The race to clean up outer space

Earth's orbit has become so crowded with defunct satellites and debris that scientists worry about accidental collisions affecting new space missions. Governments and startups are now working on ways to fix this great mess


The year was 1957. The Soviet Union had just launched the world’s first man-made satellite, Sputnik-1, in October, marking the beginning of the “space age”. Sputnik-1 ran out of battery power in roughly 21 days but kept orbiting Earth for three months. In January 1958, the sphere-shaped satellite finally fell back into Earth’s atmosphere, burning up during re-entry. But this isn’t the case with all man-made satellites and objects that have been put in space since then.
Sputnik-1 kicked off what has come to be known as the “space race”. Since 1957, countries around the world have launched over 6,000 rockets, which have placed around 10,680 satellites in orbit, according to the European Space Agency’s (ESA’s) Space Debris Office. Around 6,000 of these satellites are still in space, but only about 3,300 are functioning. The rest are stuck in orbit due to Earth’s gravitational pull as space debris, swirling around our planet at dangerous speeds.
Some of these stranded objects—which include abandoned launch vehicle stages, derelict spacecraft, rocket fragments and even specks of paint—can be as small as a marble but still cause massive damage to functioning satellites or manned spacecraft on impact. According to the US space agency Nasa, the average impact speed of orbital debris with another space object is 10km per second. This can reach about 15km/s—more than 10 times the speed of a bullet. If you have seen Alfonso Cuarón’s 2013 movie Gravity, you know how lethal they can be.
Space debris poses a danger not only to exploration missions but also to newer activities such as private space tourism. In the near future, space travel will be open to individuals. Companies like Virgin Galactic hope to make space tourism affordable—but space junk presents a unique risk.
“It’s getting bigger and bigger. Current data says there are some 3,000 dead satellites and a little over 30,000 pieces of junk which are larger than 10cm in size. The number is critical,” says Jahnavi Phalkey, science and technology historian and director of Science Gallery Bengaluru. “It’s dangerous also to newer missions. The speed at which these things travel, it could damage a new satellite, a manned-space mission or the International Space Station (ISS), where you actually have people living,” she says on the phone.
There are very real fears that there may be so much space debris soon that it could inhibit new launches. In fact, the Kessler Syndrome, a term proposed by astrophysicist and former Nasa scientist Donald J. Kessler in 1978, describes a situation where the amount of man-made space debris reaches such a critical point that just one instance of collision between space debris could lead to a cascade of collisions—and ultimately, a runaway chain reaction. Think of it as a domino effect in space.
The ESA’s Annual Space Environment Report, released in September, notes that while the amount of mission-related objects, such as payloads and rockets, released into space since the 1960s is declining steadily, the number of pieces, the debris’ combined mass and area has only grown. This has resulted in “involuntary collisions” between operational payloads and space debris. After a point, even limiting the number of new space launches will not help. Collisions between existing debris will continue to produce more pieces of space junk.
This is something space missions in certain Earth orbits already have to factor in daily, says Stijn Lemmens, a senior space debris mitigation analyst at ESA’s Space Debris Office in Darmstadt, Germany. “In particular in low Earth orbits, i.e. orbits with an altitude below 2,000km above Earth’s surface, missions need to be prepared to receive, and in some cases act when the risk of collision is too high.... For example, in ESA’s fleet this implies on average one collision avoidance manoeuvre per satellite per year, and a 24 hours by 7 days monitoring of the risk,” Lemmens explains on email. The ISS, for instance, has had to make 28 collision avoidance manoeuvres since 1999, data from Nasa’s Orbital Debris Program Office shows; this includes three such manoeuvres last year. It’s almost like avoiding a rogue vehicle on a highway that might hit you head on. The fact that these have to be done more frequently now only highlights how severe the problem has become.
Space-faring nations around the world have begun to acknowledge the issue, while some startups and private companies are devising technologies to deal with space waste. A different kind of race is unfolding now: a race to clean up space.
ClearSpace SA, a Switzerland-based startup founded in 2018, is aiming to launch the world’s first active debris removal mission in collaboration with ESA by 2025. The mission, which actually hopes to remove a piece of space debris, will be the first of its kind. In India, a young Bengaluru-based space startup, Digantara Research and Technologies, is working on setting up orbit debris tracking and monitoring services. Japanese company Astroscale’s ELSA-d mission, all set to launch from Kazakhstan’s Baikonur Cosmodrome in March, hopes to demonstrate multiple ways of capturing and removing defunct objects from orbit. Another company from Japan, Sumitomo Forestry, working with researchers from Kyoto University, is hoping to develop and launch the world’s first wooden satellites, called LignoSat, by 2023 to cut down on space junk. They believe these satellites, made from wooden material that is highly resistant to temperature and harsh environments, will burn up during re-entry, without releasing harmful elements into the atmosphere. The Indian Space Research Organisation (Isro) has also firmed up its space situational awareness capabilities—knowing the exact location of your space assets, tracking and predicting any possible threats—in recent months, launching a dedicated centre and project to protect its space assets from debris.
Collision course
One of the worst space collisions occurred in February 2009 when two communications satellites collided approximately 800km above Siberia. One of them was a decommissioned Russian communications satellite, Cosmos (Kosmos) 2251, the other a still-functioning US commercial communications satellite, Iridium 33. Their combined weight was around 1,560kg. The collision produced around 2,000 pieces of space debris.
While some of the trackable satellite fragments eventually re-entered Earth’s atmosphere and burnt up, this accidental hypervelocity, or high-speed collision of two orbiting satellites, became a prime example of the threat that space debris poses to functioning satellites and other spacecraft.
Anti-satellite (Asat) testing, which involves intercepting and destroying a satellite, as well as destruction of spacecraft that are no longer operational, has contributed to the problem. China’s 2007 Asat test on one of its own old weather satellites, the Fengyun-1C, created some 3,000 fragments of space debris. In March 2019, India conducted a similar Asat test demonstration, dubbed Mission Shakti, using a ballistic missile to destroy its Microsat-R satellite. The demonstration reportedly created more than 400 pieces of debris, most of which re-entered the atmosphere. India currently has 100 active and defunct spacecraft in orbit and 121 spent rocket bodies and catalogued debris, according to Nasa’s November 2020 Orbital Debris Quarterly News, which publishes the latest in orbital debris research, including data from the US Space Surveillance Network. Figures from 2019 indicate that India had 163 rocket bodies and pieces of debris in space.
ESA has noted that explosions caused by leftover batteries and energy sources in rockets and spacecraft too cause more fragments to scatter in space.
As is the case every year, hundreds of space missions and rocket launches are planned for 2021. China’s main space contractor, the China Aerospace Science and Technology Corporation, is aiming for 40 orbital launches this year. Isro is not only planning its Chandrayaan-3 launch this year, it also hopes to execute India’s first manned mission in December.
Kessler’s “collision cascading” scenario becomes an important factor here.
“It is difficult to predict when we will reach, or indeed if we have already crossed the point that certain regions (in space) become too cluttered with space debris to effectively use them,” says Lemmens. “However, it is clear that our current global practices of leaving too many objects stranded in orbit or at risk of explosion are not sustainable, and that once the point of ‘too much’ is reached, it will be very hard to undo it.”
Cleaning up the mess
There appears to be no single solution to the problem of exponential increase in space debris.
But initiatives like ClearSpace SA are trying to tackle the problem. In December, ESA signed an €86 million (around ₹766 crore) contract with an industrial team of companies led by ClearSpace to purchase the world’s first active debris removal mission, ClearSpace-1, scheduled to be launched in 2025. Apart from the Swiss outfit, the industrial team includes companies from European countries like the Czech Republic,Germany, Sweden, Poland, Portugal and Romania. The UK too is part of the exercise.
“ClearSpace’s goal is to bring in a solution to clean (space debris) and prevent this exponential (growth). We want to make sure that we never get to the full end of that exponential. Where we are today, collisions between space debris will keep on happening,” says Muriel Richard-Noca, co-founder of ClearSpace SA, in a video call from Lausanne. “We want to diminish that effect as much as we can. We are at the point where, if we don’t do anything today, there will be big consequences tomorrow. If we don’t start cleaning now, in a few decades it is going to be really hard for us to place more satellites in space.”
The ClearSpace-1 chaser spacecraft will initially be launched into a lower 500km orbit. It will then be raised to a target orbit of 660km, where it will attempt to rendezvous and capture the upper part of a Vespa (or Vega Secondary Payload Adapter), which was used for a rocket launch in 2013, with the help of four robotic arms. This object, which weighs around 112kg ( almost as much as a small satellite), has been in a “gradual disposal” orbit—where satellites or objects are placed when they are no longer operational. Once it has been captured, both the piece of debris and chaser spacecraft will de-orbit and burn up during re-entry.
Studies conducted by ESA and Nasa have shown that active debris removal missions can be efficient in eventually stabilising the space environment. But planning a removal sequence—based on the size of the debris or object, the kind of collision threat it poses and whether it’s located in a densely populated orbit—will be crucial.


Several active debris removal demonstrations—with mock pieces of debris—have been conducted in the past. The University of Surrey’s RemoveDEBRIS mission in 2018-19, which was led by researchers at the Surrey Space Centre, is a case in point. It successfully demonstrated multiple technologies that could be used to capture debris, including a tethered space harpoon and nets.
Astroscale too is aiming to showcase multiple techniques of spotting and capturing pieces of orbital debris through its ELSA-d mission. "Technology-wise, ELSA-d is the first end-to-end debris removal demonstration mission. When the servicer satellite is up there, it first needs to identify and approach an object or piece of debris," says Nobu Okada, founder and CEO, Astroscale, in a video call from Tokyo. "After a synchronised capture, the object will then be stabilised and de-orbited. We will be carrying a mock object—a client satellite—which will be separated in space and then captured by the servicer using proximity-rendezvous technology and a magnetic docking mechanism," he explains.

Capturing a moving piece of debris in space, however, is by no means easy. “There are two main challenges. What we are creating is a space robot that will reach the target debris, look at it and calculate how it is tumbling,” says Richard-Noca. “Objects in space are free-floating and they can tumble on every axis at quite high speeds or low speeds…. The intent here is to analyse and reconstruct the object’s movement once we get there with advanced image processing techniques such as deep-neural networks. These techniques will enable autonomous navigation around the debris and its capture. That is the image-processing challenge,” she adds.
The second technological obstacle—how do you capture an object in space that is tumbling? “When a cargo mission goes to the ISS, both of them talk (or communicate) to each other and remain stable. In our case, the capture is what we call ‘uncooperative’. There is no signal coming from the debris to help us and we have to catch up with its tumbling. The capture is the most critical operational challenge,” says Richard-Noca.
India's space debris horizon
The race to tackle orbital debris has seen space agencies place greater emphasis on space situational awareness and traffic management. Today, we rely on satellites in low Earth orbit for a host of key services: telecommunications, the global positioning system, weather and meteorological data, among other things. In such a scenario, protecting space assets becomes all the more important. However, there are no safeguards against a piece of space debris generated by one country damaging the assets of another nation. “There are no natural boundaries in space,” says Phalkey.
In December, Isro set up a dedicated directorate of space situational awareness and management (DSSAM), which includes the NEtwork for space object TRacking and Analysis project, also known as Netra. This project’s control centre, set up within the Isro Telemetry, Tracking and Command Network (Istrac) campus in Bengaluru, will act as a hub for space situational awareness activities in the country. A radar and optical telescope facility will help the organisation safeguard its operational assets and predict the atmospheric re-entry of derelict satellites and rocket bodies, a press note explains.
S. Chandrashekar, a former Isro scientist and visiting chair professor at the National Institute of Advanced Studies, Bengaluru, says tracking space debris is a problem for every country. “All space-operating entities and agencies need such systems today,” he says. “Without knowing what’s happening in space, how can any space agency function? If it is a transmitting satellite, you can locate and track it easily. The moment a satellite starts drifting, and at some stage it may not transmit at all, then you have a problem... It’s going to take a long time to come down but you still need to know where it is,” says Chandrashekar, who was with Isro for almost 20 years, on the phone. “In the earlier days, space was much less populated. When I was at Isro, I never heard of a satellite colliding with another satellite. Even if two satellites were in the same orbit, it’s highly unlikely they were going to hit each other. It was not such a problem. But space is very crowded now.”
While ground-based monitoring systems are good at tracking orbital debris, this activity can be executed with much more precision from space. Recently, Canadian firm NorthStar Earth & Space announced that it was partnering with French-Italian aerospace manufacturer Thales Alenia Space to develop a commercial satellite system that would help track objects, such as other satellites, from space. The “Skylark constellation” is expected to launch in 2022, with a full system of 12 satellites expected in 2024, NorthStar’s co-founder Stewart Bain was quoted as saying in a Reuters report.
Digantara is working on a similar system that would rely on a constellation of 40 satellites and Lidar (light detection and ranging) technology to create a database and visualisation platform that will help track and map objects in low Earth orbit. “You can think of it as something like Google Maps, but for space,” says Anirudh Sharma, co-founder of Digantara. The firm, founded in 2018, also offers services like early-launch support and orbit determination to satellite operators and launch companies. “Ground-based monitoring systems (that track objects in space) have certain limitations when it comes to line of sight, range, atmospheric disruption… That is why we are building a space platform which uses Lidar,” he says.
How long could it take to stabilise the situation? Internal studies done by ESA show that if continuous debris removal actions or missions start as late as 2060, they will only have a 75% beneficial effect compared to an immediate start—so it’s a case of now or never
The company hopes to launch its first satellite payload in December to demonstrate its “in-orbit space debris monitor” technology. The eventual goal is to send out the 40 satellites across three phases. “We haven’t decided where we will launch from yet. That decision will be taken six months before launch but we are hoping that our timing matches with Isro’s PSLV launch. We are looking at a window between December 2021 to February 2022,” says Sharma. To ensure its own solution doesn’t add to or create more space junk, Sharma says Digantara’s satellites will use propulsion systems to de-orbit at the end of their lifespan.
How long could it take to stabilise the situation? Internal studies done by ESA show that if continuous debris removal actions or missions start as late as 2060, they will only have a 75% beneficial effect compared to an immediate start—so it’s a case of now or never. Phalkey says: “We have to go as far as required and conduct space-cleaning activities for as long as it’s required. While we create new technologies to ensure that this doesn’t happen in the future, the past needs to be cleaned up.”
The task at hand, however, remains enormous. Take Vanguard-1, for instance—launched in 1958, it’s the oldest human-made object still in space. It orbits Earth as space junk and even though it doesn’t pose any significant threat or collision risk, it won’t de-orbit before 2198.
It’s a problem of our own making, says Phalkey. “Instead of looking spacewards, look inwards. What have we done to the planet, the resources on Earth.... We are making it unliveable.” Like our effort now to limit climate change, clean our polluted oceans and air, the effort to clean up space for future exploration will have to be a sustained one.



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