Anyone who’s seen the Oscar-baiting visual spectacle that is Gravity, starring Sandra Bullock and George Clooney, knows in vivid 3D detail just how dangerous space debris can be. Leaving aside the scientific veracity – or lack thereof – of the movie, the cluttered environs of our immediate cosmological neighbourhood is an issue that is being taken quite seriously by the countries of our little planet, since most of the crafts up there are the satellites we need for everyday services like communication, navigation and entertainment.
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The problem isn’t so much the number of operational satellites that are needed to feed our voracious appetite for satellite television, instant communication and the knowledge of just where the nearest Starbucks is and how to get there. It’s the defunct satellites that are no longer useful, but are just hanging around in Earth’s orbit with nowhere to go.
In recent years, space agencies have gathered together to form an Inter-Agency Space Debris Coordination Committee and NASA has handbooks, procedural requirements and technical standards all aimed at limiting the junk in orbit around our world.
In Europe, the European Space Agency (ESA) has committed to freeing up orbits within 25 years under the European Code of Conduct for Space Debris Mitigation – an ambitious target considering dormant satellites in low-Earth orbits of as little as 750km altitude can stick around for a hundred years or more, ticking time bombs that threaten new sats with obliteration as they hurtle through space.
The agency now says that it’s close to a real test of the method it’s hoping will get space junk out of the sky in the quarter century target – a Gossamer Deorbiter Sail. The first of its kind in the world, the gossamer sail system is an aerodynamic drag technique that’s designed to take down telecoms satellites when they reach the end of their life. The sail is ultra-lightweight and extremely compact, taking up a space of just 15x15x25cm on the satellite and weighing only 2kg. It can deploy in minutes, expanding to 5m2, creating enough drag to pull a craft of up to 700kg out of orbit to burn up in the high atmosphere.
The ESA said on Friday that the sail, which was developed by the University of Surrey’s Space Centre, has now been subjected to rigorous testing, including thermal, vibration and vacuum tests. The team is hoping to see it get its first tryout in orbit using a demonstration satellite by the end of 2014, providing it can get a piggy-back launch opportunity.
“We are delighted to have completed the design, manufacture and testing of ESA’s Gossamer Deorbit Sail, the first of its kind internationally,” said Professor Vaios Lappas from the university.
“The project has been able to show that the design of a low-cost and robust end-of-life deorbiting system not only is possible, but it can also lead to tangible products with a strong commercial interest.”
Although the gossamer sail is the first of its kind, it’s not the only sail-type system currently being tested. For example, NASA finished its first-ever deployment of a solar sail in low-Earth orbit, the NanoSail-D, at the end of 2011. The US space agency’s system measures around 9.3m2 when open and deployed in just five seconds in the test. The demonstration satellite “sailed” through space for 240 days – using solar radiation pressure to get around with the help of a control system – before burning up during re-entry in September that year. NASA is using the data from the mission to better understand the drag influences of the Earth’s upper atmosphere.
Aside from being a larger sail, NASA’s NanoSail-D is different because it’s made of a polymer material called CP1, but like the Gossamer Deorbiter Sail, it’s only a few thousandths of a millimetre thick, a fraction of the diameter of a human hair. The Gossamer system is made from aluminised Kapton, which is the same polyimide film that is used in items like flexible electronics and space suits because of its ability to remain stable across a wide range of temperatures from -269°C to +400°C (−452°F to +752°F).
The ESA, which funded the project through its Advanced Research in Telecommunications Systems programme, intends to use the system primarily for satellites in low orbits like those belonging to Iridium, Orbcomm and Globalstar, which provide satellite phone and messaging services and low-speed data communications. But the sail could also potentially be used on satellites in higher orbits, using a solar sailing technique like NASA’s NanoSail-D.
In its first orbital test, the Gossamer Deorbiter will deploy once the demonstration satellite is at an altitude of somewhere around 700km. To hoist the sail, a telescopic mast will first extend the mechanism so it doesn’t catch on any of the satellite’s appendages or protrusions, before the sail pops out. Once the sail is open, the craft will take two or three weeks to put the system’s solar sailing propulsion through its paces.
After that, the sail will be rotated to up the atmospheric drag and bring the satellite out of orbit. Just a hundred kilometres further down, there is enough atmosphere to cause re-entry and burn the craft up in a mere two to 12 months. That will put the European agency will within its 25-year deadline, as well as providing options for getting rid of the bits and pieces jettisoned over the course of a multiple payload launch.
“The impressive mass-efficiency and atmospheric effectiveness that Surrey Space Centre has achieved for the device will be key for its success in commercial space,” said Sven Erb, the ESA’s technical officer. “The sail will be an important step in ensuring sustainable exploitation of space in the future.”
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