In the past five years, more satellites have been launched into Earths atmosphere than the preceding 60 years combined. And now, scientists believe that climate change is set to increase the number of old satellites that will turn into floating obstacles.
Thats according to a study published last week in the Nature Sustainability journal by a team of aerospace engineers at MIT. The researchers examined how greenhouse gases are impacting Earths upper atmosphere and, in turn, the objects orbiting within it. They found that, as emissions increase, theyre actually altering the natural process that allows satellites to fall out of orbit and disintegrate, resulting in a kind of space junk pile-up.
If this trend continues, it could have ripple effects for everything from weather tracking and broadband internet access to national defense.
Captured by astronaut Don Pettit aboard the International Space Station, this long-exposure photograph showcases Earth’s city lights, the upper atmosphere’s airglow, and streaked stars. The bright flashes at the center are reflections of sunlight from SpaceX’s Starlink satellites in low-Earth orbit. [Photo: NASA]
How the atmosphere naturally removes space junk
Most satellites are located within low Earth orbit, or around 400 to 1,000 kilometers above the planets surface. Under normal conditions, after these satellites reach the end of their lifespans (when their engines can no longer maintain enough velocity for orbit), natural atmospheric drag pulls them down to lower altitudes, where air molecules cause them to disintegrate before ever reaching the Earths surface. Its essentially the atmospheres natural space junk cleaning protocolbut climate change might be slowing it down.
William Parker is a graduate student at MITs AeroAstro program, and he served as the lead author on the new study. Parker explains that greenhouse gases have a warming effect within the troposphere (the atmospheric layer closest to Earth), but in further layers, they actually have the opposite effect. Because greenhouse gases keep heat trapped close to the Earth, more distant layerslike the thermosphere, where the majority of satellites orbitare actually cooling down over time.
That cooling leads to contraction, Parker says. The whole atmosphere is sort of shrinking. As the atmosphere shrinks, he adds, so, too, does the natural drag force thats supposed to pull satellites downward. That means that there’s less atmospheric density for the satellites to experience, which means that we don’t have this cleaning force in low Earth orbit that we’ve always had to rely on.
Preventing a satellite debris pile-up
As the atmospheres natural cleaning force diminishes, satellite operators may soon encounter a significant build-up of debris in low Earth orbit.
Experts theorize that, beyond a certain critical mass, such a build-up could lead to something called The Kessler Effect: a series of space collisions that snowball as debris increases. Just this past year, Parker notes, Space Xs satellite service Starlinkwhich operates around 60% of all active satelliteshad to perform 100,000 collision avoidance maneuvers to prevent space collisions.
If we don’t take action to be more responsible for operating our satellites, the impact is that there are going to be entire regions of low Earth orbit that could become uninhabitable for a satellite, Parker says.
If nothing is done to mitigate greenhouse gas emissions, the MIT teams simulations show that the maximum satellite capacity in low Earth orbit could decrease by 50% to 66% by 2100. In a more likely scenario where some effective climate action is taken, Parker says the capacity is still predicted to drop by 24% to 33% in that same time frame.
Currently, satellites play a central role in global weather tracking, access to internet service, online banking, national defense protocols, and more. If satellite operators have to spend more and more energy avoiding obstacles, providing those essential services will become increasingly difficultand expensive.
It’s going to mean that all of the products that we get from space are going to be degraded, because satellites now have a secondary objective, Parker says. The primary objective has always been to collect data or to provide some service, like connection to the internet. Now, the secondary objective is just to make sure that you don’t get destroyed in a collision with a debris object. It’s something that operators have only had to start worrying about in the last five to 10 years.
The long-term solution is taking more action to eliminate greenhouse gas pollution. In the meantime, Parker says, satellite operators should try to operate at lower altitudes to ensure that theres enough drag to remove debris from the atmosphere, as well as taking proactive steps to return spacecraft from orbit before they can even become debris. He also believes that a real set of international space traffic management rules could help prevent overcrowding.
There used to be this mantra in the space industry that space is big, and that’s an excuse to not treat it with the respect that it should be treated with, Parker says. Thats outdated, and we need to do a better job at managing this resource that we have and sharing it in an equitable way.
