The payload for FIRST (far infrared and submillimeter telescope)

The FIRST mission is one of the cornerstones of ESA´s Horizon 2000 programme. It consists of a large, accurate dish (4.5 to 8 metre diameter) and a powerful collection of scientific instruments for operation in the spectral region 500 to 3000 GHz (wavelengths of 600 down to 100 microns). The scientific emphasis is on studying the complex astrophysical processes that occur when gas, dust, radiation and magnetic fields interact in such objects as protostars, `starburst´ galaxies and quasars. The intention is to match the high angular resolution and collecting area provided by the large size of the dish by a suite of instruments combining high sensitivity and spectral resolution. For this wavelength range there are three candidate technologies available, each of which has optimal properties for different applications, as discussed