Thermal Testing of the Structural and Thermal Model of the HyperSpectral Instrument for the CHIME Mission

The CHIME (Copernicus Hyperspectral Imaging Mission for the Environment) mission is a key component of the European Union’s Earth Observation programme, Copernicus. The CHIME satellite will carry a unique payload designed to provide routine hyperspectral observations. Its HyperSpectral Instrument (HSI) will acquire a continuous spectral signature ranging from 400 to 2500 nm at a spatial resolution of 30 meters. In 2024, the Structural and Thermal Model (STM) of the HSI underwent thermal vacuum testing, a crucial step towards the Critical Design Review (CDR) scheduled for early 2025. This paper presents the results of the STM thermal balance test for the HSI, including thermal model correlation, and the status of the thermal control design at CDR. The focus is on key elements of the thermal control system, such as the baffled passive cryogenic radiator, which cools three separate focal planes to 170 K. The radiator is connected to the focal planes via a cryogenic chain that utilizes graphite thermal straps and ethane heat pipes. During the STM thermal balance test, the cryogenic chain exhibited higher-than-expected temperatures, prompting an investigation into potential additional heat leak sources within the instrument design and test equipment. This paper will detail the findings of this investigation, the performance of the ethane heat pipes under gravity conditions, and the overall results of the thermal balance.