As that number grows, so does the number of objects that will eventually need to be removed from orbit, to prevent pile-up of space junk that could threaten the future viability of human space activity.
Government-backed projects are exploring active debris removal (ADR) technologies to tackle the problem, planning to pluck debris from low Earth orbit and push it towards a fiery end in the upper atmosphere. A truly sustainable future might involve going even further, however – and according to Oxfordshire firm Astroscale, that might mean recycling dead satellites in orbit and reusing components to upgrade other devices.
The company, which exhibited and presented at the Space-Comm Expo at London’s Excel Centre in March, is involved in several ‘space sustainability’ and in-orbit servicing projects with major partners. These include the UK’s ADR mission – which aims to remove two inactive British satellites from space – for which it is developing the Cosmic (Cleaning Outer Space Mission through Innovative Capture) spacecraft.
“They're not prepared to be removed, so we have to find a solution that can attach to the launch adapter ring of the satellites and bring them down from orbit,” said Sharon Parker-Lines, Astroscale’s deputy managing director of government and regulatory affairs, to Professional Engineering. “We would then go back up and attach ourselves to the next asset and bring that down.”
‘Deorbiting’ will involve descending below the International Space Station, to ensure the satellites cannot collide with human space flights or other activity when released to burn up in the atmosphere – accidentally creating more debris from a high-speed collision would be the worst-case scenario, so safety is of paramount importance.
Defunct satellites targeted in ADR missions could be damaged, and might even be spinning or ‘tumbling’ in an uncontrolled way. Astroscale craft will therefore have to do a ‘safety ellipse’, matching the tumble rate of the target object using onboard thrusters.
“All of this is done autonomously, because the spacecraft has to make these decisions really, really quickly, and our default system is to abort if there's anything that the spacecraft picks up that's an anomaly,” Parker-Lines said at the Space-Comm Expo.
“By doing the safety ellipse, we're not going to hit something unintentionally. We can spin out and get ahead or behind the object and come back to a pre-determined ‘home’ position and start again.”
Once the ADR craft has synchronised with the tumble rate of the ‘client’, a robotic arm will reach out and gently clasp the adapter ring “like fingers on a hand”. The delicate operation also requires the onboard computer to autonomously calculate changes to the centre of gravity, to ensure that the two combined devices do not enter a new tumble.
The company is testing these technologies at the German Aerospace Centre (DLR) in Göttingen, using a specialist vacuum chamber to replicate space conditions and link simulations with real-world data.
A final technical review is due to end the current stage of the competitive project this month, with Astroscale waiting for more information about potential launch plans from the UK Space Agency. If all goes to plan, it hopes to launch by 2028.
Simply burning up satellites in the atmosphere (also known as ablation) might not be a completely sustainable solution, however, as deorbiting devices releases particles that could become ozone-destroying chemicals.
A 2024 study by researchers at the University of Southern California found a typical 250kg satellite can generate roughly 30kg of aluminium oxide nanoparticles during reentry, which could stay in the atmosphere for decades. Deorbiting satellites generated an estimated 17 tonnes of aluminium oxide compounds in 2022, but future reentry of megaconstellations could release over 360 tonnes per year, “which can lead to significant ozone depletion” according to the paper.
Astroscale has these wider sustainability concerns in mind, according to Parker-Lines, and is ultimately aimed at an orbital ‘circular economy’. The company plans to make its craft refuellable as the market develops, so it can complete even more missions per flight, and it is working on projects that fill in other pieces of the puzzle.
Last year, Astroscale Japan worked with the Japanese Aerospace Exploration Agency (Jaxa) on the Adras-J inspection satellite mission, which caught up with and surveyed a three-tonne upper stage rocket body in orbit.
“That's like a double-decker bus, and what would you do with that double-decker bus on Earth? You would refuel it,” said Parker-Lines.
The company plans to do just that in a recently announced project with the US Space Force. Launching in summer 2026, the 300kg Refueler spacecraft from Astroscale US will carry a tank of hydrazine satellite propellant to above geostationary orbit, where it will refuel a client spacecraft in two planned operations.
Sustainable use of orbit could also eventually involve in-orbit recycling. “Instead of bringing a spacecraft down below the International Space Station, letting it burn up, wouldn't it be great if we could take it to a recycling plant on orbit, and that key components that could be reused and recycled could be taken out, and we could deal with the debris some other way? We shouldn't shy away from that as being an end game,” said Parker-Lines.
“It needs an industry shift. It can't be driven by one company thinking sustainably. It has to be brought into the way that we build satellites, the way that we prepare them to be in orbit, and how long we want them to be in orbit.”
Astroscale recently worked with BAE Systems on a six-month feasibility study and development of an ‘in-orbit refurbishment and upgrading service’ to “advance the transition away from the current single-use culture in space”. The partners hope to launch an in-orbit demonstration mission by 2030.
Ultimately, Parker-Lines said, boosting the sustainability of space operations will allow the sector to continue thriving. “For me, space sustainability isn't about stopping people doing things. It's not telling other constellations you can't launch. It's talking about ‘How can we be more sustainable in space?’”
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Content published by Professional Engineering does not necessarily represent the views of the Institution of Mechanical Engineers.