To PLAnetary Transit Or NOT? An extremely large field of view camera with a CaF2 component tested in thermo-vacuum

TL;DR

This paper reports on extensive thermo-vacuum testing of a 200mm class optical camera with a CaF2 lens, demonstrating its robustness and suitability for space missions like PLATO.

Contribution

It provides the first comprehensive thermo-vacuum test results of a CaF2 lens in a space-like environment, confirming its viability for space optical systems.

Findings

CaF2 lens successfully passed all thermo-vacuum tests

The material showed no fragility issues during handling and testing

The prototype met the requirements for space mission applications

Abstract

Because of its nicely chromatic behavior, Calcium Fluoride (CaF2) is a nice choice for an optical designer as it can easily solve a number of issues, giving the right extra degree of freedom in the optical design tuning. However, switching from tablet screens to real life, the scarcity of information -and sometimes the bad reputation in term of fragility- about this material makes an overall test much more than a "display determination" experiment. We describe the extensive tests performed in ambient temperature and in thermo-vacuum of a prototype, consistent with flight CTEs, of a 200mm class camera envisaged for the PLATO (PLAnetary Transit and Oscillations of Stars) mission. We show how the CaF2 lens uneventfully succeeded to all the tests and handling procedures, and discuss the main results of the very intensive test campaign of the PLATO Telescope Optical Unit prototype.