Speaker
Description
Development of aerobraking MLI and deployable flaps
EnVision, the upcoming medium class mission to Venus, will implement an aerobraking maneuver in the upper Venus atmosphere, in order to decrease velocity and reach its final mission orbit. In addition to the body of the satellite, it is intended to use dedicated aerobraking flaps, as extensions of the solar array assembly. During breaking, the exterior of spacecraft and flaps will not only be subjected to aerothermal heat flux, but also to high concentrations of atomic oxygen (ATOX), which is known to strongly degrade materials.
In order to protect the satellite from these conditions, dedicated multi-layer insulation (MLI) will be required. The foreseen thermal conditions are already challenging, requiring high-temperature capable materials. While extensive heritage on MLI materials in high temperature environments is available, the combination with high ATOX fluence is unprecedeted for European missions. Many typical outer layer materials, such as Polyimides, are known to be not suitable in sustained ATOX environments. Thus, an investigation was done into a suitable lay-up.
Much of the focus of the investigation was on the outer layer materials, as it would be needed to sustain the ATOX flux and protect the inner layers. Candidate materials, including coated titanium and polyimide foils as well as glass fabric, were investigated regarding their high-temperature stability. The deciding test of this sample level test campaign was, however, a plasma wind tunnel test, combining ATOX exposure with heat flux.
Based on the findings of the sample level test campaign, a lay-up was selected from which a representative test specimen for a 3d calorimeter and cycling test was built. This breadboard was cycled more than 2000 times between -160°C and +350°C and its performance was evaluated 3 times; at beginning of life, mid of life and end of life. This was done in order to investigate a potential change in MLI performance over the lifetime.
The development of the aerobraking flap (incl. MLI and associated support structure) is currently ongoing. The design has been chosen such that it is highly scalable and compatible with different solar array models and configurations. For the drag surfaces, the same materials as for the spacecraft are foreseen. Preliminary mechanical and thermal analyses showed promising results. The hinges were identified as key components, depending on the solar array supplier, especially for thermal performance, as the unprotected hinges may introduce significant heat into the aerobraking flap assembly.
In this talk, the testing campaign for the MLI selection will be presented and the current design and status of the aerobraking flap will be discussed.
