Space is having a moment. China launched the initial Tianhe module for its Tiangong space station this spring, and SpaceX followed shortly after with the first crewed mission from US soil since 2011. In July, Virgin Galactic and Blue Origin inaugurated suborbital tourist flights with their company leaders on board. Almost every week, it seems, more private companies and governments announce new concepts, flights, and projects.
The recent activity, although exciting, raises some concerns. The amount of space debris is growing, despite requirements for satellite deorbit and disposal, and the problem will soon escalate. About 11,000 satellites have been launched in the 64 years since Sputnik 1 in 1957 (Exhibit 1).
Now we’re at the point where about 70,000 satellites could enter orbit if proposed plans come to fruition—an explosion of interest based on potential new markets, innovative architectures, and more sophisticated technologies (Exhibit 2). Even if all the proposed constellations fail to deploy, many more satellites will be in space. Unless actively deorbited, they will remain there for months to hundreds of years, depending on the altitude.
We looked at space debris—what’s been done so far, the growing risk, and the government response—to find some solutions.
Beware of giant satellites—and floating paint chips
Exactly what is space debris? Many people think this phrase refers to a gigantic hunk of metal about to crash into a major city, but only some of the millions of objects in orbit are as large as old upper-stage rockets and space stations. Much of the rest consists of tiny particles, such as paint flecks. The US Space Surveillance Network was tracking about 20,000 pieces of debris in orbit in 2019 (Exhibit 3).1 Today, there are about 27,000 pieces of debris,2 most of which are over ten centimeters in diameter. The trajectories of the rest—and what they might hit and when—are uncertain.
The US Space Surveillance Network was tracking about 20,000 pieces of debris in orbit in 2019; today, there are about 27,000 pieces. The trajectories of the rest—and what they might hit and when—are uncertain.
Given the speed at which orbital objects move, even a collision between small debris and another object on a crossing trajectory can be catastrophic. The International Space Station (ISS), which is designed to survive impacts by debris up to one centimeter in diameter, was damaged in May 2021 when an object about five millimeters in size punched a hole in the thermal covering of its robotic arm. The ISS, which has had to maneuver repeatedly to avoid larger debris, didn’t suffer functional damage, but the incident reminded us that even major space systems are vulnerable to hits from tiny objects.
Don’t be surprised if reports of collisions increase over the next few years. There is only about one tracked object for every 18 million cubic kilometers in low-Earth orbit, but this number doesn’t include potentially lethal smaller debris, nor does it account for the relatively greater density of objects in certain orbits and the distance each object moves over any given time. Both of those factors increase the chances of collision, even in a largely empty environment. Space debris cannot be controlled and may be in the skies for centuries, depending on the orbits and collision dynamics, so the problem will remain.3
What goes up doesn’t necessarily come down
Experts have been discussing the space junk problem since the 1960s, leading NASA’s Donald Kessler to author a groundbreaking 1978 report on the chain of reactions that could occur once debris reached a certain level—an effect now referred to as the Kessler syndrome. A few high-profile collisions have also focused attention on the problem. In 2007, China tested an antisatellite (ASAT) weapon by intercepting a nonoperational weather satellite (an FY-1C polar-orbit satellite of the Fengyun series). The resulting explosion created a cloud of space debris with more than 3,000 objects—the largest ever tracked.4 Similarly, a 2009 collision between the defunct Russian satellite Kosmos 2251 and an Iridium commercial communications satellite produced more than 2,000 pieces of debris.5 Exhibit 4 shows the amount of debris created after some of the largest collisions.
Governments and other agencies have proposed some remedies to reduce space debris. The United States, for instance, issued a 2011 report on debris mitigation, and the United Nations recently created guidelines on the long-term sustainability of space activities.6 Even more unusual, the G-7 forum of developed economies published a statement in June 2021 that highlighted the increasing danger of space debris and encouraged international cooperation to address the problem.7 Overall, however, not much has changed in the past decade when it comes to taking concrete action.8
Extraterrestrial collisions can have heavy economic consequences, and increased use of space will take those costs even higher. Many new satellites are in huge “megaconstellations” that dwarf previous systems, and their number could grow tenfold over the next five to ten years.
Time to take out the extraterrestrial trash
So what can be done about mitigating the risk of collisions as the amount of debris rises? Our analysis suggests that we need solutions that consider four main categories of objects:
- Active satellites. These are not debris, but their growing numbers, and their potential increase by an order of magnitude, present a real concern. Operators can reduce the risk of collisions with satellites by improving situational awareness, coordinating with other operators to conduct evasive maneuvers, and creating “end of life” disposal requirements.9
- Uncontrollable dead satellites and other large items (such as upper stages and rocket bodies). These objects cause the greatest damage and potential chain effects, but they also offer the greatest potential return on debris-removal measures.
- Minor debris that can’t be tracked. One mitigating measure might involve creating satellites that are more likely to survive some impacts.
- Small debris that is tracked (or will be when sensors improve). Operators now maneuver active satellites around these debris, but removal technologies could be worth exploring, as discussed below.
Addressing the problem of space debris requires a multitrack approach. National and international government agencies now require satellite operators to have a disposal plan before issuing a constellation license, but further measures could go a long way. NASA has already established a working group to examine what new roles the agency can take to mitigate the growth of orbital debris and promote space sustainability.10 Regulatory and licensing agencies could also encourage greater collaboration among operators to reduce collisions.
When it comes to situational awareness—tracking satellites and reporting their movements—both government agencies and private companies could spur progress through various measures, such as adding more sensors (ground- and space-based) with higher resolution.
Active removal of space debris may finally be possible in some cases. One start-up recently began a test mission to prove that it had the capabilities required for space debris docking and removal.11 Other debris mitigation efforts will likely focus on the removal of inactive satellites and larger intact objects, at least initially. OneWeb, for example, has announced plans to collaborate with Astroscale on debris removal, and SpaceX has also discussed the possibility of using its Starship craft to clean up space debris.