The Spectrometer Telescope for Imaging X-rays (STIX) is one of 10 instruments on board Solar Orbiter, a confirmed M- class mission of the European Space Agency (ESA) within the Cosmic Vision program scheduled to be launched in 2020. STIX applies a Fourier-imaging technique using a set of tungsten grids (at pitches from 0.038 to 1 mm) in front of 32 pixelized CdTe detectors to provide imaging spectroscopy of solar thermal and non-thermal hard X-ray emissions from 4 to 150 keV. The instrument passed the Preliminary Design Review (PDR) in early 2012.
32 coarsely pixelized Cadmium-Telluride detectors register the energy and timing of an incident X-ray photon over an energy range from 4-150 keV.
STIX is a so-called Fourier imager. On 30 of the detectors, the incoming photon flux is spatially modulated by means of two grids placed at a distance of 55 cm apart to form a so called Moiré-pattern. The spatial modulation on each detector contains encoded information on the location and size of the X-ray source. By combining this information from all 30 detectors, an image can be reconstructed.
A movable attenuator can be placed in front of the detectors in case of very high photon flux to reduce pile-up and detector deadtime.
STIX plays an important role in enabling Solar Orbiter to achieve two of its major science goals of (1) determining the magnetic connection of the Solar Orbiter spacecraft back to the Sun and (2) understanding the acceleration of electrons at the Sun during solar eruptions and their transport into interplanetary space.
The remote-sensing X-ray measurements made with STIX will determine the intensity, spectrum, timing, and location of accelerated electrons near the Sun. Working with other instruments onboard Solar Orbiter, STIX will help provide direct tracing of the magnetic structure, field line length, and connectivity. In this way, STIX, together with RPW and EPD, is able to magnetically link the heliospheric region observed at the spacecraft back to regions on the Sun where the electrons are accelerated.