The ESA Astronomy Missions at L₂: FIRST and Planck

Abstract

FIRST and Planck are approved ESA Astronomy missions with different objectives but with similar requirements of a highly stable thermal environment and sky viewing conditions unobstructed by Earth and Sun. A class of orbits near the second Lagrangian point L₂ in the Sun-Earth system has been selected for these projects.

FIRST will investigate a region of the electro-magnetic spectrum still unexplored (85– 670 µm) i.e. the far infrared. These observations are expected to reveal very cold and distant building blocks of the universe.

Planck is a third-generation tool for the mapping of the cosmic background radiation anisotropy. The study of this “relic” radiation will allow a study of unprecedented accuracy of the universe as it was only 300,000 years after the Big Bang.

Both scientific payloads require sub-Kelvin temperatures at the limit of today’s cooling technology for space.

The two spacecraft will be launched from Kourou by a single Ariane 5 in early 2007, into a nearly equatorial and nearly parabolic orbit. This orbit can be chosen to be on the stable manifold of a large amplitude Lissajous orbit around L₂. The choice of the target Lissajous orbit will depend on the launch date. FIRST will then remain on this orbit, without any further, deterministic maneuvers. Planck will perform an “amplitude reduction maneuver” onto the stable manifold of another Lissajous orbit which at the end has a maximum Sun-spacecraft-Earth angle of less than 10° as required for the Planck mission design. The scientific observations at L₂ will last a minimum of three years (FIRST) and one year (Planck).