The JWST Single-Stream Proposal Process

JWST proposals are submitted via a single-stream process through the Astronomer's Proposal Tool, where all information about the proposed science and observations are provided up front at the time of submission.

Proposal process

For most proposals, JWST follows a "single-stream" process where a single submission is made for each proposal by the proposal deadline which, when accepted, can flow quickly into the planning and scheduling process.  A single-stream process for JWST proposal submission has been adopted for three reasons: 

  1. Similar to Spitzer, JWST visits will be continuously scheduled in an event-driven process, as opposed to discrete orbits. JWST proposers must therefore specify more information up front than HST proposers so that the total time required for an observing program can be determined (e.g., how much wall clock time, not how many discrete orbits).  This information is then made available to the TAC as part of the review process. This includes accounting for slews and instrumental overheads that are often hidden from Hubble observers since they occur during Earth occultation. 

  2. The single-stream process reduces the time between proposal acceptances and the start of an observing cycle. While the technical review of accepted proposals often results in suggested changes to the accepted proposals, this process is much less onerous and time consuming than (for instance) a full "Phase II" process as implemented for HST.  Additionally, getting new proposals into scheduling more quickly helps to increase the amount of JWST data that is available when the subsequent round of proposals is written, thus accelerating the intellectual cycle as new discoveries guide the direction of new JWST observations. (Cycle 1 was an exception because much more time was available for the technical review, and a thorough technical review was important since the observatory and instrumentation were new to both proposers and the technical staff.)

  3. A “single-stream” approach enables the rapid construction of the long range plan (LRP). This helps to quickly incorporate accepted proposals into the scheduling system and allows the planning and scheduling system to promptly assign execution position angles to observations that need these constraints (e.g., all NIRSpec MSA-based observations). 

The proposal system has been developed to enable users to, in most cases, enter essentially complete proposals at initial submission. Accepted proposals can then flow directly into the scheduling system with little delay. This is similar to the process that has been used with other space observatories such as Spitzer and Chandra, but differs from the two step proposal system familiar to HST users. Note that this single-stream process is independent from the budget proposal process. Successful proposers will still have to submit a budget in line with the eligibility requirements, see the Proposal Policies and Funding Support article in the current Call for Proposals section of JDox.


Submitted proposals must include sufficient information to define scheduling constraints for all visits (where each visit is directed at a specific target). Astronomers will submit their observing requirements using a set of observation templates for specific instrument modes within the Astronomer's Proposal Tool (APT). The submitted observing requirements include a full list of targets, specifications of the observations (instruments, filters, exposure times, dithers, observational sequence), and all user-requested scheduling constraints (including roll angle and other timing constraints). Complete APT files are required at submission so that APT can compute the direct overhead duration, which is defined by the sum of slews, the guide star and target acquisitions, mechanism motions, and small angle maneuvers, which are summed together to determine the total instrument overheads. 

In a few cases, APT may issue warning flags when APT template values are not adequately determined, or when it is not possible to fully determine whether a proposal is schedulable. Even in those cases, the complete APT file will contain sufficient information to estimate direct overheads and observing constraints. If such a proposal is accepted, a program coordinator or instrument scientist will address these issues prior to scheduling. Generally, APT will generate a TAC review report that does not contain any technical flags.

Proposals may be submitted with APT warning flags, although proposers are strongly encouraged to resolve as many issues as possible. For proposals with APT errors, these should be resolved prior to submission whenever possible. Contact the JWST Help Desk for assistance if necessary. 


Proposals that cannot be fully specified at the time of submission are exempted from the single-stream process described above.  Details on the types of proposals that are exempted and the kind of information that is required for submission are specified each cycle in the relevant Special Submission Requirements article. Note that these exceptions may partly depend on evolving APT functionality, and therefore these special requirements might change from one proposal Call to another. 

How APT can help

Several strategies are being employed to help JWST users prepare APT files for initial proposal submission.  Training materials and demo proposals can be found in the APT Help page in JDox

Observation templates in APT

In APT, once a user selects an instrument and an observing mode, the APT GUI changes to show only those parameters that need to be set for that mode. Each instrument and mode combination thus has an observation template format specific for that mode. (Note: coordinated parallels require two instrument mode definitions in the same observation template.) Once the relevant parameters for that observation have been specified, the template is complete and ready for further processing. Each instance of a template represents a single observation (although an observation may have one or many visits encoded within that observation, a process that is handled automatically within APT).

Schedulability and guide star availability checks

APT verifies that the proposed observations are schedulable given the specified constraints, including checks for guide star availability over the period of schedulability. When one or more templates have been filled out, running the Visit Planner step in APT executes a range of checks that look into the schedulability of the proposed observation(s). In addition to observatory viewing constraints, this check also assesses the availability of guide stars as a function of time, thus producing valid windows where the observation can schedule. The proposer may not choose specific guide stars or exact scheduling windows, as the schedulers need flexibility to prepare the most efficient LRP. 

Minimization or elimination of time-consuming optimization steps

APT is tasked with nearly all of the "heavy lifting" in the proposal process. The user specifies observations, and if the proposed observations require many visits to be performed, this is handled internally in APT, by breaking the observations into visits as necessary, performing the relevant accounting of overheads through Smart Accounting, and reporting the results back to the user. (An HST user may be familiar with the phase II process of trying various combinations, or ordering of their proposed observations to make best use of their orbit allocation. None of that is necessary for JWST proposing).

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    This article is a generalized version of an older Cycle 1 article
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