GoKawiilResearchers in Germany are melting chunks of satellites in high-temperature plasma wind tunnels to simulate how space debris burns up in Earth’s atmosphere. These tests are revealing in relation to trends about satellite reentry as the population of objects in low Earth orbit swells today.
Only a handful of facilities around the world are capable of conducting reentry simulation tests like the German researchers are performing. In particular, the researchers raise concern that ashes from reentry that remain in the upper atmosphere could increase ozone depletion and alter the atmosphere’s thermal balance in the process.
Three or more large satellites or used rocket stages burn up in Earth’s atmosphere every day, according to the European Space Agency’s Space Environment Report published last year. Every year, hundreds of tons of human-made objects reenter the atmosphere and evaporate, leaving behind clouds of microscopic ash along with some fragments that happen to fall all the way to the ground.
Researchers say the amount of satellite ash and the number of human-made objects hitting Earth so far is relatively low. However, the rapidly increasing numbers of launches to low Earth orbit now threaten to increase the levels of space junk reentering the atmosphere.
As of June, according to the ESA, some 18,000 operational and defunct satellites orbit the planet. And companies like SpaceX and Blue Origin have ambitions to launch hundreds of thousands of satellites, including giant orbiting data centers, in the next decade. China, too, is targeting up to 140 launches this year, and filing ambitious plans with the International Telecommunication Union for more launches toward its own megaconstellation of satellites and its own orbiting data-center fleets.
Since most satellites are currently designed to be replaced every five years with newer technology, tens of thousands of tonnes of old spacecraft could be vaporizing in Earth’s atmosphere in the foreseeable future.
Meanwhile, the amount of space rocks today entering the atmosphere, to be clear, outstrips the amount of reentering space junk. An estimated 44 tonnes of space rock enters the atmosphere per day, most of which burns up. But space rocks and satellites are chemically very different things. While space rock consists mostly of silicon with small amounts of metals such as nickel and iron, space junk is predominantly made of aluminum and titanium.
“When a satellite demises, it does not disappear,” says Fabian Hufgard, a researcher working on his Ph.D. at the Institute of Space Systems at the University of Stuttgart in Germany. “It’s still there in the atmosphere in the form of small particles of aluminum, and we don’t know what these particles actually do in the atmosphere.”
Hufgard is a member of a research group that uses plasma wind tunnels to recreate the end-stage conditions of satellites disintegrating and burning up as they spiral back to Earth. Observations from the ground and from aboard planes show that most of this destruction happens at altitudes between 60 and 80 kilometers—too high for balloons and planes to reach, but too low for satellites to sample. To date, testing space-debris chemistry and physics has been extremely difficult.
Researchers are working to close that gap with a combination of computer modeling, remote observations, and experimental research.
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