Introduction

STEP/MiniSTEP homepage http://www.estec.esa.nl/spdwww/future/html

Study activities during the reporting period included five Phase A mission studies: two in solar system sciences, two in astronomy and one in fundamental physics. These studies led, after peer review, to the selection of Planck as the M3 medium- size mission of the Horizon 2000 long-term programme.

Further studies were carried out in preparation for the Cornerstone missions designated in the Horizon 2000 Plus plan. The 'Interferometry' Cornerstone is not yet fully defined as two options are being pursued: the Global Astrometric Interferometer for Astrophysics (GAIA) and an alternative mission to search for extra-solar terrestrial planets (Darwin). A considerable effort was made, in concert with the community involved, to reduce the cost of the fundamental physics Cornerstone LISA (Laser Interferometer Space Antenna) by optimising the mission design while maintaining the original goal of detecting and studying low frequency gravitational waves.