Preliminary Thermal Design of the Extreme Ultra Violet Spectrometer (EUS) Instrument for Solar Orbiter 2006-01-2042
The ESA Solar Orbiter is planned for launch in the 2013 to 2015 time frame and aims to study the Sun in unprecedented detail. The Extreme Ultra Violet Spectrometer (EUS) Instrument will provide plasma diagnostic observations of solar plasmas over a broad temperature range from chromosphere to corona for the study of all solar atmospheric phenomena. In broad terms, the instrument comprises a telescope and a spectrometer, the latter containing detector units that must be cooled to about −80 °C.
The Solar Orbiter will be inserted into an approximately 150 day solar orbit with an aphelion of about 0.8 Astronomical Units (AU) and a perihelion of about 0.2 AU. Instrument observations are likely to occur for about 30 days centered on perihelion. During the Cruise phase the spacecraft will be as far as 1.2 AU from the Sun. The nominal operational mission is almost three years (about seven orbits), with potentially an extended mission of a further two or three years.
There is a significant difference in heat inputs that occur during the mission. At perihelion during the operational phase the heat flux is about 34 kW/m2, but it is less than 1 kW/m2 during the Cruise phase. During the operational phase, the maximum solar heat load on the instrument is of the order 130 W, whilst the minimum is less than 10 W. The basic thermal design challenge is therefore the need to reject large quantities of heat input when close to the Sun and also to minimize heat loss when further from the Sun.
This paper summarizes the Solar Orbiter mission, highlights the thermal design challenges, and presents the results of the preliminary thermal design activities undertaken at RAL on the EUS instrument.