More than 10,500 satellites are circling Earth as of late 2023, according to the European Space Agency (ESA). Out of these spacecraft, 8,600 are currently in service. This number, however, keeps growing, and experts fear that maintaining order in space may become nigh impossible in just a few years. It's a situation that could lead to regions of low-Earth orbit being unusable, a catastrophe for our satellite-dependent civilization. Fortunately, engineers are already developing technologies to prevent chaos from ruining the orbital environment.
What’s going on in space?
In 2010, there were only about 1,000 satellites orbiting our planet. By 2030, there may be 100,000 or more, according to existing predictions. This steep rise is mostly due to the development of internet-beaming mega-constellations such as SpaceX’s Starlink. Operators of these systems plan to launch tens of thousands of satellites in the next decade, and that gives space sustainability researchers a real headache.
Although space is big, the paths of satellites traveling in similar orbits do intersect from time to time, which creates a risk of collisions. As objects in Earth’s orbit travel at mind-boggling speeds of nearly 30,000 kilometers (18,000 miles) per hour, these orbital smashes do pack a real punch. A head-on collision between two satellites would spawn thousands of space debris fragments that could clutter the near-Earth space for decades.
Satellite operators receive warnings from the US Space Surveillance Network whenever their spacecraft are on a collision course with another satellite or a piece of space junk. The more satellites in space, the more warnings the operators receive and the more often they have to move their craft to get out of each other’s way.
For example, in the period between December 1, 2022, and May 31, 2023, all Starlink satellites in orbit at that time combined had to conduct more than 25,000 collision avoidance maneuvers. Because SpaceX continues launching more and more satellites, this number is set to double in the six-month period between May 31 and December 1, according to Hugh Lewis, a professor of astronautics at the University of Southampton. Soon, traffic in space will be as busy as that of a metropolitan ring road and in need of proper policing.
How do we keep track of stuff in space?
Keeping space safe requires an understanding of where orbiting objects are. Most operational satellites are fitted with GPS trackers that signal their position with great accuracy. But space debris – defunct spacecraft, spent rocket stages, and fragments from past explosions and collisions – can only be tracked with Earth-based radars and telescopes. The job of keeping tabs on traffic in space has traditionally been the responsibility of the US Space Surveillance Network, a system of ground-based radars operated by the US Space Force.
In recent years, private companies, such as US-based LeoLabs, have rolled out their own radar networks with the aim of providing better information to satellite operators.
Most existing debris-tracking radars, however, can reliably track only objects larger than 10 centimeters (4 inches). There are currently about 36,500 such objects, according to ESA. But these objects represent only a tiny fraction of the clutter in near-Earth space. Researchers estimate that about 1 million fragments between 1 and 10 centimeters (0.4 to 4 inches) in size, as well as 130 million pieces smaller than 1 centimeter, zip around Earth completely out of control.
Even such small objects can cause serious damage. In 2016, a piece of space debris the size of a bullet punched a 40-centimeter-wide (16-inch) hole into the solar panel of the European Earth-observing satellite Sentinel-1. The spacecraft survived and continues to image our planet to this day, but ESA said at that time that the mission may not have been that lucky had the junk hit Sentinel-1’s main body.
New orbiting debris sensors can keep up with small stuff
A new technology developed by Belgium-based start-up Arcsec promises to improve our knowledge of the whereabouts of treacherous space bullets, such as the one that hit Sentinel-1. Instead of searching for these tiny space debris fragments from Earth, Arcsec will look for junk directly from space. The good news is that Arcsec’s novel space debris detectors take advantage of devices mounted on existing satellites – their star trackers – and that means that it will cost close to nothing to get the new sensors into space.
Satellites use star trackers to determine their position and tilt with respect to key stars in their field of view. But other satellites, space debris pieces, and meteorites cross this field of view as well. New software developed by Arcsec will use these sightings to calculate the orbits of these objects, Arcsec said in an emailed statement. Providers of space situational data will be able to use those measurements to calculate the risk those objects pose to operational spacecraft.
Arcsec said their debris trackers will be able to reliably spot fragments as small as 3 centimeters (1.1 inch). The space debris tracking software could be remotely uploaded onto existing satellites fitted with Arcsec’s earlier star-tracking devices. Soon, there can be an entire space junk monitoring fleet in space and things may get a little safer. If all goes well, space bullets will no longer be catching satellites by surprise.
New tech on the ground is catching up
Ground-based detectors, too, are getting better at spotting smaller space junk, LeoLabs told IFLScience in an email. The ability of a radar system to detect smaller debris depends on the frequency of the signal the radar emits. Most debris-detecting radars use the so-called ultra high frequency (UHF), which emits radio waves with wavelengths 0.1 to 1 meters (0.3 to 3.2 feet) in length. But these radars are not good at spotting small debris fragments. Shorter wavelength, higher-frequency radars, such as those using the so-called S-band, are much better, LeoLabs said. The shorter radio waves, however, don’t travel through space as efficiently as the longer ones and struggle to reach higher orbits.
Supersensitive optical cameras are now being developed that can see smaller space junk and detect it higher above the planet than the S-band radars can. UK-based space situational awareness company Raytheon NORSS told IFLScience that optical cameras are cheaper than radars and more efficient in tracking more distant objects.
The company has recently developed a new debris-tracking camera called LOCI (for Low Earth Orbit Optical Camera Installation) that constantly scans the sky and tracks objects that transit through its view. By detecting and analyzing how the object reflects light, researchers can gain a lot of additional information about its state. Unlike radar, the LOCI camera can track multiple objects at once.
The old-fashioned way of keeping things safe in space involves teams of analysts evaluating conjunction warnings received from the US Space Surveillance Network to decide whether a collision avoidance maneuver is necessary.
But the number of collision alerts keeps growing together with the number of satellites in orbit, and companies are beginning to struggle to stay on top of things. They are looking for automated solutions that could process available data faster and more efficiently, and make more informed decisions.
SpaceX’s Starlink is a pioneer in the field, although not much is known about the autonomous satellite collision avoidance system the company relies on.
In an update on its running blog in February 2022, SpaceX wrote that the onboard collision avoidance system its satellites use combines data from the US Space Surveillance Network and other space situational awareness data providers, evaluates the risks and, if necessary, allows the satellites to “duck” autonomously to avoid a collision.
Experts think that entrusting the management of orbital traffic to AI and machine learning is the only way to maintain orbital order in the future.
Portugal-based start-up Neuraspace, which is developing an AI-driven, space situational awareness system, told IFLScience in an email that “current solutions that rely on manual processes, traditional technologies, and sensors cannot cope with [the expected] 15-fold increase in space assets.” In other words, there soon will be too many satellites in space and too many debris monitoring sensors, providing too much data for humans to reliably sift through.
AI algorithms, such as those developed by Neuraspace will help satellite operators make decisions with a hundred times better efficiency, the company believes, and reduce the number of people needed to assess the collision alerts by 80 percent.
“It saves time and effort in analysis and computation and offers a reliable solution in the form of maneuvering suggestions that are based on accurate computation and analysis,” Neuraspace wrote.
But more is needed to prevent the orbital environment from getting out of control. While active satellites can avoid each other, pieces of space debris cannot.
On January 27 this year, LeoLabs announced on X, formerly known as Twitter, that two rather massive pieces of space debris – a decades-old Russian rocket stage and an equally ancient defunct Russian satellite – nearly smashed into each other 984 kilometers (611 miles) above Earth. The two objects missed each other by only about 6 meters (20 feet), LeoLabs estimated. A head-on collision would have produced thousands of space debris fragments.
For this reason, space agencies and commercial companies alike are developing new types of spacecraft that could act as orbital junk collectors. In 2026, ESA plans to launch a mission called ClearSpace-1, which will attempt to catch a 112-kilogram (247-pound) rocket adaptor and drag it into the atmosphere where the junk would burn up.
Coincidentally, the US Space Surveillance Network recently spotted small fragments being shed from the target of the ClearSpace-1 mission, indicating that it may have been hit by a small piece of space junk. The incident underscores how volatile the orbital environment has become.
Japan-headquartered Astroscale also has active debris removal missions in the works, including the COSMIC (Cleaning Outer Space Mission through Innovative Capture) project, which will attempt to remove two small defunct UK-made satellites in 2026.
ESA estimates that 5 to 10 large space debris objects need to be removed every year to prevent the amount of space debris from getting out of control. But for now, we are only adding and not subtracting.