How does the Sun influence the heliosphere? To answer this and other fundamental questions related to solar physics, the Solar Orbiter spacecraft lifted off from Cape Canaveral Air Force Station in Florida, USA, on board an Atlas V launch vehicle at 05:03 CET on 10 February 2020 (23:03 on 9 February, local time). "Once it has reached its target orbit, the spacecraft will approach Earth's host star to within 42 million kilometres and will also be able to provide detailed images of the Sun's polar regions for the first time," explains Carsten Henselowsky, Solar Orbiter Project Manager at the German aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) Space Administration. "Among other things, we want to use the mission to investigate the formation of the solar wind and magnetic field."
Solar Orbiter will acquire the first detailed images of the Sun's polar regions
What is unique about the mission is not only the first-time imaging of the polar regions with high-resolution optical instruments, but also the combination of remote sensing by telescopes and on-board measurements in the direct vicinity of the Sun. For at least seven years, Solar Orbiter will circle the Sun in an elliptical orbit and collect information about electric fields, energetic particles and seismic waves, among other things. With a minimum approach distance of 42 million kilometres, the spacecraft will come so close to the Sun that the spacecraft and instruments will face major challenges. They will have to withstand temperatures ranging from minus 180 to more than 500 degrees Celsius.
Scientists intend to use the data from Solar Orbiter to better understand the processes in the heliosphere – the solar atmosphere that surrounds the Solar System like a large plasma bubble. "However, the new findings will not only be used for space research," says Henselowsky. "They should also help to better protect infrastructure systems on Earth and in near-Earth space. This is because the Sun not only affects Earth's climate, but also what is referred to as space weather. Solar storms, for example, affect electrical systems on the ground, as well as satellites and their communication and navigation services."
During the operation of Solar Orbiter, the scientific data will be combined with those from other missions, thereby continuing previous investigations. Supplementary measurements will also be carried out in coordination with ongoing missions, such as the NASA Parker Solar Probe mission that was launched in 2018, in order to fill gaps that exist in knowledge gained during previous missions.
The long journey to the Sun
During its journey to the Sun, the Solar Orbiter probe must gain momentum several times in order to save fuel. This will be achieved by using the gravitational forces of Earth and Venus during swing-by manoeuvres. It will take Solar Orbiter just over one-and-a-half years to reach its target orbit. During this transfer phase, the on-board instruments that perform local measurements will already begin their tasks. The remote sensing instruments will begin operating once the spacecraft reaches its scientific orbit around the Sun.
Extensive German participation in the instrument suite
German research facilities and institutes are involved in six of the 10 instruments on Solar Orbiter. The main German instrument is the Polarimetric and Helioseismic Imager (PHI) instrument, which was developed as an international collaboration under the overall management of the Max Planck Institute for Solar System Research (MPS) in Göttingen, with the participation of the Kiepenheuer Institute for Solar Physics (KIS) in Freiburg. The aim of PHI is to provide maps of the magnetic vector and of the line-of-sight (LOS) velocity in the solar photosphere. The MPS is also involved in the instruments Extreme Ultraviolet Imager (EUI) for the generation of image sequences of the different atmospheric layers of the Sun, the Multi Element Telescope for Imaging and Spectroscopy (METIS) for imaging the corona in the near and extreme ultraviolet range, and Spectral Imaging of the Coronal Environment (SPICE), which will characterise the plasma properties of the solar corona.
The Energetic Particle Detector (EPD) instrument, to which Kiel University (Christian-Albrechts-Universität zu Kiel; CAU) has contributed several sensors, will measure the properties of suprathermal and energetic particles in the solar wind. The Leibniz Institute for Astrophysics Potsdam (AIP) is participating in the Spectrometer/Telescope for Imaging X-rays (STIX) instrument.
The Solar Orbiter mission is being carried out under the overall leadership of the European Space Agency (ESA) with extensive participation by the US National Aeronautics and Space Administration (NASA). The development and construction of the scientific instruments and the Solar Orbiter spacecraft, as well as the scientific operations and processing of the data obtained, are being financed by the DLR Space Administration with funds from the German Federal Ministry for Economic Affairs and Energy (Bundesministerium für Wirtschaft und Energie; BMWi).