Over the years, the Low Earth Orbit (LEO), the region between the Earth’s surface and 2,000km, has become a junkyard. Since the launch of Sputnik 1 in 1947 there have been 5,250 launches, according to the European Space Operations Center (ESOC). 23,000 artificial satellites are in orbit today, with only 1,200 operational.
The density of ‘space junk’ led to crashes, like in 2009 when an Iridium communication satellite collided with a Russian Cosmos satellite. The impact created 2,200 large pieces of debris. Overall there is now over 166 million man-made pieces of debris less than 1cm in diameter, 750,000 pieces between 1 and 10 cm and 29,000 pieces over 10 cm orbiting the Earth. These come in all form and shape, from old rocket paint flakes to shards of solar panels and entire dead satellites. With speeds reaching 17,500 mph, these true space bullets are a real threat to space activity.
Movie enthusiasts may remember the debris waves of the movie Gravity, which destroyed every habitable spacecraft they met in mere seconds, but in April 2017 in an article for ABC Australia, Dr Karl Kruszelnicki revealed the ISS itself also happened to be hit by space debris, leading astronauts to “take shelter in the Soyuz re-entry space craft, ready to abandon ship and make an emergency landing on Earth” in case of damages beyond repair, with “plenty of close calls.” The risks over multimillion dollars satellites and human lives is taken very seriously by government agencies all over the globe, and researchers work on innovative technologies to try solving the problem.
A first step is tracking. Ground based telescopes and laser radar (lidar) follow chunks of debris 24/7 ready to call the ISS or satellites operators to have them move out of the way by activating their thrusters if they estimate the fragments’ trajectory brings them too close. Before shutting it down in 2013, the US Air Force had a system that could track about 20,000 space objects as small as 75cm in diameter. The current NASA / DoD system tracks more than 17,000 orbital debris. In 2016, Lockheed Martin was chosen to develop a “Space Fence” able to monitor up to 200,000 debris.
The $1 billion system is expected to enter service in 2018. And recently, aerospace engineers from MIT developed a new refinement for lidars: radars using high-powered laser to pinpoint debris in the sky. The new laser sensing technique relies on laser polarimetry, the study of reflection pattern of laser light, to decipher not only where but what kind of space junk they are looking at. Are they plastic or metal, bare or covered in paint? These differences are far from anecdotal, as explain Michael Pasqual, a former MIT’s Department of Aeronautics and Astronautics graduate. “If you can figure out what a piece of debris is made of, you can know how heavy it is and how quickly it could deorbit over time or hit something else.” Precise measures of an object mass and momentum give a more accurate estimation of its potential for destruction. According to Kerri Cahoy, the Rockwell International Career Development Associate Professor of aeronautics & astronautics, and an associate professor in the Department of Earth, Atmospheric, and Planetary Sciences at MIT, the technique can easily be implemented on existing ground-based systems.
Once located, you then have to dispose of the debris. Thales Alenia Space is developing the Space Transportation Bus that should enter service in 2020 and be able to grab big debris. Other techniques aim at grabbing the objects and re-entering the atmosphere with them so they burn up. This could be done either with a cubical satellite that would launch a net to catch space junk, such as the Swiss CleanSpace One, or with a paper-thin membrane that would wrap itself around the debris, such as the Brane Craft.
But many of these technologies face challenges. Grabbing and other forceful interactions, like the use of a harpoon, can lead to unintended reaction, with objects possibly spinning out of control on a new trajectory. Suctions cups simply do not work in space. Sticky substances, like tape, cannot resist the extreme temperature swings found in space. And magnets are useless with nonmagnetic debris… But a Stanford University research team may have found a way. “What we’ve developed is a gripper that uses gecko-inspired adhesives,” said senior author Mark Cutkosky, professor of mechanical engineering. Geckos are small lizards whose feet have microscopic flaps allowing them to climb walls thanks to an intermolecular effect. The gripper reproduces this feat (although short of the animal intricate ability) and has been successfully tested on Earth and aboard the ISS. The next step would be an actual test outside the station in space. For Aaron Parness, group leader of the Extreme Environment Robotics Group at NASA’s Jet Propulsion Laboratory, a successful outcome would allow wide applications, from debris catching to “climbing robot assistant that could crawl around on the spacecraft, doing repairs, filming, and checking for defects.”
Written by ADIT – The Bulletin and republished with permission.