Speaker
Description
Ion-Beam (IB) deflection is one of three primary mitigation techniques evaluated for use in the 2025 PDC hypothetical asteroid impact exercise. Unlike the other two techniques, Kinetic Impactors (KI) and the use of Nuclear Explosive Devices (NEDs), the ion-beam option is a gentle, slow-push method that, over the course of months to years, can change an asteroid trajectory significantly without the risk of fragmenting or disrupting the body in a possibly unpredictable way. IB deflection is accomplished using a spacecraft equipped with Solar Electric Propulsion (SEP), that carries a large amount of xenon propellant, rendezvouses with the asteroid, positions itself several asteroid diameters away, and orients such that the exhaust beam from one or more of its ion thrusters impinges almost entirely on the asteroid. Each ion thruster is paired with an identical one firing in the opposite direction so that the spacecraft maintains its position relative to the asteroid. Since the ions beam at very high velocity (~70 km/s), a considerable amount of momentum can be imparted over time.
The IB deflection technique offers several advantages over other techniques, in addition to avoiding the risk of unintended or unpredictable fragmentation/disruption. 1) An IB mission can deflect an impact trajectory off the earth equally well in either direction, while a KI mission is generally uni-directional, possibly requiring a much larger deflection. 2) With IB, the momentum imparted to the asteroid should be highly predictable, and not dependent on asteroid properties such as strength, porosity, topography, surface composition, etc. 3) Whereas with KI and possibly also Nuclear, it would be highly desirable to assess size, mass and other properties prior to designing the spacecraft, in order to avoid the possibility of unintended disruption, with IB the spacecraft design could start much earlier, even before the asteroid properties were well known. 4) An IB spacecraft could monitor deflection progress on its own, while for KI a separate rendezvous spacecraft would be required for that purpose. 5) The effectiveness of IB deflection can be amplified via multiple independent spacecraft operating in parallel, whereas such “stacking” of multiple deflections could be much more complex for impulsive mitigation methods.
In this paper we outline our simulations of several realistic ion-beam missions which could successfully deflect the hypothetical PDC25 asteroid over the wide range of masses possible at Epoch 1, and for any impact location along the risk corridor. We consider IB spacecraft with power levels in the 22-80 kW range, using up to three pairs of ion thrusters. We show that for a large subset of possible asteroid masses and possible impact locations, IB offers the only viable non-nuclear method to achieve a successful deflection. If launched early enough, even a modest (22kW) IB spacecraft could deflect the majority of cases. If the asteroid is large and the impact location near the center of the capture disk, however, a single IB spacecraft may not be sufficient, and multiple copies of the spacecraft would be required to operate in parallel to move the trajectory off the Earth.