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ESA makes plans to capture derelict satellites

Jenny Winder, News Writer
Feb 23, 2014, 8:00 UTC

Sen—A future European Space Agency (ESA) mission plans to capture derelict satellites adrift in orbit. Part of an effort to control space debris, this ambitious mission is set for discussion with industry experts.

ESA's Clean Space initiative is studying the e.DeOrbit mission for removing debris, aiming to reduce the environmental impact of the space industry on Earth and space alike.

Holger Krag, of ESA's Space Debris Office explained in a statement: "If Europe manages to perform the first successful active removal actions, this would mean that we are mastering a complex technology including the approach of uncontrolled targets, capturing, servicing and de-orbiting with the help of an agile vehicle."

Earth is surrounded by more than 17,000 trackable objects larger than a coffee cup, which threaten working missions with catastrophic collision. Even a 1 cm nut could hit with the force of a hand grenade.

The only way to control the debris population across key low orbits is to remove large items such as derelict satellites and launcher upper stages. These are not only collision risks but also time bombs: they risk exploding due to leftover fuel or partially charged batteries heated up by orbital sunlight. The resulting debris clouds would make these vital orbits much more hazardous and expensive to use, and follow-on collisions may eventually trigger a chain reaction of break-ups.

Artist illustration of space debris. Image credit: ESA.

The e.DeOrbit mission is designed to target debris items in well-trafficked polar orbits, between 800 km to 1,000 km altitude. At around 1600 kg, e.DeOrbit will be launched on ESA's Vega rocket.

The first technical challenge the mission will face is to capture a massive, drifting object left in an uncertain state, which may well be tumbling rapidly. Sophisticated imaging sensors and advanced autonomous control will be essential, first to assess its condition and then approach it.

Several capture mechanisms are being studied in parallel to minimise mission risk. Throw-nets have the advantage that a large enough net can capture anything, no matter its size and attitude. Tentacles, a clamping mechanism that builds on current berthing and docking mechanisms, could allow the capture of launch adapter rings of various different satellites. Harpoons work no matter the target’s attitude and shape, and do not require close operations. Robotic arms are another option.

Apart from deorbit options based on flexible and rigid connections, techniques are being considered for raising targets to higher orbits, including tethers and electric propulsion.

Whatever the platform design, it will need to cope with the possible rapid tumbling of the target as only so much spin can be absorbed without the catcher craft itself going out of control.

A symposium on 6 May in the Netherlands will cover studies and technology developments related to e.DeOrbit, with ESA and space industry representatives presenting their research and outlining their plans.