On-orbit JWST backgrounds from stray light and thermal emission

Erin C. Smith; Jane R. Rigby; Michael W. McElwain; Charles W. Bowers; Randy A. Kimble; Christopher C. Stark; Paul A. Lightsey; Macarena Garcia Martin; Alistair C. H. Glasse; Ben Sunnquist; Brian Brooks; Martha L. Boyer

doi:10.1117/12.2630524

27 August 2022 On-orbit JWST backgrounds from stray light and thermal emission

Erin C. Smith, Jane R. Rigby, Michael W. McElwain, Charles W. Bowers, Randy A. Kimble, Christopher C. Stark, Paul A. Lightsey, Macarena Garcia Martin, Alistair C. H. Glasse, Ben Sunnquist, Brian Brooks, Martha L. Boyer

Author Affiliations +

Proceedings Volume 12180, Space Telescopes and Instrumentation 2022: Optical, Infrared, and Millimeter Wave; 121800R (2022) https://doi.org/10.1117/12.2630524
Event: SPIE Astronomical Telescopes + Instrumentation, 2022, Montréal, Québec, Canada

Abstract

Backgrounds observed by JWST will be a critical parameter for overall observatory sensitivity. JWST’s background, sensitivity and other performance requirements drove the observatory’s open architecture, sunshield geometry, orbit at L2 and other unique characteristics. These requirements were verified by analysis, to be measured for the first time on-orbit. Modeling JWSTs backgrounds is complex, as JWST backgrounds have multiple components including: backgrounds from in-field sources (such as Zodiacal Light) and stray light from scattering of sky sources outside the field; thermal selfemission of optical surfaces; and scattering of thermal self-emission from other Observatory surfaces. The unbaffled telescope design allows stray light paths from multiple directions. The 5-layer sunshield passively cools and shades the telescope and science instruments; however, there are thermal paths that may affect thermal performance. In-field backgrounds and stray light from sky sources can depend on the telescope’s pointing and observation date. The thermal emission contributions will depend on the Observatory’s sun orientation and recent history. The JWST Background Tool (JBT) uses the stray light models, in-field backgrounds, and thermal models to predict the expected backgrounds. Onorbit, several positions were measured at multiple wavelengths with NIRCam and MIRI to probe JWST’s backgrounds and validate model predictions. These results may be used to update the JWST Exposure Time Calculator in preparation for the Cycle 2 proposal call. This conference proceeding will provide a summary of the modeling backgrounds and report on the measured on-orbit backgrounds.

Conference Presentation

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Erin C. Smith, Jane R. Rigby, Michael W. McElwain, Charles W. Bowers, Randy A. Kimble, Christopher C. Stark, Paul A. Lightsey, Macarena Garcia Martin, Alistair C. H. Glasse, Ben Sunnquist, Brian Brooks, and Martha L. Boyer "On-orbit JWST backgrounds from stray light and thermal emission", Proc. SPIE 12180, Space Telescopes and Instrumentation 2022: Optical, Infrared, and Millimeter Wave, 121800R (27 August 2022); https://doi.org/10.1117/12.2630524

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