Thermal Model Correlations of Europa Clipper REASON Antennas With and Without Modeling Solar Lamps and Comparison of Model Predictions and Flight Data

Europa Clipper, NASA's largest spacecraft for a planetary mission, was launched in October 2024 to conduct flybys of Jupiter’s moon Europa, with the goal of investigating its icy shell and potential subsurface water. The Radar for Europa Assessment and Sounding: Ocean to Near-surface (REASON) instrument, a radar system aboard the spacecraft, utilizes radio waves to detect water beneath Europa’s ice. In July 2023, the Jet Propulsion Laboratory (JPL), with support from ATA Engineering (ATA), successfully completed thermal vacuum (TVAC) testing of the stowed REASON qualification unit antennas. Following testing, ATA correlated thermal models to the test data and conducted flight verification and validation analyses. During testing, a xenon short arc lamp was employed to replicate sunlight, with a radiometer measuring incident flux. Due to the antennas’ black BR127 coating—characterized by high and similar solar absorptivity and infrared (IR) emissivity—and the uncertain IR/solar fraction of the lamp, ATA chose not to explicitly model the lamp in Thermal Desktop. Instead, a far-point solar source with a subtended angle and spatial flux variation was implemented, ensuring accurate simulations. A parallel exploration of explicit lamp modeling revealed minimal temperature sensitivity to IR/solar fraction of the lamp attributable to the antennas’ black coating. Both approaches—with and without modeling the lamp—resulted in identical thermal conductance, verifying the validity of the simplified method (i.e., without modeling the lamp). Challenges in lamp correlation included tuning the IR/solar fractions, inconsistent radiometer measurements, and correlating lamp output with heat flux. After ATA’s integration of the correlated REASON models to JPL’s Clipper system model, the predictions of the integrated model closely matched (to a maximum temperature difference of 3 °C) the flight telemetry data that was collected when the orientation of the solar panels transitioned from 0° to 45° shortly after Clipper’s launch. For future testing, heater plates may be advantageous for uniformly coated black components. If solar lamps are desired, detailed lamp characterization using radiometers and thermocouples (TCs) is recommended to address heat flux and temperature correlation challenges effectively.