Pac-Man inspired space debris clean-up

24th July 2015

EPFL (École polytechnique fédérale de Lausanne)

Nat Bowers

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Space debris is the collection of objects travelling at up to 17,500 mph in orbit around Earth, including spent rocket stages, old satellites, fragments from disintegration and more. According to NASA, there are more than 20,000 pieces of debris larger than 10cm and 500,000 pieces of debris larger than 1cm being tracked, as well as the many millions of pieces of debris that are too small to be tracked.

This debris, even in small sizes, can be incredibly dangerous at such speeds.

The CleanSpace One project, run by the Space Engineering Center at EPFL, aims to start mitigating the impact on the space environment by acting responsibly and starting to remove debris from orbit. Among the first pieces of Space Debris being targeted is the tiny SwissCube satellite, which has been in Earth orbit for more than five years at an altitude of roughly 720km with 98.4° inclination. It measures 100x100x113.5mm and weighs just 820g.

Muriel Richard-Noca, head of the project, emphasises the extreme delicacy of the mission: “It only takes one error in the calculation of the approach for SwissCube to bounce off CleanSpace One and rocket out into space.”

Christophe Paccolat, a PhD student working in EPFL’s Center for Space Engineering and Signal Processing 5 Laboratory, commented: “SwissCube is not only a 10x10cm object that’s tough to grasp, but it also has darker and lighter parts that reflect sunlight differently. These variations can perturb the visual approach system and thus also the estimates of its speed and distance.”

The visual approach algorithms on the cleanup satellite’s cameras are currently being tested. To be accurate, they must take into account a variety of parameters, such as the angle of illumination of the Sun, the physical data of CubeSat, the relative speed at which it is moving and all the uncertainties involved in this measurement, and the speed of its own rotation.

Following collaboration with microengineering students from the University of Applied Science in Geneva, they opted for the so-called 'Pac-Man' solution. The prototype resembles a net in the form of a cone that unfolds and then closes back down once it has captured the small satellite.

“This system is more reliable and offers a larger margin for maneuvering than a claw or an articulated hand,” says Michel Lauria, Professor of Industrial Technology at the university.

The development of the approach and capture systems has passed the prototype stage, which involved making critical choices for the project. The next stage will combine putting together the first version of the engineering models – which will be more accurate than the prototypes – and more extensive tests. CleanSpace One could be launched as early as 2018.