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The amount of space junk, formed from defunct satellites, abandoned rockets and in-orbit collisions, grows each year. Miniaturisation of satellite technology and deployment of large commercial ‘constellations’ has meant a considerable increase in space traffic since 2015, according to the European Space Agency (ESA), risking a rise in collisions and destruction of robotic or crewed missions.
This could lead to a “cascade of collision events,” according to ESA’s 2022 Space Environment Report. “Even in case of no further launches into orbit, it is expected that collisions among the space debris objects already present will lead to a further growth in space debris.” Thankfully, several projects are accelerating efforts to remove debris from orbit. Here are three of the most intriguing.
Magnetic capture
For a few brief seconds on 25 August 2021, a simulated piece of space debris floated free in orbit. It had arrived in space attached to the Elsa-d ‘servicer’ spacecraft developed by Japan-headquartered Astroscale, before being released and gently nudged away.
A capture mechanism extended from the servicer, which then initiated thrust to travel towards the client. As it made contact, the two were locked together again by a magnetic grapple, destined to descend together and burn up in the atmosphere.
The test was the first demonstration of the bold commercial ambitions of Astroscale, which has its operations centre in the Harwell Space Cluster in Oxfordshire. The company hopes that its upcoming Elsa-M craft will be able to capture and push multiple pieces of debris down towards Earth in each mission.
The space tether
Astroscale’s approach needs propellant to push servicer and client towards Earth, but what if satellites could efficiently deorbit themselves without fuel? That is the aim of the E.T.Pack-Fly consortium, co-ordinated by the University Carlos III of Madrid (UC3M) and recently funded by the European Innovation Council.
The project’s electrodynamic space tether consists of a very thin and very long aluminium tape, about 2cm wide and 2km long. It is designed to work by using the plasma and the geomagnetic field around Earth to generate an electric current. This electrodynamic effect results in a force known as the Lorentz drag, which deorbits the satellite. The tether is also designed to stabilise the orientation of the satellite, and to control the deorbiting to avoid possible collisions with other objects.
The project will start in September, aiming to launch a device into orbit in 2025.
Battery boost
Both Astroscale and E.T.Pack-Fly aim to provide efficient and sustainable deorbiting, but they require launching extra mass into space. According to engineers at the Aerospace Corporation, which runs a US government-funded research centre in California, satellites already have a potential solution onboard – their batteries.
“Everybody knows about lithium-ion batteries and their risk to go into thermal runaway and spewing fire,” said Dr Joseph Nemanick, a senior research scientist in the corporation’s energy technology department. “The Lithium-ion Battery Deorbiter is turning that into a strength.”
The deorbiter is designed to activate thermal runaway in a controlled manner, channelling red-hot gases through a nozzle to generate thrust. Described as the first “zero-added-mass onboard spacecraft technology,” a proof of concept has been demonstrated in the Aerospace Propulsion Research Facility. The team said the estimated thrust could reduce by 55% the “residual orbit time” for a small satellite in low Earth orbit.
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