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Paper: Science Concept for an Improved JWST Mosaic Planning Tool
Volume: 512, Astronomical Data Analysis Software and Systems XXV
Page: 543
Authors: Valenti, J. A.
Abstract: The James Webb Space Telescope (JWST) will spend a significant fraction of its mission lifetime obtaining mosaic data. In the Science Operations Design Reference Mission, which is a plausible pool of JWST science programs, approximately one third of the science time is used for mosaics, including 50% of the NIRCam imaging time and 70% of the MIRI imaging time. The baseline mosaic capability for JWST produces a rectangular grid of pointings with overlap, skew, and rotation parameters. JWST uses a sunshield for passive cooling, so the instantaneous range of allowed roll angles is narrow and depends on when an observation is scheduled. This means baseline mosaics are often valid only in relatively narrow scheduling windows, especially when using rectangular NIRCam tiles. The flexible mosaic concept presented here would allow users to specify an irregular sky region of interest, possibly containing interior subregions that need not be mapped. A simple heuristic algorithm automatically determines a tile pattern that fully covers the sky region at one roll angle. A first pass determines the minimum number of tiles needed to completely cover the sky region as a function of roll angle. A second pass determines the fraction of the sky region covered by a fixed number of tiles as a function of roll angle. The proposer requests and the TAC approves a fixed number of tiles, simplifying subsequent accounting. More importantly, the mosaic can be rescheduled without contacting the observer. The tool also provides the user with feedback on guide star availability for all tiles as a function of roll angle. This simplified mosaic approach would make it easier for proposers to submit nearly complete programs, shortening the time between proposal submission and program execution. This concept has not yet been approved for implementation, but could be ready for Cycle 2 of JWST.
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