Solar Orbiter must make a dangerous passage near Earth

Launched almost two years ago, Solar Orbiter will finally be able to begin its main mission. The probe which must observe the Sun will pass one last time near the Earth on November 27, 2021, for a dangerous but necessary maneuver.

A visitor is about to pass very close to the Earth. Around 5:30 a.m. on Saturday, November 27, 2021, you certainly won’t see it with the naked eye, but Solar Orbiter will be in the vicinity. The probe supposed to explore the Sun will fly at an altitude ofbarely 460 kilometers, or just a few dozen kilometers above the International Space Station.

But why such a performance? Not for showing off, but simply to save fuel. Nearly two years after its launch, the probe is far from having finished its journey and is using the Earth as a springboard, to set off again in the direction of our star in the most beautiful way. ” This is his last passage near the Earth, specifies to Numerama Desi Raulin, Solar Orbiter operation project manager at CNES, it will be used to reduce the energy related to the speed of the ship before aligning it correctly for the rest of its journey. »

Go through the debris wall twice

This apparently very complicated method was chosen to allow Solar Orbiter to approach the Sun several times without burning its wings, but also without spending too much fuel. Since its launch, it has already made a first pass near its target, before returning to Venus, then again to the Sun. For the rest of his mission, he will go back and forth between the Sun and Venus several times, each time benefiting from the planet’s gravitational assistance, and trying to go to different levels near the Sun to vary the points of view.

But this passage near the Earth has a peculiarity that is not found on Venus: we are big polluters. Solar Orbiter will encounter obstacles that it does not have on Venus: space debris. During its journey, it will cross two particularly risky zones: first, at an altitude of 36,000 kilometers, a first circle of debris made up in particular of communication satellites which are placed in this so-called geostationary orbit. When they are no longer active, they descend slightly to pass into a graveyard orbit, where all the devices that are inactive, but impossible to bring back to Earth, are located.

And it is not finished for Solar Orbiter, since a little further, it will cross another circle around the 2000 kilometers of altitude, with there also many objects in low orbit. And its trajectory will obviously make it cut these two orbits, twice each!

The Solar Orbiter overview
The overview of Solar Orbiter. Source – ESA

« The risk of collision with space debris is low, tempers Desi Raulin. The trajectory of Solar Orbiter during this passage has been known for a long time, as well as the position of the various debris and satellites. In addition, if there appears to be a danger, the European Space Agency (ESA) operations teams based in Darmstadt, Germany can always operate a small maneuver to alter the trajectory. ” There is a risk, with an element of uncertainty, recognizes Desi Raulin. But this risk is calculated. Satellite surveillance is intense and permanent. »

End of the cruise for Solar Orbiter

Fortunately, because this passage is only a step before the start of the real mission of Solar Orbiter. ” We are currently in the cruising phase, says Desi Raulin. But after this passage near the Earth, we pass in the operational phase. This cruise is used to test the probe’s instruments, but also and above all to properly position it and precisely define its trajectory with a view to its final objective, the study of the Sun. Normally, during this period, the instruments do not work quite as they will when the time comes, which does not prevent scientists from gleaning some data here and there.

Thus, since its departure, Solar Orbiter has already collected some measurements that are useful for researchers, and the spacecraft will start again during this passage near Earth. He will study the magnetic field which is related to solar winds, an area of ​​research where it is particularly important to have multiple points of view at the same time to compare data.

For Desi Raulin, so far, the mission has been a success: “ The probe collected more data than expected during the cruise phase. This is a very good point, but the most important part for the scientific community will begin soon. »

The next step now is March 2022. The spacecraft will pass close to the Sun, just 50 million kilometers from the star, with all of its instruments deployed and fully operational for the first time. The opportunity to see a little more closely the strange phenomena happening on its surface, in particular the “campfires”, phenomena already seen by Solar Orbiter during its last visit, and which are suspected of warming the world. outer atmosphere of the star, much hotter than its surface. In addition, the probe will go to see the poles of the Sun during its future passages, which has never been explored before. With such a program, a few debris disks should not stop it.

Look at the world from space

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