Testing of Louver Operability after Spacecraft Launch Distortions

Thermal louvers are a vital component to the overall success of a Spacecraft's mission. They provide passive control of heat flow into and out of the Spacecraft's thermal control system. During hot environments, louver vane blades open and dump excess heat to space. Conversely, during cold environments, louver vane blades close and help retain heat in the system. These devices, along with other thermal mechanisms, provide thermal balance across the Spacecraft, which enable all accommodated components to stay within their allowable flight temperatures as power-efficiently as possible. Spacecraft typically accommodate louvers on the bus or primary structure. Because louvers are inherently structurally soft devices, the primary structure of the Spacecraft provides the necessary stiffness to maintain a relatively flat interface during ascent and operations. In the case of Europa Clipper, eight large louvers were required for the environment during the Jupiter Tour phase. Adequate surface area was not available on the cylindrical primary structure so a radiator panel has been developed to accommodate all eight louvers. As such, this secondary structure radiator panel behaves quite differently than primary structure. During ascent, the radiator panel will experience severe displacements both across its mounting struts as well as over the panel itself. This environment acts to distort the radiator panel and thus the louvers mounted to it. This unique dynamic environment posed many risks to the rather soft and flexible louver mechanism. Testing was performed to determine whether predicted radiator panel surface distortions during launch would impact louver operability once on orbit. Louver deflections and mode shapes were determined analytically using the Spacecraft-level finite element model. Cyclical deflection tests were performed on an Instron with pre/post thermal functional checks in a thermal chamber. The louver was initially tested on a flat interface as a baseline. A corner of the louver was deflected to ±0.034” using a radiator panel surrogate test fixture nearly 2,200 times. After being subjected to repeated distortions, the louver was reset to the flat baseline and a full thermal cycle functional check was performed to verify the louver operated correctly at both the hot and cold set points. It was found that the louver performed within specification after being subjected to the cyclical distortions. This paper will discuss the background of this unique louver accommodation, the modeling and analytical approach used in determining the distorted mode shape, test set up and execution, results and lessons learned.