In an episode of Star Trek: The Next Generation, a pair of outspoken scientists reveal how warp drives—the show’s ubiquitous propulsion system used to get travelers around space—can be incredibly environmentally destructive. From then on, the characters take care to limit the damage of their spaceflights.
Could a similar scenario now play out in the real universe, minus the faster-than-light engines? Atmospheric scientist Christopher Maloney believes so. In a new study, he and his colleagues modeled how black carbon belched out by rocket launches around the world is likely to gradually warm parts of the middle atmosphere and deplete the ozone layer. They published their findings on June 1 in the Journal of Geophysical Research: Atmospheres.
“There’s a lot of momentum currently going on, in terms of rocket launches and satellite constellations going up, so it’s important to start researching this to study what impacts we could potentially see,” says Maloney, who’s based at the National Oceanic and Atmospheric Administration (NOAA) Chemical Sciences Laboratory in Boulder, Colorado.
Maloney and his colleagues’ models start with typical launch trajectories, in which rockets blast a spray of tiny particles called aerosols out of their engine nozzles. The most dangerous exhaust component is black carbon, or soot. Rockets release tons of those microscopic particles in the stratosphere, especially between 15 and 40 kilometers above the ground, above where aircraft fly. Modern jet engines also expel black carbon, but in much smaller quantities. Falling defunct satellites emit aerosols too, as they burn up in the stratosphere. Since these particles persist in the stratosphere for about four years, they can accumulate, particularly in areas where space traffic is concentrated.
Maloney and his team used a high-resolution climate model to predict the effects this pollution will have on the atmosphere, studying how aerosols of different sizes could heat or cool regions of space at different latitudes, longitudes, and altitudes. They found that within two decades, temperatures in parts of the stratosphere could rise by as much as 1.5 degrees Celsius, or 2.7 degrees Fahrenheit, and that the ozone layer could thin slightly in the northern hemisphere. They generally conclude that more rockets means more warming and increased ozone loss, which could pose a problem, especially because humans, wildlife, and crops need the ozone layer to protect them from ultraviolet radiation.
By their accounting, each year, rocket launches collectively expel around 1 gigagram, or 1,000 metric tons, of black carbon into the stratosphere. Within two decades, that could easily ramp up to 10 gigagrams or more, thanks to the growing number of rocket launches. The researchers consider multiple black-carbon emission scenarios, including levels reaching 30 and 100 gigagrams, which, though extreme, could happen within a couple more decades if rocket engine technologies and trends don’t change much. They focus their analysis on widely used kerosene-burning rocket engines, such as the first-stage boosters of SpaceX Falcon, Rocket Lab Electron, and Russian Soyuz rockets.
With the global launch rate climbing by about 8 percent per year, they anticipate as many as 1,000 hydrocarbon-burning rockets blasting off every year by the 2040s. That’s partly thanks to dropping launch costs and the burgeoning of the commercial space industry, as well as the rockets needed to launch growing satellite networks like SpaceX’s Starlink, Amazon’s Project Kuiper, and OneWeb. Suborbital spaceflights, like Blue Origin’s and Virgin Galactic’s, penetrate the stratosphere too.