LYRA: The solar UV radiometer aboard the ESA Proba-2

Abstract

LYRA is the solar UV radiometer that will embark in 2006 aboard Proba{2, a tech- nologically oriented ESA micro-mission. LYRA is designed and manufactured by a Belgian{Swiss{German consortium (ROB, PMOD/WRC, IMOMEC, CSL, MPS & BISA) with additional international collaborations. It will monitor the solar irra- diance in 4 UV passbands. The channels have been chosen for their relevance to Solar Physics, Aeronomy, and Space Weather: 1/ 115-125 nm (Lyman{®), 2/ the 200{220 nm Herzberg continuum range, 3/ Aluminium ¯lter channel (17{30 nm) including He II at 30.4 nm, and 4/ Zirconium ¯lter channel (1{20 nm). The ra- diometric calibration will be traceable to synchrotron source standards (PTB & NIST), and the stability will be monitored by on-board calibration sources (VIS & NUV LEDs). These allow to distinguish between possible degradations of the detectors and ¯lters. Additionally, a redundancy strategy maximizes the accuracy and the stability of the measurements. LYRA will bene¯t from wide bandgap de- tectors based on diamond: it will be the ¯rst space assessment of a pioneering UV detectors program. Diamond sensors make the instruments radiation-hard and solar-blind: their high bandgap energy makes them insensitive to visible light and, thus, make dispensable visible light blocking ¯lters, which seriously attenuate the desired ultraviolet signal. Their elimination augments the e®ective area, and hence the signal-to-noise, therefore increasing the precision and the cadence. The SWAP EUV imaging telescope will operate next to LYRA on Proba{2. Together, they will establish a high performance solar monitor for operational space weather nowcast- ing and research. LYRA demonstrates technologies important for future missions such as the ESA Solar Orbiter