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  The Ion Beam Shepherd enables a novel contactless debris removal strategy in which the debris orbital motion is actively controlled by exploiting the momentum transmitted by a collimated beam of quasi-neutral plasma impinging against its surface. The beam can be generated with state-of-the art ion engines from a "shepherd spacecraft" coorbiting nearby with no need for physical attachment with the body. The spacecraft, placed at a distance of 10-20 meters from the object would use an ion thruster pointed towards the debris, as well as a second propulsion system to compensate for the ion engine reaction and to keep a constant distance between the debris and the shepherd satellite throughout the orbit maneuvering process.

  The high-speed plasma ions (typically xenon) impact the target transferring their ion momentum and thereby producing a force and a torque upon the debris. According to experimental tests and numerical models available in the literature, 1 keV energy ions penetrate the substrate of a metal such as aluminum a few nanometers and deposit their kinetic energy on the target. The neutralized ions then abandon the surface with debris thermal velocities, which are several times smaller than the incoming ion velocities, and therefore their momentum can be neglected. Backsputtering e ffects do occur, but the energy of the sputtered material is typically about two orders of magnitude smaller than the one of the incoming ions, so that the contribution to momentum transmission of the backscattered material can also be neglected when computing the net force transmitted to the target.

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