Hit film Gravity offers a hyper-realistic portrait of life in space, including the possibility that an avalanche of space debris could be fatal. This is a real threat, so we'd better be ready. Here are ideas that scientists, engineers and other experts have proposed to reduce the space junk threat, and clean up our orbital disasters.
Before we get into the nitty-gritty of Active Debris Removal (ADR), it’s worth reviewing the problem that is space debris.
Since the dawn of the space age, there have been more than 4,900 launches and some 6,600 satellites parked into orbit. Of these, about 3,600 remain in space, of which approximately 1,000 are still operational. No doubt, we’ve introduced rocket-loads of material to space — a hefty portion of which has largely escaped our control. Approximately 65% of all catalogued space junk originated from break-ups in orbit, including those caused by about 240 explosions (mostly explosions of rocket bodies) and some 10 collisions.
As it stands, the total amount of space debris amounts to
- 29,000 for sizes larger than 4 inches (10 cm)
- 670,000 larger than 0.4 inches (1 cm)
- 170 million larger than 0.04 inches (1 mm)
These objects consist of such things as spent upper stages of rockets, decommissioned or broken satellites, and mission related detritus, like launch adapters, lens covers, and even thin copper wires.
These objects are tracked by the US Space Surveillance Network who maintain a catalogue of space debris exceeding 2 to 4 inches (5 to 10 cm) in low Earth orbit (LEO) to 40 inches (1 m) at geostationary orbit (GEO).
The danger these objects pose to astronauts, satellites, and space stations is no joke. As so beautifully demonstrated in Gravity, Newton’s First Law of Motion is a total bitch in orbit. All this debris is spinning around the Earth at horrendous speeds and with reckless abandon; there’s no atmosphere to provide any kind of resistance.
A 4-inch chunk of space debris would completely wreck a satellite, while a piece measuring a half-inch would most likely disable a spacecraft and pierce through the International Space Station shields. Even an object no more than a millimeter could destroy delicate subsystems.
And yes, collisions have happened. The first unintentional collision between two satellites happened on February 10, 2009, at 482 miles (776 km) above Siberia. A private U.S. communication satellite, Iridium 33, and a Russian military satellite, Kosmos-2251, smashed into each other at speeds exceeding 7.27 miles/second (11.7 km/s). Both satellites were completely annihilated, producing more than 2,200 trackable fragments. To put it into perspective, that’s about 80 times the speed of a passenger jet.
There’s also the fictional scenario proposed in Gravity to consider. In the movie, the Russians use a rocket to destroy one of their own satellites. It creates a massive debris field that orbits the Earth once every 90 minutes, but it sets off a chain reaction — called the Kessler Syndrome — in which other satellites are struck, producing even more objects and an ever-widening debris field. It’s like an avalanche, but in space. And as the film shows, it would be a horrible, dangerous mess.
And in fact, a similar situation has already happened, but on a much smaller scale. Back in 2007, in a show of force, China’s military shot down one its defunct weather stations, unintentionally spewing thousands of pieces of debris into orbit.
Troublingly, the odds of a Kessler Syndrome happening are increasing over time as more stuff gets thrown into space.
So, how can we clean up all this junk? And could we ever clean up a massive debris field like the one portrayed in Gravity. The answer is yes — but it’ll take some ingenuity and a considerable amount of patience.
Before we get into clean-up efforts, it’s worth talking about prevention and mitigation. One thing we can start to do is make to satellites and space stations more durable. Things like reinforced shielding to protect against hypervelocity impacts (from both space debris and meteoroids). Satellites should also be made more maneuverable.
But we should also do our best to prevent space junk from happening in the first place. To avoid collisions, for example, the orbits of all debris and potential targets need to be known ahead of time. Thankfully, this information is provided by the U.S. Strategic Command (USSTRATCOM) catalogue. The ESA’s Space Debris office provides conjunction event predictions and estimates of collision risks as a service to ESA missions and third parties.
We could also tax space junk offenders, making them pay for not just the debris they leave in space, but for the duration they leave it in space, thus incentivizing them to clean up their mess.
Okay, time to tidy-up Earth’s orbit.
Scientists and engineers have proposed many different Active Debris Removal strategies for cleaning up space junk, some better than others. We’ll review a good number of them, but let’s look at the top four contenders first.
Better known as ElectroDynamic Debris Eliminator (EDDE), the idea here would be to send a satellite into space to capture objects with a net and harpoon. Yes, really — capturing satellites and other objects that have gone astray with actual nets. The strategy is compact, low-cost, and it could piggyback on any launch to LEO.
These satellites could be maneuverable all over LEO and could be moved to virtually any inclination. And importantly, the satellites would be reusable, thus capable of removing many targets. Its designers estimate that a single EDDE could remove 136 objects in three years — and that 12 EDDEs could remove all 2,465 LEO debris weighing more than 2 kg in seven years.
This will only work, however, for larger objects.
But why use nets when you can use balloons? It’s an idea called the Gossamer Orbit Lowering Device, or GOLD System proposed by Kristin Gates. The system concept would use a very large ultra thin balloon envelope to increase the aerodynamic drag on a wayward object by a factor of several hundred, causing the space junk to enter the Earth’s atmosphere quickly and burn up. The GOLD System could reduce the natural orbit decay of some objects from centuries to just a few months. The inflatable system is simple, effective, and features better long-term collision risk than any system (except possibly propulsive tug, which we’ll review next). (Image: GOLD/Kristin Gates)
For larger objects, like the broken 8,100 pound Envisat, a dedicated robot could be sent on a suicide mission to force the satellite into re-entry. Take the EPFL’s “CleanSpace One” project for example (see video below). In their model, a cube satellite would chase, grab, and destroy space litter. The cost would be prohibitive, though — about $200 million for each mission.
The Surrey Space Centre is working on a HybridSail — a system combining a large deployable reflective sail with tethers for pulling objects out of orbit. It would achieve this “de-orbit” as a result of aerodynamic drag and momentum exchange with charged tethers and ionosphere plasma.
In this scheme, a small cube satellite would dock with a piece of space debris. Then, with a magnetic attitude control system, it would de-tumble an object to stabilize its roll, pitch, and yaw attitude. Then, it would deploy its tethers and its 5m x 5m sail, thus initiating the de-orbiting phase.
We could also release a cloud of tungsten dust into orbit to create atmospheric drag at orbital altitudes. With the decrease in velocity, thousands of pieces of space junk would have their orbital integrity compromised. Smaller bits of debris would slowly lose their orbits over the course of a couple of decades (so this isn’t an instant solution).
Image: Plansee Group.
To do so, a cloud of tungsten dust — tiny particles no more than 30 micrometers across — would be released about 680 miles up, creating a relatively thick layer of small particulate matter that would completely shroud the planet. The tungsten, which is nearly twice the density of lead, would add a serious amount of weight to any small debris they latch on to.
It’s an awesome idea — a solution that would probably be the most ideal for a Kessler Syndrome scenario. But for larger objects, it wouldn’t work so well.
What’s more, it would have a potentially catastrophic effect on all the stuff in orbit we don’t want to de-orbit, like functioning satellites. It could also damage sensitive equipment, like solar panels. Consequently, it’s considered feasible only for “start over” mode — as a way to completely clean-up space.
This is a weird one: the Ballistic Orbital Removal System. According to James Hollopeter of GIT Satellite, rockets filled with water could be shot into space. After releasing their payload in orbit, it would create a field of crystallized water that would be penetrated by orbiting junk, causing it to slow way the hell down, and fall out of orbit. It sounds crazy — but it’s similar to the tungsten dust idea. Water is low tech and readily accessible, whereas robotic satellites are extremely complex, fragile, and expensive.
There’s also the potential for ground-based lasers. Called LODR, or Laser Orbital Debris Removal, this scheme would use high-powered pulsed lasers shot from the surface to create plasma jets on space debris. This would cause them to slow down and then re-enter and either burn up or crash into the oceans. We already have the technology, which has been around for about 15 years, but it would cost about $1 million per object.
Not having to go to space is a great advantage, but the physics behind the scheme are still iffy. The feasibility for ADR remains unclear.
Another similar idea, as outlined at the ESA’s recently concluded international conference on space debris in Darmstadt, Germany, is to use a satellite that can fire electrically charged atoms, or ions, at an object to gradually slow it down and drag it back to Earth.
Instead of using grappling claws, harpoons, and nets, we could also move large objects without having to touch them. Moreover, we don’t have to throw them into the atmosphere — we could deposit the objects into geosynch.
To do so, ADR satellites could be equipped with electrostatic charge control and low-thrust propulsion to avoid any contact. One such proposed system is the Geosynchronous Large Debris Reorbiter (GLiDeR) which would use active charge emissions and direct streams of charged particles at the debris.
Designer Vaughan Ling has conceptualized an orbital garbage collector and recycling plant.
Image: Vaughan Ling.
He describes it like this:
My fantasy concept is a system composed of the collector, a net dispenser and a recycling station in low earth orbit. Considering the launch cost can range from $4-5k per pound, not including the precious metals often used for satellite constrution, I thought that recycling could be a viable business one day. The collector would use nuclear power + highly efficient VASIMR rockets for propulsion and a detachable holding bay for dropping off at the station plus an arm similar to Canadarm on the space shuttle and ISS.