Design of VISTA, a quartz crystal thermogravimetric analyzer for Hera mission

In this work, the mechanical design of VISTA (Volatile In-Situ Thermogravimetric Analyzer), a quartz crystal microbalance for space application is presented. VISTA was selected as part of the scientific payload onboard the Milani CubeSat, within the framework of the ESA Hera mission targeting the Didymos binary asteroid system. The mission will reach the asteroid complex after the NASA DART (Double Asteroid Redirection Test) mission pierced the Didymos secondary body, and aims to characterize the system after the impact. VISTA sensor will measure volatiles and dust particles around Didymos by thermogravimetric analysis performed with the quartz crystal microbalances. Embedded resistors, deposited on the quartz crystals, and a TEC assure an active temperature control at the sensing region, allowing to condensate, sublimate, and desorb volatiles from the sampled material. Sample mass variation can be inferred by measuring the crystals beating frequency before and after the desorption. Moreover, the chemical composition of the sampled material can be inferred by measuring the temperature of the sensing crystal during the desorption. The latter functionality can be performed using the deposited resistors as temperature sensors. The thermomechanical design of VISTA is presented, resulting from the design phase performed by developing finite element models of the instrument to assure mechanical resistance within the mission environment. The obtained results highlight the compliance of the design with the mission requirements. Finally, preliminary results of the VISTA integration activities are shown. Indeed, the next phase of this research activity foresees assembling an engineering model of the instrument to be qualified within the mission environmental conditions.