There's no easy answer to being a space janitor

We don't know how best to remove debris from Earth's orbit... yet.


Earth’s orbit is getting crowded.

Last year, a record 2,409 objects were sent to orbit, the bulk of which were satellites settling into the increasingly cluttered region up to 1,200 miles above our planet’s surface known as low Earth orbit. Another 2,000-plus satellites have joined them so far this year, according to the UN’s Online Index of Objects Launched into Outer Space. As the presence of artificial objects in orbit grows, so too does the accumulation of debris, or space junk — and the risk of collisions. Dealing with existing waste and preventing its unchecked growth has become imperative, but it’s a problem that doesn’t have one simple solution.

Currently, the US Department of Defense’s Space Surveillance Network tracks more than 25,000 objects larger than four inches wide, most of which are concentrated in low Earth orbit, and there are an estimated millions of smaller objects still that are trickier to pinpoint. This includes everything from defunct satellites and spacecraft fragments to things as small as a paint chip, all of which can cause damage to other equipment due to the extreme speeds orbiting objects travel at. As yet, there have been no successful missions to remove extant debris from orbit. Proposals for removing this debris fall into two broad (and imperfect) categories: pushing them further from Earth into graveyard orbits where they pose less risk, or pulling them toward Earth where they'll deorbit and burn up in the atmosphere.

One such system is being developed and tested by Astroscale. The company, headquartered in Japan, demonstrated a magnetic capture-and-release tactic in 2021 with its ELSA-d mission, which simulated the strategy using an extra satellite it brought with it as mock debris. In a real-world scenario, its magnet would lock on to debris floating through space and drag it down to deorbit. Astroscale is selling its own docking plates that satellite operators can affix to their equipment ahead of launches, so it can easily be removed after a mission’s end. It's partnered with UK-based OneWeb to test how this will work, and plans to execute a full removal demonstration using one of the company's internet satellites in 2025 under the ELSA-M mission.

Astroscale will also soon launch its ADRAS-J spacecraft in partnership with Japan’s space agency, JAXA, to demonstrate the ability to safely approach and inspect a real target ahead of future removal attempts. And, it's gearing up for a separate mission dubbed COSMIC that will use a robotic arm to grab objects in orbit, this time aiming for a pair of dead British satellites. That is expected to launch in the next few years.

The European Space Agency similarly commissioned Swiss startup ClearSpace for a junk removal mission that’s slated to launch in 2026. It’s expected to be the first mission to actually remove a real piece of debris from orbit, rather than perform a simulated capture. Ironically, the target of the ClearSpace-1 mission — an approximately 250-pound defunct rocket upper stage dubbed Vespa — was struck by untracked debris in August. The event created more debris, but ESA says it left the object intact and still in position for capture. ClearSpace will attempt to grab onto Vespa using a giant robotic claw, and the two will deorbit together, ending with them both burning up in Earth’s atmosphere.

Researchers have also experimented with the use of harpoons and nets to catch objects floating through space. The first mission to demonstrate these active debris removal techniques was one called RemoveDEBRIS, which launched in 2018. In 2018 and 2019, the craft successfully performed simulated debris capture by firing out a net and ensnaring a mock target, and by shooting a harpoon at a target to pierce and hook onto it. The company behind the project — Surrey Satellite Technology — does not appear to have any follow-up missions planned.

A cost-benefit analysis released last year by NASA noted that the benefit of space tugs like these could surpass their upfront costs in a matter of decades, but using space- or ground-based lasers to nudge debris out of orbit could break even much sooner. Lasers can move objects either through the momentum of their photons, or through a process called ablation, in which thrust is generated when the laser vaporizes bits of debris. The latter especially could be used for both large and small objects, either to deorbit debris or move trackable pieces out of another satellite’s way to avoid a collision.

“The process of laser ablation and photon pressure induces a change in velocity in the target debris, which ultimately alters the size and shape of its orbit,” said West Virginia University engineer Hang Woon Lee, who NASA recently granted up to three years of funding for research into this tactic. Doing so could mean “avoiding potentially catastrophic events,” he said. Using multiple lasers at once, instead of a single beam, could produce even greater effects.

Others yet are looking into means of recycling space debris, both to cut down on junk and to limit the reliance on reentries for its removal. While reentry is among the preferred disposal methods, it doesn’t come entirely without side effects of its own, which haven’t yet been well studied. Scientists have begun to speak up about the potential ozone-depleting effects of having large numbers of satellites disintegrate in Earth’s atmosphere, which releases pollutants like aluminum and nitrogen oxides. There are concerns about harmful pollution in the ocean, too, where spacecraft parts that don’t fully break apart end up.

A NASA visualization of debris in low-Earth orbit

Companies like Neumann Space and CisLunar Industries are developing the means to melt down metal parts from debris in space and reuse that material as fuel. The former’s Neumann Drive converts metal rods into plasma to generate thrust, and was just recently integrated into a satellite for the first time to begin tests of the system in space. CisLunar, on the other hand, is building the technology to create those metal fuel rods, along with other materials that could be repurposed to support other missions.

In the US, policymakers are starting to clamp down on commercial entities contributing to the pollution. The FCC handed out its first-ever fine for space debris in early October, and revised its guidelines last year for operations in low Earth orbit, with a new mandate that states satellites in LEO must be transitioned out of orbit within 5 years of completing their missions. The Federal Aviation Administration (FAA) is also eyeing more stringent policies, and proposed a new rule in September that would require commercial launch operators to have a plan in place to remove rocket upper stages from orbit within set timelines, from 30 days to 25 years depending on the circumstances.

Thanks to the rapid acceleration of commercial space activities in the 2020s, we’ve seen an unprecedented number of new satellites arrive in orbit, and there are many more yet on their way. With more launch providers on the scene and innovation in reusable launch systems, led by SpaceX with its Falcon 9 rockets, launches have become less costly and more attainable. And competition to provide space-based internet connectivity by way of satellite “megaconstellations” is intensifying; SpaceX’s Starlink fleet is now at about 5,000 and counting, Amazon just launched the first two prototypes of its eventual 3,200 Project Kuiper satellites and OneWeb has placed over 600 satellites in orbit as of early 2023.

Scientists have long warned about the potentially catastrophic chain reactions that could be caused by space junk if it’s allowed to get out of hand. In the 1970s, NASA scientists Donald Kessler and Burton Cour-Palais argued in a paper that rampant debris could spur collisions that in turn create more debris, and cause more collisions. The risk of impacts between satellites increases, too, as more are pumped into orbit. We’ve already seen a glimpse of how disastrous that could be. In 2009, a commercial Iridium 33 satellite collided with a long-defunct Russian military satellite, Cosmos 2251, creating nearly 2,000 pieces of large debris.

Satellite destruction on a mass scale would have grave consequences both in space and on Earth. It could interfere with science activities and space exploration, and threaten the safety of astronauts aboard the International Space Station. It would also disrupt communications on the ground, removing major sources of internet and cellular connectivity, and GPS. Weather services we’ve long relied on would be interrupted.

More than half of all satellites that have ever been sent to orbit are still up there, a lot of them inactive. “Imagine how dangerous sailing the high seas would be if all the ships ever lost in history were still drifting on top of the water,” ESA Director General Jan Wörner said in 2019, when ClearSpace-1 was announced. “That is the current situation in orbit, and it cannot be allowed to continue.”