Improvements in the calibration of GIADA's measurement subsystems

The Grain Impact Analyzer and Dust Accumulator (GIADA) is an in-situ instrument devoted to measure the dynamical properties of the dust grains emitted by the comet. Using the GIADA Proto Flight Model (PFM), installed in a clean room in our laboratory, an extended calibration activity citep{Sordini14} has been carried out taking into account the knowledge gained through the analyses of IDPs and cometary samples returned from comet 81P/Wild 2 citep{Brownlee et al. 2006, Rotundi et al. 2014}. GIADA consists of three measurement subsystems: the Grain Detection System, an optical device measuring the optical cross-section of single grain without affecting its dynamical properties; the Impact Sensor that measures the momentum released from each grain that impacts its sensitive surface, and the Micro Balance System, a network of five Quartz Micro Balances measuring the cumulative dust deposition from different space directions citep{DellaCorte14}. The results of the analyses on data acquired with the GIADA PFM and the comparison with calibration data acquired during the pre-launch campaign allowed us to improve GIADA performances and capabilities. We report the results of the following main activities:- definition of a correlation between the two GIADA Models, i.e. PFM and In-Flight Model on-board Rosetta;- characterization of the sub-systems performances (signal elaboration, sensitivities, space environment effects);- new calibration measurements and related curves by means of the GIADA PFM using realistic cometary dust analogues citep{Ferrari14}. All the analyses performed during this extended calibration activity are allowing to fully characterize the dynamic parameters of the dust particles ejected by the comet 67P/Churyumov-Gerasimenko citep{Rotundi et al. 2015, Fulle et al. 2015, Della Corte et al. 2015}.