A spin-off of space technology: highly accurate reflector panels for a prototype ALMA radiotelescope

The ALMA (Atacama large millimetre array) project aims at a realisation of a 64-element radiotelescope ground array with 12 m Cassegrain antennas as single receiving elements. The receivers will operate between 30 and 900 GHz, thus putting very stringent requirements on each separate element or 12 m Cassegrain antenna. National Radio-Astronomy Organisation, NRAO, (USA) and European Southern Observatory, ESO, (Europe) have collaborated to realise, in 2003, two prototype antennas (for details, see www.eso.org under Atacama project). Surface accuracy requirements are below 10 μm rms. An interesting technology has been selected for the reflector panels in one prototype: electroforming. The technology applied for the antenna reflector panels comes as a spin-off from a dedicated space technology development carried out for the XMM X-ray satellite project (www.esa.int and search for XMM). The technological developments needed to arrive at such accurate reflector panels are described, together with results and related achievements.