Almatech Contribution

In the frame of ESA’s Solar Orbiter mission, Almatech has been selected to design, develop and test the main filters of the X-Ray telescope named STIX.

In order to be transparent to X-Rays while withstanding the thermal load on the instrument as well as on the spacecraft, beryllium filters called windows have been developed.

The windows will be directly facing the sun light and will be subjected to elevated temperatures above 500°C, and their primary objective consists in filtering the radiations that come into the X-Ray detector.

The main challenge consisted of designing, manufacturing and testing a completely new optical coating in order to satisfy the challenging requirements of temperature and thermo-optical properties of the windows surfaces.

Considering this mission’s unprecedented exposure to the sun (13 Solar constant), the thermal loads on the filter design implied a verification by thermo-elastic analysis of the filters system over a wide temperature range of -90°C to +507°C.

“Being entrusted by ESA to develop these windows was a great honor and a big responsibility as they are a mission critical item, meaning if they fail the entire mission will be at risk. So a lot of pressure but also a lot of excitement! We had to optimise both the material substrate in beryllium and the coating to provide the necessary shielding of the instrument while still allowing the X-rays to come through. We managed to fulfill all requirements and are now waiting for the launch!”

Adeline Bernet

Principal Engineer

About the mission

Solar Orbiter is a Science mission of jointly developed between ESA and NASA, that was selected as the first medium (M)-class mission of ESA’s Cosmic Vision  programme for launch in 2019. Solar Orbiter’s goal is to address the central question of Heliophysics: how does the Sun create and control the heliosphere? Solar Orbiter is designed to identify the origins and causes of the solar wind, the heliospheric magnetic field, the solar energetic particles, the transient interplanetary disturbances, and the Sun’s magnetic field.

About the payload

The Spectrometer/Telescope for Imaging X-rays (STIX) instrument will image in X-rays the extremely hot Plasma heated to tens of millions of degrees and the high-energy electrons accelerated to nearly the speed of light that are emitted during a solar flare.

The Solar Orbiter mission (Credit ESA)

Maximum temperature

Solar Constant



High temperature thermo-optical coating development for X-Ray transparent filters
Bernet, L. Blecha, F. Rottmeier
Presented at the ISMSE 2015