Multiple aerospace companies, including SpaceX and OneWeb, have vowed to someday launch thousands of satellites into low Earth orbit, but these mega-constellations could make space a more congested and dangerous place. That’s why NASA is recommending in a new report that these companies make sure their future satellites are taken out of orbit as soon as they complete their missions.

Currently, there are about 4,000 intact spacecraft living in orbit around Earth, only 1,800 of which are operational. Yet, many companies want to dramatically increase that number. Satellite operators are eager to launch thousands of probes that can beam internet connectivity down to Earth, providing global coverage. SpaceX has filed applications with the FCC to launch nearly 12,000 internet-beaming satellites — first, an initial constellation of 4,425 probes, followed by a constellation of 7,518. Meanwhile, the European company OneWeb received approval to launch up to 720 satellites from the FCC, and it recently requested permission to launch an additional 1,260.

“[these companies] need to pay attention to certain areas to make sure they do not pollute the near Earth space environment.”

If all these constellations are successfully launched around the same time, the number of operational satellites in orbit would quadruple, raising the risk of catastrophic and cascading satellite collisions. NASA wanted to know the potential impact of such a crowded space environment. So in a new study, the space agency envisioned future scenarios in which huge constellations of thousands of satellites dominate low Earth orbit to determine what kind of effect that would have. Based on their research, NASA scientists argue that nearly all of these satellites — 99 percent — will need to be taken out of orbit as soon as they have completed their time in space. This should prevent the number of collisions between satellites from increasing over the next few centuries.

“Because of the number of spacecraft involved in large constellations, [these companies] need to pay attention to certain areas to make sure they do not pollute the near Earth space environment with significant orbital debris,” Jer-Chyi Liou, the chief scientist of orbital debris at NASA who helmed the new study, tells The Verge.

The aerospace industry is particularly concerned with spacecraft collisions because these accidents can create multiple pieces of debris zooming through space at thousands of miles per hour. And these fragments can threaten other spacecraft in orbit, causing further crashes and damage. Many are concerned that these collisions could cause a cascade effect, where crashes become more and more frequent so that low Earth orbit becomes too crowded to safely sustain satellites — a hypothetical future referred to as the Kessler syndrome. Fortunately, collisions have been a rare occurrence so far. But in 2009, a derelict Russian satellite smashed into a US communications probe, creating thousands of pieces of debris.

crashes become more and more frequent so that low Earth orbit becomes too crowded

To figure out the risks, Liou and his team estimated how many extra satellites might be deployed into space over the next few years, along with how much room these probes will take up. The team assumed that between 6,700 and 8,300 additional probes could be added. They also figured the spacecraft would weigh around 330 and 660 pounds each and that these probes would operate for about five years in orbit. “We tried to use the information available in the public domain from the companies that are proposing large constellations to come up with sizes for these large constellations,” says Liou.

These hypothetical futures ultimately led the team to come up with the 99 percent recommendation. The advice: for every 100 satellites, 99 need to be de-orbited as soon as their missions are over, typically within five years of it ending. That entails lowering the altitude of the satellite so that it quickly succumbs to Earth’s gravity and burns up during the descent through our planet’s atmosphere. If this doesn’t happen, then the population of spacecraft in low Earth orbit starts to grow significantly over the years.

The more objects in orbit, the higher the chances are that spacecraft will have unplanned crashes. For instance, the NASA team tested out what would happen if only 90 percent of these large constellations were de-orbited on time. In that situation, the number of collisions would be about 260 over the next 200 years. But if 99 percent are taken down in time, then only 34 crashes would happen in the same time period. That’s just slightly higher than the risk is now.

Liou acknowledges that 99 percent is a fairly high number to adhere to, but it’s necessary to keep low Earth orbit a safe place for spacecraft. “If you don’t achieve 99 percent, the population increase in the environment is significant,” he says. Plus, similar studies have come to the same conclusion. Scientists at the European Space Agency suggested last year that large constellations would need to be disposed of at a rate of 95 percent.

Beyond the need for de-orbiting spacecraft, the NASA study listed a couple of other recommendations for satellite operators. For instance, these probes will need to be extra hardened to withstand any collisions with debris in space, notably micrometeoroids. That way, if a small rock does hit one of these satellites, the vehicle doesn’t get damaged so badly that it can’t de-orbit in time. Additionally, these satellites cannot explode easily. Ever since humans started sending spacecraft into orbit, there have been nearly 200 accidental explosions in space, according to Liou, which can create debris that endangers other spacecraft. Liou recommends that satellites in this mega constellations will need to be built in such a way that the probability they might explode is less than one in 1,000.

Those recommendations will increase the time and money needed to make these spacecraft and operate satellite networks. But adhering to those rules would ensure that the space near Earth remains usable for the foreseeable future. When the FCC approved SpaceX’s license for its internet satellite constellation, it did say that the company will need to provide an “updated description of the orbital debris mitigation plans for its system,” despite providing details and analysis in its filing. SpaceX told the FCC it would de-orbit its satellites within five to seven years. Meanwhile, OneWeb has also boasted that its de-orbit plans are highly reliable, and will take them out of orbit within five years. OneWeb declined to comment to The Verge, and SpaceX did not respond with a statement in time for publication.

There are other backup options that would also ensure these satellites get out of orbit faster. It’s possible that these satellites could be outfitted with a “de-orbit kit,” such as a balloon or sail; these tools increase the surface area of a satellite, allowing it to get bombarded by more particles in the upper atmosphere, which ultimately drag the satellite downward. This may be difficult, though, if the satellites are too high up and far away from the atmosphere. Adding such kits can also be costly. “The cheapest solution is going to be relying on the propulsion of the satellites and making the propellant tank bigger,” Jonathan Goff, president and CEO of startup Altius Space Machines, tells The Verge.

Still, what happens if a spacecraft goes dead and cannot propel itself down to a lower altitude? That’s where a plan B should come in, says Goff. “You make your plan A as reliable as possible, but you also have a plan B,” he says. That’s why numerous engineers like Goff have proposed alternative ways to clean up inoperative spacecraft and push these vehicles out of orbit. Some proposals include vehicles with harpoons, nets, or lasers — all of which can help drag defunct satellites downward.

But there are also plans for vehicles that can catch up to satellites and grapple them, either to perform repairs or to place them on an expedited descent to Earth. That’s the kind of spacecraft that Goff is working on at Altius. He proposes that these companies might want to add some kind of grappling fixture so that future servicing spacecraft might grab hold of them more easily. That way, future servicing satellites could maybe even repair or refuel the defunct satellites instead of disposing of them. Then, satellite operators wouldn’t need to replace the satellite with a future launch. “You need the tow trucks, but we’d also like to be the towing service that says, ‘Well, let’s see if we can get your car running again,’” says Goff. “So you can go from providing backup de-orbit services to branching out to ‘Can we do things to fix or upgrade to extend the life of these constellations?’”

“that future can’t happen if we destroy the low Earth orbit environment or at least make it significantly worse.”

We’re still years away from these constellations becoming fully operational in orbit. OneWeb is targeting its first launch for the end of the year or early next year, and SpaceX is tasked with launching a couple thousand satellites before 2024 in order to keep its FCC license. But, ultimately, Liou is hopeful that these companies will move forward safely with their mega constellations. “They have engaged in discussions with the orbital debris community from the very beginning,” he says. “They have a good understanding of the key areas we need to address.”

Goff says that the collision issue is an extremely important thing to consider if we ever want to do more ambitious missions in low Earth orbit, such as launch private space stations. “I want to see that future, but that future can’t happen if we destroy the low Earth orbit environment or at least make it significantly worse.”