The Origins Survey Spectrometer (OSS) for the Origins Space Telescope: Enabling Unbiased Spectral Surveys of Galaxies through Cosmic Time.

The Origins Survey Spectrometer (OSS) is a multi-purpose wideband spectrograph for the Origins Space Telescope. The sensitivity possible with the combination of the actively-cooled 5.6-meter Origins telescope and new-generation far-IR direct detector arrays is outstanding; potentially offering a 10,000x improvement in speed over Herschel and SOFIA for individual pointed measurements, and factor of more than 1,000,000 for spatial-spectral mapping. Massive galaxy detection rates are possible via the rest-frame mid- and far-IR spectral features, overcoming continuum confusion and reaching back to the Epoch of Reionization. OSS covers the full 25 - 585 micron band instantaneously at a resolving power (R) of 300, using 6 logarithmically-spaced grating modules. Each module couples at least 30 and up to 100 spatial beams simultaneously, enabling true 3-D spectral mapping, both for blind extragalactic surveys and for mapping all phases of interstellar matter in the Milky Way and nearby galaxies. Furthermore, two high-resolution modes are provided. The first inserts a long-path Fourier-transform interferometer into the light path in advance of the grating backends, enabling R up to 38,000 x [100 microns / lambda], while preserving the grating-based sensitivity for line detection. The second incorporates a scanning etalon to provide R up to 300,000 for the 100-200 micron range for velocity-resolved tomography in proto-planetary disks using the lower rotational transitions of HD and water. OSS requires large arrays of direct detectors with the per-pixel sensitivity meeting or exceeding the photon background limit due to zodiacal and Galactic dust: NEP~3e-20 W/sqrt(Hz). The total pixel count for all 6 bands is ~100,000 pixels. We review the rapid progress in this area, and outline milestones for demonstrating flight readiness (TRL 6). We thank NASA, GSFC, Caltech/JPL, Ames, IPAC, STScI and industry partners Ball Aerospace, Northrop-Grumman, Harris, and Lockheed-Martin for their generous support of the Origins study. To learn more about Origins see our websites (https://origins.ipac.caltech.edu and https://asd.gsfc.nasa.gov/firs/) and report (https://asd.gsfc.nasa.gov/firs/docs/OriginsVolume1MissionConceptStudyReport.pdf).