  Asteroid impacts pose a major threat to all life on Earth. The age of the
dinosaurs was abruptly ended by a 10-km-diameter asteroid. Currently, a nuclear
device is the only means of deflecting large Potentially Hazardous Asteroids
(PHAs) away from an Earth-impacting trajectory. The Enhanced Kinetic Impactor
(EKI) concept is proposed to deflect large PHAs via maneuvering space rocks.
First, an unmanned spacecraft is launched to rendezvous with an intermediate
Near-Earth Asteroid (NEA). Then, more than one hundred tons of rocks are
collected from the NEA as the EKI. The NEA can also be captured as the EKI if
the NEA is very small. Finally, the EKI is maneuvered to impact the PHA at a
high speed, resulting in a significant deflection of the PHA. For example, to
deflect Apophis, as much as 200 t of rocks could be collected from a NEA as the
EKI based on existing engineering capabilities. The EKI can produce a velocity
increment (delta-v) of 39.81 mm/s in Apophis, thereby increasing the minimum
geocentric distance during the close encounter in 2029 by 1,866.93 km. This
mission can be completed in 3.96 years with a propellant cost of 2.98 t.
Compared with a classic kinetic impactor, the deflection distance can be
increased one order of magnitude. The EKI concept breaks through the limitation
of the ground-based launch capability, which can significantly increase the
mass of the impactor. We anticipate that our research will be a starting point
for efficient planetary defense against large PHAs.
