choice of prime instrument,
• the requested exposure time, justification for the exposure time, target count rates, and assumptions made in their determination,
• information on whether the observations are time-critical.

Technical documentation about XMM-Newton is available from the XMM-Newton webpage.

Justify Duplications

(This item applies to GO Proposals.)

Justify, on a target-by-target basis, any potential duplication with previously accepted observing programs. Use the ‘Duplication’ checkbox in the Observation Summary to identify the duplicating observations. See Data Rights and Duplications for policies on duplications and the procedure for how to check for duplications..

Next: HST Proposal Implementation and Execution