“Since the start of the space age, we’ve had a throwaway culture – a bit like plastics in the ocean,” says Nick Shave, managing director of Astroscale UK, an in-orbit servicing company headquartered in Japan.
Getting a satellite into orbit around the Earth used to be a big deal. From the launch of the first, Sputnik, in 1957, as it became easier and cheaper to put satellites into space, the numbers have boomed. In 2022, there were about 6,000 and by 2030, one estimate suggests there will be nearly 60,000 satellites in orbit around our planet.
Look up on a clear night now and you may well see a bright train of dots traversing the sky. These are part of SpaceX’s “megaconstellation” of satellites, Starlink, which offers increased access to broadband communication across the world.
But regulations on how people behave in space are piecemeal and the main international law, the UN’s 1967 Outer Space treaty, is more than 50 years old.
There’s now a huge amount of junk, or space debris, in orbit. Almost 37,000 objects more than 10cm in size are being tracked by space surveillance networks, according to the European Space Agency (Esa) figures for September.
“That stuff’s dangerous, don’t get me wrong,” says John Janka, global government affairs and regulatory chief officer at the communications company Viasat, who is based in Washington DC. “But there’s also – according to Esa, more than 1m pieces of debris between 1cm and 10cm that are lethal and non-trackable. What does that mean? It means you can’t see it, you can’t avoid it, and today you can’t shield your satellite against it.”
But the concern over debris is about more than it damaging an individual satellite or craft. Space operators are acutely aware of a danger known as the Kessler effect or syndrome, named after the Nasa scientist Donald J Kessler, who in 1978 along with Burton G Cour-Palais, published a theory that as the number of satellites increased, so would the probability of collisions. As collisions increase, the more debris is produced, and the greater the risk of more collisions. At a critical mass, one collision could trigger an unstoppable cascade of collisions, such that an entire orbit could be rendered useless.
A 2022 overview paper by Viasat paints an almost apocalyptic picture: “If a tipping point is reached, all of humanity would watch helplessly as space junk multiplies uncontrollably. Without timely intervention, we risk bringing the space age to an inglorious end, and trapping humanity on Earth under a layer of its own trash for centuries, or even millennia.”
It continues: “Not only an abrupt end to space exploration, but also the loss of all the benefits of space technology – including navigation, weather forecasting, climate measurements, and even satellite broadband (the intended purpose of the megaconstellations being deployed).”
As well as numbers, Janka points out, size is an issue. “We’re putting up tens of thousands of satellites, and we’re putting up increasingly bigger satellites into low Earth orbit – bigger in terms of cross-sectional area and mass – we’re finding that we’re having perhaps some unanticipated impact on things like collision risk.”
He compares it to a bigger sail on a boat catching more wind. “The bigger satellite, the more cross-sectional area, the greater chance of being hit by debris.” And bigger satellites create more debris when they are hit.
So what’s the solution? Tracking and manoeuvring satellites to avoid collisions is one way to manage risk. Elon Musk’s SpaceX manages its Starlink satellites in this way, and de-orbits those deemed “at an elevated risk of becoming non-manoeuvrable”.
Many agree manoeuvrability is important. Shave describes it as “critical in orbit”. However, it may not ultimately be a failsafe solution because of the sheer number of satellites due to fill the skies in the years to come.
“Collision avoidance is a complete misnomer,” says Hugh Lewis, professor of astronautics at the University of Southampton, “because you can’t avoid a collision when you don’t know whether a collision is actually going to happen or not.”
But a manoeuvre to avoid a future collision does reduce the probability, he explains, so while the risk “never goes away”, it gets smaller. “Now multiply that [small risk] by 10,000 satellites,” he says.
Lewis, also a technical adviser to the Earth Space Sustainability Initiative (Essi), talks about “the law of truly large numbers”. “You can have really rare events and if you give enough opportunity for that event to occur, then it generally does, which is why we tend to see these big catastrophes that happen even though they are really quite rare. The same thing is true with spacecraft [collisions].”
Satellites may be put into different orbits depending on what their function is. For example, those put into low Earth orbit (LEO) are relatively close to Earth, 160-200km above the surface, and are good for Earth observation. Others put into high Earth orbit, 36,000km above Earth, may be useful for weather monitoring. Satellites also use different frequencies or parts of the electromagnetic spectrum to communicate and – just as with radio frequencies on Earth – operators need to apply for this limited resource through the UN’s International Telecommunication Union.
And as companies and nations vie for this finite resource – with early entrants able to hog orbits and bandwidths, this raises questions of how we divide up the sky equitably, sharing access to its benefits globally.
Ian Christensen, a senior director at the Secure World Foundation, a US-based nonprofit, says that “in general constellation operators are doing well” on manoeuvring their craft out of harm’s way. For example, he says Starlink has a “higher threshold for collision avoidance than is typical” and its automated collision-avoidance system is “risk averse”.
“The concern comes from how different constellations will interact with one another … so as Chinese systems start to deploy, as Amazon Kuiper starts to deploy, as others come in, how do we ensure that they are coordinated, that operators are exchanging positional data, so that other operators know where they are?”
He says the concern is over how to build this coordination in the absence of a global system.
Coming together globally is “inevitable” according to some, who argue that the space community should work together sooner rather than later, learning from the evolution of other technological gamechangers such as mobile phone networks and the internet.
“We’re hoping we can skip to the end. Let’s not go through the 10, 20, 30 years doing it incorrectly,” says Michael Cheng, an advisory member of Essi and member of the Outernet Council.
These nonprofits are lobbying the space industry to develop “interoperable” systems. That is, that different operators agree on and use standardised hardware, software and network connectivity so that their satellites and space systems can “talk to one another”.
“We would like to see more efficient use of communications technologies and communications networks,” says Cheng, who is also chief product officer at the communications company Aalyria, a Google spinout.
To help build resilience into communications systems, the firm has developed a “network orchestration tool” or software called Spacetime that monitors moving antennae and can find the best routes or connection options between moving satellites. It may also help operators exchange network capacity with one another once licences are in place, says Cheng.
He compares the current communications network in space to the early days of mobile phone networks on Earth where leaving the jurisdiction of one operator meant “exorbitant” roaming charges for the customer, while now different mobile phone operators have protocols and standards in place making the system easier for everyone.
Sharing and standardising systems across space would make things more efficient and therefore more sustainable – for instance, by reducing the amount of hardware that needs to be launched.
“We are betting on our ability to technologically outpace – or use technology to leverage our way out of whatever horrible things are happening,” says Cheng, who argues that only by working together can we keep space sustainable. He cites one big success story for humanity – the banning of CFCs to help close the hole in the ozone layer. “Humanity managed to collaborate and do a good thing there with making that hole smaller and smaller.”
Cheng also notes, however, that the ozone layer may be under threat once more – this time from spent satellites. A study published earlier this year in Geophysical Research Letters suggested that in future the used satellites from megaconstellations could produce over 360 tonnes of aluminium oxide particles annually as they burn up in the Earth’s atmosphere. These can linger for decades and lead to “significant ozone depletion”.
Most agree the idea of interoperable systems makes sense, although Janka cautions that it doesn’t stop the “overconsumption problem”. “I think having a level of standardisation in the right areas to help enable space sustainability is critical,” says Shave. He says the CEO of Astroscale, Nobu Okada, likens the situation in space now to having more cars on the roads in the early 20th century. “You didn’t stop cars going on the road,” he says. “You managed them better.”
His company won a £1.95m contract with the UK Space Agency last month for the next stage of its Cleaning Outer Space Mission through Innovative Capture (Cosmic) spacecraft project, which aims to pluck inactive British satellites from space using a robotic arm. If all goes to plan, it hopes to launch Cosmic in 2027-28.
The mission’s goal of “active debris removal” may provide another avenue for keeping orbits sustainable. “It’s imperative we do that,” says Lewis. “We are having to deal with the legacy of derelict objects abandoned over decades.”
With the threats to sustainability in space, some might argue we should stop launching satellites altogether. But, argues Lewis, space services are now “part of our economy”. He asks instead: “How do we grow our use in a sustainable way?”
Janka’s firm wants to see the satellite industry modelling how different scenarios and solutions might work. He also calls for better regulation, adding that over the past year, the industry has recognised this with an umbrella group, the Global Satellite Operators Association, agreeing on the importance of working with regulators. “We need to regulate, because we’re dealing with what’s potentially a ‘tragedy of the commons’. And unfortunately, with human behaviour being what it is, we can’t work on the assumption that everybody’s going to do the right thing,” he warns.
Whether it’s interoperable systems, technological fixes, or better rules for how we use space, the issue of how we keep our activities in space sustainable is for everyone. “What happens in space very much affects what happens on the ground,” says Cheng.
“It’s not just about us. It’s about tomorrow… it’s about next century,” says Lewis, “and being able to leave a legacy that enables other generations to use space in the way we’re enjoying.”