Small satellite tightens the net around space junk
Worn-out satellites and used rocket stages are among the millions of pieces of space junk that orbit Earth. The junk is to be removed, so a small satellite is trying to catch the orbiting waste by means of nets and harpoons.
In the morning of 16 July 2015, three International Space Station astronauts wake wake up to a disturbing message from mission control: a piece of space junk from an old Soviet weather satellite is heading straight towards the ISS at a speed of some 50,000 km/h – 20 times faster than a bullet.
The mission control experts cannot tell if the space junk is going to hit the space station or not, but they are sure that a collision would knock a hole in the hull and cause all air inside it to quickly escape into space. The only thing the astronauts can do is to hide in the return space capsule and hope for the best.
Luckily, the space junk did not hit, but the incident demonstrates the increasing problem of space junk. Over the past decades, the quantity of space junk has increased explosively, and the problem is only getting worse, as still more satellites are launched. The junk is a mixture of worn-out satellites, parts of space rockets, and fragments from collisions and explosions in space.
The junk does not only endanger the lives of astronauts, it also threatens to pulverize the world’s satellite networks and finally block our access to space. So, scientists from the University of Surrey, England, have launched a satellite that is to try to remove the dead satellites.
Scientists fear chain reaction
The space junk is monitored by telescopes and large radar systems on Earth, that can spot objects as small as 5-10 cm. Today, 20,000+ artificial objects with a total weight of some 8,000 tonnes – more than the Eiffel Tower – are orbiting Earth. Up to 1,700 of those are functional satellites, whereas the rest is junk. In other words, there is 10+ times more space junk than functional satellites. However, most fragments are too small to be detected by a radar, so the total number of objects is unknown, but counted by the million.
In 2009, an inactive Russian satellite hit one of the American Iridium satellites that allow satellite telephone communication. The collision took place at a speed of 40,000+ km/h, and apart from jamming the network, it resulted in thousands of new pieces of space junk, which are now threatening other satellites. Space researchers fear more collisions like this one, and they are
particularly afraid of a chain reaction, in which wreckage from destroyed satellites will hit more satellites, causing more space junk. Such a chain reaction is known as the Kessler effect, and if it happens, it could have major consequences for civilisation.
Today, we depend on satellites that allow us to navigate via GPS, get reliable weather forecasts, communicate over long distances, watch satellite TV, etc. If hundreds of satellites were destroyed, all people in the world would suddenly lose many of the services that we take for granted every day. But it would also stop all activity in space. The satellites would be turned into hundreds of thousands of pieces of space junk, which would speed about, shrouding Earth in an impenetrable blanket of lethal projectiles. This would make it very difficult to launch new satellites and reestablish all the satellite networks that it took decades to expand.
Satellite to fish for space junk
The space agencies agree that we have reached a critical point, at which one unfortunate collision could trigger an unstoppable disaster, and so, several of the world’s space agencies are taking action.
To begin with, engineers focus on the space junk in low orbits of less than 2,000 km above Earth. At altitudes of 800-1,000 km, there is particularly heavy traffic. The junk must be slowed down, so it can fall towards Earth and burn up in the atmosphere instead of orbiting for decades or centuries. But that is easier said than done. The agencies have chosen to rely on crafts that catch up on the orbiting space junk, catch it, and force it into the atmosphere.
Several different clean-up technologies are in the pipeline, and the small European RemoveDEBRIS satellite has already been launched to test two "fishing" methods. The satellite is to show if it is possible to catch space junk by means of a net, and whether a harpoon can hit a target in space.
First, RemoveDEBRIS releases a nanosatellite that inflates a balloon to make the target the size of an ordinary satellite. Secondly, it tries to make a net "swallow" the balloon. The net involves the advantage that it can catch space junk of all shapes and sizes. A large net can be used in connection with most small pieces that orbit close together – just like when fishermen catch more fish of different sizes in one net. The disadvantage is that a net takes up space, weighs a lot, and can only be used once.
A harpoon, however, takes up less space than a net, and even a small harpoon can hold on to a large satellite in an orbit around Earth, where everything is weightless. A clean-up satellite can, moreover, fit several harpoons into the space that one net would take up, so more dead satellites could be collected in different places. But the use of harpoons requires more preparation, as the harpoon must hit the place, in which it stands the best chance of getting stuck, and it cannot puncture fuel tanks, which might cause an explosion and a marked deterioration of the situation. RemoveDEBRIS brings its own target, which it is to try to hit with a harpoon fired in a state of weightlessness.
Finally, RemoveDEBRIS will remove itself from the orbit by employing a large slow-down sail. Even hundreds of km into space, there are air molecules, that objects orbiting Earth collides with, and if the space junk gets a much bigger surface, it will hit more molecules, causing it to fall faster. The sail will allow RemoveDEBRIS to fall down after 10 weeks instead of remaining in an orbit around Earth for 100+ weeks.
RemoveDEBRIS is only a test mission for the real clean-up projects that are in the pipeline. One of them is the e.Deorbit mission, which ESA will launch in 2023 to neutralise the huge Envisat environment satellite that stopped working in 2012. Several experts consider Envisat the most hazardous piece of space junk orbiting Earth as we speak. Envisat is the size of a small bus, and according to the engineers responsible for RemoveDEBRIS, its removal into the atmosphere will be the major test of space’s new waste collectors. If they can capture it, they can capture anything.