Images courtesy of the Surrey Space Centre
When satellites reach the end of their working lives, they may continue to orbit in a dormant state for many decades. In a project funded by ESA, Surrey University (UK) has developed a new technique for deorbiting ageing satellites in a safe manner.
By unfurling an ultra-lightweight “gossamer sail” to increase aerodynamic drag, a deorbiting satellite more quickly leaves Low Earth Orbit (LEO) and disintegrates in the Earth´s atmosphere, reducing the risk of catastrophic collisions and helping to maintain a sustainable space environment for future generations.
When not in use, the Gossamer Deorbit Sail is extremely compact; its dimensions are 15x15x25cm and it weighs just 2kg. Upon deployment, it expands to 5x5m, which is large enough to bring down a satellite of up to seven hundred kilos in weight. The system consists of a set of extremely lightweight carbon-fibre booms supporting a sail made from 7μm thick aluminized Kapton membrane with rip-stops and a telescopic deployment mechanism.
The sail was developed at the University’s Surrey Space Centre, with funding provided through ESA’s ARTES 5.1 program. It has been subjected to rigorous testing, including thermal, vibration, and vacuum tests, and the team hopes to see it deployed in a mission by the end of 2014 by including it as part of another mission. Once the small ï»¿demonstration ï»¿
satellite is in orbit, the sail will be deployed for testing. The initial tests taking 2-3 weeks will demonstrate solar sailing propulsion. After this, the sail will be rotated to increase the effect of atmospheric drag and so deorbit the test satellite. At an altitude of 600 km, there is enough atmosphere to cause fairly rapid re-entry and it should disintegrate in a mere 2 to 12 months.
Under the European Code of Conduct for Space Debris Mitigation, published in 2008, ESA has committed itself to freeing up orbits within 25 years. However, a dormant satellite at an altitude of 750km could easily remain in orbit for a century or longer, forming an obstacle to launching new satellites in that same orbit as well as contributing to the problem of “junk” in space.
In LEO, there is still sufficient atmosphere to generate the needed drag using the sail. Even with the sail, it could still take many years for the spacecraft to re-enter and disintegrate. But it would be much more mass-efficient than carrying extra propellant, which would be some ten times heavier.
For satellites in orbits above 750km, the sail could potentially make use of solar radiation pressure to perform the necessary end-of-life manoeuvres with the help of an attitude control system.
If a deorbit sail is included in future launches, this would ensure that decommissioned satellites can be retired well within the 25-year deadline. In due time, it could also be deployed for other clean-up activities, such as any deorbiting adapter which is jettisoned in the course of launching multiple payloads.
Professor Vaios Lappas from the University of Surrey commented: “We are delighted to have completed the successful design, manufacture and testing of ESA’s Gossamer Deorbiter, the first of its kind internationally.”
“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,” Lappas said.
Dr. Sven Erb, ESA Technical Officer added, “The impressive mass-efficiency and atmospheric effectiveness that Surrey Space Centre has achieved for the Deorbit Sail device will be key for its success in commercial space. The device will be an important step forward in ensuring sustainable exploitation of space in the future.”
A furled gossamer sail unit during testing at the Surrey Space Centre