Progress Towards Understanding the Degradation and Performance Characteristics of the PROBA2-LYRA Instrument

The Large Yield Radiometer, LYRA is a solar radiometer on the ESA PROBA2 spacecraft launched November 2, 2009. LYRA has been designed to provide measurements of the solar XUV to MUV (soft X-ray to middle ultraviolet) region of the solar spectrum. The LYRA instrument observes in four broad spectral channels, from soft X-ray to UV, chosen for their relevance to solar physics and space weather. Each of the four channels has the capability of acquiring irradiance measurements at a nominal cadence of 20 Hz, but can be increased to 100 Hz. Each of the four channels has suffered from significant degradation almost immediately after launch. The degradation observed in the LYRA channels is significant and detrimental to the potential science. Preliminary work in this effort has shown that the most likely cause of the observed degradation is contaminant buildup on the filters at the front of the instrument. In this work, we present initial results of our investigation into the performance characteristics and observed degradation. We have developed and will present results from our three-step approach: 1. Develop models for each LYRA channel using measured calibrations and instrument design parameters; 2. Use the models to estimate the sensitivity changes due to possible degradation sources (thickness and composition); 3. Evaluate corrected sensor performance by comparing the measured data with independent measurements from currently operating instruments.