Submitted single-stream JWST proposals should include all information necessary to accurately estimate direct overheads, and be ready for scheduling in the JWST long range plan.
Introduction and motivation
For most proposals, JWST follows a "single-stream" approach where a single submission is made for each proposal by the deadline. The JWST proposal system has been developed to enable users to, in most cases, enter essentially complete proposals at initial submission. Only certain classes of proposals need to be revised after the proposals are accepted.
A single-stream process for JWST proposal submission has been adopted for three reasons:
- As was the case for Spitzer, JWST visits will be scheduled in an event-driven continuous process, as opposed to discrete orbits. JWST proposers must therefore specify more information up front than Hubble proposers so that the total time required for an observing program can be determined, and that information is available to the Time Allocation Committee (TAC). This includes accounting for slews and instrumental overheads that are often hidden from Hubble observers since they occur during Earth occultation.
- For cycle 2 and beyond, a single-stream process minimizes the time between proposal deadlines and the start of an observing cycle. This, in turn, maximizes the amount of Webb data that's available when the subsequent round of proposals is written, thus accelerating the intellectual cycle as new discoveries guide the direction of new Webb observations. Cycle 1, however, is the exception because proposal submission occurs well before JWST launch and commissioning. In this case, a single-stream submission allows a longer and more thorough review of accepted proposals and more opportunities to provide support to successful proposers.
- A “single-stream” approach enables the rapid construction of the long range plan (LRP) and helps speed accepted proposals into the scheduling system.
This is similar to the process used for other space observatories such as Spitzer and Chandra, but is different from the two-step proposal system familiar to many HST users. Of course, there are exceptions to this general approach, but only a fraction of accepted proposals will require a second round of inputs prior to scheduling.
A faster turnaround can be achieved if proposals can be scheduled for observing soon after they are recommended by the Webb telescope Time Allocation Committee (TAC) and accepted by the STScI Director. This means that most submitted proposals must include sufficient information to define scheduling constraints for all visits (where each visit is directed at a specific target).
Following Spitzer's example, astronomers will submit their observing requirements using a set of templates for specific instrument modes. These templates are available in 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. The sooner that information is available, the sooner an initial Webb LRP can be prepared using all visits in all the accepted programs.
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 valuable information to estimate direct overheads and observing constraints. If this program is accepted, a program coordinator or instrument scientist can quickly address these issues prior to scheduling. Generally, APT will generate a TAC review report that does not contain any technical flags.
Proposals that cannot be fully specified at the time of submission are exempted from the nominal single-stream process. Because these exceptions partly depend on APT functionality (and this is expected to evolve with time), details on the types of proposals that will be exempted and the kind of information that will be required for submission will be specified in the call for proposals for each cycle. However, at least two cases have been identified to date. These include:
- Target of Opportunity proposals, where the target and observation properties cannot be fully specified up front in the proposal process; and
- NIRSpec Multi-Object Spectroscopy proposals; where the initial placeholder observation specifications cannot be completely specified until after a fixed position angle has been supplied to the proposer by the JWST planning system. This can only happen after the proposed observations have been placed into the Long Range Plan and a position angle has been assigned.
See also: NIRSpec Multi-Object Spectroscopy
How APT can help
Several strategies are being employed to help JWST users prepare LRP-ready APT files for initial proposal submission.
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. Once the relevant parameters for that observation have been specified, the template is complete and ready for further processing. Each instantiation of a template represents a single observation (although an observation may have one or many visits encoded within that observation).
Schedulability and guide star availability checks
Using APT, a proposer must carry out guide star and schedulability checks, verifying that the observations are schedulable given the specified constraints. When one or more templates have been filled out, the user runs the Visit Planner step in APT. This important step 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.
In some cases, because of the nature of the observations, it is not possible to determine whether a proposal is schedulable. This is the case, for example, for target of opportunity (ToO) proposals since they're linked to an event that may occur at an unknown time (e.g., novae, supernovae, gamma-ray bursts, newly discovered comets, newly discovered transiting planets, etc.). The details on what information will be required for submission will be specified in the call for proposals.
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, 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 will be required for JWST).
Review and implementation
Once the STScI director has approved the full list of JWST programs for the next cycle, a first version of the LRP may be constructed with the information provided in the single-stream proposals and also in the programs excepted from the nominal single stream process, as rough scheduling windows can be determined based on their target lists. This first draft of the LRP is useful for identifying conflicts in the schedule between approved programs and for identifying other issues not flagged by APT (e.g. severe persistence due to bright sources observed in previous programs, excesive heat load on the cooler mechanism operations due to MIRI mechanism movements and internal lamps usage, need for momentum dumps, etc). Any reviews of the approved programs may be prioritized based on the LRP scheduling window, with programs with targets that have scheduling windows early in the cycle receiving top priority.
Complex large programs with timing constraints (e.g., large mosaic images, exoplanet transit observations, coordinated observations with other facilties) impose significant constraints on the LRP; thus, it is important to incorporate these into the schedule as early as possible. To do so, any approved programs without full observing requirements must provide updates to their programs shortly after approval. It is expected that the target lists, total time requests, and observatory resources will be provided upon submission in a manner similar to HST phase I proposals, but specific pointings, dither patterns, and timing constraints must be provided rapidly after approval.
When all the LRP-ready programs are submitted, they will be reviewed to ensure that the submitted observing plan is consistent with the TAC allocation and that the approved programs are checked for duplications. Additionally, programs which are likely to cause severe persistence may be flagged so that they may be scheduled so as not to impact subsequent programs. Programs flagged by APT with scheduling issues, such as missing guide stars, would also be reviewed at this stage. Unlike HST instruments, JWST instruments do not require 'health and safety' reviews. Challenging JWST programs may require additional reviews, which may be done after the LRP is built. These operationally-complex programs are primarily those which require target acquisitions such as coronagraphy and spectroscopy. NIRSpec MSA configuration reviews would not impact the JWST proposal cycle timeline, as these would occur throughout the year as the pre-imaging is obtained.
After the initial program reviews and construction of the LRP, additional reviews by program coordinators and instrument scientists to further validate each program could be executed throughout the cycle without impacting the intellectual cycle of JWST. Any significant changes to an approved JWST program will be evaluated by the telescope time review board and will only be approved if they significantly improve the scientific return of the program.
Lotz, J., Reid N., Lee, J. 2014, JWST-STScI-004085
Implementation of a Single-Stream JWST Proposal Process