The Janus COM mechanism onboard the JUICE probe to the Jovian system

Abstract. After the successful launch of the JUICE (JUpiter ICy moons Explorer) on the 14th of April 2023 all the on board subsystems and instrument are testing their functionalities. The JANUS (Jovis, Amorum ac Natorum Undique. Scrutator) telescope is the imaging system on board the spacecraft and is an optical camera devoted to the study of global, regional and local morphology and processes on the Jovian moons, and to perform mapping of the clouds on Jupiter. Following the heritage of the successful design of the OSIRIS WAC camera, on board the Rosetta mission, the group of researchers at CISAS “Giuseppe Colombo”- Università degli studi di Padova, led by prof. S. Debei, in collaboration with colleagues of the Leonardo spa Company developed the mechanism responsible for the protection of the telescope during cruise phase. The COver Mechanism (COM) provides the external closure of the JANUS Optical Head Unit (OHU). It shields the optical parts from contamination, it is light and dust tight and works in the plane of the telescope entrance window avoiding the exposure of the inner surface of the cover itself and the core part of the telescope to the external dust and pollution. The lower part of the cover provides, also, a reference surface for the in-flight calibration of the telescopes. The main functional and environmental requirements of this mechanism can be identified and summarized as follows: the door provides optics and detector protection from sunlight and contamination; the subsystem, located at the main entrance of the JANUS OHU outer Baffle, provides the function of opening and closing of the cover. The opened Cover allows the JANUS OHU and detector to face the outer environment to perform planetary observations during science mission phases and to perform in-flight calibration observation of different targets (e.g., moons, stellar fields). This paper presents the design, the mechanical solutions adopted for a reliable system and the results of the test performed on ground in order to qualify the JANUS COM mechanism before flight.