JWST Cycle 1 GTO Proposal Submission Policies

The requirements for JWST Cycle 1 Guaranteed Time Observations (GTO) proposals are described, including eligibility and observing restrictions.

Observing time in Cycle 1

JWST observing programs are allocated against wallclock time, with 8,776 hours available to schedule in an annual cycle. Up to 10% of the time is available for Director's Discretionary Time programs. In Cycle 1 the total time devoted to Guaranteed Time Observer and General Observer programs is estimated to be 7,900 hours.

Who may submit to the GTO

Any of the selected NASA, ESA, or CSA instrument teams (for NIRCam, NIRSpec, MIRI, and FGS/NIRISS), or selected scientists, or any member of these teams (with PI approval), may submit for the JWST GTO opportunity. Specifically these teams and individuals are: the NIRCam Team, the NIRSpec Team, the U.S. MIRI Science Lead, each of the eight U.S. MIRI Science Team members, The European MIRI Science Team, The FGS/NIRISS Team, The U.S. Telescope Scientist, and each of the six interdisciplinary scientists.

Proposal confidentiality

Proposals submitted to STScI will be kept confidential to the extent allowed by the review process. For accepted proposals, the scientific justification section of the proposal remains confidential, but other sections become publicly accessible, including PI and Co-I names, project titles, abstracts, description of observations, special scheduling requirements, and details of all targets and exposures. 

Data rights

GTO investigators may have exclusive access to their science data during an exclusive access period, or proprietary period, that is nominally 12 months following the date on which the data are archived. At the end of this proprietary period, the data become available for analysis by any interested scientist through the Mikulski Archive for Space Telescopes (MAST). GTO proposers may request shorter proprietary periods, or may waive their proprietary rights altogether, if they so chose. Because of the potential benefit to the community at large, GTO proposers should give this possibility consideration.

Duplication policies and procedures

Some duplicate observations may be permitted if there is sufficient scientific justification to do so. The Telescope Allocation Committee must explicitly recommend for implementation any General Observer (GO) programs that duplicate GTO observations. Potential duplications among the GTO teams will be reviewed by the STScI Director, checked against priorities set in Policy 9 of the NASA-SMD Policies. In all cases, the STScI Director will make the final approval. A more complete description of what constitutes a duplication with JWST instrumentation, and the procedures for checking and reviewing potential duplications, can be found on JWST Duplicate Observations Policy.


Resources to U.S. GTO investigators are provided directly by NASA, in response to the JWST Phase E Funding Call. GTO investigators have already been notified of their awards, which will be phased over the FY17 through FY23 period.

Types of observations and restrictions

Most observations of external targets are expected to be scheduled as primary observations, which are observations that determine the telescope pointing and orientation. There are, however, certain restrictions that apply to some types of targets.

Coordinated science parallel observations

There is the opportunity for some Coordinated Science Parallel Observations, in which simultaneous observations may be made with instruments other than the primary instrument. Coordinated Science Parallel observations should have science goals that support or complement the prime science programs. The permitted instrument combinations are also detailed below. Pure Science Parallel Observations, which utilize instruments other than the primary on observations from unrelated proposals, cannot be requested by GTO or ERS programs. 

GTO investigators may request Coordinated Science Parallel observations if they are scientifically justified. In Cycle 1, coordinated parallels will be available with the following instrument combinations:

  1. NIRCam imaging and MIRI imaging,
  2. NIRCam imaging and NIRISS WFSS,
  3. NIRCam imaging and NIRISS imaging (NIRCam must be the prime instrument),
  4. NIRSpec MOS and NIRCam imaging (NIRSpec must be the prime instrument),
  5. MIRI imaging and NIRISS WFSS.

Only direct imaging with standard narrow, medium, or broad band filters are allowed for NIRCam and MIRI observations in these coordinated parallel modes.

The observation specifications submitted by the GTOs must include a specific justification for any coordinated parallel observations. It should be clearly indicated whether the parallel observations are essential to the interpretation of the primary observations or the science program as a whole, or whether they address partly or completely unrelated issues. The justification will be reviewed by the STScI Director.

Further description of what defines Coordinated or Pure Science Parallels, and the restrictions on each, can be found on JWST Science Parallel Observation Policies and Guidelines

Target of opportunity observations

A target for JWST observation is deemed a Target of Opportunity (ToO) if it is associated with an event that may occur at an unknown time. ToO targets include objects that can be identified in advance, but which undergo unpredictable changes (e.g., some dwarf novae), as well as objects that can only be identified in advance by class (e.g., novae, supernovae, gamma ray bursts, newly discovered comets, etc.). ToOs are generally not suitable for observations of periodic phenomena (e.g., eclipsing binary stars, transiting planets, etc.). ToO proposals must present a detailed plan for the observations to be performed if the triggering event occurs. 

The science description submitted with the GTO observation specifications must include a description of any ToO observations. Those descriptions will be reviewed by the STScI Director to ensure that they are sufficiently specified so that other similar phenomena, with distinct goals, may be pursued by GO community.

The minimum turn-around time for Non-disruptive ToO activation, without significant impact to the schedule, is 14 days. Disruptive ToOs can be triggered with turn-around times less than 14 days, provided all of the proposal details (except possibly the precise target position) are available in advance. However, because of the significant effect disruptive ToO observations potentially have on the JWST schedule, each cycle will be restricted to a total of 8 disruptive activations. Moreover, due to their scheduling impact, Disruptive ToOs required to be triggered within 3 days will incur an additional overhead of 0.75 hours (45 minutes) per activation. Linked subsequent observations do not necessarily incur additional overheads, unless they are specified as time critical visits.

In Cycle 1, GTO programs will be limited to 2 disruptive activations, with the remaining 6 reserved for GO programs. There is no limit on the number of Non-distruptive ToOs per cycle.

Information on activating an approved target of opportunity program is in JWST Target of Opportunity Program Activation.

Solar system observations

JWST can observe most targets within our Solar System, although there are a few exceptions. Mercury, Venus, and the Moon cannot be observed due to the orientation of JWST's sunshade. Similarly, due to limits in the observatory's allowable solar elongation angle field of regard (85° to 135°, see schematic below), some solar system targets are visible only at set times of the year, as is the case with fixed targets.

Figure 1. JWST allowable field of regard

JWST Allowable Field-of-Regard

Time constrained, time critical, and coordinated observations

Time constrained observations with JWST are observations explicitly required to begin within a specified date and time interval. They impose restrictions on the JWST scheduling system depending on the length of the constrained interval surrounding a start date and time. Time critical observations are those required to start within a constrained window that is less than 24 hours (to be revised). Due to their impact on the schedule, time critical observations will incur an additional overhead of 1 hour per visit. Observations with execution windows greater than or equal to 24 hours are not considered to have a significant impact on the scheduling, and therefore do not incur any additional overheads. See JWST Observing Overheads and Time Accounting Overview for a description of accounting, including Smart Accounting, and overhead terms.

There are several kinds of time constrained observations that could be considered time critical in some way. Some scientific examples might include observations of specific phases of variable stars, many transiting exoplanet observations, and some solar system observations. Observations that require a particular telescope orientation (or position angle) are implicitly time constrained as the orientation of JWST is fixed by the date of observation, for a period that is no less than 5 days. The JWST Target Visibility Tool may be useful in determining these time constraints on a fixed orientation at a given date of observation.  

Coordinated JWST observations with other observatories are by definition time constrained observations, which may or may not be time critical. Linked subsequent observations do not necessarily incur additional overheads, unless they are also specified as time critical visits with critical scheduling windows. Linked observations that are scheduled to occur within 24 hours (to be revised) of a previous observation will be considered time critical observations, incurring the additional overhead.

Proposals may request time constrained observations for a specific date or range of specific dates, when scientifically justified. The science description submitted with the GTO observation specifications must include a description of any time constrained observations.

Follow-up observations of JWST pre-imaging 

Same-cycle follow-up spectroscopic observations of sources identified through JWST imaging programs are permitted. For example, a proposal may request imaging with either NIRCam or MIRI as a means of identifying a specific type of target (e.g. high redshift galaxies) for subsequent spectroscopy with NIRSpec. In that case, the proposal must specify the anticipated number density and magnitude distribution. 

Modifications to observing programs

As described in the GTO Proposal Submission Process, GTO Cycle 1 proposals must be submitted using the Astronomer's Proposal Tool by June 25 2019. Those submissions are public, and will provide the GTO reference program for the GO community. The proposals must be finalized by March 31 2020, approximately 5 weeks prior to the Cycle 1 GO deadline. Minor modifications to individual observations may be required. GTO proposers may drop specific targets at that juncture, but may not add new targets. Once finalized, the GTO program will remain frozen until the Cycle 1 GO program is announced in August/September 2020. The program modification policy summarised here comes into effect at that time.

In brief, modifications may be requested to refine programs to better achieve the approved science goals; they may also be required to accommodate changes in instrument performance with respect to the expectations at the time of the proposal submission. Minor modifications to observations may be made in consultation with the program coordinator or contact scientist. Major modifications to observations are requested by the GTO Principal Investigator by submitting a Program Change Request to the STScI Director; any program modification that affects the scheduling of an observation is a major modification. Modifications may be permitted if they are scientifically justified and have minimal impact on the overall observing schedule. All modifications to observing programs must receive explicit approval by the STScI Director or their official designee.

Full details are provided here, JWST Observing Program Modification Policy, including definitions of minor and major modifications, and a description of the review process.

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