The far-infrared enhanced survey spectrometer (FIRESS) for PRIMA

FIRESS is the multi-purpose spectrometer proposed for the PRobe far-Infrared Mission for Astrophysics (PRIMA). The sensitive spectrometer on the cold telescope provide factors of 1,000 to 100,000 improvement in spatial-spectral mapping speed relative to Herschel, accessing galaxies across the arc of cosmic history via their dust-immune far-infrared spectral diagnostics. FIRESS covers the 24 to 235 micron range with four slit-fed grating spectrometer modules providing resolving power between 85 and 130. The four slits overlap in pairs so that a complete spectrum of any object of interest is obtained in 2 pointings. For higher-resolving-power studies, a Fourier-transform module (FTM) is inserted into the light path in advance of the grating backends. The FTM serves all four bands and boosts the resolving power up to 4,400 at 112 microns, allowing extraction of the faint HD transition in protoplanetary disks. FIRESS uses four 2016-pixel arrays of kinetic inductance detectors (KIDs) which operate at the astrophysical photon background limit. KID sensitivities for FIRESS have been demonstrated, and environmental qualification of prototype arrays is underway.