Design and development of the PRIMAger instrument for PRIMA

PRIMA (PRobe far-Infrared Mission for Astrophysics) is an infrared space observatory designed to operate over the next decade. It would be equipped with a 1.8 m telescope actively cooled to 4.5 K, and the project is currently in the concept study phase as part of NASA's Probe Explorers program. PRIMA will carry two instruments: FIRESS and PRIMAger.

PRIMAger will offer two observation modes: hyperspectral imaging and polarimetric imaging. Both channels will use ultra-sensitive kinetic inductance detector (KID) arrays covering wavelengths from mid-infrared to far-infrared. The hyperspectral mode will cover the 24–84 µm range with a spectral resolution of R ≥ 8, ensured by a linear variable filter placed in front of the detector. The polarimetric mode will provide polarimetric imaging in four broad bands from 92 to 235 µm, using KIDs with three polarization orientations.

A European consortium will develop the cold unit of the PRIMAger instrument, while the Readout Electronics and Continuous Adiabatic Demagnetization Refrigerator (CADR) will be provided by Goddard Space Flight Center (GSFC) and shared between the two instruments. The main structure of the instrument is the optomechanical assembly, cooled at 1 K. It supports the two focal plane array assemblies incorporating 0.125 K detector stages and provides interfaces for the 0.125 K thermal link, the readout cables, and the filters.

This paper presents the technical requirements and expected performance of the instrument, as well as the associated design of the sub-systems ensuring compliance. A major challenge will be in-flight performance verification. It also details the development strategy, including the planned verification and test program.