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Hubble Space Telescope
What's New for Cycle 25

  • Pre-allocated Cycle 26 Orbits: STScI will pre-allocate some orbits for Cycle 26 during the Cycle 25 TAC to reduce some anticipated pressure in the time allocation of the first cycle of JWST. The Cycle 25 TAC will make recommendations on 3,550 orbits to be scheduled in Cycle 25, and an additional 1200 to be scheduled in Cycle 26. The pre-allocated time will be applicable only to small (<35 orbits) programs that are not coordinated (joint) proposals, target of opportunity, or time critical observations. Proposers are encouraged to submit proposals for both cycles in response to this call. More details are given in Section 1.4 and Section 3.2.
  • Large Joint HST-Chandra Programs: STScI and the Chandra X-ray Center (CXC) are collaborating to offer the opportunity to propose science programs that require substantial allocations of observing time on both observatories. CXC is providing up to 600 ksec of Chandra observing time to STScI that can be awarded to Large Joint HST-Chandra Programs, defined as programs that require 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. These allocations are in addition to the 400 ksec/100 orbits available for regular Joint HST-Chandra Programs. Large Joint HST-Chandra programs may be submitted for review to either the HST r eview or the Chandra review, but not to both More details are given in Section 3.5.
  • Budget submission deadline: Please note that the budget submission deadline for this cycle, August 10, 2017, is separate from the Phase II deadline, July 20, 2017.
  • Proprietary periods: The default proprietary period for data from Small and Medium GO programs is 6 months. Large, Treasury, and Calibration program data have no proprietary periods by default. Any request for non-zero proprietary periods for programs in these categories must be justified.
  • GO proposals to observe Venus: will not be permitted in Cycle 25. Proposers will have the opportunity to submit Director' Discretionary time requests for observations of Venus given a sufficiently compelling science program. More details are given in Section 4.1.

    Important Features Carried Over From Cycle 24:

  • JWST Preparatory proposals: STScI is encouraging the community to submit GO proposals for observations that complement and enhance the scientific impact of future JWST observations. Those proposals should be identified using the "JWST Preparatory Proposals" option in APT. Proposers should use the Special Requirements section for the PDF submission to describe the connection with specific JWST observations. The TAC will consider the potential impact of the overall program, including both the HST observations and future JWST observations. Following the recommendation of the Space Telescope Users Committee, JWST Preparatory proposals will have a default proprietary period of 0 months. Proposers may request a proprietary period; that request will be reviewed by the TAC. More details are given in Section 6.4.
  • Mid-Cycle proposals: Up to 200 orbits per cycle will be available for Mid-Cycle GO programs (see Section 3.10). Mid-Cycle programs were initiated in Cycle 23 to provide the community with an opportunity to propose for in-cycle observations of recently-discovered, non-transient objects. Mid-Cycle proposals may be submitted anytime between 15 August 2016 and 31 January 2017.
  • E/PO Proposals: As you may be aware, NASA’s Science Mission Directorate is restructuring its education program. As a result, we regret to inform the community that we are unable to issue a call for Cycle 24 E/PO proposals. We will keep the HST Cycle E/PO community informed of future opportunities should they become available.
  • Past HST Usage information is no longer either requested or required in Phase I submissions.
  • Proposal format: Following the recommendation of the Space Telescope Users Committee, printed copies of proposals will list investigators alphabetically without identifying the Principal Investigator.
  • Spectroscopic Legacy Archive: Cycle 24 proposers will be able to mine the new HST Spectroscopic Legacy Archive for high-level data products intended to accel- erate the scientific use of existing spectroscopic data. This archive will contain “science grade” co-added spectra of all usable public data, combining exposures for each target from across visits, programs, and cycles. This data will be organized into “smart archives” by target type (such as "hot stars" and "white dwarfs") and by scientific purpose ("IGM absorption sources") so that samples can be readily con- structed and downloaded without manual interaction with MAST. The first genera- tion of these products for the FUV modes of COS will be available online via MAST in early 2016. We encourage the development and submission of Archival Programs based on these new products.
  • Archive changes credentials to Single Sign-On: As of April 2015, the Archive’s account management system has been replaced by the STScI Single Sign-On (SSO) System. Most users will need to register for a new account. As an Archive user, the only difference you should see (apart from a different registration process) is that instead of a username, you will login with your email address. You can check whether or not you currently have an SSO account here ( It is not necessary to register for an account to search the Archive catalogs or retrieve public data. However, to retrieve proprietary data, such as recently archived HST data, an SSO account is required. When retrieving proprietary HST data, the Retrieval Options page will ask you to enter your SSO email and password. This will be used to verify that you are authorized to retrieve the data. (You can also use your SSO account to retrieve public HST data, instead of doing so anonymously, if you wish.)
  • Solar System and Exoplanet Proposals: Starting Cycle 24, the "Planets" mirror panels will review proposals covering exoplanet and debris disk science. Proposals for archival research/observations of Solar System targets will be reviewed by a separate panel.
  • Scientific Keywords: STScI has revised and updated the Scientific Keywords that are valid for use in the Phase I proposal templates. The revised list of keywords is given in Appendix B:Scientific Keywords.
  • Medium Proposals (those requesting between 35 and 74 orbits) are continued as a separate proposal category ( see Section 3.2.2). This cycle, Medium Proposals are reviewed by the panels and ranked together with the Small Proposals. Each panel is assigned a quota. The total orbit pool is nominally 650 orbits in size, although the TAC has the ability to decrease or increase this number in order to balance the pressure between Regular, Medium, and Large Proposals.
  • New Supported Sample Sequence for WFC3/IR: The sample sequence SPARS5, intermediate between RAPID and SPARS10, is intended to allow the efficiency and uninterrupted time series of SPARS10 and yet be short enough in cadence to better isolate an exoplanet-host star from a nearby stellar companion in spatially-scanned observations using IR grism. See the article in WFC3 STAN Issue 20.
  • New Supported WFC3/UVIS Apertures: The apertures UVIS2-C512C-CTE and UVIS2-C1K1C-CTE enable observers to automatically place a small target near a readout amplifier to reduce CTE losses while still reading out all of the detector. See the article in WFC3 STAN Issue 20.
  • New Supported Coronagraphic Position for the STIS CCD: For Cycle 24 STIS/CCD imaging observations with the BAR5 coronagraphic position will be supported. This is intended to provide high contrast at inner working angles as small as 0.25 arcseconds. See the STIS coronagraphy webpage and the articles in the November 2015 and March 2014 STIS STAN for additional details, and what for additional updates on the performance of this new position in future STIS STAN articles.

Important Features Carried Over From Cycle 23:

  • The Ultraviolet (UV) Initiative will continue in Cycle 24. This initiative is designed to take full advantage of the unique UV capabilities of Hubble while they still exist. Small, Medium, Large, and Treasury GO Proposals are all eligible, but SNAP Proposals are not. The available UV instrument modes include ACS/SBC imaging, COS spectroscopy, STIS/MAMA imaging and spectroscopy, STIS/CCD spectroscopy (UV gratings only) and WFC3/UVIS imaging (UV filters only; this does not include F336W, the U-band filter). The UV Initiative also extends to Archival (AR) Proposals, in the Regular AR (Section 3.4.1), Legacy AR (Section 3.4.2), and Theory (Section 3.4.4) categories. STScI will ask the review panels and the TAC to give particular consideration to UV-specific AR Proposals in the review process. More details are given in Section 6.3.
  • COS Lifetime Position: In February 2015 COS FUV spectra were moved from the second COS Lifetime Position (LP2) to the third (LP3) in order to alleviate the continuing effects of gain sag. The typical spectral resolution (λ/Δλ) has declined by about 5% for observations with the primary science aperture (PSA). Changes in the COS extraction and calibration pipeline have improved the calibration of point-source observations. COS/FUV observations at LP3 targeting extended objects or using the Bright Object Aperture (BOA) are more complex. In these cases the standard pipeline calibration will not always produce the flux accuracy achieved for point sources observed with the PSA, and it will be the responsibility of the user to evaluate the adequacy of the spectral extraction and, if necessary, undertake any customized extractions. See Chapter 3 of the COS Data Handbook for more information.
  • The Hubble Source Catalog (HSC) combines tens of thousands of single visit-based WFC3, ACS, and WFPC2 source lists from the Hubble Legacy Archive (HLA) into a single master catalog with roughly 100 million individual sources, hence providing entry into the field of database astronomy. Searches that would require months or years to perform in the past can, in many cases, be done in seconds with the HSC. This resource may be used to support a wide range of new archival proposals, a few potential examples are listed in Section 7.4 of the HST Primer (e.g., variability over more than a 20 year lifetime in many cases, astrometry with better than 10 milli-arcsecond accuracy, cross-matching with a wide variety of catalogs).
  • The budget categories for Regular Archival proposals (including Theory and Calibration) are no longer required, removing the Small and Medium categories used for planning purposes in previous cycles. See Section 3.4 for further details. Proposers should still provide a Management plan as described in Section 9.7.
  • Joint HST-NRAO Proposals will continue in Cycle 24, allowing proposers to request time on both HST and NRAO facilities in a single proposal. For a joint HST-NRAO proposal to be successful, the project must be fundamentally of a multi-wavelength nature and must require all proposed observations to meet the science goals. Proposers should take special care to justify both the scientific and technical reasons for all observations included in their joint proposal. Proposers must always check whether appropriate archival data exist, and provide clear scientific and technical justification for any new observations of previously observed targets. Further details are given in Section 3.9.
  • In addition to the joint HST-NRAO Proposals, it is possible to request time on Chandra (Section 3.5), XMM-Newton (Section 3.7), and NOAO telescopes (Section 3.8) as part of a proposal for HST observations.
  • The MAST Data Discovery Portal ( is a one-stop Web interface to access data from all of MAST’s supported missions, including HST, Kepler, GALEX, FUSE, IUE, EUVE, and Swift-UVOT. In addition to data at MAST, users can search for data available through the Virtual Observatory (VO), either by providing a resolvable target name or coordinate, or by using the “Search the VO” button for a given MAST data product. The VO gives Portal users access to data spanning the electromagnetic spectrum, from radio to high energy, including images, spectra, catalogs, and NASA ADS records.
  • We remind users that an extensive catalog of High-Level Science Products (HLSPs) is hosted on the MAST archive HLSP webpage, including imaging and spectroscopic atlases of many classes of astronomical object. HLSPs are community-contributed, fully-processed images and spectra that are ready for scientific analysis. The HLSP catalog is a useful resource for preparing new proposals. In addition, agreeing to provide new HLSPs back to MAST can increase a proposal’s scientific value and hence its chance of success (this is a requirement for Treasury GO and Legacy AR Proposals).

Release Documents

    The Call for Proposals describes the policies and procedures for submitting a HST Phase I proposal. Go to the CP.

    The Primer provides an introductory overview of the Hubble Space Telescope and explains how to calculate the appropriate number of orbits for an observing proposal. Go to the Primer.

    Science Justification Templates for Cycle 27 HST Phase I

  • Full Set of HST Documentation

HST Phase I Roadmap

    The Roadmap is a step-by-step guide to proposing and submitting an HST proposal. Download APT here.

DD Time

Up to 10% of the available HST observing time may be reserved for Director's Discretionary (DD) allocation.

Mid-Cycle Proposals

Up to 200 orbits per cycle will be available for Mid-Cycle GO programs. Mid-Cycle programs were initiated in Cycle 23 to provide the community with an opportunity to propose for in-cycle observations of recently-discovered, non-variable objects. As such, they complement Director’s Discretionary programs, which target unexpected transient phenomena and time-critical observations..

Special Programs from Past Cycles

Status of Current and Past Programs:

Past Proposal Opportunities