29 July 2016 A display model for the TOU of PLATO: just a cool toy or a benchmark of opportunities?
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We produced a "toy-model" of one Telescope Optical Unit of PLATO, the Medium sized mission selected by ESA to fly in 2024. This is a six lenses dioptric very wide field camera with a window in front to take care of radiation impact on the first lens whose optical glass cannot be replaced with a radiation hardened one. The main aim of this project is just to produce a "cool" model for display purposes, in which one can "explore" the details of the inside through some openings in the tube, in order to visually inspect some of the fine details of the opto-mechanics. While its didactic and advertising role is out of doubt, during its construction we realized that some interesting outcome can be of some relevance for the project itself and that some findings could be useful, in order to assess the ability of producing with the same technology some (of course of much more modest quality) optical systems. In this context, we immediately dropped the option of producing the lenses with opaque material painted with a color resembling a refractive material (like blue for instance) and decided to actually produce them with transparent plastic. Furthermore the surfaces are then finely polished in order to give them basic optical properties. Such an optical system has only very coarsely the converging properties of the original nominal design for a number of reasons: the refractive indexes are not the nominal ones, the quality of the surfaces and their nominal values are only roughly, within a few percent, the targeted one, and the way the surfaces are built up makes them prone to some diffraction effects. However, the bulk of the lens and the surface roughness will give a large magnification of the scattering effects that will be experienced, at a much lower level, on the actual flight model. We investigated through propagation of a laser beam and by digital camera the main stray light modes that this toymodel offers. In other words, the model amplifies, to a large extent, the negative bulk scattering and spurious reflection just because surfaces and materials are orders of magnitude rougher that the intended ones. Even if this did not allow to attempt to make any quantitative measurement, in order to scale down to the actual one, we used it to look out independently for the main sources of stray light and we compared them with the one discussed by the optical design team, obtained using professional ray tracing code. Finally, we point out some of the technicalities used in the design to mimic the finest mechanical elements that cannot be safely incorporate in the final design and to produce pieces of size much larger than the maximum volume allowed by our 3D printer in a single shot.
© (2016) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
M. Dima, M. Dima, D. Greggio, D. Greggio, M. Bergomi, M. Bergomi, F. Biondi, F. Biondi, J. Farinato, J. Farinato, G. Farisato, G. Farisato, D. Magrin, D. Magrin, L. Lessio, L. Lessio, L. Marafatto, L. Marafatto, M. Munari, M. Munari, I. Pagano, I. Pagano, R. Ragazzoni, R. Ragazzoni, V. Viotto, V. Viotto, D. Piazza, D. Piazza, } "A display model for the TOU of PLATO: just a cool toy or a benchmark of opportunities?", Proc. SPIE 9904, Space Telescopes and Instrumentation 2016: Optical, Infrared, and Millimeter Wave, 990432 (29 July 2016); doi: 10.1117/12.2232938; https://doi.org/10.1117/12.2232938


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