JANUS is a multi-filter optical camera part of the JUICE ESA Mission, that has been launched last April from the French Guiana towards the Giovian system, where it will arrive in 2031. During the design phase of the instrument an extensive Straylight Analysys has been carried on, but after AIV the need to update the analysis on the base of the 'as built' system has become desiderable, to better interpretate the calibration data and prepare for science phase. We here report about this update, covering the rationale of the update, the used methodology and the obtained results.
JANUS (Jovis Amorum Ac Natorum Undique Scrutator) is a high-resolution camera operating in the spectral range 340-1080 nm and designed for the ESA space mission JUICE1 (Jupiter Icy moons Explorer) planned for launch in 2023 and arrival at Jupiter in 2031. The main scientific goal of the mission is the detailed investigation of Jupiter and its Galileian moons: after three years in Jupiter orbit and many fly-bys with the icy moons, JUICE will be the first spacecraft to be inserted in orbit around Ganymede in 2032. During the final stage of the mission, JANUS is expected to provide images of the moon surface with ground sampling up to 7.5 m/pixel in both panchromatic and narrow band spectral ranges. Leonardo Spa is the JANUS prime contractor and is in charge, on behalf of the Italian Space Agency (ASI) and in collaboration with the science team led by Parthenope University and the Italian Institute of Astrophysics (INAF), of developing and integrating the Opto-Mechanical Structure of JANUS Optical Head Unit (OHU). The present paper will discuss the procedure adopted for the integration of the OHU and the results in terms of optical quality of the system in flight conditions. Ensuring a Modulation Transfer Function (MTF) close to the diffraction limit at the Nyquist frequency of 71.4 cy/mm constitutes the main challenge for the telescope integration and sets the maximum acceptable transmitted wavefront error to be at most a few tens of nm over the whole field of view.
The Advanced Infrared Detection Assembly Dual Band (AIDA-2B) project, part of the Skyward instrument, is an imager that consists of a main Aluminum alloy metallic frame attached to the Sensor Head Unit (SHU) chassis by means of thirteen screws. The imager features several subassemblies among which the FOV change & focusing mechanism. This mechanism has two separately actioned trolleys that allow the FOV change and focusing movement. Each trolley moves on two linear ball slides and is actuated by a lead screw. In order to achieve challenging optical performance target in the infrared range, the introduction of chalcogenide glass is required. IG4 is the material selected for the lens installed on one of the two trolleys of the focusing mechanism. Such material features excellent thermal properties (such as almost constant refraction index in the whole temperature range), but suffers from an extreme fragility and very weak mechanical properties. In order to employ such material in a challenging mechanical environment such as an airborne IRST instrument a 'floating' design is necessary, with the glass attached to the mechanical mounting by means of adhesive pads, and no metal-glass contact. A description of the design solutions developed, manufactured and qualified for the most critical optical mount inside the Instrument is presented. This paper contains a collection of mechanical results obtained on the optical mount breadboards, including a description of environmental tests performed. Three configurations for the lens mounting have been designed and tested: 1. C-shaped profile; 2. Thin ring; 3. Crown ring. The comparison between these high stability optical mounts based on adhesive joints, as well as the acceptance criteria derived in order to establish the flight worthiness of the manufactured and assembled hardware, are presented in this paper.
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