Review and Implementation of Rapid Response Observations on JWST

Description of the different pathways for obtaining rapid response observations with JWST. 

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JWST has the capability to accommodate observations of newly-discovered transient objects that require rapid-turnaround observations. In addition, there are occasions when it is important to repeat a failed observation on a shortened timescale. This document describes the procedures followed in implementing such observations.

Scheduling JWST

The JWST observing schedule is constructed on a weekly basis. Individual visits are drawn from the long-range plan (LRP) and combined to maximize observing efficiency. STScI begins working on the schedule on Monday. The Science Mission Specification (SMS) is transferred to Goddard the following Thursday. The first observation is scheduled for Sunday evening. There is therefore a 14-day period, the 7-day SMS preparation and the subsequent week of actual observations, where adding an observation of a transient source or repeat observation requires re-building the schedule. The situation is seldom as simple as a one-for-one swap; generally, multiple programs are affected. The impact obviously increases through the building process, with changes during the observing week requiring an intercept of the executing SMS.

Rapid response observations are classified in three categories:

  • Non-disruptive observations, where the turnaround time requested is more than 14 days;
  • Disruptive observations, where the turnaround time is between 2 and 14 days;
  • And ultra-disruptive observations, where the turnaround time requested is less than 2 days.

NIRSpec MOS programs must be finalized at least 4 weeks before execution. Consequently, NIRSpec MOS is not available for disruptive or ultra-disruptive programs.

These categories apply to both transient sources and repeats of failed observations.

Observations of Transient Sources

Observations of transients can be requested through two avenues: Target of Opportunity (ToO) programs, which are reviewed and recommended by the annual Telescope Allocation Committee (TAC); and Director’s Discretionary Time (DDT) programs, which are submitted during the cycle.

For ToO observations, the request for activation will be reviewed to ensure that the observing parameters and science are consistent with those approved by the TAC. The Phase II APT file is already in place, although it may require modifications to accommodate the particular characteristics of the target.

For DDT observations, the submitted proposal is sent for review to several external (to STScI) experts in the field. Their recommendations are compiled by the DDT team in science policies and passed on to the Director for approval. The activation time for a DD program is measured from when the Director approves the program, not when the DD is submitted. The review process generally takes from ~3-10 days, depending on the urgency of the request. Under exceptional circumstances, a proposal may be sent to the Director for approval without external review; such cases are very rare, and the community is strongly encouraged to submit ultra-rapid response programs as ToOs to minimize delays.

Repeats of Failed Observations 

Principal Investigators of JWST programs can request a repeat of a failed or degraded observation by submitting a Webb Observation Problem Report (WOPR). WOPRs are reviewed by the Telescope time Review Board (TTRB) which first identifies the reason for the failure. If the observation failed due to observer error (eg wrong coordinates), then the request is usually rejected. However, if the source of the failure was an observatory issue (eg skipped observation, guide-star failure), then the observation will generally be scheduled for repeat. Exceptions may occur if the program is 90% complete; in that case, the Principal Investigator must provide a clear scientific justification for the repeat observation.

Given the process, ultra-disruptive repeat observations are not possible. Repeat observations will only be scheduled on a disruptive timescale (<14 days) if there is a compelling scientific case for doing so.

Scheduling Rapid Response Observations

Adding an observation of a transient requires replacing a currently-scheduled observation of another science program. Any activation involves a trade in science achieved versus science deferred or even lost entirely.

Requests for rapid response observations provide very limited opportunity for interactions with the PI.  It is absolutely crucial that both ToO and DDT programs provide clear specifications of when the observations need to be scheduled, of the flexibility in scheduling, and how the science return depends on when the observations are scheduled. This information must be included in the submitted proposal in the Special Requirements section.

In brief, proposers should

  • Limit observing constraints (orientation, timing) to those essential to achieve the science goals. Any constraint impacts schedulability, and proposals that set unrealistically tight constraints may not be schedulable.
  • Be very clear at the outset on the flexibility of timing constraints.
  • Wherever possible, avoid submitting ToO triggers or DD proposals on a Friday or a weekend.

On receipt of either the ToO activation or the DD submission (prior to approval), the schedulers examine the upcoming observing plan to determine likely scheduling opportunities. That process takes technical considerations into account, such as the current observatory performance, anomalies, observational constraints, upcoming observatory housekeeping, and staff availability. Observational constraints (e.g., specific timing and orientation) impact the way the observation is placed relative to the extant schedule. Housekeeping activities optimize the performance of the observatory generally, such as flight software (FSW) updates, station-keeping manoeuvres, and download connections with the Deep Space Network.  The JWST Mission Office is closely involved in these decisions.

In addition, JWST’s schedule includes many time-critical or highly constrained observations, such as exoplanet transits, measurements of Solar System phenomena, observations requiring strict orientation constraints, or coordinated observations with other observatories. Displacing any observation requires consideration of how easily that observation can be re-scheduled, and of the consequent science impact on that program. If necessary, the science policies group will be asked to adjudicate on the proposed trade.

Communications with the Principal Investigator 

STScI communicates with the PI of a science program only when necessary. STScI communication with the PI of a science program is limited to information requests for clarification and reporting the outcome of a ToO, DD, or WOPR request. This policy holds for rapid response observations. For WOPRs, the communications are handled by the TTRB who will contact the PI for additional information only if deemed necessary. The Science Policy Group handles communications with PIs of DD programs; the JWST Mission Office works with the Program Coordinator on communications with PIs of ToO programs. The PI will be informed of the outcome of either a ToO activation request or a DDT program submission. There is only limited communication regarding the final scheduling decision since that involves technical considerations regarding observatory operations and science trades with other JWST programs.

Related links

Policies for the Telescope Time Review Board

Director's Discretionary Time

Target of Opportunity Program Activation

Notable updates
Originally published