Structural and Thermal Challenges, Tailored Solutions, and In-Flight Behavior of the Solar Orbiter PHI E-Unit

The structural and thermal design of an electronics unit (E-Unit) are a key topic in a space mission. It must provide convenient interfaces and be compliant with the payload requirements and with the harsh environmental conditions. The aim of this work is to highlight the challenges and the state-of-the-art solutions for structural and thermal aspects of the E-Unit of the Polarimetric and Helioseismic Imager (PHI) instrument, part of the payload launched on board of Solar Orbiter, an European Space Agency (ESA)/NASA mission. The stringent requirements because of the large elliptical orbit and the 10-instrument assemblage demanded a particular design strategy that should help practicing engineers from different fields when dealing with similar constraints. These requirements address the mechanical, thermal, electronic, outgassing, and electromagnetic characteristics of the PHI instrument. One of the aspects analyzed is the design of customized modules to withstand the high structural loads and to enhance the thermal dissipation of high-density printed circuit boards (PCBs), under very tight budgets. Furthermore, critical concerns are discussed, such as preventing the arcing from a high-voltage power supply, along with achieving very accurate positioning of the internal connectors. The main conclusions of its qualification campaign are included as well. Finally, the thermal in-flight data were analyzed, demonstrating good agreement with the temperature predictions.