Satellites fall towards Earth faster, scientists think solar wind is the ‘culprit’

In late 2021, operators of the European Space Agency’s (ESA) Swarm constellation of satellites noticed a worrying situation, with satellites measuring the magnetic field around the Earth starting to sink into the atmosphere at an unusually fast rate – 10 times faster than before . The change coincides with the start of a new solar cycle, which experts believe could be the start of tough years for spacecraft orbiting Earth. “The altitude of these satellites has dropped by about 2.5 kilometers per year for the past five or six years,” said Anja Stromme, ESA Swarm mission director. “But since December, they have been sinking rapidly. From December to April, the sinking The rate of sinking reached 20 kilometers per year.” Satellites orbiting close to Earth will always experience drag from the residual atmosphere, gradually slowing the spacecraft down and eventually allowing them to fall back to Earth. This atmospheric drag forces ISS controllers to perform periodic “re-acceleration” maneuvers to keep the station orbiting 400 kilometers above Earth. This drag also helps clean up space junk in the near-Earth environment. Scientists know that the strength of this drag depends on solar activity — the amount of solar wind that the sun emits, and the amount of solar wind varies with the solar cycle, which takes 11 years each. Since last fall, the star has woken up, spewing more and more solar wind, producing sunspots, solar flares and coronal mass ejections at increasing rates. Earth’s upper atmosphere was also affected. All spacecraft with orbital altitudes around 400 kilometers are bound to encounter this problem.

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