Since the 1950s, humans have been sending probes and satellites into space. But we’ve also left behind a lot of junk.
In addition to operational satellites, there are millions of pieces of space debris, which consists of defunct man-made objects, principally in the low Earth orbit (LEO). While this includes larger items such as discarded rocket stages, broken spacecraft and various pieces of metal and plastic, it can also mean objects that are far smaller like flecks of paint that have fallen off spaceships. Some of this waste was even left on the Moon during the 60s and 70s, fragments of space missions from decades ago.
This refuse circles the Earth at the speed of tens of thousands of kilometers per hour. This creates a huge risk for important satellites, which provide vital services like GPS and weather warnings, and even small pieces of junk are travelling in orbit at a speed of five miles per second, meaning any collision can cause a lot of damage. A crash between two larger pieces of junk may even have catastrophic results.
An apocalyptic scenario.
Imagine two old satellites. Each just slightly larger than 10 cm (4 inches) in diameter. They collide and completely disintegrate in the process, creating two ever-spreading clouds of fragments, which travel at the same speed and trajectory as the satellites.
After a short while, one of these clouds impacts another piece of space hardware and tears it apart, doubling the number of fragments in circulation. The process happens again, and another object is impacted. Then again. And again. All the while increasing in pace.
One collision turns into an expanding avalanche, a cascade of destruction, before the entire orbit turns into a field of fragments, all moving at incredible speeds. The LEO becomes an impenetrable barrier, and no satellite, spacecraft or space station can survive there. Space exploration would be impossible under such conditions. Satellite communication, GPS navigation, mapping and weather prediction all become a thing of the past. Humanity must wait for centuries before the debris field deorbits due to natural causes. Only then will we be able to try and reach space again.
This apocalyptic scenario was first envisioned in 1970s by Donald Kessler, an American astrophysicist and former NASA scientist known for his studies regarding space debris. This theoretical scene was dubbed the Kessler syndrome, also sometimes called the Kessler effect, collisional cascading, or ablation cascade. It rose to public attention when it was used as a plot device in several prominent pieces of fiction, most notably the film Gravity (2013), which followed the fate of two astronauts who must work together to survive after the consequences of the Kessler effect leave them stranded in space.
The prospect of being near-permanently cut off from space kickstarted several projects, which have been steadily growing in number over the last decade or so. Thousands of scientists started seeking solutions to the space debris problem and an increasing amount of time and effort has been dedicated to its prevention.
NASA has been running Orbital Debris Program since 1979 and The European Space Agency (ESA) Space Debris Working Group, which later evolved into Space Debris Office, was established in 1986. In 1991, the Inter-Agency Space Debris Coordination Committee (IADC) was founded. Later, this was joined by all major space agencies, including the China National Space Administration (CNSA) and Russia’s ROSCOSMOS.
In 1993, the first ESA conference on space debris attracted a couple of dozens of researchers from several countries. In April 2021, the 8th edition of the conference had over 530 registered participants, many of them professionals who have devoted their entire career to the problem of space debris. This is just one example of how things changed. Globally, there are now working groups, initiatives, international communication channels and scientific journals entirely dedicated to the issue.
Most early documentation produced about space junk can be best surmised as a plea to end inaction. However, this sentiment is clearly a thing of the past. There are now thousands of people working to combat the issues.
So, have these efforts led to tangible results?
Harpoons and lasers
Much like the problem of waste here on Earth, there are multiple methods proposed to deal with the issue of space debris. However, the most dramatic sounding solutions are by no means the most effective.
A potential LEO cleanup brings to mind hunter satellites that cast nets or harpoons in an attempt to catch debris and deorbit. Several devices of this kind have been tested, the latest of them being the one manufactured by British company Astroscale and launched in early May 2021.
In most cases, such missions cost millions of dollars and can only remove one large piece of debris. It’s not exactly a sustainable endeavor. Of course, these are just the initial steps designed to demonstrate the possibility of such a mission, which is as difficult as it is dangerous. But even if such cleanups became cheaper in the future, they aren’t expected to be the only way to avoid the Kessler syndrome.
A cheaper and more efficient method would be lasers, which could be mounted on the ground or on a satellite. A focused beam would heat up one side of a piece of debris and create enough force to propel it. This method would be most effective when used to remove debris between one centimeter and ten centimeters in diameter. The ‘laser broom handle’ is one of the most serious and most-discussed proposals in the scientist community.
But it comes with its own set of problems. For one thing, having a powerful laser that could shoot down satellites doesn’t exactly sit well with the international community. Essentially, it means wielding powerful anti-satellite weaponry, and raises questions about responsibility and control. In the 1990s, the United States Air Force (USAF) almost built a similar device under Project Orion, but it was abandoned due to the controversy.
A junk-cleaning laser would also be quite expensive and difficult to operate with today’s technology. But it is undeniably more convenient than sending disposable cleaner satellites, which means that one day such a project will probably be completed. However, that day is probably quite far in the future.
Mitigation
No single method of active space debris removal is ideal. Like many other things, prevention is far more effective, which is why the majority of scientific effort is aimed at the mitigation of space debris.
Fundamentally, we need to create as little space junk as possible. This would include deorbiting spent rocket stages immediately after they payload delivery and satellites as soon as they expire, emptying fuel cells and batteries to prevent unwanted debris-creating explosions and ensuring new satellites are more resistant to impact damage, so that even in an event of a collision with a smaller piece of junk, a blast of fragments is not sent flying into space.
Limiting the orbital life of a satellite is a complicated issue, which requires precise and resource-consuming engineering efforts. A satellite must be deployed at orbit, where the atmosphere will drag it just far enough for it to fall down after the expiration date. However, not all satellite manufacturers and operators want this to be the case and a lot depends on their compliance.
Cataloging existing debris is another large issue. Most space junk is small and detecting it is difficult. Determining its precise orbit is even more so. Enormous radars and telescopes are used, with many of them specifically dedicated to this purpose. It’s impossible to overstate the cost and the scope of this effort, and the level of international coordination required. But without it, space operations would not be possible. Debris avoidance, based on monumental amounts of data generated by cataloguing efforts, is a standard procedure for any satellite. Its successful implementation allows for satellites to function, but also to avoid the creation of further debris.
The current state of affairs
In 2013, an overview of the progress of active debris removal was published by several scientists from the French space agency. It began with quite a horrifying statement: “According to all available findings at international level, the Kessler syndrome, increase of the number of space debris in Low Earth Orbits due to mutual collisions, appears now to be a fact.”
It’s apparent that the creation of new debris is increasing at an alarming rate. Between 2007 and 2009, and following several anti-satellite tests and collisions, the amount almost doubled. NASA classified the state as “critical”. Not only was there enough junk to start the orbit-wiping cascade, but the cascade appeared to already be happening.
Since then, according to NASA’s data, the number of objects in LEO remained approximately the same. However, the number of satellites increased by almost a quarter and debris decreased by almost the same amount.
The ESA Annual Space Environment Report published in mid-2020 concludes that almost 90% of small satellites launched into the LEO during the last decade adhere to the debris mitigation measures. This means that they can successfully avoid collisions and deorbit as soon as required. While not all orbital payloads were launched following debris mitigation guidelines, an increasing number of their operators – over 60% in 2019 – still managed to implement those guidelines after the fact.
Clearly, the mitigation measures put in place (despite the small number of launches that did not follow guidelines) were successful. Cataloguing debris, avoiding further collisions and convincing satellite operators to adhere to rules that prevent creation of further debris have all made a huge difference. It seems that the international community was able to halt the Kessler syndrome.
What does the future hold?
Of course, this does not mean that the threat has been extinguished. Since the overall number of objects in LEO did not decrease, we remain just one catastrophic collision away from the dreaded scenario.
A few years ago, when several prominent companies announced their plans to launch so-called megaconstellations of satellites, with OneWeb and SpaceX among them, there was enormous concern that we were heading back to square one. Had these constellations failed to adhere to debris mitigation measures, the apocalyptic scenario would have occurred almost immediately.
But the consequences of inaction would be felt by the constellation operators.
Stijn Lemmens, Senior Space Debris Mitigation Analyst at ESA Space Debris Office, told AeroTime: “Some large constellation operators have been active in the space debris community and are very aware of the potential space environmental problem that mis-management could trigger.”
He continued: “The counter-measures are understood and internationally communicated, as even the operation of large constellations can happen in a sustainable way when designed and implemented with the debris environment and other operators in mind.”
A special IADC statement about large constellations of satellites in LEO makes it clear that operators of megaconstellations should be far more zealous about adhering to international guidelines than, say, the operators of regular satellites. And this, it appears, is exactly what’s happening.
SpaceX has agreed to operate their constellation at a lower altitude, which would cause a failed satellite to deorbit within five years. OneWeb’s satellites will, supposedly, take no longer than a year to do the same.
These promises have, rightfully, been met with skepticism by the international community. There is little room for error when it comes to the possibility of the Kessler effect. But it is difficult to deny the progress, coordination and cooperation that has occurred during the last few decades.
And when, if ever, has humanity had the chance to boast about preventing something so potentially catastrophic?