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The invisible danger of space debris
Q&A TIM FLOHRER space debris analyst at ESA
What exactly is the space debris? Space debris is defined as all non-functional, artificial (human-made) objects, including fragments and elements thereof, in Earth orbit or re-entering into Earth’s atmosphere. Near the Earth space debris dominates over the natural meteoroid environment, except around millimeter sizes.
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Metro investigates how the growing problem of the space junk could be solved. DANIEL CASILLAS
Metro World News
Many film lovers were shocked by the scene from 2013 British-American epic adventure movie ‘Gravity,’ in which the protagonist is hit by space junk while making a tour outside the spaceship. And that moment is actually shows what could happen in reality, because there are thousands of useless objects orbiting around the Earth and posing danger to astronauts and even those on the surface of the planet. Thousands of ships and satellites have been sent into space since we began to explore space in 1957. Accord-
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PROJECTS TO ELIMINATE SPACE DEBRIS PHOTOS: ESA
ing to figures revealed by the Space Debris division of the European Space Agency (ESA), about 5250 rockets have been launched from Earth during the past 60 years. These rockets have put around 7.5k satellites on the orbit, of which only 1.2k continue to operate. In total, it is estimated that the mass of all space objects in Earth orbit is about 7.5k tones. The presence of all these ships and satellites sent from Earth has also generated tons of debris that continue to orbit uncontrollably around our planet. The National Aeronautics and Space Administration’s statistics show that more than 500k pieces of “space junk” are currently being tracked, and their quantity is rising with each launch. “As a consequence of the rising debris object count, the probability for catastrophic collisions will also grow progressively. Doubling the num-
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kilometres per hour is the speed debris is moving around space. ber of objects will increase the collision risk by approximately four times. As the debris population grows, more collisions will occur,” ESA explained in a recently published study. Specialists have already investigated different types of risks related to the presence of debris on the planet’s orbit. Most of them are present in outer space, where this garbage can crash with ships, satellites and even with the International Space Station. “There are debris-related risks in orbit and risks due to re-entries. In-orbit risks are due to collisions with operational spacecraft that would
affect us on ground as we are depending today on the uninterrupted availability of services provided through space-based infrastructure. Large space-debris objects (e.g. spacecraft, rocket bodies or fragments thereof) that re-enter into the atmosphere in an uncontrolled way can reach the ground and create risk to the population on ground,” Tim Flohrer, space debris analyst at ESA told to Metro. And the danger is not only theoretical. In fact, various accidents related to space debris have been reported. Only last year at least two major incidents occurred. The first one happened in May, when junk hit the International Space Station causing small crack in window, and the second when solar panel on ESA’s Sentinel-1A spacecraft was hit by a millimeter-sized particle of space debris. Several studies carried out
by NASA and ESA predict that the presence of junk will continue to grow and thus the likelihood of collisions. Faced with this risky scenario, scientists work on solutions to reduce the amount of space debris orbiting near Earth. For example, it has been proposed to use networks and even a robotic arm to catch the waste. However, experts have also begun to raise the need to achieve sustainable future in space in which less and less space debris occurs each time a rocket is launched. “It’s important to limit the amount of debris through space debris mitigation. All newly launched objects need to comply with post-mission disposal guidelines – especially an orbital decay in less than 25 years. Unfortunately, the simulations have shown that mitigation alone is not sufficient for a sustainable future in space”, Flohrer concluded.
A giant net
Robotic arm
ESA is investigating a possibility to launch a debris removal mission called e.Deorbit, which would target an ESA-owned satellite on low orbit. It could capture rubbish with a giant net and safely burn it in a controlled atmospheric reentry. The launch is planned for 2023.
Another option of ESA’s e.Deorbit mission is to use a long robotic arm attached to a spacecraft to capture fragments of space debris and, as with the giant network, bring them to Earth’s atmosphere and burn before re-entering the planet.
Lasser
Harpoon
American scientists at NASA are considering to use a ground-based laser to destroy space junk and mitigate debris collisions. The ‘laser broom’ concept, a powerful, megawatt-class laser would vaporize the surface of a piece of debris that is heading for another, causing junk to recoil.
Engineers at the UK-based Astrium are developing a system to harpoon useless satellites and pull them out of the space. The harpoon would be fired at the hapless satellite from close range and a propulsion pack tethered to the projectile would pull the debris downwards, to burn in the Earth’s atmosphere.
How much ‘space junk’ is orbiting the Earth? All come from the about 5250 launches we did since 1957. These launches have placed into Earth orbit about 7500 satellites, of which about 4300 are still in orbit, of which about 1200. are still functioning. In total, i.e.also including rocket bodies, about 7500 tones have been launched into in Earth orbit. A large fraction re-entered into the atmosphere. The U.S. Space Surveillance Network and maintains in their catalogue about 23 000 objects larger than ~10cm. This number also includes the ~1200 active satellites. The larger rest are space debris (intact non-functional objects and fragments). We estimate that more than 290 break-ups, explosions and collision events resulting in fragmentation have occurred. How could debris be removed? Studies on the long-term evolution of the space debris population have shown that a ‘business as usual’ scenario will lead to a progressive, uncontrolled increase of object numbers with collisions becoming the primary debris source. The most effective way to chain reaction and stabilize the debris population in key orbits is to remove large items of debris from space, especially those having a long remaining lifetime in space. At present there are two concepts under consideration: one using a net and the other a robotic arm, but this removal technology is under development. Is it dangerous for the Earth? The main risk is created from our significant dependency on spacebased infrastructure today. How can we reach a sustainable future in space? We need better compliance with the known techniques and processes to mitigate the generation of space debris. These are the most effective long-term means of stabilizing the space debris environment at a safe level. This includes as key aspects: end-of-life disposal of satellites and rocket bodies, “passivation” to prevent an accidental post-mission explosion, prevent the release of objects, and to apply “design for demise” so that objects burn up in the atmosphere during re-entry. We need to actively remove large, massive objects from space to prevent the “Kessler-syndrom,” a runaway scenario of self-sustained collisional cascading, to set in.