Daring maneuver: The ESA Solar Orbiter space probe will fly very close to Earth tomorrow morning to gain momentum. At 5:30 a.m., it will graze over North Africa and the Canary Islands at an altitude of just 460 kilometers. The risk here: For this close passage, the probe has to fly through two zones with numerous satellites and a lot of space debris – the geostationary orbit and the low earth orbit in which the space station ISS orbits.
Our sun is currently being explored up close by two space probes to uncover some of its still-existing secrets. The NASA probe Parker Solar Probe dips into the solar corona, but remains on the equatorial plane of our star. The ESA Solar Orbiter probe, on the other hand, comes less close to our star, but its elliptical orbits also allow a view of the solar poles. In July 2020 she delivered groundbreaking images of the “solar campfires” as she approached the sun.
Flight over North Africa
But now the Solar Orbiter is returning to earth for a flying visit: With the help of a close flyby of our home planet, the space probe is gaining momentum for its next orbit around the sun. In order for this passage to provide enough energy, it has to fly over the earth’s surface at an extremely short distance for space travel conditions: it will be grazing tomorrow morning at around 5:30 a.m. at an altitude of only 460 kilometers over North Africa and the Canary Islands.
The space probe flies so low on its close approach that it could be seen by binoculars in this region. The probe’s tiny, faint point of light will move 0.3 degrees per second from the surface of the earth – this corresponds to about half the width of a full moon per second.
Danger zones in orbit
This passage is extremely risky for the spacecraft, as it flies through two of the most densely populated areas in near-Earth space. The first tricky point is the two times crossing the geostationary orbit at an altitude of 36,000 kilometers, which contains not only satellites but also a lot of space debris. Then follows the flight through the low earth orbit at an altitude of 800 to 400 kilometers. This is where the density of space debris is highest – and with it the risk of collision.
The European Space Agency ESA is already monitoring the trajectories of most of the larger shot particles. If there is a threat of a collision with one of them, the Solar Orbiter has to perform an appropriate evasive maneuver. However, the smaller pieces of debris in particular are far from being fully recorded, so there is a residual risk. “The risk of a collision is low, but the situation is monitored very closely in order to be able to change the trajectory of the probe in an emergency,” explains Michael Steindorfer from the Institute for Space Research in Graz.
New look at the earth’s magnetic field
The close flyby is not only important for adjusting the orbit of the Solar Orbiter – it could also bring new scientific findings. During its passage, the space probe will collect measurement data on the earth’s magnetic field, the high-energy particles and the solar wind. In doing so, it samples altitude areas that are not covered by either the cluster satellites flying at an altitude of 60,000 kilometers or the lower circling Swarm satellites.
“This flyby is exciting: We can see our area of space through the eyes of the Solar Orbiter and then compare the results with what we already know,” says Anja Strømme, Manager of the Swarm Mission at ESA. There could well be surprises.
Course for the sun
After gaining momentum on Earth, the Solar Orbiter will set course for the Sun again. In March 2022, the space probe will complete its next perihelion – it will pass the point of its current orbit that is closest to the sun. It will approach our star up to 50 million kilometers – it is around 27 million kilometers closer to it than last time. At the same time, the inclination of the orbit was slightly increased by the flyby maneuver.
The solar orbiter will be able to deliver new, even sharper views of the sun: “Compared to the high-resolution images that we have already received, this will correspond to zooming in by a factor of two,” explains Daniel Müller, project scientist for the mission. In addition, the researchers hope to gain new insights into the solar wind and the mechanisms that shape it.
Source: European Space Agency (ESA), Institute for Space Research