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 OST telescope and new far-IR direct detector arrays is outstanding; potentially offering a 10,000x improvement in speed over Herschel and SOFIA for point-source 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. The OSS has been optimized for scientific return over the course of the OST study. It covers the full 25 to 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 the blind extragalactic surveys and for mapping 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 protoplanetary disks using the ground-state transitions HD and H2O. 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. These sensitive far-IR detector arrays are not provided by the kind of industrial efforts producing the the optical and near-IR detectors, but they are being developed by NASA scientists, including OST team members. We review the rapid progress in this area, and outline milestones for demonstrating flight readiness (TRL 6).