There has been exponential growth in debris accumulated from over 60 years of space activities. It is estimated that the total number of space debris objects in Earth orbit is in the order of: 22,000 – for sizes larger than 10 cm, 600,000 – for sizes larger than 1 cm and more than 500 million – for sizes larger than 1 mm and the number is growing all the time. And as companies such as SpaceX and OneWeb plan to launch tens of thousands of new satellites over the next few years, this hazardous debris will likely grow rapidly to pose an increasing threat to space missions and astronauts.
Space debris threat
In Nov 2021, the International Space Station was forced to maneuver itself to avoid a piece of debris spawned by a Chinese antisatellite weapon test in 2007. Faced with a threat to the zone, the agency worked with Russia’s space agency in Moscow to fire station thrusters that raised its altitude by just under a mile.
The roughly 2,000-kilogram Russian Cosmos-1408 satellite was launched in 1982 and destroyed Nov. 2021 by the direct-ascent anti-satellite missile test. “The test so far has generated more than 1,500 pieces of trackable orbital debris and will likely generate hundreds of thousands of pieces of smaller orbital debris,” the U.S. Space Command Public Affairs Office stated shortly after the ASAT test.
A Chinese satellite experienced a near miss in Jan 2020 with a piece of debris created by Russia’s destructive anti-satellite test conducted in November 2021. The Space Debris Monitoring and Application Center of the China National Space Administration (CNSA) issued a warning Tuesday of an extremely dangerous encounter between the Tsinghua Science satellite (NORAD ID: 46026) and one (49863) of more than a thousand trackable pieces of debris from the Nov. 15 ASAT test.
The large number of debris around Earth is a risk for the safety of operational satellites, but also for the impact of these objects on the Earth. Any of debris objects can cause harm to an operational spacecraft, where a collision with a 10-cm object could entail a catastrophic fragmentation, a 1-cm object will most likely disable a spacecraft and penetrate the satellite shields, and a 1-mm object could destroy sub-systems on board a spacecraft.
Space Debris Mitigation
Aerospace commentator Huang Zhicheng, said that the growing issue of space debris should be addressed, including through international legal mechanisms. “It is not only necessary to conduct research on experimental devices or spacecraft to remove space debris, but also to formulate corresponding international laws and regulations on the generation of space debris under the framework of the UN,” Huang sai
To protect against small debris , the ISS has long been shielded by multiple layers of Nextel and Kevlar body armour fabric, which blanket the station in order to protect it against meteorites and other forms of space debris. Russia’s Science-Power and Prichal Nodal modules are expected to be delivered and attached to the International Space Station in 2021 and 2022, respectively, and to later help to form the first building blocks of the country’s new space station. The new scientific and energy modules set to be attached to the Russian segment of the ISS will receive domestically-engineered body armour fabric-based anti-meteorite protection, according to Space Engineering & Technology, the official journal of Russia’s Energia rocket and space corporation. “The basalt and body armour fabrics from which the structure of the buffer shield is based are comparable in terms of their properties to the Nextel and Kevlar fabrics used in the shielding on NASA modules,” the article, written by the material’s developers, noted.
There are many concepts which have been proposed to remove debris from the space. Some of these are, to use a remotely controlled vehicle to rendezvous with the debris, capture it, and return to a central station. Another way is collect the debris in a foamy ball of aerogel. Other methods for clearing up small-scale space debris includes giant nets used to sweep up and collect the waste, and magnets that could be used to draw them out of orbit. Active de-orbiting involves removing the End-of-Life satellites with a robotic Orbital Transfer Vehicle. However, presently none of these are economically viable.
Bruce Davis and his team at the Colorado company Roccor have built new technology to help collect and bring down the leftover trash floating in space. Their technology is attached to a satellite before it gets launched. After it’s up in space for the amount time it was supposed to be, a timer goes off deploying the long sheet of metal. This helps drag down the space trash to the Earth’s atmosphere. “The reentry is so fierce that it just completely melts and vaporizes before it hits the ground,” said Davis.
A British-designed satellite has tested technology for salvaging space junk for the first time. RemoveDEBRIS, built to clean up thousands of potentially dangerous pieces of trash orbiting the Earth, deployed its net as part of a practice experiment in space in Sep 2018.
The U.S. space mission testing Kilometer-Long Space Tether to help clean up space junk
Engineers from the Naval Research Laboratory in Washington D.C. built a small cubesat that can split in two. The pieces are connected by a strong, kilometer-long tether that’s not much stronger than a piece of floss, according to SciAm — sort of like space nunchucks. TEPCE hitched a ride aboard a SpaceX Falcon Heavy rocket in June 2019
A tether in Earth’s ionosphere—an upper atmospheric layer filled with charged particles such as free electrons and positive ions—can collect electrons at one end and emit them at the other, generating an electric current through itself. The electrified tether’s interactions with Earth’s magnetic field produce an impetus known as the Lorentz force, which pushes on the tether in a perpendicular direction.
Several TEPCE components work together to create the necessary current. After separating, each of the two mini-satellites deploys a five-meter steel tape that can collect free electrons from the ionosphere. Each satellite also has a tungsten filament that uses power from onboard solar panels to heat up until it reaches a temperature at which it can emit those electrons. This produces a current that runs from the electron collector on one satellite through the tether to the electron emitter on the other.
Because each tethered satellite contains both components, the current can flow in either direction—depending on which end of the tether is gathering electrons, and which is releasing them. When the current flows in one direction the Lorentz force pushes in a direction opposite to the spacecraft’s motion, producing drag that eventually slows the satellite down and reduces its orbital altitude.
Run the current in the opposite direction and the direction of the Lorenz force will reverse as well, creating propulsion instead of drag. The resulting increase in velocity could help maintain or increase orbital altitude, enabling more complex maneuvers without requiring any additional fuel.
Now TEPCE is among a new wave of space-tether missions testing improved versions of the technology, and how it could help remove retired spacecraft. Sánchez-Arriaga is leading a separate project called Electrodynamic Tether technology for Passive Consumable-less deorbit Kit (E.T.PACK), funded by the European Commission. That mission aims to test how a tether, attached to future satellites, could deploy as a passive brake that brings down dead or decommissioned spacecraft at the end of their lives.
China’s scavenger satellites
China launched the Shijian-21 satellite from Xichang in Oct 2021 with the stated aim of testing space debris mitigation technologies. The China Aerospace Science and Technology Corp. (CASC) confirmed launch success within an hour of launch. Chinese state media Xinhua reported that Shijian-21 will “test and verify space debris mitigation technologies.”
No details of the satellite or its capabilities were made available. Coupled with the fact that space debris mitigation technologies are “dual-use,” having both civilian and military applications, the satellite is likely to attract interest and scrutiny outside China
The small satellites, including some lighter than 10kg, can grab onto uncooperative targets such as dead spacecraft tumbling in near-Earth orbit. A triple-eye sensor allows them to gauge the target’s shape, relative speed and random rotation, with a single-axis robotic arm latching onto the target when it closes to within 20cm.
The scavenger satellite then fires up thrusters and steers the junk so that it can burn up while plunging through the atmosphere. China has launched at least 10 experimental scavenger satellites over the past decade, but it is not the only country developing the technology. The European Space Agency has launched at least two satellites to learn how to catch a piece of junk in orbit using various methods, such as casting a net. And the American military has reportedly been developing technology using drifting debris as a tactical hideout for smaller satellites in space warfare.
Chinese scientists have been testing the technology since 2008, according to declassified document Small probes can latch onto targets such as dead spacecraft in near-Earth orbit – and in a military scenario could stay attached to avoid being tracked
UK launch Satellite that Captures Debris with space net
The satellite was launched aboard the SpaceX Dragon spacecraft on April 2 as part of a resupply mission for the International Space Station. The 220lb spacecraft, equipped with a net and harpoon, was designed and built by a consortium led by the University of Surrey and funded by the European Commission.
It is the first practical attempt to try out clean-up technology. Professor Guglielmo Aglietti, director of Surrey Space Centre, said he was “absolutely delighted” with the outcome. He said: “While it might sound like a simple idea, the complexity of using a net in space to capture a piece of debris took many years of planning, engineering and co-ordination.”
After the successful test it will try out more technologies in the coming months as part of an experimental phase.
Russia creates new space junk recycling system
Russian Space Systems (RSS) has developed a recycling system capable of taking hold of decommissioned satellites in the Earth’s orbit to grind and process them into fuel, the media reported. The space debris disposal system, weighing about 2.5 tonnes, will be able to capture “decommissioned small satellites in low orbits (from 500 to 700 km),” Project Developer and RSS Research Engineer Marina Barkova told TASS news agency in March 2019.
“The system consists of a trap that includes a net in the form of a cupola and a cone and a processing device. When a satellite gets into the trap, it undergoes the stage of its processing through a grinder and a special mill,” she specified. A satellite thus chopped inside the system will then be mixed with oxygen and hydrogen and turned into fuel. This fuel will be used in the system’s engines for manoeuvres and a fly over to the next satellite that has used up its service life. An onboard computer and the robotised devices of controlling the space chopper will get power from solar panels, Barkova explained.
Initially, the new “satellite hunter”, which is estimated at about $117 million, is expected to be launched to an altitude of 400 km to do without a booster to save funds. However, its target orbit will be 800-1,500 km, she said. According to NASA’s data, there are over 2,200 active and more than 5,000 decommissioned satellites in orbit today as well as over 14,000 fragments of space debris. Overall, almost 20,000 objects have been registered in the Earth’s orbit to date. The recycling system will search for space junk “using the data of Russian and international catalogues of space objects,” the report noted.
Lasers for Debris Removal
NASA’s Ames Research Center in 2011 proposed the use of 5KW laser to fire at debris which would slow the speed of the debris forcing it to enter into earth’s atmosphere where it would get burnt. It also estimated that such a laser could migrate ten pieces of junk a day, which could promise debris free future.
Recently Chinese scientists made such proposal as part of a study titled “Impacts of orbital elements of space-based laser station on small scale space debris removal,” which recently appeared in the scientific journal Optik. The study was led by Quan Wen, a researcher from the Information and Navigation College at China’s Air Force Engineering University, with the help of the Institute of China Electronic Equipment System Engineering Company.
Now Chinese Scientists at the Air Force Engineering University in China in a paper, titled Impacts of orbital elements of space-based laser station on small scale space debris removal, have proposed to remove space debris by fragmenting them into smaller, less-harmful pieces using space-based lasers. NASA began researching how to move space junk with lasers in 2011. The proposed process would slow galactic garbage enough for it to hopefully burn up in Earth’s atmosphere. The China is concerned of debris that would be generated when its space station Tiangong-1, will be “de-orbiting” or falling to Earth later this year. China is only second to US in launching satellites in space too and space debris is also threat to its rapidly expanding space programme.
However China is also developing lasers for anti satellite uses. Many American officials have reported that China has secretly fired laser weapons on American spy satellites to disable them by “blinding” their sensitive surveillance devices. China has conducted two laser based anti-satellite tests recently, during an exercise of the PLA. This was disclosed by Konstantin Sivkov, deputy head of the Moscow-based Think Tank, Academy of Geopolitical Problems, in an interview to Voice of Russia In Nov 2014. China is not alone in developing laser based weapons, US Dating back to Regan-era under “Star Wars” program planned space based lasers missile-defense system, proposing to blast missiles out of orbit after launch.
For the sake of their study, the team conducted numerical simulations to see if an orbital station with a high-powered pulsed laser could make a dent in orbital debris. They found “The simulation results show that, debris removal is affected by inclination and RAAN, and laser station with the same inclination and RAAN as debris has the highest removal efficiency. It provides necessary theoretical basis for the deployment of space-based laser station and the further application of space debris removal by using space-based laser.”
In 2014, Chinese researchers in 2014, proposed a project of a space-based laser system that can eliminate debris of 1–10 cm and succeed in protecting a space station. Many space-faring nations such as America, Russia, the European Union have done research on space debris eliminated by laser. However, most research concentrates on ground-based laser systems but pays little attention to space-based laser systems, observed the researchers.
“There are, however, drawbacks of a ground-based system: a rather long distance, 350–1000 km, must be bridged to focus a laser beam on a particle with a radius of only a few centimeters, and an extremely high steering accuracy must be met. In addition to a formidable target detection and acquisition system, a very large beam director mirror is needed to obtain a high enough laser fluence and power density on a target to produce a noticeable impulse. A large fraction of the laser beam power will be wasted because a transmitter telescope cannot produce a small enough focal spot at these long distances.”
“Only continued processing of a debris particle over several orbital revolutions may be sufficient to lower the orbit substantially and allow the atmosphere eventually to do its cleaning work. Another opportunity to continue the processing on a certain particle exists only when it passes over the station again. Several stations around the globe may, therefore, be preferred, if the time for final elimination should be reduced. Cleary, the system can only be used in a preventive way and cannot counter an immediate collision threat.”
Space based laser method gives much more flexibility to counter the debris problem. Direct ablation mode and ablation back-jet mode are two modes in debris eliminated using a laser. The former mode is primarily aiming at tiny debris particles, and laser energy is used to burn down debris particles. The latter mode is pointed at larger debris particles, and laser energy is used to transfer orbit of debris. Debris particles would be burned down by the drastic aerodynamic heating effect.
“Under laser irradiation, part of the debris material is ablated and provides an impulse to the debris particle. Proper direction of the impulse vector either deflects the object trajectory or forces the debris on a trajectory through the upper atmosphere, where it burns up.”
Anti Satellite Laser Directed energy weapons
Laser DEW propagate energy between the weapon and the target by the means of a laser beam. There are several advantages of using directed energy weapons against the orbital segment in offensive counter-space operations. First, directed energy attacks take place at the speed of light, therefore, the result of the attack is near instantaneous, thereby minimizing the effectiveness of enemy defenses. Second, there is plausible deniability associated with soft kill and non lethal satellite attacks. Laser can sustain continuous operation, limited only by the available power. The desired results can be tailored from non-permanent disruption and degradation to permanent degradation and destruction.
Depending on their power, lasers can damage, disrupt, or destroy a satellite by overheating its surface, puncturing the outer surface of the spacecraft to expose internal equipment, or by blinding critical on-board mission or control sensors. The idea of a space-based laser gun was disclosed in the journal Chinese Optics in December 2013 by three researchers, Gao Ming-hui, Zeng Yu-quang and Wang Zhi-hong. All work for the Changchun Institute for Optics, Fine Mechanics and Physics – the leading center for laser weapons technology.
In future wars, the development of ASAT [anti-satellite] weapons is very important,” they wrote. “Among those weapons, laser attack system enjoys significant advantages of fast response speed, robust counter-interference performance and a high target destruction rate, especially for a space-based ASAT system. So the space-based laser weapon system will be one of the major ASAT development projects.”
According to the article, an anti-satellite attack in space would employ a ground-based radar to identify a target satellite, a special camera to provide precision targeting and a deployable membrane telescope that would focus the laser beam on the target satellite. The researchers propose building a 5-ton chemical laser that will be stationed in low-earth orbit as a combat platform capable of destroying satellites in orbit. Given funding by the Chinese military, which is in charge of China’s space program, the satellite-killing laser could be deployed by 2023.
Chemical lasers are the only systems that have produced megawatt-level outputs, however, they require special handling because of toxic chemicals hence fallen out of favor. Fiber lasers have emerged most promising technology, for directed energy weapons due to their many advantages like: high electrical to-optical efficiency (40%), high reliability for operation in harsh military environments, and high beam quality near diffraction-limited light output.
China has a dedicated programme for developing high power solid state laser and adaptive optics to maintain the quality of laser over large distance, which can be used against satellites. In 2013, Raycus succeeded in developing China’s first 10 kW fiber laser－making China the second country to master the technology in the world. Last year, a 20 kW fiber laser produced by Raycus was unveiled at the laser technology and industry development forum held in Wuhan, Central China’s Hubei province. That product is expected to enter mass production by 2018, according to the company.
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