“The change coincided with the onset of the new solar cycle, and experts 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 [12 miles] per year.”
Satellites orbiting close to Earth always face the drag of the residual atmosphere, which gradually 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 perform regular “reboost” maneuvers to maintain the station’s orbit of 250 miles (400 km) above Earth. This drag also helps clean up the near-Earth environment from space junk.
Scientists know that the intensity of this drag depends on solar activity — the amount of solar wind spewed by the sun, which varies depending on the 11-year solar cycle…. [S]ince last fall, the star has been waking up, spewing more and more solar wind and generating sunspots, solar flares and coronal mass ejections at a growing rate. And the Earth’s upper atmosphere has felt the effects. “There is a lot of complex physics that we still don’t fully understand going on in the upper layers of the atmosphere where it interacts with the solar wind,” Stromme said. “We know that this interaction causes an upwelling of the atmosphere. That means that the denser air shifts upwards to higher altitudes.”
Denser air means higher drag for the satellites. Even though this density is still incredibly low 250 miles above Earth, the increase caused by the upwelling atmosphere is enough to virtually send some of the low-orbiting satellites plummeting. “It’s almost like running with the wind against you,” Stromme said. “It’s harder, it’s drag — so it slows the satellites down, and when they slow down, they sink….” The lower the orbit of the satellites when the solar storm hits, the higher the risk of the spacecraft not being able to recover, leaving operators helplessly watching as the craft fall to their demise in the atmosphere….
All spacecraft around the 250-mile altitude are bound to have problems, Stromme said. That includes the International Space Station, which will have to perform more frequent reboost maneuvers to keep afloat, but also the hundreds of cubesats and small satellites that have populated low Earth orbit in the past decade…. “Many of these [new satellites] don’t have propulsion systems,” Stromme said. “They don’t have ways to get up. That basically means that they will have a shorter lifetime in orbit. They will reenter sooner than they would during the solar minimum.”
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