VISTA: Dust and Volatile Sensor for the ESA Hera Mission

Abstract VISTA (Volatile In-Situ Thermogravimeter Analyzer) is a QCM (Quartz Crystal Microbalance) based device designed to characterize the dust environment of the Didymos asteroid system by detecting the presence of dust particles with sizes smaller than 5-10 $\mu $ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>μ</mml:mi> </mml:math> m and sub- $\mu $ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>μ</mml:mi> </mml:math> m, as well as volatiles and light organics, within the framework of the European Space Agency (ESA) Hera Mission. Thanks to its customized subsystems design, VISTA is capable of monitoring deposition and desorption/sublimation processes in the space environment, as well as molecular contamination (in support to other instruments) originating from outgassing sources during different mission phases, and of performing Thermo-Gravimetric Analysis (TGA) on the collected materials. The VISTA Model development for Hera started in 2020 and continued through 2023, and included an Engineering Qualification Model 0 (EM 0 ), an Engineering Qualification Model (EQM), a Flight Model (FM) and a Flight Spare (FS). The EM 0 was electrically and mechanically representative of VISTA, while the EQM, FM and FS share the same mechanical structure and electrical connections. The prototype, as well as the Engineering, Flight and Spare Models, were delivered to the prime contractor, Tyvak International. VISTA Models are composed by three different subsystems: two quartz crystals mounted in a sandwich-like configuration; the Proximity Electronics; and the Thermal Control System, which includes two integrated and customized heaters and a Thermo-Electric Cooler to cool the sensor and facilitate dust and volatiles deposition. The VISTA EQM, FM and FS successfully passed the Qualification and Acceptance Test Campaigns. The main results obtained from simulations of particles and volatiles deposition in a vacuum chamber, heating cycles, and Thermo-Gravimetric Analyses are reported in this work.