We present a practical and effective method of planetary defense that allows
for extremely short mitigation time scales. The method uses an array of small
hypervelocity kinetic penetrators that pulverize and disassemble an asteroid or
small comet. This mitigates the threat using the Earth's atmosphere to
dissipate the energy in the fragment cloud. The system allows a planetary
defense solution using existing technologies. This approach will work in
extended time scale modes where there is a large warning time, as well as in
short interdiction time scenarios with intercepts of minutes to days before
impact. In longer time intercept scenarios, the disassembled asteroid fragments
largely miss the Earth. In short intercept scenarios, the asteroid fragments of
maximum ∼10-meter diameter allow the Earth's atmosphere to act as a "beam
dump" where the fragments burn up and/or air burst, with the primary channel of
energy going into spatially and temporally de-correlated shock waves. It is the
de-correlated blast waves that are the key to why PI works so well. The
effectiveness of the approach depends on the intercept time and size of the
asteroid, but allows for effective defense against asteroids in the 20-1000m
diameter class and could virtually eliminate the threat of mass destruction
posed by these threats with very short warning times, though longer warning is
always preferred. A 20m diameter asteroid (∼0.5Mt, similar to Chelyabinsk)
can be mitigated with a 100s prior to impact intercept with a 10m/s disruption.
With ~1m/s internal disruption, a 5 hours prior to impact intercept of a 50m
diameter asteroid (∼10Mt yield, similar to Tunguska), a 1 day prior to
impact intercept of 100m diameter asteroid (∼100Mt yield), or a 10-20 day
prior to impact intercept of Apophis (∼370m diameter, ∼4Gt yield)
would mitigate these threats.Comment: 174 pages, 130 figures. Published in Advances in Space Research (ASR)
10-22; https://www.sciencedirect.com/science/article/pii/S027311772200939
