PRONAOS : a two meter submillimeter balloon borne telescope Original Research Article

PRONAOS is a French balloon borne 2 meter sub-millimeter telescope for astronomy. Developed and operated from 1986 to 1999, it has been a precursor for the two European space missions to be launched in 2007: FIRST and Planck-Surveyor. PRONAOS has been built as a light and autonomous space platform able to resist the very hostile environment at the altitude of 40 kilometers. It has thus driven many technological developments such as a light carbon-fiber active optics, a daylight star-tracker, high sensitivity 300 mK bolometers and a pointing system with a 5 arc-seconds accuracy. With three successful stratospheric flights the major scientific contributions of PRONAOS have been : 1) The first measurement of the positive part of the spectral distortion of the Cosmic Microwave Background toward a cluster of galaxies. 2) The discovery of a cold dust phase in the Galactic interstellar medium, with temperatures ranging from 12 to 15 K, and evidence for new dust emissivity properties.