JWST New and Important Features

Important new features for proposers to consider in Cycle 3 are covered in this article.

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What's new for Cycle 3


  • Cycle 3 proposers should use the Astronomer's Proposal Tool (APT) version 2023.5.1 or higher in proposal preparation, released 24 August 2023. See the release notes for details. 
  • Allow NRAO Joint Observatory for JWST Cycle3
  • Add NIRCam WFSS template science Pure Parallel
  • Create interface for optional first, short exposure in NIRISS SOSS template
  • Change SURVEY Allocation method to match HST Snapshot for Cycle 3


  • Cycle 3 proposers should use the JWST Exposure Time Calculator (ETC) version 3.0, released 24 August 2023. This release features accuracy updates based on in-flight measurements, updates to IFU strategies, and new instrument-specific options for Cycle 3. See the release notes for details, and be sure to review the known issues for this release. Instructions for downloading the new version of the Pandeia engine and the associated data are found in the JWST Documentation and the Pandeia Engine News page.
  • Reduced count rate in MIRI imager. The photon count rate and the derived flux of the MIRI imager are lower than what is predicted at wavelengths between 12.8 and 25.5 µm, as mentioned in this news item on August 24, 2023. The current version of the Exposure Time Calculator (ETC) does not include this effect. Users wishing to propose observations for Cycle 3 in filters F560W through F1800W can assume the SNR calculations in the ETC are sufficiently accurate (nominally, the signal-to-noise ratio goes as the square root of the count rate). For the F2100W and F2550W filters, adding margins of 5% on the signal-to-noise ratio to mitigate for the observed loss is strongly recommended. Proposals that do not follow this recommendation will not be granted supplementary time through the TTRB for inadequate exposure times and any adjustments will need to come from the TAC allocated duration.

Other tools

  • The ExoCTK suite of tools has been updated to version 1.2.5. PandExo has also been updated to version 3.0 --- both updated to reflect Cycle 3 updates. Both tools are available online. See the JWST Observer News article for more details.

Proposal Review

  • As in Cycle 2, GO proposals requesting ≤ 15 hours and Regular AR proposals will be distributed for external review. Further details on the review process are given here


  • Page limits

The page limits for Cycle 3 proposals will remain the same as for Cycle 2. They may be revised in future cycles.

  • Exclusive Access Period (EAP)

The current default EAP is 12 months; discussions are currently on-going regarding a possible reduced, non-zero value. At this time, no decisions have been taken. The feedback from the community survey is an important factor in the outcome.

  • APT template

    Proposers should make sure that they the mark the APT coversheets appropriately using the menus that expand out on the Proposal Information page, such as "Explain unschedulable observations", "Supply Meteoroid Zone Justification", "Request custom time allocation", "Future Cycles", and "Coordinated telescopes", providing all the requested information.  If these fields are not marked and filled out in the APT coversheet those requests might not be met, even if they are described in the proposal. For more information, see Filling Out the APT Proposal Form


  • Survey programs

Survey programs consist of similar, relatively short observations of a targets drawn from a large sample; unlike GO programs, They will serve two main purposes in Cycle 3: supplementing the Long Range Plan to maintain observing efficiency if there is a shortfall of GO programs; and providing simple observations that can be executed when data volume is constrained by external factors. Survey programs have no guaranteed completion fraction. Proposals are for a number of targets, not time; proposers must specify the minimum number of targets to achieve the science goals in the Special Requirements section. See Survey Proposals for further information. NIRSpec MOS and MIRI MRS are not available for Surveys.  

Artemis 2 is planned for launch during Cycle 3. Data downlink capability may be severely limited during that mission, and proposers are encouraged to submit low-data volume Survey Programs that can be scheduled at that time. 

  • Target of opportunity 

Ultrarapid and disruptiveToOs are not permitted with NIRSpec MOS. 

Standard ToO proposals have a duration of one cycle. Proposers may apply for "carry-over" status if the target phenomena have a low probability of occurrence during one cycle. Carry-over ToOs are allowed for both disruptive and non-disruptive observations.  

As with other GO categories, non-disruptive ToO proposals can request triggers in up to 2 future cycles i.e. in cycles N, N+1 and N+2. Disruptive ToO proposals are restricted to the current cycle. Future cycle ToOs are not eligible for carry-over status.    

Requests for carry-over status or future cycle allocations should be justified in the APT Special Requirements and marked on the APT coversheet. 

In the case of duplications, triggers from previous cycle proposals have priority. 

  • Joint JWST proposals

In addition to the Joint JWST Proposal opportunities with ALMA, Chandra, HST, NASA Keck, NOIRLab and/or XMM-Newton, new to Cycle 3 is that proposers may request NRAO observations for individual targets in their JWST program. A total of up to 5% of the available time on the VLA, GBT or the VLBA per year is available to highly rated proposals. Similarly, NRAO will be able to award up to 50 hours of JWST time per cycle to highly rated proposals. There is no guarantee that joint observations will be obtained simultaneously with JWST observations. See Joint Proposals for further information. Proposers taking advantage of these Joint JWST Proposal opportunities should enter their request in the "Coordinated Telescopes Section" in the APT Proposal Information section. Joint JWST programs with more than one observatory are allowed. 

  • Long-Term programs

Proposers may request time in up to three cycles (3, 4, and 5). Long-term Proposals should describe in the PDF Attachment the entire requested program and provide a cycle-by-cycle breakdown of the number of hours requested. The cycle-by-cycle breakdown needs to be entered in the APT coversheet using the "Future Cycles” menu. If this field is not marked and filled out, the Long-term request might not be met, even if it is described in the proposal. The APT file should only contain the observations corresponding to the current cycle. APT files for time awarded in Future Cycles will be requested at a later time. 

  • Pure parallels 

Pure parallel observations are only paired with same cycle prime programs. Due to the way that they are implemented the number of pure parallel opportunities executed cannot be guaranteed.  In particular, if data volume issues are anticipated, the primary observations have priority and pure parallels are dropped.  A set of Frequently Asked Questions has been added to the Pure Parallels documentation to provide clearer guidance on the current constraints on pure parallel programs.

  • Super-computing 

Successful JWST proposers will be eligible to apply for NASA High-End Computing Time. Please indicate whether you intend to apply for HEC time in the text of the "Special Requirements" section of the PDF submission. More information on NASA HEC Program can be found on https://www.hec.nasa.gov.

  • Citizen science with JWST

GO and AR proposals may also include a citizen science component in support of the science goals. Funded support for those activities must be compliant with the JWST General Grant Provisions and is limited to no more than 10% of the total budget. NASA document SPD-33 provides guidelines on citizen science projects. 

Next: JWST Proposal Checklist

Notable updates
    Added section called "Long-Term programs"
    Added section called "Super-computing"
    Added  Joint JWST programs with more than one observatory are allowed. 
    Added  link to FAQ on pure parallels.  
    Page limits reverted to those in Cycle 2. 
    Note on updated ExoCTK and PandExo. 
Originally published