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Space fishing: ESA floats plan to net space junk


February 28, 2014

Netting a satellite (Image: ESA)

Netting a satellite (Image: ESA)

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With the film Gravity hoovering up awards for its portrayal of astronauts dodging colliding satellites, now seems a good time to talk about the very real threat posed by space debris. It’s small wonder, then, that ESA’s Clean Space initiative is looking at developing a satellite that can rendezvous with space debris and render it harmless by netting it like fish. The proposal is just one of the ideas to be discussed as part of a symposium this May focusing on the space agency's e.DeOrbit mission.

According to ESA, there are 17,000 trackable objects larger than a coffee cup orbiting the Earth and many more down to the size of paint chips. This may not seem like anything very dangerous, but at orbital velocity, even a paint chip can hit like a bullet and a steel nut has the impact of a hand grenade.

Furthermore, as the aftermath of the 2009 collision between the Iridium 33 and Kosmos 2251 satellites demonstrated, an encounter with a bit of space debris can turn a satellite into a cloud of shrapnel endangering other spacecraft. It wouldn't be a cascade of cinematic destruction as in Gravity, but the real-life damage would make space travel in the more crowded orbits more hazardous and expensive.

And it’s more than just collisions. ESA points out that while many pieces of space debris are defunct satellites, there are also the upper stages of launch vehicles. These satellites and rockets are not just collections of metal and circuitry. There are also tanks still containing propellants and batteries still carrying a partial charge. Any of these could explode under the right circumstances.


Though still in its very early stages, the e.DeOrbit mission is aimed at clearing debris from one of the “sea lanes” of low-Earth orbit; the widely- raveled polar orbits at an altitude of 800 km (500 mi) to 1,000 km (625 mi). The e.DeOrbit satellite would weigh about 1,600 kg (3,500 lb) and fly into orbit atop one of ESA’s Vega rockets, but there’s still a lot of very basic design to be sorted out.

Part of the problem is fairly straightforward. The e.DeOrbit has to be able to rendezvous with an object that’s in an unknown condition, inoperative, and probably tumbling. The spacecraft would have to be able to approach the object and assess the situation from a distance. This means that it needs a propulsion system, navigational systems, cameras, and the ability to keep station with great precision.

The tricky bit rears its head when it comes to actually doing something about the debris. That’s because it’s all a matter of tradeoffs. If there’s more than one way to skin a cat, and there’s also more than one way to snare a dead satellite. A robot arm that can reach out and grab a satellite seems an obvious method, but that means getting close to a tumbling object with the danger of the e.DeOrbit spinning out of control, too.

Another way is to fire harpoons and then reel the target in on a tether, but that means aiming, dealing with recoil, and the danger of creating more debris. Then, for the more science fiction minded, there’s the ion beam shepherd that uses a beam of charged particles to push the derelict craft, but that technology is still very immature.

According to an ESA report (PDF), the two most promising methods of capture are mechanical tentacles and nets. In the former, the satellite approaches the target and steadies itself against it using a robotic arm. Then a set of tentacles spread out and embrace the target while the arm keeps the e.DeOrbit satellite from bouncing against it. For the latter method using nets, the e.DeOrbit satellite shoots out a weighted net on the end of a tether. The net spreads as the weights fan out, then engulfs the target as the tether pulls tight.

This still seems pretty simple until you realize that grabbing the debris is only half the job done. The e.DeOrbit satellite must still despin the target and then it’s got to do something with it. That’s where the complexity comes in.

The questions facing ESA include basics, such as whether to use chemical rockets, an electric propulsion system, or a combination. How much will each of these cost? How will that affect the size of the satellite? Can ESA handle it on its own or will it mean partnering with another space agency?

Then there’s the question of what to do with the debris. One way to get rid of it would be to boost it into a higher orbit of 2,000 km (1,250 mi). The overall risks are less in doing this, but it still means the debris is in orbit and, worse, there are now two objects where there was only one before. The alternative is bringing it down below 600 km (375 mi) in altitude, so it burns up in the atmosphere, but this has a greater overall risk because the debris has to be aimed to burn up over an uninhabited strip of ocean to avoid danger to those on the ground.

How to answer these questions is part of the reason behind the e.Deorbit symposium to be held on May 6 in the Netherlands, where ESA and space industry representatives will pool their ideas.

Source: ESA

About the Author
David Szondy David Szondy is a freelance writer based in Monroe, Washington. An award-winning playwright, he has contributed to Charged and iQ magazine and is the author of the website Tales of Future Past. All articles by David Szondy

A cargo shroud closed back up into a container could catch small debris by working as a Whipple shield and carry it back down to burn up on reentry.

2nd May, 2015 @ 5:25 a.m. (California Time)

What's wrong with space based lasers.

2nd May, 2015 @ 5:25 a.m. (California Time)

I like the space junkyard at the moon idea. There is just too much valuable resources up there not to consider it.

Also the costs of a more reusable long term plan to process these things and send them to the junk yard with as much reusable equipment as possible (provided it's cost effective) should be considered against this idea.

Is it getting so bad that you can't wait a few more years to develop something better?

How many missions would be done with these non reusable ones compared to the cost of development?

Also for the rotation problem have you considered a little stabilizer thruster pack that could be shot at the craft with a sticky side. It be attached to a very long string that would at least attach the string onto the satellite. It would have to be as minimal as possible to not cause problems itself, to be transported up to space and to have multiple of them maybe.

Ben O'Brien
2nd May, 2015 @ 5:25 a.m. (California Time)

Considering the cost per kilo to get material into LEO, it seems to me that whoever can round up that debris and park it will at some point in the near future be sitting on a goldmine. NASA has already clearly stated it wants to manufacture spare parts either in orbit or on board long duration missions. More than one company has proposed mining the asteroid belt. They should consider de-bugging the process of orbital metals refinement by starting on the stuff they don't need to travel 2.2 AU or more to reach. The junk cluttering up terrestrial 'near' space. Then when the process has been developed, start hauling asteroids here...

2nd May, 2015 @ 5:25 a.m. (California Time)

A cargo shroud closed back up into a container could catch small debris by working as a Whipple shield and carry it back down to burn up on reentry.

2nd May, 2015 @ 5:25 a.m. (California Time)

What am I missing? For every 1kg of space junk out there, you're going to have to create and leave-behind 10kg or more of expelled propellant (gas/particles) in it's place (to maneuver the heavier de-orbit craft and stabilize it after rendezvous, then to relocate the junk).

Getting hit by a (tracked, and avoidable) blob of 1kgjunk sounds like way less risk than smashing into an invisible and unavoidable cloud of used propellant of 10x+ the mass.

Personally, I'd be happy to be rid of all those satellites anyhow. Yeah, GPS is neat, but we can find other ways now, and nothing else I can think of needs satellites anymore (or, can't be replaced by improving internet infrastructure). There's enough spying and weapons on earth already, filling up space with more is just anti-social.

2nd May, 2015 @ 5:25 a.m. (California Time)

@ christopher

We live at a time of changing climate and have a real need to get a fix on just how much it is changing and what changes it is causing in turn to other earth systems. For instance, with large numbers of the population living in coastal regions it is important that we get an accurate fix on just how much sea-level is rising and likely to rise so that we can identify how many people are going to need to move home and how soon.

There are other functions for which a satellite is essential, or almost essential, such as measuring electro magnetic pulse emissions from the sun. Without getting advance warning of any coming our way, we could not take precautions, which could lead to massive black-outs, with all that could mean for life and limb. Other satellites are used to monitor agricultural problems caused by disease or drought etc. In an over-populated world, food production is going to rise right up the agenda and will need all the assistance it can get. And, of course, we must not forget all the science that is done via satellites, such as space telescopes of various kinds and exo-planet hunting, to name but two.

Mel Tisdale
2nd May, 2015 @ 5:25 a.m. (California Time)

Hmmm ... I wonder, as the atmosphere envelope expands due to Global Warming. Will it be enough to help drag some of that stuff out of orbit?

Mark Keller
2nd May, 2015 @ 5:25 a.m. (California Time)

Deploy from ISS & ELV boosters. Or place in orbit in modules, open up on command & begin netting space debris, all sizes & shapes into said net. Controlled by ISS Module added? Expand ISS with Space Debris collection control module: SDCCM. Link to Houston Manned Space. & ESA Manned Space Hqs.

Stephen Russell
2nd May, 2015 @ 5:25 a.m. (California Time)

We need small maneuverable rockets something like the ones proposed for drones. They have video feedback and several kinds of sensors to locate junk satellites. They also have enough propellant to reach mach 3+ for several minutes inside the atmosphere, so with a few more steering nozzles they should be able to maneuver in a vacuum even more easily. I heard they cost around $500 each. Add a tether shooting gizmo.

I think if they can place satellites within a few inches of a selected location, they could determine an optimum speed and position to release the tether so the fuel (momentum) used in reaching the target can also be used to send it into the atmosphere: It's radio controlled from the ground. The delivery vehicle places it in the general area as it's target. It approached the target but doesn't have to match it's speed exactly, fires it's net and probably gets slung in an arc so it has to stabilize the mutual orbit which could take up a lot of fuel, but if it only has to slow the target, a spinning motion won't matter. If it has enough fuel for another job, it detaches once the target is heading downward.

2nd May, 2015 @ 5:26 a.m. (California Time)
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