Ion-beam shepherd

An ion-beam shepherd (IBS) is a concept in which the orbit and/or attitude of a spacecraft or a generic orbiting body is modified by having a beam of quasi-neutral plasma impinging against its surface to create a force and/or a torque on the target.

Ion and plasma thrusters commonly used to propel spacecraft can be employed to produce a collimated plasma/ion beam and point it towards the body.

In order to keep a constant distance between the target and the shepherd spacecraft the latter must carry a secondary propulsion system (e.g. another ion or plasma thruster) compensating for the reaction force created by the targeted ion beam.

The concept has been suggested as a possible solution for active space debris removal,[2][3][4][5] as well as for accurate deflection of Earth threatening asteroids.

Proximity formation flying guidance and control[7] as well as collision avoidance are among the most critical technological challenges of the concept.