The DIANA instrument for Tianwen 2 mission

The CNSA (China National Space Administration) Tianwen 2 mission [1] will study and sample the Kamo’oalewa near-Earth asteroid and then rendezvous with the 311/PANSTARRS Main Belt Comet (MBC). The mission is scheduled to launch in May 2025, with arrival at Kamo’oalewa in 2026. Then, the spacecraft will land on the asteroid and collect samples of its surface, and deliver them to Earth around 2027. The main spacecraft will then head for 311P/PANSTARRS, which has asteroid-like orbital characteristics but also features comet-like activity. The mission aims at providing insight into the composition and evolution of near-Earth objects and understand the distribution of water and organic molecules and the history of the early Solar System.The mission includes several instruments, such as multispectral cameras, thermal emission spectrometer, imaging spectrometer, mass spectrometer, a magnetometer and a dust analyser. The dust analyser is a suit of different sensors, including the DIANA (Dust In situ ANAlyser) instrument.DIANA is based on Quartz Crystal Microbalance (QCM) devices, aiming at detecting dust and volatiles content, as well as assessing contamination on board the spacecraft. This kind of sensors converts mass changes into fundamental resonance frequency variations, according to Sauerbrey equation [2]. DIANA can be heated thanks to the crystals built-in heaters [3] or cooled by a Thermo-Electric Cooler (TEC). Thanks to its customized design [4], DIANA is capable of performing Thermo-Gravimetric Analysis (TGA), a technique widely used to study mas variation processes as a function of temperature, in order to measure the abundance of volatile compounds of astrobiological interests (e.g. water, organics) in the cometary dust and reveal the occurrence of contaminants that could condense on the crystal.DIANA payload is composed by: 1) a sensor head (DIANA SH1), that works at low temperature (i.e. 225-400K), to measure the dust flux and the amount of physically absorbed water, as well as contamination assessment during Tianwen2 cruise phase; 2) a sensor head (DIANA SH2), that works at higher temperatures (up to 500K), to measure the dust flux and amount of organic components; 3) a Main Electronics Unit (MEU), to read SH1 and SH2 frequencies and temperatures and set the heating ramp rates for TGA.The technical characteristics of DIANA are shown in Table 1, while the two sensor heads are shown in Figure 1.Table 1. DIANA technical characteristics.Figure 1. DIANA sensor heads: SH1 on the left and SH2 on the right.DIANA was developed by an Italian Consortium led by INAF-IAPS (Istituto Nazionale di AstroFisica-Istituto di Astrofisica e Planetologia Spaziali), in collaboration with CNR-IIA (Consiglio Nazionale delle Ricerche-Istituto sull’Inquinamento Atmosferico) and Politecnico di Milano-MetroSpace Lab. The MEU was developed in collaboration with Shanghai Institute of Technical Physics (SITP).Acknowledgments: DIANA development activities are funded by the Italian Space Agency through the ASI-INAF Agreement 2022-27-HH.0.References:[1] Zhang, X. et al. (2019), LPSC abstracts, 1045[2] Sauerbrey, G. (1959), Z. Phys, 155, 206–222[3] Palomba, E. et al. (2016), OLEB, 46, 273-281[4] Martina, C. et al. (2024), IAC abstracts, 8785