The objective is to develop a compact and in-plane opening louver with variable thermo-optical properties for applications where deployment of classical louver blades is not possible or convenient because of lack of space/clearance

Louvers are active thermal control elements that are typically placed over external radiators to be able to tune heat rejection from typically a factor 1 (fully closed) to 5 (fully open). The most commonly used louver is the bimetallic, spring-actuated, rectangular blade louver also known as venetian-blind louver. One of the known drawbacks of this technology is the mass and volume it requires, in particular with regards to the deployment of blades. This activity will address the possibility to establish a (mini) compact and in-plane opening design which will provide easier accommodation, reduced mass and higher view factor to space with a radiating surface free from specular reflections, which can occur with classical louvers where sources are in view of blades. The targeted applications are typically for mini-satellites, however, an array of such devices could in principle be accommodated on a large radiative area. The design is an output of the activity but several options are already foreseen. A promising one could be something similar to the photocamera optical lens aperture blade system, which allows variable quantity of light to enter the camera lens. The idea would be to finish the surface beneath the blades with a certain absorptivity/emissivity finish (e.g. high emissivity) and the outside of the blades with another absorptivity/emissivity finish (e.g. low emissivity). The blades could open and close with a memory alloy system triggered by the temperature variation of the substrate structure where the dissipative unit is mounted or with a piezo-drive system. The advantage of this concept is that the underneath radiative surface has a higher view factor to space with respect to the classical louvers where a certain view factor to the open blades exists. This concept has also the advantage of avoiding possible specular reflection on the underneath radiative surface from sources in view with the open blades. This concept is compact and can be applied to mini-satellites. It may eventually also be applied to rovers by adding a transparent thin surface to the top part to avoid dust deposition and mechanisms blockage when operating in an environment such as Mars surface. This is only one of the possibilities and the fact that an iris opening concept has been designed and qualified for an ISS air flow device and proved to be capable of working at different temperatures and be friction free is encouraging to consider it as one of the starting concepts. The following tasks shall be implemented: 1/ Literature and patent survey 2/ Establishment and consolidation of requirements for each element e.g. coatings, blades, mechanisms etc. 3/ Establishment of at least 3 concepts, analysis and preliminary testing to trade-off and down-select the most promising solution 4/ Prototype design and manufacturing on the basis of the most promising concept 5/ Testing to demonstrate a TRL 3 and results 6/ Recommendations for future activities