The first leg of the journey is some 8000 kilometres, but this is just a tiny fraction of the distance that it will travel to the Sun. In late October 2019, the ESA Solar Orbiter spacecraft will embark on its journey from the testing centre at the Industrieanlagen Betriebsgesellschaft (IABG) in Ottobrunn, Bavaria, to NASA’s launch site at Cape Canaveral in Florida. Solar Orbiter’s up to three-and-a-half year journey through space is scheduled to take place early in the morning of 6 February 2020, Central European Time. Its objective is to explore the centre of the Solar System, the Sun, and the origins of the heliosphere it creates.

The spacecraft will carry 10 highly specialised scientific instruments on board. Four German research institutes have made important contributions to the project. The DLR Space Administration financed the development and construction of the German scientific instruments and contribution to the Solar Orbiter spacecraft, with funds from the Federal Ministry for Economic Affairs and Energy.

“Solar Orbiter  has undergone almost 10 years of design, development and testing. Construction was completed in late 2018 by Airbus in Stevenage, United Kingdom, and was subsequently transported to the IABG in Ottobrunn, near Munich,” says Carsten Henselowsky, Solar Orbiter Project Manager at the DLR Space Administration. Over the past few months, the orbiter has undergone thorough testing at the IABG. The main focus was to examine its structural integrity, as well as its thermal and mechanical properties via vibration, radiation and thermal vacuum tests. The mechanical tests also included ensuring the successful deployment of the spacecraft’s solar array. Its electrical functions and compliance with the strict requirements for the individual scientific instruments and data transmission were also verified at the IABG.

The transportation of Solar Orbiter to the launch site in Florida marks another important milestone in the project. “Once the spacecraft arrives at Kennedy Space Center, the final preparations will commence for its launch atop an Atlas V in February 2020,” says Henselowsky. Solar Orbiter is a project within the European Space Agency (ESA) Cosmic Vision 2015-2025 Programme, with strong NASA involvement. Germany is the biggest contributor to the ESA Science Programme, providing around 20 percent of the funding. The DLR Space Administration manages Germany’s contributions to ESA.

Ten instruments to examine the solar environment

The objective of the mission is to investigate physical phenomena and processes both on the solar surface and interior. Solar Orbiter will also study the inner heliosphere – the area around the Sun that is strongly affected by the solar wind’s magnetic field and stream of energetic particles. The mission intends to answer a key question in solar physics: how does the Sun create and control the heliosphere?

The heliosphere is a vast area of space, extending beyond the orbits of the planets of the Solar System, in which fundamental processes of solar physics, astrophysics and plasma physics can be examined in detail. These physical conditions cannot be reproduced in a laboratory on Earth, nor can they be investigated remotely over astronomical distances. In order to study how the Sun controls the heliosphere, measurements need to be conducted near the Sun itself, where the magnetic field and energetic particles are still relatively pristine and have not been altered by other influences.

The instruments on board Solar Orbiter will make these investigations possible by surveying the physical properties of the solar wind within the immediate vicinity of the spacecraft (in situ). The spacecraft will also examine the solar surface and atmosphere using high-resolution remote sensing instruments. This will make it possible to study the effects of events taking place on and inside the Sun, such as coronal mass ejections.

German contribution to the mission

Four German research institutes are participating in six of the 10 scientific instruments on board Solar Orbiter with hardware contributions. The Mission Operations Centre (MOC) is located at the European Space Operations Centre (ESOC) in Darmstadt, while scientific operations will be managed from the European Space Astronomy Centre (ESAC) in Villafranca, Spain.

Solar Orbiter instruments with German involvement 

EPD The Energetic Particle Detector will measure the composition, timing and distribution functions of suprathermal and energetic particles; In
stitute of Experimental and Applied Physics at the University of Kiel.

EUI The Extreme Ultraviolet Imager will provide image sequences of the solar atmospheric layers above the photosphere; Max Planck Institute for Solar System Research.

METIS Multi-Element Telescope for Imaging and Spectroscopy will show the corona in the near and extreme ultraviolet range (UV and EUV); Max Planck Institute for Solar System Research.

PHIT he Polarimetric and Helioseismic Imager will determine the magnetic field vector and the velocities of matter in the solar photosphere (helioseismology); Max Planck Institute for Solar System Research (PI Institute) and the Kiepenheuer Institute of Solar Physics.

SPICE The Spectral Imaging of the Coronal Environment will perform extreme ultraviolet imaging spectroscopy to characterise the plasma properties of the solar corona; Max Planck Institute for Solar System Research.

STIX The X-Ray Spectrometer/Telescope will provide imaging spectroscopy of solar thermal and non-thermal X-ray emission; Leibniz Institute for Astrophysics, Potsdam.