SPM, a submillimeter photometer for PR0NAOS

Abstract SPM is a multi-channels photometer designed to obtain the best sensitivity at the focus of the 2 m balloon-borne PRONAOS telescope. Its scientific goals include the measurement of cosmological background anisotropy, which is important for understanding the origin of the structure in the universe and the observation of cold solid matter in the interstellar medium as an indicator of the physical conditions that prevail in star forming regions. SPM consists of warm optics that ensure beam switching and in-flight calibration, a liquid helium cryostat that contains filters and the 3 He cooled bolometers, and electronics for housekeeping and data handling. The spectral bands are 180–240 μm , 240–340 μm , 340–540 μm and 540–1200 μm . They are defined by dichroics, which allows simultaneous observations in the four bands. The expected NEΔT in flight is significantly less than 1 mK in all the bands. SPM will fly with PRONAOS in May 1994.