HST Cycle 27 Proposal Categories
This page describes all proposal types in detail. Proposals can be General Observer (GO) or Archival (AR) in nature, and can be joint projects with other observatories. STScI also accepts Mid-cycle and Director's Discretionary time proposals.
Overview of Proposal Categories
HST observations can be requested with a General Observer (GO) or a Snapshot (SNAP) Proposal. A GO Proposal in Cycle 27 can be Small, Medium, Large, Calibration, Long-Term, or Treasury. Funding for projects that do not require new HST observations can be requested with an Archival Research (AR) Proposal. An AR proposal can be a Regular AR, Legacy AR, or Theory Proposal. AR proposals can also take advantage of Cloud Computation for compute-intensive analyses.
Proposals can request observing time on Chandra, XMM-Newton, TESS, NOAO telescopes, and NRAO facilities in conjunction with requests for HST observations. Mid-cycle proposals may be submitted at any time, those recived prior to September 27, 2019 will receive consideration for execution begining in October 2019. Investigators may also request Director’s Discretionary (DD) time at any time for unanticipated and scientifically compelling astronomical observations.
General Observer (GO) Proposals
A GO Proposal may be submitted for any amount of observing time, counted in terms of HST Orbits. The proposal categories are intended to ensure that compelling science programs of different sizes have comparable success rates.
GO Proposals are classified as Small (1-34 orbits), Medium (35-74 orbits), and Large (75 or more orbits). The HST Primer's Orbit Calculation Overview page describes how the required number of orbits can be calculated for a particular set of observations. Proposals in each of these categories can request observing time in future cycles when this is scientifically justified (long-term proposals). The additional category of Treasury Proposals is designed to stimulate certain types of ambitious and innovative proposals that may not naturally fit into the Small, Medium, or Large Proposal categories.
Submitters of Medium, Large, and Treasury Proposals should note that all HST observations are accepted with the understanding that the timescale on which the observations will actually be obtained will depend on scheduling opportunities and demands on HST resources. Experience has shown that programs with scheduling constraints may require execution over an extended period.
In general, proposals are either accepted or rejected in their entirety. Accordingly, you are urged to request the actual number of orbits required to achieve your science goals.
For accepted proposals, a Program Management Plan is required with the budget proposal submissions.
Small GO Proposals
Small GO Proposals are those that request between 1 and 34 orbits.
It is anticipated that up to 1700 orbits in total will be available for the allocation of Small Proposals in Cycle 27. A total of 2740 orbits in this category were allocated for execution in Cycles 25 and 26 combined.
Medium GO Proposals
Medium GO Proposals are those that request between 35 and 74 orbits.
Medium proposals will be reviewed by the panels and ranked together scientifically with the Small Proposals, but the panels will not be charged for them. Each panel will have a specific quota dependent on the Medium Proposal pressure in the panel. It is anticipated that up to 700 orbits in total will be available for the allocation to Medium Proposals in Cycle 27. This nominal allocation is consistent with previous cycles, when in 14 Medium Proposals were selected totaling 686 orbits in Cycle 24, 18 were selected in Cycle 25 totaling 868 orbits, and 26 were selected in Δ Cycle 26 totaling 814 orbits. However, the TAC has the ability to recommend an increase or decrease in the Medium proposal allotment to balance the over-subscription between Small, Medium, and Large Proposals categories.
Large GO Proposals
Large GO Proposals are those that request 75 orbits or more.
Large Programs should lead to a clear advance in our understanding in an important area of astronomy. They must use the unique capabilities of HST to address scientific questions in a comprehensive approach that is not possible in smaller time allocations. Selection of a Large Proposal for implementation does not rule out acceptance of Medium Proposals to do similar science, but target duplication and overall program balance will be considered.
Approximately 1000 orbits will be available to new Large and Treasury Proposals in Cycle 27. Descriptions of previous programs are available on the Treasury, Archival Legacy and Large (TALL) Programs webpage. Most Large Proposals accepted in previous cycles were allocated between 100 and 150 orbits, although larger orbit requests are welcome if scientifically justified.
Data taken for all Large Programs have no exclusive access period as a default. Proposers may request a exclusive access period, and that request should be justified in the ‘Special Requirements’ section of the proposal. Such a request will be subject to review by the TAC.
Investigators submitting Large Proposals should consult the Large Program Scheduling User Information Report (.pdf) and the HST Orbital Viewing and Schedulability page. These documents contain necessary information for developing a Large Program that is feasible with respect to HST orbit scheduling. Proposers should include additional technical detail on the scheduling aspects of their program in the ‘Description of Observations’ section. The shorter orbital visibility will be enforced in Phase II for each approved Large Program.
Long-Term GO Proposals
Medium, Large, and Treasury GO Proposals may request HST observing time in more than one cycle if a clear scientific case is made.
Long-Term Proposals must be limited to cases where long-baseline, multi-epoch observations are clearly required to optimize the scientific return of the project.
Long-Term Proposals require a long time baseline, but not necessarily a large number of HST orbits, in order to achieve their science goals. Examples include astrometric observations or long-term monitoring of variable stars or active galactic nuclei.
You may request time in up to three observing cycles (27, 28, and 29). Long-Term Proposals should describe the entire requested program and provide a cycle-by-cycle breakdown of the number of orbits requested. The Cycle 27 review panels and TAC will only be able to award a limited amount of time in future cycles, so a detailed scientific justification for allocating time beyond Cycle 27 must be presented. Scheduling concerns are not a sufficient justification. The sum of all orbits requested in Cycles 27, 28, and 29 determines whether a Long-Term Proposal is Medium or Large (or counted against the Cycle 27 orbit pool in the panels). Target-of-Opportunity Proposals are eligible to be Long-Term if certain conditions are met.
GOs with approved Long-Term Proposals need not submit continuation proposals in the subsequent cycles (and hence, GOs who had Cycle 27 time approved in Cycles 25 or 26 do not have to submit a Phase I continuation proposal, although a new Phase II and budget submission will be required for each cycle).
Budget requests submitted for the first cycle of a Long-Term Proposal should include costs only for the effort to reduce and analyze the data obtained in the first cycle. Separate budget proposals are required in each subsequent cycle; see Grant Funding and Budget Submissions.
Treasury GO Proposal
Treasury Proposals are those designed to create datasets of lasting value to the HST project that should be obtained before HST ceases operations. A Treasury Program is defined by the following characteristics:
The program should focus on the potential to solve multiple scientific problems with a single, coherent dataset. It should enable a variety of compelling scientific investigations.
Enhanced data products are desirable to add value to the data. Examples are reduced images, object catalogs, or collaborative observations on other facilities (for which funding can be provided). Funding for the proposed data products will depend on their timely availability, as negotiated with the STScI Director. They should be delivered to STScI in suitable digital formats for further dissemination via the HST Data Archive or related channels.
Data taken under a Treasury Program will usually have no exclusive access period (see Data Rights), although brief exclusive access periods may be requested if that will enhance the public data value. Such requests are subject to TAC approval.
The following additional characteristics are particularly encouraged:
Development of new techniques for observing or data reduction.
Creation and dissemination of tools (software, web interfaces, model, etc.) for the scientific community to work with the data products.
The emphasis in Cycle 27 remains on observations whose value is maximal if taken soon. However, Treasury Proposals may request observing time to be distributed in future cycles if scientifically required (similar to the situation for Medium and Large Long-Term GO Proposals). In this cycle approximately 1000 orbits of HST time will be available for new Large and Treasury Proposals. Descriptions of previous Treasury Programs are available on the HST Treasury, Archival Legacy and Large Programs webpage.
Treasury Programs will be selected by the TAC as part of the normal peer review process. Successful proposals will be reviewed by STScI to ensure observing efficiency. STScI resources may be made available to approved Treasury Programs by decision of the STScI Director. In particular, some programs require substantial pipeline processing of their data to generate the final products. Examples are large mosaics for surveys, or co-additions of many exposures in deep fields.
Investigators submitting Treasury Proposals must select the Treasury Program flag on the APT cover page, use an orbital visibility that enhances schedulability (use the Increase Schedule Flexibility flag in APT), and include additional technical details on the scheduling aspects of their program in the “Description of the Observations” section. Note that a proposal can be both Large and Treasury. Submitters of Large Treasury Proposals should consult the Large Program User Information Report, which can be found on the HST Documents webpage (linked from the Cycle 27 Announcement webpage.) This document contains a discussion of the issues surrounding Large Program scheduling.
Treasury Proposals should be identified in the 'Special Proposal Types' section of the proposal.
The Scientific Justification section of the proposal (see HST Cycle 27 Preparation of the PDF Attachment) should include a description of the scientific investigations that will be enabled by the final data products, and their importance. The Description of the Observations section of the proposal should not only describe the proposed observations and plans for data analysis, but should also describe the data products that will be made available to STScI and the community, the method of dissemination, and a realistic time line.
Detailed Program Management Plans should be submitted with the budget submissions.
Calibration GO proposals
HST is a complex observatory, with many possible combinations of observing modes and spectral elements on each instrument. Calibrations and calibration software are maintained by STScI for the most important and most used configurations. However, STScI does not have the resources to calibrate fully all potential capabilities of all instruments. On the other hand, the astronomical community has expressed interest in receiving support to perform calibrations for certain uncalibrated or poorly calibrated modes, or to develop specialized software for certain HST calibration and data reduction tasks. In recognition of this, STScI is encouraging outside users to submit Calibration Proposals, which aim to fill in some of the gaps in our coverage of the calibration of HST and its instruments.
Calibration Proposals must be identified in the ‘Special Proposal Types’ section of the proposal.
Calibration Proposals should not be linked explicitly to a specific science program, but should provide a calibration or calibration software that can be used by the community for existing or future programs.
Users submitting Calibration Proposals must contact the appropriate instrument group to discuss their program prior to submission.
Successful proposers will be required to deliver documentation, data products, and software products (depending on the case) to STScI to support future observing programs or archival research. Funding is available to support Calibration Proposals in the same manner as for normal science programs, with the exception that scientists affiliated with STScI are not eligible for any funding to support their role (as PI or Co-I) in a Calibration Proposal.
Calibration Proposals will be reviewed internally at STScI by the Instruments Division. The internal review will provide the TAC with an assessment of the feasibility of the proposal, how the proposal complements or extends the existing calibration program, and the type of science impacted by the proposed calibrations. Proposers should summarize the relevance and overall scientific utility of the calibration techniques and products described in their proposal.
Proposed science programs that have special calibration requirements should not be submitted as Calibration Proposals, and should instead be submitted according to its size categorization (Small, Medium, or Large). Such a proposal should describe the necessary calibration observations in the PDF attachment (see HST Cycle 27 Preparation of the PDF Attachment).
Investigators interested in the submission of a Calibration Proposal are encouraged to study the Instrument Handbooks to determine the level at which STScI provides calibration and characterization. Examples of the kinds of topics that have been addressed by previous Calibration Programs include:
- Calibration of faint photometric standards for ACS and WFC3.
- ACS photometric zero point verification.
- Calibration of the ACS emission line filters
See the HST Scientific Instruments webpage for a complete description of the instrument calibration plans and accuracies, and for other potential topics.
The data obtained for a GO Calibration Proposal will nominally be non-exclusive access, as is the case for regular calibration observations. Proposers may request a exclusive access period (which should be explained in the ‘Special Requirements’ section of the proposal), but such a request will be subject to panel and TAC review and will be granted only in exceptional circumstances. Calibration Proposals may also be submitted as Snapshot Proposals or Archival Proposals. AR Proposals are appropriate in cases where the necessary data have already been taken, or for programs that do not require specific data but aim to develop specialized software for certain HST calibration and data reduction tasks.
Snapshot (SNAP) Proposals
Snapshot (SNAP) Programs consist of separate, relatively short observations with typical durations of 45 minutes or less (including all overheads and the final data dump). During the process of optimizing the HST observing schedule, the scheduling algorithm occasionally finds short time intervals where it is impossible to schedule any exposures from the pool of accepted GO Programs. In order to make the HST schedule more efficient, STScI has developed the capability to insert Snapshot exposures of objects selected from a large list of available candidates. In Cycle 27, up to 1000 SNAP observations may be accepted to provide a sufficiently large pool of candidates.
Characteristics of SNAPs
Accepted SNAP Programs are allocated a specific number of targets. However, there is no guarantee that any individual target will be observed, because SNAPs are placed on the schedule only after the observing sequence has been determined for the higher-priority GO targets. The number of observations actually executed depends on the availability of appropriate schedule gaps. In general, only a fraction of the allocated targets will be observed. Unlike GO Programs, SNAP Programs cannot request observing time in future cycles. However, un-executed SNAPs remain active at decreased priority for a second cycle.
There is no commitment on the part of STScI to obtain any specific completion factor for SNAP Programs.
The average expected completion rate for SNAP Programs is ~33%. However, the actual completion rates for individual programs vary, depending on several factors including the number of targets and the average duration and sky distribution of the observations. In general, shorter-duration and well-distributed SNAP observations have a higher number of scheduling opportunities and a higher chance of being executed than longer duration and/or spatially clustered SNAP observations.
Investigators interested in proposing for SNAPs are encouraged to consult the SNAP User Information Report, which contains details on how SNAPs are scheduled, the rules pertaining to them, and other useful information.
Budget proposals for SNAPs should be submitted, and will be reviewed, based on the average completion rate. Additional funding may not be requested for SNAPs that execute at a higher rate.
Calibration SNAP Proposals
Calibration Proposals may also be submitted as SNAP Proposals. As with GO Calibration Programs, all data obtained will be non-exclusive access unless proposers specifically request an exclusive access period. Successful proposers will be required to deliver documentation, and data products, and software (when applicable) to STScI to support future observing or archival programs.
Users submitting Calibration Proposals are required to contact the appropriate instrument group to discuss their program prior to submission.
Calibration Proposals must be identified in the ‘Special Proposal Types’ section of the proposal.
Guidelines for SNAP Proposals
Please consider the following when developing your SNAP Proposal:
- Your willingness to waive part or all of the exclusive access data-rights period. This willingness is included in the selection criteria.
- You need not give a complete list of all targets and their coordinates in your Phase I proposal. However, you must specify the number of targets, and unambiguously identify the targets (e.g., reference to target lists in papers, or give a detailed description of the target characteristics). SNAP exposures may not be used for targets of opportunity observations.
- In the ‘Observation Summary’ section of the proposal you should provide a typical example of a SNAP exposure.
- SNAP Programs cannot request observation times longer than 45 minutes, including guide star acquisition and target acquisition. In general, shorter duration SNAP observations have more scheduling opportunities than longer ones.
- SNAP observations should not include any special scheduling constraints (e.g., CVZ or telescope orientation requirements). However, the special requirement BETWEEN may be used in the Phase II Program in some circumstances; for details see the SNAP User information Report.
- A SNAP observation must not have any links to other SNAPs (e.g., relative timing or orientation constraints), even if the SNAPs are of the same source.
- SNAP Programs may not contain identical observations of the same source in different visits, unless there is a scientific motivation for obtaining observations of the same source at different times (e.g., monitoring or follow-up observations). In the latter case, multiple identical visits of the same source may be requested; they should be counted as multiple targets (e.g., 10 different SNAP visits of the same galaxy count as 10 targets). Due to the nature of SNAPs, repeated observations are not guaranteed.
- Moving-target SNAP Programs are acceptable only if the timing requirements are of at least one month duration. Solar system targets interior to the orbit of Jupiter are not permitted. Timing constraints will reduce the chance of a target being scheduled. Due to the amount of effort required in implementing moving target SNAP Programs, these observations ordinarily cannot be revised during the observing cycle, once the initial processing has been completed.
- SNAP Programs with the ACS/SBC are not allowed.
- The number of spectroscopic COS and STIS/MAMA SNAPs (other than those using the NUV-PRISM) is limited to 150, due to the target and field bright-object checking requirements. For the same reason, imaging and moving target SNAPs with COS or STIS/MAMA modes are not allowed. Variable STIS/MAMA and COS SNAP targets must have well-defined MAXIMUM UV fluxes, which will be used for the bright-object checking. There are no restrictions on the numbers or variability of proposed STIS/CCD SNAP targets, which do not require bright-object checking and have a higher expected completion rate since they are not restricted to SAA-free orbits. Thus, use of the CCD NUV configurations should be considered instead of the MAMA NUV when possible.
- STIS/CCD SNAPs are allowed for both imaging and spectroscopic modes.
- STIS/MAMA SNAP Proposals should be limited to one or a few straightforward configurations. Specifically, use of the NDQ filters is not allowed. Use of the 0.2x0.2 echelle aperture is recommended for first-order programs without a scientific long-slit requirement, in order to expedite the field-screening process. Excessively complex STIS/MAMA SNAP targets, fields, or instrumental configurations may not be implemented in Phase II because of the limited resources available for bright-object checking, combined with the relatively low expected completion rate; if you are in doubt on this issue, contact the STScI Helpdesk.
- Programs that require both GO orbits and SNAP targets should be submitted as two separate proposals. The proposals should refer to each other so the reviewers will be aware the proposals are part of the same project. This allows you to ensure that some essential targets are observed (the GO Program) with the rest of the targets being sampled statistically (the SNAP Program).
- Because SNAP targets are added to the observing schedule at a late stage of the schedule building process, moving-target SNAP Programs may not use any detector that requires bright object screening (e.g. STIS/MAMA or COS). It is simply not practical to screen the field for any background objects that might violate bright-object screening limits.
Archival Research (AR) Proposals
Observations that are no longer exclusive access are available for analysis by interested scientists through direct retrieval from the HST Data Archive or from the Hubble Legacy Archive (HLA). The retrieval is free and does not involve financial support. The HST Archival Research (AR) Program can, however, provide financial support for the analysis of such data sets. AR Phase I proposals must outline an Analysis Plan for the program. Detailed budgets are due in Phase II only (as is the case for GO Proposals). Proposals for AR funding are considered at the same time, and by the same reviewers, as proposals for observing time, on the basis of scientific merit.
Only U.S. Investigators are eligible for funding of Archival Research.
Regular AR Proposals
The general goal of a Regular AR Proposal is to analyze a subset of data from the HST Archive to address a specific scientific issue. The analysis must improve on the previous use(s) of the data, or the scientific questions addressed must differ from those tackled by the original programs that obtained the data.
There is no limit to the amount of funding that may be requested in a Regular AR Proposal. The majority of the awards in recent cycles have been under $120,000, with a median around $50,000. However, STScI actively encourages the submission of more ambitious AR Programs for which larger amounts of funding may be justified. Budget details are not required in the Phase I submission. Detailed Program Management Plans are required with the budget submissions, and should be commensurate with the work plan scoped by the Phase I.
An AR Proposal will be considered to be a Regular AR Proposal, unless it is identified in the 'Special Proposal Types' section of the proposal as an AR Legacy, Theory, Cloud-Computation, or Calibration Proposal. Multiple Special Proposal Types can be selected.
Legacy AR Proposals
A Legacy AR Proposal is defined by the following characteristics:
- The project should perform a homogeneous analysis of a well-defined subset of data in the HST Archive.
- The main goal should be to provide a homogeneous set of calibrated data and/or ancillary data products to the scientific community.
- The results of the project should enable a variety of new and important types of scientific investigations.
- We also encourage the development of software tools for dissemination to the community. The development effort can be the main focus of the program provided that the tools have broad application to HST data.
The main difference between a Regular and a Legacy AR Proposal is that the former aims at performing a specific scientific investigation, while the latter will also create data products and/or tools for the benefit of the community. While Legacy AR Proposals will be judged primarily on the basis of scientific merit, the importance and broad applicability of the products produced by the Legacy Proposal will be key features in judging the overall scientific merit of the proposal.
It is a strict requirement for Legacy AR Proposals that the proposed data products be created and distributed to the community in a timely manner. Data products should also be delivered to STScI in suitable digital formats, to allow dissemination via the HST Data Archive or related channels.
It is anticipated that Legacy AR Proposals will be larger in scope and requested funds than most Regular AR Proposals. While there is no lower limit on the requested amount of funding, it is expected that most Legacy AR Proposals will require at least $120,000, and possibly up to a few times this amount, to accomplish their goals. Commensurate with the expected scope, Legacy AR Proposals are allowed to be multi-year projects, although this is not a requirement. Multi-year projects will be funded on a yearly basis, with continued funding beyond the first year subject to a performance review. Legacy AR Proposals will be evaluated by the TAC (see Proposal Selection Procedures) in conjunction with Large and Treasury GO Proposals. Descriptions of past programs are available on the HST Treasury, Archival Legacy and Large Programs webpage.
The Scientific Justification section of the proposal should include a description of the scientific investigations that will be enabled by the final data products, and their importance. The Analysis Plan section should describe the plans for data analysis, the data products that will be made available to STScI and the community, the method of dissemination, and a realistic timeline.
Calibration AR Proposals
Calibration Proposals may be submitted as AR Proposals. AR Proposals are appropriate in cases where the necessary data have already been taken, or for programs that do not require specific data but aim to develop specialized software for certain HST calibration and data reduction tasks. Examples of topics that have been addressed by Calibration Programs of the type discussed here are:
- Calibration of Lyman-alpha flat fields
- Creation of a coronagraphic PSF library for STIS/CCD
- Characterization of the spectroscopic PSF for STIS/CCD
For a complete description of the instrument calibration plans/accuracies, and for other potential topics, please see the Scientific Instruments webpage.
Users submitting Calibration Proposals must contact the appropriate instrument group (accessible via the STScI Helpdesk) to discuss their program prior to submission.
AR Theory Proposals
The opportunity exists under the HST Archival Research Program to obtain financial support for theoretical research. Research that is primarily theoretical can have a lasting benefit for current or future observational programs with HST, and it is appropriate to propose theory programs relevant to the HST mission.
A Theory Proposal should address a topic that is of direct relevance to HST observational programs, and this relevance should be explained in the proposal. Funding of mission-specific research under the HST Theory Program will be favored over research that is appropriate for a general theory program (e.g., the NASA Science Mission Directorate Astrophysics Theory Program; ATP). The primary criterion for a Theory Proposal is that the results should enhance the value of HST observational programs through their broad interpretation (in the context of new models or theories) or by refining the knowledge needed to interpret specific observational results (a calculation of atomic cross sections may fall under the latter category). The results of the theoretical investigation should be made available to the community in a timely fashion.
Theory proposals should describe the impact on observational investigations with HST. Review panels will consist of observational and theoretical astronomers with a broad range of scientific expertise. They will not necessarily have specialists in all areas of astrophysics, particularly theory, so the proposals must be written for general audiences of scientists. The ‘Analysis Plan’ section of the proposal 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. This section should also describe how the results of the theoretical investigation will be made available to the astronomical community, and on what time-scale the results are expected.
As with the other AR Proposals, there is no limit to the funding that may be requested in Theory Proposals. It is expected that most Legacy Theory Proposals will require at least $120,000, and possibly up to a few times this amount, to accomplish their goals. Commensurate with the expected scope, Theory Proposals are allowed to be multi-year projects, although this is not a requirement. Multi-year projects will be funded on a yearly basis, with continued funding beyond the first year subject to a performance review. While regular Theory proposals will be evaluated by the panels, Legacy Theory Proposals will be evaluated by the TAC (see Proposal Selection Procedures) in conjunction with Large and Treasury GO Proposals. Descriptions of past programs are available on the HST Treasury, Archival Legacy and Large Programs webpage.
The Scientific Justification section of the proposal should include a description of the scientific investigations that will be enabled by the final data products, and their importance. The Analysis Plan section should describe the plans for data analysis, the data products that will be made available to STScI and the community, the method of dissemination, and a realistic timeline.
Detailed Program Management Plans are required with the budget submissions.
AR Cloud Computation Studies
All non-exclusive access data for current Hubble instruments (ACS, COS, STIS, WFC3, FGS), have been made available as part of the Amazon Web Services (AWS) public dataset program (aws.amazon.com/public-datasets/). Providing these data in close proximity to AWS faciliates new types of compute-intensive analyses that may have not previously been possible due to individual researcher or research group compute resources. Proposals to make use of this dataset should select the Cloud Computation check box next to the AR category in APT, and be prepared to include a line item in their budget for AWS costs (limit $10,000).
Example use cases for leveraging this data could include: Large scale (re)analyses of data to measure photometric properties or proper motions, computationally-intensive tasks such as training machine learning classifiers, and live community-facing services.
- Link to HST data on AWS: https://registry.opendata.aws/hst/
- AWS machine learning services: aws.amazon.com/machine-learning/
- AWS spot computing: aws.amazon.com/ec2/spot/spot-and-science/
- Educational & research use cases: aws.amazon.com/government-education/research-and-technical-computing/
Guidelines for AR Proposals
Please consider the following when developing your AR Proposal:
- In general, any HST data that you wish to analyze must reside (or be expected to reside) in the Archive, and be released from exclusive access rights by the start of Cycle 27 (October 1, 2019).
- Users should consult the Large Searches and Requests webpage for information on searching for and downloading large datasets.
- Programs that require funding for Archival Research and also new observations should be submitted as two separate proposals: one requesting funding for the Archival Research, and the other proposing the new observations. The proposals should refer to each other so that the reviewers will be aware that the proposals are part of the same project.
- Investigators are allowed to submit an AR Proposal to analyze data that was obtained in a previous GO Program on which they were themselves PI or Co-I, but only if the goals of the AR Proposal differ significantly from those for which GO funding was awarded previously.
- STScI encourages the submission of AR Proposals that combine HST data with data from other space-missions or ground-based observatories, especially those data contained in the Mikulski Archive for Space Telescopes (MAST). STScI is an active partner of the Virtual Observatory (VO), and MAST is implementing VO technology to make its data holdings available. In particular, the MAST Data Discovery Portal is available at http://mast.stsci.edu/explore. The Discovery Portal is a one-stop Web interface to access data from all of the MAST supported missions, including HST (in particular the Hubble Legacy Archive- HLA, and Hubble Source Catalog- HSC), TESS, Kepler, GALEX, FUSE, IUE, EUVE, and Swift-UVOT.
Suggestions for AR Proposals
STScI would like to point out the following sources for Archival Research:
- The data being obtained for the Frontier Fields Program.
- The data obtained by the HST Pure Parallel Program.
- The data obtained for the Hubble Deep Field (HDF), the Hubble Deep Field-South (HDF-S) and the Hubble Ultra Deep Field (UDF).
- The data obtained by the HST Treasury Programs, which are described on the HST Treasury, Archival Legacy and Large Programs webpage. Community-contributed high-level science products from imaging and spectroscopic surveys (including GOODS, GRAPES, and GEMS) are available from the MAST High Level Science Product webpage.
- Projects that utilize the Hubble Source Catalog. A few potential examples are listed in the HST Primer.
Joint Observing Programs
STScI has reached agreements with several other observing facilities (Chandra, XMM-Newton, TESS, NOAO, NRAO) to award time for joint programs in which HST science is the prime science, but multi-wavelength observations from another ancillary observatory are critical for the science goals of the proposal. Joint programs may be for any amount of HST time.
Joint HST-Chandra Observing Proposals
If your science project requires observations from both HST and the Chandra X-ray Observatory, you can submit a single proposal to request time on both observatories to either the HST Cycle 27 or the Chandra Cycle 20 review. This avoids the “double jeopardy” of having to submit proposals to two separate reviews. A description of past HST joint programs is available on the HST Joint Programs webpage.
Joint HST-Chandra proposals are of two types:
Regular HST-Chandra Proposals: By agreement with the Chandra X-ray Center (CXC), STScI will be able to award up to 400 kiloseconds of Chandra observing time. Similarly the CXC will be able to award up to 100 orbits of HST time to highly rated proposals awarded Chandra time in its TAC process. The only criterion above and beyond the usual review criteria is that the project must be fundamentally of a multi-wavelength nature, and that both sets of data are required to meet the science goals. Time will only be awarded to joint proposals if both data sets are required for the proposed science. It is not essential that the project requires simultaneous Chandra and HST observations. Chandra time will only be awarded in conjunction with new HST observations (and should not be proposed for in conjunction with an AR or Theory Proposal).
Large HST-Chandra Proposals: By agreement with the CXC, STScI will be able to award an additional 600 kiloseconds of Chandra observing time for Large joint programs. These programs are defined as requiring at least 75 orbits of HST time and at least 400 ksec of Chandra observations. Similarly, CXC will be able to award up to 150 orbits for Large Programs submitted to the Chandra TAC. As with Regular HST-Chandra Proposals, the only criterion above and beyond the usual review criteria is that the project must be fundamentally of a multi-wavelength nature, and that both sets of data are required to meet the science goals. It is not essential that the project requires simultaneous Chandra and HST observations.
Of the 1 Msec of Chandra observing time that can be awarded in the HST review, only approximately 15% of the observations may be time-constrained. In addition, only one rapid ToO can be awarded (less than 20 days turn-around time). A Chandra ToO is defined as an interruption of a command load, which may include several predictable observations within that one-week load. HST Cycle 27 proposers should keep their Chandra requests within these limits.
Regular proposals for combined HST and Chandra observations should be submitted to the observatory that represents the prime science (not to both observatories). Large HST-Chandra proposals (or Very Large Programs, as CXC defines them) may be submitted to either, but not both, observatories. STScI reserves the right to disallow HST observations that duplicate those approved via any joint program unless the duplications are justified in the original proposals. The Chandra Cycle 21 deadline is March 14, 2019 at 6 pm EDT. While there is multi-wavelength expertise in the review panels for both observatories, typically the HST panels will be stronger in IR/optical/UV science and the Chandra panels in X-ray science.
Establishing the technical feasibility of the Chandra observations is the responsibility of the PI, who should review the Chandra documentation or consult with the CXC. A description of the technical information that should be included in the proposal is given in Joint HST-Chandra Observations. For proposals that are approved by HST, the CXC will perform detailed feasibility checks in Chandra Cycle 20. The CXC reserves the right to reject any previously HST-approved observation that proves infeasible, impossible to schedule, and/or dangerous to the Chandra instruments. Any Chandra observations that prove infeasible or impossible could jeopardize the overall science program and may cause revocation of the corresponding HST observations. Duplicate Chandra observations may also be rejected by the CXC.
Joint HST-Chandra Proposals must be identified in the ‘Special Proposal Types’ section of the proposal. Also, you must include technical information about the Chandra observations in the ‘Coordinated Observations’ section of the proposal.
Joint HST/XMM-Newton Observing Proposals
If your science project requires observations from both HST and the XMM-Newton Observatory, you can submit a single proposal to request time on both observatories to either the HST Cycle 27 or the XMM-Newton Cycle AO-19 review. Joint HST/XMM-Newton Proposals should be submitted to the observatory that represents the prime science facility (not to both observatories). A description of past HST joint programs is available on the HST Joint Programs webpage.
By agreement with the XMM-Newton Observatory, the HST TACs will be able to award up to 150 kiloseconds of XMM-Newton observing time. Similarly the XMM-Newton TACs will be able to award up to 30 orbits of HST time. The only criterion above and beyond the usual review criteria is that the project must be fundamentally of a multi-wavelength nature, and that both sets of data are required to meet the science goals. Time will only be awarded to joint proposals if both data sets are required for the proposed science. XMM-Newton time will only be awarded in conjunction with new HST observations (and should not be proposed for in conjunction with an AR or Theory Proposal). Proposers should take special care in justifying both the scientific and technical reasons for requesting time on both missions.
It is not essential that the project requires simultaneous XMM-Newton and HST observations. No XMM-Newton observations with a reaction time of less than five working days from the trigger date will be considered. Target of Opportunity (ToO) Proposals must state explicitly whether the HST observations require a disruptive ToO. No more than one disruptive ToO will be allocated per proposal. It is the responsibility of the PI to inform both observatories immediately if the trigger criterion is fulfilled.
Proposals for combined HST and XMM observations should be submitted to the observatory that represents the prime science (not to both observatories). STScI reserves the right to disallow HST observations that duplicate those approved via any joint program unless the duplications are justified in the original proposals. The XMM-Newton AO-19 deadline is nominally in early October 2019. While there is multi-wavelength expertise in the review panels for both observatories, typically the HST panels will be stronger in IR/optical/UV science and the XMM panels in X-ray science.
Establishing the technical feasibility of the XMM-Newton observations is the responsibility of the PI, who should review the XMM-Newton Instrument Handbooks. A description of the technical information that should be included in the proposal is given in Joint HST-XMM Observations. All standard observing restrictions for both observatories apply to joint proposals. For proposals that are approved, both projects will perform detailed feasibility checks. Both projects reserve the right to reject any approved observation that is in conflict with safety or schedule constraints, or is otherwise deemed to be non-feasible.
Joint HST/XMM-Newton Proposals must be identified in the ‘Special Proposal Types’ section of the proposal. Also, you must include technical information about the XMM-Newton observations in the ‘Coordinated Observations’ section of the proposal.
Joint HST-TESS Observing Proposals
By agreement, STScI will be able to award a limited number of short cadence target slots from the Transiting Exoplanet Survey Satellite (TESS) mission. During its primary mission, TESS stares at one part of the sky for a duration of ~27 days and yields full-frame image data covering a 24 x 96 degree field of view with a long 30-minute cadence and also downlinks postage stamps of a select number of targets at a short 2-minute cadence. The observations are collected in a single broadband red-optical bandpass. TESS then steps to a different part of the sky to stare for another ~27 days, until it observes a complete hemisphere over 1 year.
The joint HST-TESS program can allocate short cadence observations for up to 100 targets from those available to the community via the TESS Guest investigator (GI) call. Proposers should identify which targets should be considered for TESS observations and provide an explicit justication that a 2-minute cadence is sufficient to achieve their science goals. Observations will only be obtained for approved HST targets. Data will already be made public for the one hundred thousand (100,000) top-prioritized Candidate Target List (CTL) targets for each hemisphere and GI Cycle (see http://archive.stsci.edu/tess/index.html), and are therefore not eligible for joint observations. There is no guarantee that the HST and TESS observations will be simultaneous. TESS GI Cycle 2 will extend from approximately July 2019 to July 2020; proposers should not expect any observations earlier than August 2019. Accepted targets will be passed to the TESS GI Program Office by STScI. Additional information can be found on the TESS GI Program Office website.
Joint HST-NOAO Observing Proposals
By agreement with the National Optical Astronomy Observatory (NOAO), STScI will be able to award time on NOAO facilities to highly ranked proposals that request time on both HST and NOAO telescopes. The award of time on NOAO facilities will be subject to approval by the NOAO Director, after nominal review by the NOAO TAC to avoid duplication of programs. Joint HST/NOAO Proposals should be submitted to the observatory that represents the prime science facility (but not both). The important additional criterion for the award of NOAO time is that both the HST and the ground-based data are required to meet the science goals of the project. Time will only be awarded to joint proposals if both data sets are required for the proposed science. It is not essential that the project requires simultaneous NOAO and HST observations. Under this agreement, NOAO time will only be awarded in conjunction with new HST observations (and should not be proposed for in conjunction with an AR or Theory Proposal). Major results from these programs would be credited to NOAO and HST. A description of past HST joint programs is available on the HST Joint Programs webpage.
NOAO has offered up to 5% of its available time to proposals meeting the stated criteria. NOAO observing time will be implemented during the two 2020 NOAO observing semesters (2020A for February to July 2020, and 2020B for August 2020 to January 2021). Time cannot be requested for the preceding semester, 2019B. Time may be requested only for those facilities listed on the NOAO/NASA Collaboration webpage. Under this agreement approximately 15-20 nights per telescope per year will be available on most (but not all) NOAO telescopes. Only a fraction of the time is available on some facilities - the WIYN and SMARTS telescopes - and so the 5% cap applies only to this fraction. In addition, time on heavily-subscribed resources may be limited by the NOAO Director.
Establishing the technical feasibility of the proposed NOAO observations is the responsibility of the PI, who should review the NOAO documentation or consult with NOAO directly. A description of the technical information that should be included in the proposal is given in Joint HST-NOAO Observations. If approved for NOAO time, the PI must submit, by the nominal September 30, 2019 deadline, an NOAO Phase II form giving detailed observing information appropriate to the particular NOAO telescope and instrument. In addition, for NOAO time on Gemini, successful PIs will be required to submit a complete NOAO proposal by the nominal September 30, 2019 deadline on the standard NOAO proposal form. This will be reviewed by the regular NOAO TAC.
NOAO will perform feasibility checks, and reserves the right to reject any approved observation determined to be infeasible, impossible to schedule, and/or dangerous to the telescopes or instruments. Any NOAO observations that prove infeasible or impossible could jeopardize the overall science program and may cause revocation of the corresponding HST time allocation.
Joint HST-NOAO Proposals must be identified in the ‘Special Proposal Types’ section of the proposal. Also, you must include technical information about the NOAO observations in the ‘Coordinated Observations’ section of the proposal.
Joint HST-NRAO Observing Proposals
By agreement with the National Radio Astronomy Observatory (NRAO), STScI will be able to award time on NRAO facilities to highly ranked proposals that request time on both HST and NRAO telescopes. NRAO has offered up to 3% of the available time on its North American facilities, namely the Robert C. Byrd Green Bank Telescope (GBT), the Very Large Array (VLA), and the Very Long Baseline Array (VLBA), for allocation by the HST TAC, subject to a maximum of 5% of the available time in any given array configuration. In return, STScI has offered 30 orbits of HST time for allocation by the NRAO TAC to proposals submitted on or before either of the two NRAO semester deadlines. These are nominally February 1, 2019 for semester 2019B, and August 1, 2019 for semester 2020A. Joint HST/NRAO Proposals should be submitted to the observatory that represents the prime science facility (not to both observatories). STScI reserves the right to disallow HST observations that duplicate those approved via any joint program unless the duplications are justified in the original proposals. A description of past HST joint programs is available on the HST Joint Programs webpage.
NRAO observing time awarded through the HST Cycle 27 review will be implemented during the 2019B and 2020A observing semesters. The award of time on NRAO facilities will be subject to approval by the NRAO Director, after nominal review by the NRAO TAC to avoid duplication of programs. The important additional criterion for the award of NRAO time is that both the HST and the radio data are required to meet the science goals of the project. Time will only be awarded to joint proposals if both data sets are required for the proposed science. It is not essential that the project requires simultaneous NRAO and HST observations. Under this agreement, NRAO time will only be awarded in conjunction with new HST observations (and should not be proposed for in conjunction with an AR or Theory Proposal). Major results from these programs would be credited to NRAO and HST.
Establishing the technical feasibility of the proposed radio observations is the responsibility of the PI, who should review the NRAO documentation or consult with NRAO directly. If approved for NRAO time, the PI must submit detailed observing information appropriate to the relevant NRAO facility. A description of the technical information that should be included in the proposal is given in Joint HST-NRAO Observations.
NRAO will perform a technical review of proposals approved by the HST TAC, and reserves the right to reject any approved observation determined to be infeasible, impossible to schedule, and/or dangerous to the telescopes or instruments. Any NRAO observations that prove infeasible or impossible could jeopardize the overall science program and may cause revocation of the corresponding HST time allocation. We therefore urge proposers to discuss technical concerns with appropriate staff at both observatories. Discussions with NRAO staff should occur via the NRAO helpdesk.
Proposers must always check whether appropriate archival data exist, and provide clear scientific and technical justification for any new observations of previously observed targets. Observations awarded time that duplicate observations already approved by HST or NRAO for the same time period may be canceled, or data sharing and cooperation among different groups may be necessary, as determined by the two observatories. This includes ToOs with similar trigger criteria, with or without previously known coordinates.
Be aware that some HST targets might not require new NRAO observations because the joint science goals can be met using non-exclusive access archival data from the VLA, VLBA, or GBT that are available at http://science.nrao.edu/facilities/vla/archive. Also note that VLA continuum images from sky surveys at a wavelength of 20cm and at a FWHM resolution of 45 arc seconds (see http://www.cv.nrao.edu/nvss/) or 5 arc seconds (see http://sundog.stsci.edu/top.html) are available.
All scientific data from NRAO telescopes have a exclusive access period where the data are reserved for the exclusive use of the observing team. The data archive policy and exclusive access periods are given at
This policy applies to NRAO data taken through the joint HST-NRAO program.
Joint HST-NRAO Proposals must be identified in the ‘Special Proposal Types’ section of the proposal. Also, you must include technical information about the NRAO observations in the ‘Coordinated Observations’ section of the proposal.
Mid-Cycle GO Proposals
Up to 300 orbits per cycle will be available for Mid-Cycle GO programs. Mid-Cycle programs provide the community with an opportunity to propose for in-cycle observations of recently-discovered, non-transient objects. As such, they complement Director’s Discretionary programs, which target unexpected transient phenomena and time-critical observations. Instructions and up-to-date information can be found on the Mid-cycle Proposal Submission Page.
Mid-Cycle GO Proposals must meet the following prime criteria:
- Proposers must provide a well-justified explanation of why the proposal could not have been submitted in response to previous Calls for Proposals: for example, the target source may have been identified subsequent to the most recent proposal deadline.
- Proposers must provide a clear description of the scientific urgency of these observations and why they should be executed in the present cycle.
Proposals should be submitted via the Astronomer’s Proposal Tool (APT) as type GO, using the Mid-Cycle template for the pdf attachment. 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 Request, submit a question to http://hsthelp.stsci.edu for investigation/resolution.
Mid-Cycle proposals may be submitted at any time. Proposals received prior to September 27, 2019 will be considered for implementation in the October 1, 2019 to February 28, 2020 time-frame, and those received between October 1 and January 30, 2020 will be considered for implementation in the March 1 to September 30, 2020 time-frame.
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.
- Proposals must comply with the guidelines for anonymizing proposals.
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 exclusive access 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.
Members of the STScI Science Policies Group will undertake an initial review of GO Mid-Cycle proposals to determine whether the proposals meet prime criterion #1. Proposals that do not meet that criterion 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-submission of rejected proposals from past cycles (including past mid-cycle opportunities) will be rejected automatically unless a clear justification is given as to why circumstances justify a new mid-cycle submission.
Mid-Cycle proposals will receive scientific review by members of the community.
Director's Discretionary (DD) Time Proposals
Up to 10% of the available HST observing time may be reserved for Director’s Discretionary (DD) allocation. Scientists wishing to request DD time can do so at any time during the year, by using APT. Instructions and up-to-date information can be found on the DD Proposal Submission webpage.
Observations obtained as part of a DD Program generally do not have a exclusive access period, and are made available immediately to the astronomical community. However, DD proposers may request and justify exclusive access periods in their proposals.
Upon receipt of a DD Proposal, the STScI Director will usually seek advice on the scientific merit and technical feasibility of the proposal from STScI staff and external specialists. A proposal for DD time might be appropriate in cases where an unexpected transient phenomenon occurs or when developments since the last proposal cycle make a time-critical observation necessary.
Recognizing the limited lifetimes for major space facilities such as HST and Chandra, DD Proposals for timely follow-up of new discoveries will also be considered even if the astrophysics of the phenomena do not require such rapid follow-up. In such cases, the proposers must demonstrate that the observations will provide a critical link in the understanding of the phenomena and that carrying them out quickly is particularly important for planning future observations with major facilities. They should then also indicate their plans for quickly making the scientific community aware of their discoveries, to enable subsequent wider community follow-up.
DD observations should not generally be requested if any of the following is true:
- The observations could plausibly have been proposed in the most recent regular proposal cycle, possibly as a Target-of-Opportunity Proposal. Requests to reserve ToO targets that have not been discovered would not be appropriate.
- The observations were proposed in a recent regular proposal cycle, and were rejected.
- The observations were proposed in a recent Mid-cycle, and were rejected.
- The proposed observations could wait until the next proposal cycle with no significant reduction in the expected scientific return.
- Proposals must comply with the guidelines for anonymizing proposals.
The primary criteria for acceptance of DD Proposals are high scientific merit and a strong demonstration of the timeliness of the observations. Under extraordinary circumstances, observations of Venus may be proposed for Director's Discretionary time. Proposals must make an appropriately compelling science case.
Weekly HST Command Loads are uplinked to the telescope on Sunday evenings; for nominal operations, the observing schedule is determined eleven days in advance of the uplink date. Although it is technically feasible to interrupt the schedule and initiate observations of a new target, short-notice interruptions place severe demands on the planning and scheduling process, decreasing overall observing efficiency and delaying other programs. Hence, requests for DD time must be submitted at least two months before the date of the requested observations, if possible. Requests for shorter turn-around times must be exceedingly well justified. In the case that a DD Program with a turn-around time of less than one month is accepted, the PI or his/her designee is required to be reachable by STScI personnel on a 24 hour basis between the submission and the implementation of the program, for Phase II preparation.
Subject to availability of funds from NASA, STScI will provide financial support for U.S. PIs and Co-Is of approved DD Programs (see HST Cycle 27 Grant Funding and Budget Submissions).
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