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Lisa telescope assembly optical stability characterization for ESA

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Author: Verlaan, A.L. · Lucarelli, S.
Type:article
Date:2017
Publisher: SPIE
Source:Sodnik, Z.Cugny, B.Karafolas, N., International Conference on Space Optics, ICSO 2014, 7-10 October 2014, La Caleta, Tenerife, Canary Islands, Spain, 10563
series:
Proceedings of SPIE - The International Society for Optical Engineering
Identifier: 842173
ISBN: 9781510616158
Article number: 105634C
Keywords: Optical stability · Optical engineering · High Tech Systems & Materials · Industrial Innovation · Physics & Electronics · OPT - Optics · TS - Technical Sciences

Abstract

The LISA Optical Stability Characterization project is part of the LISA CTP activities to achieve the required TRL level for all of the LISA technologies used. In 2012 the LISA mission was reformulated and transferred to the New Gravitational Observatory (NGO), which has similar performance requirements. This activity targets the demonstration of the Telescope Assembly (TA), with a structure based on CFRP technology, to show that total deformations corresponding to a system CTE of 10-7 K-1 can be passively achieved, i.e., without a dedicated thermal control. In addition it is required to prove that the structure exhibits highly predictable mechanical distortion characteristics when cooling down to ˗90°C, during outgassing in space and when going from 1g environment to 0g. A dedicated test setup is designed and realized to allow monitoring dimensional variations of the TAstructure using three interferometers, while varying the temperature in a thermal vacuum chamber. Critical parameters of the verification setup are the length metrology accuracy in thermal vacuum and the stability. For practical application also a high degree of flexibility and ease of operation are required. The test programme includes CTE measurements and thermal gradient characterization of the Telescope Assembly. This paper describes the current development status of the telescope structure. Previously the test facilities as well as the first test results were presented. In this paper the results of these thermal vacuum experiments are described. These results then are analyzed using FEM analysis and compared to the predicted performance. From this comparison modifications are derived to finely trim the thermo-elastic behavior of the telescope assembly. A second thermal vacuum experiment is performed to validate the improved thermo-elastic performance of this off-axis telescope. A third experiment has been performed, which confirms the findings of the second test.