Lessons Learned from the Solar Correlation and Early Flight Thermal Performance of the Solar Orbiter SPICE Instrument

The Spectral Imaging of the Coronal Environment (SPICE) instrument is one of ten instruments comprising the science payload of ESA�s Solar Orbiter mission. Launched in February 2020, and successfully commissioned by July, SPICE was built at the STFC Rutherford Appleton Laboratory and is a high resolution imaging spectrometer operating at extreme ultraviolet wavelengths.

With Solar Orbiter ultimately reaching a perihelion of 0.28 AU (corresponding to a solar flux of approximately 17 kW per square metre or 13 solar constants), the thermal performance of SPICE under extreme solar loading is a crucial element of the instrument�s design. The instrument�s primary mirror is of particular importance for managing this solar load; it is designed to reflect ultra-violet wavelengths that are of scientific value whilst being transmissive to visible and infrared wavelengths. This allows a significant portion of the solar energy to pass through the instrument and back into deep space. During thermal balance testing, an intense UV lamp was the best approximation available to provide data for correlating the solar properties of the instrument. The correlation process therefore had to also account for the spectral differences between the UV lamp and the true solar spectrum.

This paper will discuss the real world challenges in such a correlation and compare the outcome of the original correlated model with flight data acquired at 0.88 AU and 0.54 AU during the commissioning phase of Solar Orbiter. In particular, the insight gained on designing and modelling instruments for such extreme thermal conditions in deep space will be explored. The approach taken for SPICE will be compared with similar solar missions and lessons learned for future solar missions will be identified.