How it works
The force and torque transmitted to the target originate from the momentum carried out by the plasma ions (typically xenon) which are accelerated to a few tens of kilometer per second by an ion or plasma thruster. The ions that reach the target surface lose their energy following nuclear collision in the substrate of the target material. 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.Applications
The concept has been suggested as a possible solution for active space debris removal, as well as for accurate deflection of Earth threatening asteroids. Further in the future the concept could play an important role in areas such as space mobility, transportation, assembly of large orbital infrastructures and small asteroid capturing in Earth orbit.Control
Beam divergence angles of ion and plasma thrusters, typically greater than 10 degrees make it necessary to have the shepherd flying not more than a few target diameters away if efficient beam overlap is to be reached. Proximity formation flying guidance and controlA. Alpatov, S. Khoroshylov, and C. Bombardelli "Relative Control of an Ion Beam Shepherd Satellite Using the Impulse Compensation Thruster", Acta Astronautica, Vol. 151, 2018, pp 543–554. as well as collision avoidance are among the most critical technological challenges of the concept.References
External links
* http://www.aero.upm.es/ Universidad Politécnica de Madrid (UPM) * http://sdg.aero.upm.es/ Space Dynamics Group at UPM * https://web.archive.org/web/20120426091458/http://web.fmetsia.upm.es/ep2/page.php?page=index&lang=en Equipo de Propulsión Espacial y Plasmas (UPM) * http://www.esa.int/act, ESA Advanced Concepts Team * http://leosweep.upm.es/en, LEOSWEEP project {{Planetary defense Aerospace engineering Planetary defense