JWST New and Important Features

Important features for proposers to consider in Cycle 2 are covered in this article.

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What's New for Cycle 2


  • Micrometeorid impact mitigation in Cycle 2

JWST is subject to micrometeoroid impacts that can damage the primary mirror and, in the long term, reduce image quality. Such impacts are more probable when JWST is pointed in its direction of motion. Consequently, as a mitigation strategy, in Cycle 2 JWST will limit the time spent carrying out observations in the Micrometeroid Avoidance Zone (MAZ), a region with radius 75 degrees centered on the direction of orbital motion at any given time. These constraints will necessarily lead to shorter visibility windows at ecliptic latitudes below 75 degrees. Science observations that require pointing in the direction of motion (such as time-critical observations) will not be affected.

The Visit Planner in the Astronomer’s Proposal Tool has been updated to provide information on the likelihood of visits falling within the Micrometeroid Avoidance Zone (MAZ). See the APT Micrometeorid Avoidance page. Visits that overlap the MAZ by more than 70% will be flagged for attention. If it is not possible to reduce the overlap below 70% (for example, time critical observations, or observations that require specific orientations, e.g. pairing NIRCam and NIRSpec coordinated parallels), proposers must provide a justification in APT. That information will be available to STScI, but not to the TAC.

All proposers are strongly encouraged to minimize visit overlap with the MAZ. Following the TAC process, it may be necessary to iterate with the Principal Investigators if certain regions are over-populated with observations. STScI will work with proposers to optimize the schedulability of their programs while preserving, as far as possible, the science goals.

If the total MAZ usage exceeds 15% of the cycle time, certain observations or programs may be delayed to future cycles; if, after mitigation, the total usage remains above 20%, observations may be disallowed. Further information on reducing MAZ overlap can be found in the APT Micrometeorid Avoidance page.


  • Survey Programs

Proposers may request short (typically < 90-100 minute) observations to fill gaps identified in the scheduling process. Proposals should include the number of targets needed to address the science goal(s) and example observation(s) in APT. The TAC will be instructed to disregard the telescope time request automatically generated by APT. See Survey Proposals for further information.

  • Joint JWST Proposals

Proposers may request ALMA, Chandra, HST, NASA Keck, NOIRLab and/or XMM-Newton for individual targets in their JWST program. There is no guarantee that joint observations will be obtained simultaneously with JWST observations. See Joint Proposals for further information.


  • JWST can track moving targets at faster rates than anticipated before launch. Targets moving up to 75 mas/s can be tracked by JWST without streaking.
  • Simultaneous NIRCam Coronagraph Short Wavelength (SW) and Long Wavelength (LW) observations are now offered. In this mode, both SW and LW coronagraph observations can be obtained at the same using the same mask.
  • NIRISS Imaging observations can now be requested with NIRISS as the prime instrument.
  • The Exposure Time Calculator (ETC) 2.0 will go live between November 30th and December 7th. ETC 2.0 will incorporate commissioning results and reflect in flight performance.

Next: JWST Proposal Checklist

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