Image: Tohoku University
Space junk, more formally called space debris or waste, includes all human-made objects that are in Earth’s orbit that are no longer in operation. This can include old satellites, rocket parts and their fragments from collisions and breakups. It is a common topic being discussed within the space industry because of the growing concern for the damage these objects can
cause. This raises questions about what technologies can help get rid of them.
Satellites are a common source for possible space debris. Once no longer working, satellites may be purposefully disintegrated by manoeuvring the spacecraft to go into the Earth’s atmosphere at a speed that is high enough to enable to the heat from the friction with the air to burn up the
satellite as it falls back to Earth. Larger spacecraft and satellites that may not fully burn up are purposefully placed in a “graveyard orbit” at a height of 36,000 kilometres. Higher than the orbit of any operating satellites, this special orbit is the designated resting place for satellites to reduce the possibility of future collisions and to mitigate debris. Unfortunately,
not all dead satellites have successfully reached or been assigned to this orbit. Furthermore, some of these satellites risk releasing coolant once in this graveyard orbit, which can freeze into solid alloy deposits to form more debris. The International Telecommunications Union now requires proof that a satellite can be moved out of its orbit at the end of its lifespan, and
intends for them to be placed in this graveyard orbit.
Debris may even include lost equipment. During the first-ever American spacewalk, astronaut Ed While lost a glove. Other items lost to space include a wrench, a toothbrush, pliers, a tool bag, a thermal blanket and a camera.
The majority of collisions in Earth’s orbit causing debris have been unintentional. For example, low-speed collisions have occurred during failed docking activities when a vehicle tries to connect with a space station. In 1994, the Russian space station Mir collided with the manned Soyuz TM-17 spacecraft and this happened again in 1997 with the Progress M-34 supply ship.
A drifting thermal blanket photographed in 1998 during Space Shuttle mission STS-88 (NASA)
Significant international interest has been drawn from a variety of unintentional high-speed collisions between working satellites and debris. This includes the 1996 collision between debris from an Ariane rocket and a French military reconnaissance satellite and a 2013 crash between two miniaturized satellites.
In, a 2009 the first ever collision took place between two satellites: the American Iridium 33 communications satellite and the retired Russian Kosmos-2251 satellite (animation below). Researchers agree that significant debris resulted from this high-speed crash (around 2,000 pieces greater than 10 centimetres), which main in orbit for many years and pose a risk for other collisions with satellites and other debris in orbit. The collision happened at a speed of 10 kilometres per second (this is well over 100 times faster than the top speed of Lamborghini’s Gallardo sports car).
Even intentional collisions have occurred with the intent of destroying satellites in Earth’s orbit. These activities have been pursued to remove satellites that may pose a hazard if they were to re-enter the atmosphere or for the testing of anti-satellite weaponry. These weapons are designed to destroy satellites for military purposes. To test this technology, the Chinese
destroyed their Fungyun FY-16 weather satellite in 2007 as part of an anti-satellite missile test. This was criticised for the amount of debris it created. This event produced the largest debris cloud ever generated by a single event in Earth’s orbit and is said to have created one-sixth of all the debris that can be tracked by radar.
In total, it is estimated that over seventeen thousand traceable objects orbit the Earth. The European Space Agency’s Space Debris Office claims that nearly 7500 satellites have been placed in orbit, of which approximately only 1200 are still in operation. The total debris estimates for debris objects are 29 000 objects greater than 10 cm, 750 000 objects from 1 cm to 10 cm, and 166 million objects from 1 mm to 1 cm. It is important to remember that even the smallest pieces of debris can cause significant damage because they are traveling incredibly fast.
There are many concerns about what impacts these thousands of pieces of debris could have. Orbiting at an altitude of 300-400 kilometres and housing an average of six astronauts at a time, the International Space Station can maneuverer to avoid hazardous collisions with debris. The station is also equipped with Whipple shielding, which is an impact shield that acts as a bumper to break up and disperse the particles of a colliding object. Another concern is if this amount of debris could become too much for us to work in space at all. In 1978, a NASA scientist proposed the “Kessler Syndrome”. He explained that space debris is subject to a runaway chain reaction because collisions between these objects increase the amount of debris in Earth’s orbit. Simply, this effect suggests that collisions increase the likelihood of
further collisions. In fact, Kessler proposed that this amount of debris could reach a critical amount that would make space activities and satellite operation unlikely for several decades.
Image of the entry hole created on Space Shuttle Endeavour's radiator panel by the impact of unknown space debris. (NASA)
In order to address the growing concerns about the amount of space debris present in orbit around the Earth, some different technology concepts have been proposed to help reduce it. Although there is no international treaty minimizing space debris, the United Nations Committee on the Peaceful Uses of Outer Space has published guidelines. As well, government space agencies have set standard practices for debris mitigation. Research and
development is currently underway to support the robotic refuelling of satellites. This would mean rather than having dead satellites orbiting the Earth, they could be refueled to extend their life and to minimize the amount of new satellites that are launched to replace them. The Canadian aerospace firm MacDonald, Dettwiler and Associates is developing space-based
robotics systems to support the servicing of satellites and debris removal.
Other considerations have included dedicated vehicles or mechanisms that move dead spacecraft to the graveyard orbit. Lasers have also been researched as a way of moving the hazardous dead satellites and debris out of the way of the working satellites, but this has raised speculation
regarding whether this would add to the problem of debris if the beam destroys the object. In 2014, the Japanese space agency, JAXA, conducted tests on a magnetic net that is meant to act like trash bag for space debris to slow them down and then have the collected pieces burn up in the Earth’s atmosphere. The European Space Agency is also researching its own active
debris removal mission, which would be the world’s first. The agency hopes to develop a spacecraft to remove one of its own dead satellites from low-Earth orbit and moving into the atmosphere so that it burns up. Research is being conducted on multiple ways to capture the object, including nets, harpoons and robotic arms. For example, in April 2018 SpaceX brought the RemoveDEBRIS system to the International Space Station for testing. This
system was developed by United Kingdom’s University of Surrey Space Center and was co-funded by the European Commission, and will be released from the International Space Station. Once deployed, this platform will test debris-removing technologies including a net, harpoon and a “dragsail” instrument, which will force debris into the atmosphere to burn up
sooner and quicker.