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Fishing for Space Junk
August 28, 2015   
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A Polish research consortium is designing a system of special nets to catch defunct satellites, rocket parts and other space junk that is orbiting the Earth in the wake of 50 years of space exploration.

Thousands of pieces of manmade debris are spinning in low Earth orbit at an altitude of 180 to 2,000 kilometers. Although collisions are extremely rare, when they occur at orbital speed—about 28,000 kph—they can be dangerous and expensive.

Researchers say even the biggest pieces of space debris can be caught in special nets—similar to those used on Earth to capture wild animals—and then safely burned up in the atmosphere. The Polish scientists have already developed the first trial nets and have tested them in virtual reality and in a state of weightlessness.

While the space debris is being monitored from Earth by organizations including the United States’ National Aeronautics and Space Administration, the task is becoming increasingly difficult.

The trajectory of each item larger than 10 cm is known, enabling engineers to plan a debris avoidance maneuver if a collision seems possible. The problem is that such maneuvers are expensive because they increase fuel consumption and generate additional maintenance costs, says project manager Wojciech Gołębiowski from Warsaw-based R&D company SKA Polska.

The Polish scientists are working under the European Space Agency’s Clean Space initiative, which aims to remove the larger waste spinning in the atmosphere. According to the agency’s calculations, the annual growth of orbital junk will stabilize if five unwanted objects are removed every year.

One of the biggest pieces of space waste is the Envisat satellite, defunct since 2009. The European Space Agency plans to get rid of this troublesome piece of hardware in 2022 by catching it in a net launched from a satellite acting as an atmospheric “garbage truck.” Maneuvering to within 100 meters, the satellite will snag the giant piece of junk, bring it to a lower orbit and instigate a controlled burn over uninhabited areas. Once the Envisat satellite is removed, the agency says it will focus on other space trash.

“No mission of this kind has been performed so far, because it is rife with technological challenges. One of these is capturing the satellite,” says Gołębiowski “Even getting close to it is difficult, because the junk does not cooperate and does not transmit any signals about its position.”

In 2013, SKA Polska and navigation services provider OptiNav 3D from the northern Polish city of Słupsk, together with Italy’s STAM company, were awarded a tender by the European Space Agency to design software for cleaning up space debris. SKA Polska is coordinating the project, whose budget is nearly 2 million euros.

Along with nets, the European Space Agency is considering several kinds of capture mechanisms to collect the debris, such as robotic arms, harpoons and tentacles. Collecting space junk is difficult because the debris rotates and the capture mechanism must synchronize its own rotation with it, says Gołębiowski.

There is no room for mistakes during the procedure; if a net is launched but fails to capture the object in question, lots of money will be lost, Gołębiowski says. But a net 20 meters square is difficult to test on Earth. The best that can be done is computer simulations. “As part of the Adrinet project, we are creating a program for simulating the flight of objects and capturing them,” he says.

To verify their computer simulations, the researchers conducted an experiment to see if the net behaves in the same way in real life. The test was carried out in a state of weightlessness during a parabolic flight.

Parabolic flights are used for scientific and technological experiments in reduced gravity. They make it possible to test microgravity with humans without going through lengthy astronaut training. For this reason, parabolic flights are often used to validate space instruments and train astronauts. During a parabolic flight, the aircraft’s flight trajectory resembles a parabola. The maneuver ends with a steep descent during which the pilot can reach a state of weightlessness, typically for less than a minute.

The experiment was conducted at the National Research Council of Canada, which organizes parabolic flights. The Poles prepared prototypes of the net launcher and a small model of the Envisat satellite. Their Italian partners prepared prototypes of 25 nets. In February, 20 experiments were conducted on board a Falcon 20 aircraft. They ended in success. “The nets wound around the satellite so hard that they had to be cut off with a knife,” Gołębiowski says.

The project calls for delivery of a net launcher together with the net and a special winch. “We are building a prototype of the device and defining the parameters necessary for it to fly into space,” Gołębiowski says. SKA Polska will seek a partner to provide a satellite platform—which means the engine for the space garbage truck—and other critical components such as sensors and a control system to approach the target.

Electronics used in space must be resistant to cosmic radiation, so it must be specially adapted to the conditions. The adaptation often makes it vastly more expensive than mass-produced equipment, Gołębiowski says.

The OptiNav company, another member of the Adrinet project consortium, specializes in processing images and positioning objects in 3D. Its engineers are responsible for designing a measurement system based on a complex system of cameras and measuring devices.

OptiNav’s Arkadiusz ¦migielski says further testing is needed to determine how the net will be deployed. “After being launched, the net unravels until it reaches the target and wraps around it,” he says. “Because we don’t know how the net behaves in zero gravity, we want to launch several test nets and check how they are deployed. This is about visualizing the process.”

The main task of OptiNav was to write the software for data analysis. OptiNav’s core business is in 3D navigation for the medical community. Its main patented product is special markers that make it possible to follow objects in 3D during surgery.

The ESA is expected to award new tenders for further stages of the space debris project. The Polish researchers say they are up for the challenge.

“All indications are that in the future the removal of inactive satellites will be the responsibility of whoever launches them,” Gołębiowski says. “We have the necessary experience to handle such operations.”
Karolina Olszewska


Factfile

Thousands of pieces of space debris circulate in the skies above Earth. This celestial clutter includes not only whole, abandoned satellites, but also pieces of broken satellites, deployed booster rockets, human waste and other random objects, such as nuts and bolts left behind by astronauts and even paint chips blamed for damaging some windows on the Space Shuttle. There is also a glove lost by American astronaut Ed White during his historic 1965 spacewalk and bags of garbage from the Russian Mir space station. A collision in 2009 between a satellite owned by the U.S. company Iridium and a derelict Russian spacecraft added 2,000 pieces of debris.
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