People are messy. They tend to leave rubbish behind, no matter where they go – and expect someone else to clean up that rubbish. This is true even in outer space. The problem of orbiting dirt and the concomitant risk of it colliding with and damaging an active and probably expensive satellite has been around for some time. But it is getting worse fast. In the last three years, the number of times such bit junk has nearly hit satellites that work has roughly doubled.
That is at least the calculation made by Daniel Oltrogge, an expert whose conclusion is drawn from his two jobs. Sir. Oltrogge is an advisor to the Space Data Association, an industry association that carries orbital and maneuvering information from many satellite operators to a computer model that predicts probable collisions so that spacecraft or at least those with appropriate thrusters can be moved out of harm̵
Part of the problem is the growing number of launches that are taking place. January 13 is due to e.g. Virgin Orbit, a company in Richard Branson’s Virgin Group, another new entrant to the market, is launching ten satellites into orbit using a rocket released from a modified Boeing 747-400. Another part, however, is that every year a dozen or so large lumps of dirt are orbiting the Earth. About half of these explosions are caused by things like ignition of residual rocket fuel and bursting of old batteries and pressure vessels. The rest is the result of collisions.
The result is a chain reaction of shocks in orbits. Unlike the fictional version of such a chain reaction that annoyed Sandra Bullock’s character in “Gravity,” a film released in 2013, this real one is accelerating only slowly, so there is still time to limit it. However, if no action is taken soon, insurance premiums for satellites will increase, the cost of tracking and collision avoidance systems will have to increase and certain orbits risk becoming unusable. If things get really bad, the authorities may even have to step in to limit the number of launches.
Stopping this orbital-junk-generating chain reaction means throwing some of the excess tonnage in space into the Earth’s atmosphere, where the frictional heat at re-entry will burn it up. A clean sweep is not necessary. Removing a handful of the larger survivors each year would be enough. Exactly how many are being debated. Yamamoto Toru of Japan’s space agency, JAXA, estimates somewhere between three and seven. Ted Muelhaupt of America’s Aerospace Corporation, a taxpayer-funded research center, counts on a dozen. But even that sounds feasible. Except no one knows how to do it.
However, people plan to practice. One practice mission scheduled for lift-off in March is led by Astroscale, a Tokyo-based company. Astroscale proposes to launch a mission called ELSA-d from the Baikonur Cosmodrome in Kazakhstan. This consists of a 175 kg mother ship called a servicer and a 17 kg bellows equipped with an ferrous docking plate that acts as a dummy target. If all goes well, the serviceman will push and reclaim the bellows three times in successively harder test runs before thrusters push the entire kaboodle to burning doom in the atmosphere below.
In the first test, the service provider uses springs to push the pod out, and when it is ten meters away, it will approach it again, lock onto the docking plate using an arm equipped with a magnetic head, pull the arm back and pull it back to the service. In the second test, it pushes the bellows away at least 100 meters before it begins to approach it. A reaction wheel and a set of magnetic torque generators will then place the bellows in a tumbler involving all three axes of motion, at a speed of half a degree per second.
This is like an important twist – for lumps of circulating debris typically spin this way. A real deorbiting mission will therefore have to deal with such rotating objects. Markings on the bellows help the servicer work out the movement of his prey. Using eight thrusters, it will maneuver until these markings for its sensors appear to be stationary. This will mean that its motion corresponds exactly to the tumbling pod, and that the magnetic head can therefore be extended to perform its job.
In the third catch test, the servicer first uses his thrusters to reverse several kilometers from the pod and place the pod outside the sensor area. Then it will search for it, as it should be the case if it were in search of a real abandoned spacecraft.
Despite all the technological prowess these tests will require, however, real negligence poses a greater challenge than dummy. First, unlike the Astroscales pod, few spacecraft are designed to accelerate their own removal. In addition, the items that need to be removed the most are dangerously heavy. A spacecraft that miscalculates while trying to catch such a piece of tumbling debris could be crushed into blacksmiths, thus contributing to the problem it was supposed to solve.
To understand the matter
The commercial removal of waste demonstration, a plan by JAXA to demolish a discarded Japanese rocket stage, highlights these difficulties. Before a spacecraft can be designed to capture what leaves Japan’s space agency, which chooses as the target of the experiment, a reconnaissance mission must first be launched to study it closely. JAXA has awarded the contract for this part of the demonstration to Astroscale, which plans to do so using a craft called ADRAS-J, which will be launched in two years. To measure the movement and functions of a rocket part that can weigh tons, ADRAS-J will approach within a few meters. Once it has collected the necessary data, another spacecraft can be designed to seize the waste on a subsequent mission.
In this case, magnets will not be used to fight the target, because normal spacecraft do not have iron in them. However, the use of a harpoon to capture such an object may be possible. In a test conducted in 2019, Airbus, a European aviation giant, successfully fired a harpoon from a satellite in a piece of panels 1½ meters away. However, this cladding was attached to a boom that extended from the satellite, so this was only the most initial of experiments. A harpoon can also miss, ricochet or – worse – interrupt parts of the target, which will then contribute additional objects to the celestial scrap yard.
Another option is to shoot a net. Airbus tested this idea in 2018. This test successfully enclosed a small “cube set” that had been pushed seven meters away from the net launch vessel – although this net was not tied to the mother ship, which therefore would not have been able to eradicate targets. Tethers are actually difficult to deal with in the weightlessness of the circuit, which is why Airbus chose not to use one in this initial net-tossing experiment. And some doubt that such cosmic retiarii is a sensible idea. Chris Blackerby, Astroscale’s operations operator, expects the best approach would be to design robotic arms to attach the target vehicle’s sheath (the low cylinder that connects it to the bunkered firing phase that lifted it up from Earth) if it is still intact.
If all that works, JAXA’s waste disposal demonstration will face one last challenge. This is to perform a safe return journey. Many pieces of the re-entering complex of captive master and captivity will survive friction melting and slamming quickly into the earth’s surface. Should re-entry occur randomly, the probability of a human accident would now exceed the threshold of one in 10,000, set by NASA, the American space agency, as an acceptable level of risk in 1995, and adopted by Japan and other countries thereafter. The complex must therefore be placed in a steep descent facing an uninhabited area – probably part of the Pacific Ocean.
As for the first approval of actually orbiting dirt, it’s probably a European affair, because in 2019, the European Space Agency awarded a contract to ClearSpace, a Swiss company, to seize a piece of 100kg of rocket waste that has been looped. Earth since 2013. This mission is scheduled for 2025.
ClearSpace plans to use a fishing vessel equipped with four robotic arms. Unlike harpoons or net throws, this strategy allows repeated attempts at recovery. Still, Luc Piguet, ClearSpace’s boss, expects his spacecraft to spend at least nine months in near-target trials before securing abandoned and braking enough to get down.
An era of serious cleanup in space is still far away. In addition to the technological obstacles, it will be expensive to remove junk. In addition to the cost of lobbying something in orbit, controlled reintroduction of an object requires fuel, large thrusters, and close attention from a ground control. These things can tackle millions of dollars – maybe more than $ 20 million. – at the cost of a debiting operation. For example, ClearSpace’s mission costs as much as € 100 million. ($ 122 million), although Mr. Piguet hopes that subsequent jobs will be cheaper.
Cheaper or not, but the question is still, “who pays”? The filling of space is a textbook example of the common tragedy, where it is in everyone’s interest that a problem is solved, but no one is the only person who takes on the burden of solving it.
The solutions to tragedies from the general public must therefore usually be imposed from the outside, often by governments. One idea is a special launch tax where the proceeds are hypothesized to pay for cleanup operations. A more creative proposal is what Mr Muelhaupt calls “a bottle disposal system”. Astronauts pay a deposit for every craft they lift into orbit. If owners then failed to dismantle their equipment after its mission was over, the job could be performed by someone else, who would then charge a deposit. It would encourage people to build up debilitating capabilities in satellites from the start so that the celestial dustmen would eventually no longer be needed. A third proposal, proposed by Akhil Rao of Middlebury College in Vermont, is to charge rent, known as orbital fees, for each commercial satellite in orbit. It would have the same effect.
Support for such schemes is growing, although they will require both international agreements between countries with launch facilities and an enforcement mechanism to stop outsiders with weaker rules from banning the event.
There is another point as well. As Jean-Daniel Testé, former head of the French Air Force’s Joint Space Command, noted, equipment designed for orbital cleanup could also be used to disable satellites. Testé says that progress in orbital robotics made by France’s opponents, not to mention the lack of any international “space gendarmerie”, is leading its country to plan spacecraft to defend its military and intelligence satellites.
Testé is clever in the details. But France’s minister of armed forces, Florence Parly, has revealed more about her country’s plans than her equivalents in other powers, including America. She predicts that France will launch special “lookout” and “active defense” spacecraft to protect its assets in space. The latter is probably armed with powerful lasers. As Mrs Parly has said, “we intend to blind” threatening spacecraft. Preferably without breaking them down.