SWAP and LYRA: Space weather from a small spacecraft

Abstract

Two scientific instruments for Sun observations are being developed to be part of the payload of the ESA's second microsatellite, Proba-II (Project for On-board Autonomy). PROBA-2 is scheduled for launch in early 2007, on a low earth orbit. Like Proba-1, in orbit since October 2001, Proba-2 is a 100-kilogram class spacecraft. PROBA-II will demonstrate new advanced technologies on its scientific payload but also on new platform subsystems such as star tracker, digital Sun sensor, cool gas generator, solar array concentrator, Li-lon Battery, new central processor,... This paper is dedicated to the solar payload, comprising the Sun Watcher using Active Pixel System detector and image Processing (SWAP) and the Lyman alpha Radiometer (LYRA), both aiming at Sun observations. SWAP, the Belgian-led main instrument, will continuously provide detailed images of the solar atmosphere, by the light of extreme ultraviolet rays, at 17.4 nm, completely absorbed by the terrestrial atmosphere. SWAP will perform as an operational solar monitoring tool for space weather forecasting while it will also demonstrate new technological solutions: CMOS/APS detector, new off-axis telescope design, athermal structure,... LYRA (LYman-alpha RAdiometer) is a small compact solar VUV radiometer. This instrument is designed, manufactured and calibrated by a Belgian-Swiss-German consortium. It will monitor the solar flux in four UV passbands. The spectral channels have been carefully selected for their relevance to space weather, solar physics and aeronomy, ranging from 1 nm to 220 nm. On the technological side, LYRA will benefit from the pioneering UV detectors program using diamond technology. The LYRA data will produce valuable solar monitoring information, for operational space weather nowcasting and research. This paper will detail the instrument concepts and their preparation for delivery to the platform.