The FIRST ESA cornerstone mission

The 'Far InfraRed and Submillimetre Telescope', (FIRST), is the fourth European Space Agency (ESA) cornerstone mission (CS4) in the current 'Horizons 2000' science programme. FIRST will perform photometry and spectroscopy in approximately the 80-670 mu m range in the far infrared and submillimetre part of the spectrum. The key scientific topics to be addressed by FIRST will include subjects as diverse as how and when galaxies formed in the universe, interstellar medium physics and chemistry including large- and small-scale star formation - which in turn is linked to galaxy formation - in our own and external galaxies, and observations of solar system objects. In the course of recent years there has been a gradual shift in emphasis towards extragalactic astronomy. FIRST will have a passively cooled 3.5m diameter Cassegrain/Ritchey-Chretien telescope, to be provided by NASA, and a science payload complement of three instruments, which will be provided by Principal Investigators (PIs) and their consortia. The focal plane units of these instruments will be housed inside the payload module which provides a cryogenically cooled environment using the superfluid helium cryostat technology developed for the successful ESA Infrared Space Observatory (ISO) mission. It has been decided to perform a joint implementation of FIRST and the Planck cosmic microwave background mapping mission. The nature still has to be decided upon; the baseline being sharing a spacecraft facility - the 'merged' mission - with a Planck payload module containing the two Planck instruments and telescope to be accommodated under the FIRST service module. In this configuration the FIRST and Planck observations would be carried out consecutively and independently of each other. Irrespectively of the details of the implementation - which have only minor implications for the FIRST payload module - FIRST has teen conceived as a multi-user observatory. It will be open to the general astronomical community on the basis of calls for observing time proposals, and is scheduled to perform routine observations from year 2006, operating from an orbit around the L2 Lagrangian point in the Earth/Moon-Sun system about 1.5 million km away from the Earth.