Space debris: the scrapheap in the sky
Image credit: ClearSpace
Rising levels of space debris threaten to obliterate satellites and knockout internet access. Meet the organisations racing to stop the junk in its tracks.
The year before Elon Musk launched his first string of Starlink satellites, he dispatched a midnight cherry Tesla Roadster, ‘driven’ by a spacesuit-clad mannequin, on top of his Falcon Heavy rocket. Today, ‘Starman’ and his Tesla continue to spin through space at several thousand miles per hour while more than 1,000 Starlink satellites have reached Earth orbit to deliver high-speed satellite internet across the globe. But we have a problem.
Put simply, our Earth orbit is a mess and it’s getting messier. At the time of writing, some 6,200 satellites are circling our planet, of which nearly 3,000 are defunct and classed as ‘space junk’. This is just the big stuff.
Latest European Space Agency figures indicate that there are nearly 129 million debris objects, ranging in size from 1mm to more than 10cm. Debris ranges from paint flecks, nuts, bolts and frozen satellite coolant to astronaut tools, rocket parts, and, depending on your point of view, Starman and his Tesla, possibly still listening to David Bowie’s ‘Space Oddity’ on loop.
Clearly the opportunity for satellite-debris collisions is growing, and the new wave of mega-constellation telecommunications satellites from the likes of Starlink and OneWeb are exacerbating the problem. Starlink alone intends to eventually launch more than 40,000 satellites.
In the interim, satellite operators have been doing a good job of dodging the junk, largely thanks to the world-leading US military’s Space Surveillance Network, and similar systems in China, Russia and Europe. Indeed, come 2027, the Russian state space corporation, Roscosmos, will launch a further satellite to monitor space debris.
Still, industry figures indicate debris-satellite collisions have doubled in the last three years. Due to high impact speed in space – some ~22,000mph in lower Earth orbit – even sub-millimetre debris poses a realistic threat to space flight. If something the size of a mobile phone was to hit a satellite, it would probably mean lights out for that satellite as well as a huge chunk of internet access down on Earth.
“Space debris and the risk of satellite collisions isn’t science fiction. It is likely, it does happen and it will affect life on Earth,” says Jacob Geer, head of space surveillance and tracking at the UK Space Agency (UKSA). “We depend on satellite data for our everyday lives, including telecommunications, GPS signals as well as defence and security.
“Companies such as SpaceX and OneWeb are quite responsible, but in low Earth orbit, there is no single rubric that governs how you behave,” he adds. “More and more industry players are launching satellites, and this is causing [operators] to have more issues – I don’t think people always realise how dependent we are on space.”
Dr Jason Forshaw, head of future business in the UK and Europe at Astroscale, Japan, concurs. According to the aerospace engineer, space debris is “a colossal problem”’ and is getting worse.
He says: “We know there are millions of smaller fragments, each of which poses a threat to our satellites, and we just can’t track them all. When larger satellites collide in space, as took place in 2009 with the US and Russian satellites Iridium and Kosmos, more small fragments are created, which is incredibly dangerous.”
Geer believes international regulation is urgently needed to start tackling the debris problem, as nations around the world are currently operating differently in space. “Some people take this issue very seriously while others maybe take it seriously in a different way,” he says.
To this end, the UKSA recently partnered with the United Nations Office for Outer Space Affairs to fund and promote space sustainability, which Geer hopes will contribute towards a much-needed international push on tackling the debris problem. “If we don’t start dealing with this issue, there will be future consequences,” he adds. “More collisions will occur and we’re going to lose access to the space services that people use every day... [regulation] has been talked about a lot but I still don’t see much direct action.”
Regulation aside, both Geer and Forshaw agree that cleaning up our orbital waste is imperative. The jury is out on the best way to do this, but a decent handful of projects are under way and making very good progress.
In September last year, the UKSA dished out some £1m in funds to seven UK-based projects to develop novel sensors to detect and track debris, as well as artificial intelligence methods to analyse the vast swathes of data that will ensue. Among these, D-Orbit UK will refine recently launched star tracker sensors and develop radar to image and characterise debris moving around space objects. Lumi Space will pioneer laser ranging technology, again to spot and track objects. Meanwhile, Fujitsu will create machine-learning approaches and quantum-inspired processing to improve mission planning to remove debris.
However, Astroscale is taking activities to a new level with its End-of-Life Services Demonstration, ELSA-d. Scheduled for lift-off on a Soyuz-2 rocket from the Baikonur Cosmodrome, Kazakhstan, in March 2021, the mission comprises a 184kg mothership satellite called ‘servicer’ and a 16kg pod-like ‘client’ that serves as the dummy end-of-life satellite debris that needs to be removed from orbit. Crucially, the mothership is kitted out with vision-based navigation, rendezvous proximity sensors and a magnetic docking mechanism while the client is fitted with a ferromagnetic docking plate.
Once in space, the servicer will repeatedly release and dock with the dummy satellite debris while it moves and tumbles as many defunct space objects do, and will also ‘lose’ and retrieve the client from a distance of a few kilometres. The entire mission will be steered from a ground-based control centre in the UK and, if a success, will see both the mothership satellite and its defunct client descend together in a final, flaming de-orbit, in around two years.
“The tumbling capture is probably one of the most challenging parts of the overall mission and this demonstration has never been carried out in a semi-autonomous manner in space before,” highlights Forshaw. “When you’re capturing a tumbling object, you need to exactly align the position and velocity of the servicer with the client in multiple axes, and that is extremely complex.”
As part of this, sensors and laser rangefinders on the servicer first track the client via markings on its docking plate, with tumbling data then transmitted down to ground control. Flight dynamics calculations are then sent back up to the servicer, which then, as Forshaw says, “dances” into the correct trajectory to approach and dock with the client.
“The servicer approaches the client in a passively safe trajectory – a ‘walking ellipse’, which doesn’t allow it to collide with the client,” says Forshaw. “It then gets closer and closer, effectively locking onto the client with local sensors for the final approach, eventually docking with it using the magnetic capture system.”
With future commercial activities in mind, the ferromagnetic docking plate on the client is designed to be mounted onto any satellite, hosting the all-important optical surface markers to make the defunct space object easier to detect, approach, capture and de-orbit. Right now, Astroscale is ‘encouraging’ customers to fit launching satellites with the docking plate for the end-of-life missions that will one day come, as well as possible future servicing.
“If a satellite becomes defunct, it may need to be de-orbited in the future, so this is just one of many reasons why you would want to mount this very light and cheap docking plate on board,” says Forshaw. “We have been working closely with OneWeb on active debris removal; OneWeb has already agreed to mount docking plates onto all of its satellites.”
Importantly, in future commercial missions – already dubbed ELSA-‘M’ for ‘multi-client’ – the servicer will capture and haul several clients into lower orbits for de-orbitation before making its own final, burning descent. “The basic technologies are the same, but the cost of one servicer can be split between, say, three removals with the key limitation being when you run out of fuel,” says Forshaw.
Satellites and debris
ESA has estimated that right now there are 34,000 debris objects more than 10cm in size and 900,000 objects measuring 1-10cm in orbit. Meanwhile, a mind-blowing 128 million objects from 1cm down to 1mm in size are also littering this space, and that’s not to mention the estimated 21,000 unidentified objects and fragments. Each piece of debris travels many kilometres per second, which means an impact could at best impair working spacecraft, and at worst obliterate it altogether, creating even more debris.
To date, reception for end-of-life services has been mixed. Some satellite operators are very enthusiastic; others are not interested at all. “We do believe many satellite constellation companies are not fully engaged with a sustainability strategy, and we see the need for more regulation in this area,” says Forshaw. “I reckon we’ll see more missions like this in the next five to ten years, with many removals taking place in around 15 years’ time.
“ELSA-d is not just about debris removal and end-of-life servicing, it also opens up a whole array of in-orbit services, such as refuelling and asset relocation,” he adds. “Once you’ve shown that you can dock autonomously, you can do so many things.”
Indeed, for Astroscale, end-of-life satellites are just the beginning. The company has also joined forces with Japan’s space agency, JAXA, to demonstrate the more ambitious task of retrieving a large, more uncooperative rocket body from Earth orbit.
Right now, Astroscale is developing the navigation and imaging systems for ADRAS-J, a reconnaissance-style satellite that by late 2022 will travel within metres of the large rocket upper stage to measure its features and motion. The satellite will use much of ELSA-d’s technologies as well as infrared cameras and lidar to understand the debris environment. Forshaw says: “The sensors are different from ELSA-d, but the intelligence behind the control systems and navigation are based on similar algorithms.”
With necessary data in tow, JAXA will launch a second spacecraft to bring down the rocket, which is where the mission becomes more ‘sci-fi’. The capturing mechanism has yet to be confirmed, but the 2018 and 2019 RemoveDEBRIS satellite missions from Surrey Space Centre, Surrey Satellite Technology Ltd and Airbus relied on a net to envelope a target cubesat and a harpoon to spear and drag a piece of debris down.
At the time, Forshaw was consortium project manager for RemoveDEBRIS at the Surrey Space Centre. He says: “the nets and harpoon are good for capturing tumbling objects but can typically only be used once, which is a disadvantage compared to magnetic or robotic systems that can dock and undock multiple times.”
Given this, he expects that JAXA’s second craft will rely on a payload adapter fixture on the large rocket upper stage to dock and use a prong-like mechanism to seize the debris. “That mission won’t launch until 2025 or 2026, so a lot of technology development is still required,” he says.
Harpoons, space nets and prong-like grabbers may sound fantastic, but other space agencies are taking these technologies very seriously. In December last year, ESA signed a contract with Swiss start-up, ClearSpace, which span out of the EPFL Space Centre, to also remove an item of space debris from orbit. Scheduled for 2025, the €100m mission will use the ClearSpace-1 ‘chaser’ satellite to rendezvous, capture and take down a 1.6m x 2m part weighing 112kg, from a Vega Secondary Payload Adaptor that was placed in a disposal orbit in 2013.
The uncooperative and tumbling target is close in size, shape and mass to a typical small constellation satellite, making it a suitable first goal. More challenging captures will follow in successive missions. In a similar vein to Astroscale, ESA and ClearSpace hope to establish a commercial market for in-orbit servicing and space debris removal.
“Many people have been interested in the issue of space debris for some time, but getting all the necessary funds and backing from member states and industry has been difficult,” says Sarmad Aziz, systems engineer and ClearSpace-1 system lead at ESA. “So, ESA decided to procure this service from ClearSpace instead of carrying out a one-off mission.
“In the first instance we’ll remove this ESA debris, but the idea is to keep doing this on a commercial basis,” he adds. “If we can make this a success, then I think we’ll have a very effective template for future missions that could reduce our institutional costs and put more responsibility on industry to take ownership of these missions.”
During the first mission, the chaser satellite will be launched via a Vega-C launch system, from Europe’s spaceport in Kourou, French Guiana, into low Earth orbit. Using a guidance, navigation and control system developed by Portugal-based Elecnor DEIMOS and partners, ClearSpace-1 will match its orbit to the payload adapter and move closer to the debris using power generators, thrusters and antennas. It will then use a set of four lightweight aluminium alloy robotic arms – described by Aziz as “tentacles” – to grab and secure the debris.
“The tentacles solution provides advantages over, say, a net as it’s more rigid and stable – we’ll be able to hold onto the debris securely and in a controlled position throughout de-orbit burn,” says Aziz.
According to the systems engineer, the set-up can accommodate different-shaped debris and will be able to capture and release numerous targets. “You can imagine it capturing the target, bringing it into the orbit trajectory, letting go and then returning for another piece of debris,” he says.
The JAXA and ESA missions are both scheduled to launch in the next four to five years, while industry sources indicate that Nasa, Roscosmos and the China National Space Administration are also interested in similar endeavours. In recent months, Russian start-up StartRocket joined forces with cyber-security giant Kaspersky to create a ‘Foam Debris Catcher’ that releases polymeric foam arms to absorb any debris after a collision.
Assuming technology and economic successes can be twinned with widespread regulation, it isn’t impossible to envisage a flotilla of satellites sweeping up the debris that space travel has left behind, to make way for the thousands of satellites that will undoubtedly follow.
In 2019, an ESA Earth-observation spacecraft had to light up its thrusters to dodge a Starlink satellite, while in 2020 the International Space Station had to re-position three times to avoid debris impact. These are just two examples of the hundreds of manoeuvres that have been taking place every year to prevent the Earth orbit crash that could disrupt global internet access and telecommunications.
“There’s only ever been several thousand satellites in space but now we have providers such as SpaceX and Amazon planning to launch tens of thousands of satellites into space,” highlights Forshaw. “When the [space object] population doubles, triples and even quadruples, there is a very real and significant risk of collision and satellite operators really need to be very careful.”
While 2009 was the last time a satellite collided and was destroyed by space debris – the US Iridium satellite was wiped out by a spent Russian satellite – the risk is rising, largely thanks to the rise of constellation satellites from SpaceX, OneWeb, Amazon and at least 11 other private companies.
At the time of writing, SpaceX had 1,021 Starlink satellites in orbit, and holds a licence from the US Federal Communications Commission (FCC) to eventually place up to 42,000 satellites in orbit. The company is reported to be making 120 spacecraft every month and already has 10,000 users.
At the same time, Amazon, under ‘Project Kuiper’, has US FCC approval to launch 3,236 satellites to expand US internet access. Meanwhile OneWeb submitted a request to the FCC to put up to 48,000 satellites in space, although recently amended this figure to 6,372 satellites. Telesat, Canada, is currently building 298 satellites. All these satellites could launch in the next few years.
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