Opto-mechanical design for PRIMAger instrument of the PRIMA mission

PRobe far-Infrared Mission for Astrophysics (PRIMA), is an infrared observatory for the next decade, with a 1.8 m telescope actively cooled to 4.5 K, currently in mission concept study of Probe Explorers part of Explorer Program. PRIMAger, one of two instruments, will provide two channels, hyperspectral from 24 to 84 μm with a spectral resolution R ≥ 8 and polarimetric from 80 to 264 μm. The Laboratoire d’Astrophysique de Marseille is in charge of the system engineering, of the delivery of the opto-mechanical assembly as well as the integration of the instrument. In this paper we will describe the opto-mechanical design based on off-axis freeform Aluminium mirrors. The mechanical design will be also presented including the carbon fiber bi-pods that allow to maintain and thermally isolate the 1K structure from the 4.5K metering payload structure. We will present the development plan strategy as well as the overall verification strategy especially the optical alignment and tests.