Speaker
Description
The Plato normal front end electronics (N-FEE) unit is an iso-statically mounted structure with high radiative coupling to the telescope cavity. The mechanical mounting consists of thermally isolating Ti6Al4V blades, which result in a high dependency on radiative heat exchange with the telescope to dissipate the heat generated by the PCBs. Previous attempts to correlate the N-FEE thermal model were unsuccessful, due to the lack of representation of the radiative environment during thermal cycling tests. The successful correlation of the N-FEE thermal model was critical due to violations in temperature limits for various PCB components, as well as an uncontrolled TRP at the PLATO camera level. Mitigating the former issue will result in complications with the latter, and vice versa. As a result, a dedicated thermal balance test setup was conceived to recreate the flight-like mechanical and thermal couplings of the N-FEE. This required the design and commissioning of a radiative test cavity that is controllable for a range of temperatures with little variation to the temperature across the cavity, as well as a conductive mounting that can be simultaneously controlled to highly contrasting temperatures. The characterisation of the conductive and radiative interfaces of the N-FEE were necessary in order to derive strategic instrumentation locations and create the correct representations in the thermal model. Artificial test cases with high heat injection from different sides of the conductive interface were introduced in order to aid with model correlation. It was found that the dependence of the N-FEE on radiative heat exchange resulted in the model correlation being extremely sensitive to the magnitude of heat injected, where a small error in the heat distribution created a large discrepancy in temperature predictions. The design and commissioning of the test hardware is presented, along with the planned test phases and results. The techniques used to correlate the thermal model are discussed, and the yielded temperature predictions are compared to the readings of 36 different sensors attached to the N-FEE during thermal balance testing.
