In this paper, a validated procedure to replace the protective front-window of a commercial digital micro-mirror device (DMD) from Texas Instruments (TI) to allow its use over a large spectral range is presented. This reworking process was required since the original window employed for encapsulation is made from glass with an anti-reflection coating designed for a specific spectral range, incompatible with the required large spectral range of the demonstrator under development. In addition, a characterisation of the DMD performance in terms of spectral transmission, as well as switching time and pointing stability is presented. The motivation behind this study lies within the development of a novel instrument in the frame of the EU H2020 funded SURPRISE project. The project aims at developing a super-resolved compressive imager operating in the visible-near infrared (VNIR) and mid-wave infrared (MWIR) spectral ranges for space applications, especially targeting Earth Observation. The instrument concept is based on the use of a spatial light modulator (SLM), in this case a digital micro-mirror device (DMD), as a core element of its architecture to enable data acquisition and compression in single step based on the compressive sensing principle. Even though one of the long-term objectives is to develop a European-based SLM solution, a commercial SLM component has been selected for the demonstrator This allows reducing the development cost and initiating the development of the demonstrator in parallel to the development of a European-based solution.
Spatial Light Modulator (SLM) technologies are well established in many application fields over the last decades. Addressing challenging operational conditions, a special class of high-speed SLMs has emerged over the past 20 years, namely Micromirror Array (MMA) devices. Fraunhofer IPMS MMA technology has enabled several ultraviolet photolithography applications at industrial scale. Given the fact that these devices are available for scientific testing, we proposed to explore for the first time their functionality and performance with respect to the space application requirements for the European framework cooperation. Previous studies strongly support this approach with the investigation of several SLM technologies for space instrumentation. In this study, the key parameters of an already available 256 x 256 pixel MMA device have been assessed and its performance has been evaluated under environmental constraints of a future space mission, in terms of temperature (from -40 °C to 80 °C), vacuum (< 10-5 mbar) and vibrations in X-, Y- and Z-axes, showing zero failure rate for the MMA device after all tests. These experimental findings, together with simulations results, confirm the robustness of the MMA technology, especially against temperature changes, and encourage further activities for the development of a space-customized spatial light modulator technology.
The performance of astronomical space telescopes can be greatly impacted by straylight. That is why characterizing the straylight in such telescopes before they are deployed is paramount. Nowadays such characterization can be done by simulation or by test. Simulation can provide very useful information on the origin of straylight, helping devise solutions to reduce it and improve the performance of the telescope. However, simulation suffers from limitations due to processing power needed and assumptions made in the model which can lead to simulation results quite far from the actual performances. Standard straylight tests on the other hand provide accurate measurement of the straylight but without any insight about its origin, making it difficult to mitigate. Emerging technologies now offer new possibilities for straylight measurement using time-of-flight technics to help identify the origin of the straylight. Such technologies were reviewed and analysed in a first activity called TRIPP (Time-Resolved Imaging of Photon Paths). The results and outcome of this study are presented in the first chapter of this paper. A second chapter then presents the ongoing status of a second activity, SLOTT (Straylight Lidar Ogse verificaTion Tool) which aims to develop a demonstrator for such a time-resolved straylight verification system. With the development and test of such a tool, CSEM and its partners (TAS-CH, Difrotec, CSL, LusoSpace), supported by ESA, hopes to establish new methods to characterize and reduce the straylight propagation in future space-based telescopes.
The CLUPI (CLose-UP Imager) instrument is a high-resolution camera mounted onto the Drill of the ExoMars 2020 rover mission carried out by the European Space Agency (ESA) and Roscosmos. The CLUPI development is under the responsibility of Thales Alenia Space Switzerland whereas the Principal Investigator is Dr. Jean-Luc Josset from the Space Exploration Institute. In the frame of the development CLUPI instrument, the CSEM developed and delivered three models of a flexure-based Focus Mechanism. The CLUPI Focus Mechanism (CFM) design utilizes flexure guides to allow very accurate frictionless adjustment of the focal distance of the imager. Such design must also comply with very stringent requirement from the ExoMars mission, especially regarding the low Martian temperatures and the launch/landing load environment. This article presents the three main challenges encountered during the development of the mechanism and how these were addressed: resilience, performance and reliability. This article then draws the lessons learnt from this development including potential design improvements for a similar design and general rules to applicable to any development involving compliant mechanism.
The H2020 project PULSAR (Prototype for an Ultra Large Structure Assembly Robot) development objective is to create three demonstrators that that will pave the way for the construction of large structures in orbit. The study case considered in PULSAR is the assembly of a segmented primary mirror for next generation 35m space-based telescope. In the frame of this project, CSEM is developing Single Mirror Tile demonstrators (SMT) that host a positioning mechanism capable of adjusting the position of the hexagonal mirror in order to compensate for inaccuracies generated by the robotic assembly. This mechanism has a tripod architecture. It is composed of three linear actuators and of transmission stages, each made of a flexible pivot and of a gimbal. This mechanism allows for controlling the mirror position along three degrees of freedom (piston translation and tip and tilt rotations). The piston stroke is required to be ±3 mm with a resolution of 1 μm and a repeatability better than 5 μm while the tip/tilt strokes are ±1° with 4 μrad of resolution and 20 μrad of repeatability. The design of the tiles benefits from CSEM extensive experience in compliant mechanisms and additive manufacturing applied to the domain of scientific instrumentations for space applications.
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