SpaceX’s Starlink is the biggest of these. Currently consisting of about 6,500 satellites, the fleet is expected to mushroom to more than 40,000 at some point in the 2030s. Other mega-constellations, including Amazon Kuiper, France-based E-Space, and the Chinese projects G60 and Guowang, are in the works. Each could encompass several thousand satellites, or even tens of thousands.
Mega-constellation developers don’t want their spacecraft to fly for two or three decades like their old-school, government-funded counterparts. They want to replace these orbiting internet routers with newer, better tech every five years, sending the old ones back into the atmosphere to burn up. The rockets needed to launch all those satellites emit their own cocktail of contaminants (and their upper stages also end their life burning up in the atmosphere).
The amount of space debris vaporizing in Earth’s atmosphere has more than doubled in the past few years, says Jonathan McDowell, an astronomer at the Harvard-Smithsonian Center for Astrophysics who has built a second career as a leading space debris tracker..
“We used to see about 50 to 100 rocket stages reentering every year,” he says. “Now we’re looking at 300 a year.”
In 2019, some 115 satellites burned up in the atmosphere. As of late November, 2024 had already set a new record with 950 satellite reentries, McDowell says.
The mass of vaporizing space junk will continue to grow in line with the size of the satellite fleets. By 2033, it could reach 4,000 tons per year, according to estimates presented at a workshop called Protecting Earth and Outer Space from the Disposal of Spacecraft and Debris, held in September at the University of Southampton in the UK.
Crucially, most of the ash these reentries produce will remain suspended in the thin midatmospheric air for decades, perhaps centuries. But acquiring precise data about satellite burn-up is nearly impossible, because it takes place in territory that is too high for meteorological balloons to measure and too low for sounding instruments aboard orbiting satellites. The closest scientists can get is remote sensing of a satellite’s final moments.
Changing chemistry
None of the researchers aboard the business jet turned scientific laboratory that took off from Easter Island in September got to see the moment when Cluster Salsa burst into a fireball above the deep, dark waters of the Pacific Ocean. Against the bright daylight, the fleeting explosion appeared about as vivid as a midday full moon. The windows of the plane, however, were covered with dark fabric (to prevent light reflected from inside to skew the measurements), allowing only the camera lenses to peek out, says Jiří Šilha, CEO of Slovakia-based Astros Solutions, a space situational awareness company developing new techniques for space debris monitoring, which coordinated the observation campaign.
