1 July 2018
It’s so far so good in an ambitious attempt to start actively cleaning up the orbital environment. Following its launch as cargo to the International Space Station, the University of Surrey-led RemoveDEBRIS mission is now in orbit and being readied to conduct a series of experiments to test technologies that may lead to low-cost missions dedicated to removing from orbit hazardous objects like dead satellites.
RemoveDEBRIS is a 100kg, 1m3-sized spacecraft built and operated by Surrey Satellite Technology (SSTL), and released from the ISS by the external payload deployment system – essentially a robotic arm – run by NanoRacks, which says it is the largest payload yet released from the station. The spacecraft is carrying a pair of cubesat-sized targets, which it will release.
The RemoveDEBRIS mission will perform four automatice debris removal experiments. In October, it will try out a net developed by Airbus in Bremen which will attempt to capture one of the target cubesats.
Then, the mission will test a vision-based navigation system – from Airbus in Toulouse and CSEM in Switzerland – that uses 2D and 3D LiDaR (light detection and ranging) technology to track another target cubesat.
In early 2019 the plan is to fire a 20m/s harpoon, developed by Airbus in Stevenage, at a target made of composite material. Finally, the RemoveDEBRIS craft will deploy a large dragsail to speed de-orbit into the Earth’s atmosphere.
SSTL says its ground control station in Guildford, Surrey locked-on to RemoveDEBRIS on its first pass overhead, so “we’re officially into the spacecraft commissioning phase now.
NOT SO EASY
The principle of active debris removal is perhaps beguilingly simple: find a piece of large debris, perhaps a dead satellite or rocket body, which might collide with and destroy an active satellite to create more debris; grab ahold of it; slow it down, so gravity drags it to re-entry. Unfortunately, in practice it won’t be easy. Speaking at the Toulouse Space Show in the week after the RemoveDEBRIS deployment, Tiago Soares from the European Space Agency’s clean space office highlighted the challenges faced by the University of Surrey team with RemoveDEBRIS and his ESA colleagues, who are developing a mission concept called e.deorbit – pencilled in for launch in 2023 pending approval by ESA member states at their 2019 ministerial conference – to pull the agency’s defunct EnviSat environment monitoring spacecraft out of orbit.
Finding a target is probably the simple part, as large items in orbit are well-tracked by radar. Navigating to intercept is well-established technically, and station-keeping – at maybe 50m – is a capability well-demonstrated by missions including ESA’s Rosetta, which tracked a comet through deep space. But grappling with debris is sure to pose problems because, as Soares put it, dead satellites tend not to provide stable targets but, rather, to tumble – thus they tend to shed parts and are hard to “catch”. E.deorbit engineers are considering either a robotic arm or a net to grab EnviSat, which would make it the first-ever active, as opposed to expermental, deorbiting mission. A net might be easier to deploy than a harpoon, he said, but the tether can become a “yo-yo” if the target is tumbling.
Then, there is the issue of actual deorbiting. ESA is looking at drag options including sails, propulsion, plasma thrusters and exploiting Earth’s magnetic field. All are promising, but work done by ESA shows that hardware assumed to burn up with the heat of re-entry can in fact be remarkably resiliant – suggesting that without precision control of a de-orbiting exercise there is perhaps more chance of dropping something on populated areas than might be acceptable to space agencies or their lawyers and insurers. Hence, said Soares, the ESA clean space people are pioneering the notion of “design for demise”, to make sure a satellite breaks up and burns up on re-entry; this is new, as traditional thinking has been to design for durability: “[But] we’re learning by the day.”
While the technology remains to be proven it is too early to say much about the business model that might support a debris removal industry, but there is no question that a systematic space clean-up effort is a service that is, if anything, overdue. And, with all of this focus on the problem there must be some prospect of Europe emerging as a leader in this new sub-sector of the space industry.
To that end, RemoveDEBRIS should be taken as a promising indicator of low-cost potential. The mission got started in late 2013 as a €13m project, funded by €7m from the European Commission and the rest from the Surrey Space Centre (University of Surrey)-led consortium: low-cost satellites pioneer SSTL, Airbus, Ariane Group, Swiss private, not-for-profit research and technology organisation CSEM, French national digital technology research institute Inria, Dutch satellite builder and launch broker ISIS and South Africa’s Stellenbosch University. Says Surrey Space Centre director professor Guglielmo Aglietti: “We believe the technologies we will be demonstrating with RemoveDEBRIS could provide feasible answers to the space junk problem – answers that could be used on future space missions in the very near future.”
ESA’s e.deorbit project is arguably more ambitious, in going after real debris – which, as Soares points out, may be very difficult in practice to grapple with. Its direct budget so far is a €41m maturation phase to support a pitch for go-ahead approval next year.