In 2021, operators of the European Space Agency’s (ESA) Swarm constellation discovered something to worry about. The satellites, which assess the magnetic field around Earth, started plummeting toward the atmosphere at an alarmingly fast rate. The speed might be up to 10 times faster than before. The change occurred simultaneously with the onset of the new solar cycle, and specialists think it might be the beginning of some difficult years for spacecraft orbiting our planet.
“In the last five, six years, the satellites were sinking about two and a half kilometers [1.5 miles] a year,” Anja Stromme, ESA’s Swarm mission manager, told Space.com. “But since December last year, they have been virtually diving. The sink rate between December and April has been 20 kilometers per year.”
Satellites circling close to Earth often face the drag of the residual atmosphere, which deliberately slows the spacecraft and eventually makes them fall back to the planet. They usually don’t survive this so-called re-entry and burn up in the atmosphere. This atmospheric drag forces the International Space Station’s controllers to conduct regular “reboost.”
This drag furthermore helps clean up the near-Earth environment from space debris. Scientists realize that the intensity of this drug depends on solar activity because of the amount of solar wind emitted by the sun, which fluctuates depending on the 11-year solar cycle. The previous cycle, which officially ended in December 2019, was rather sleepy, with a below-average number of monthly sunspots and a prolonged minimum of hardly any activity.