PI — Terminal Planetary Defense. (arXiv:2110.07559v5 [astro-ph.EP] UPDATED)
<a href="http://arxiv.org/find/astro-ph/1/au:+Lubin_P/0/1/0/all/0/1">Philip Lubin</a>

We present a practical and effective method of planetary defense that allows
for extremely short mitigation time scales. The method involves an array of
small hypervelocity non-nuclear 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 $sim$10-meter diameter allow the Earth’s atmosphere to
act as a “beam dump” where the fragments burn up and/or air burst, with the
primary channel of energy going into spatially and temporally de-correlated
shock waves. It is the de-correlated blast waves that are the key to why PI
works so well. The effectiveness of the approach depends on the intercept time
and size of the asteroid, but allows for effective defense against asteroids in
the 20-1000m diameter class and could virtually eliminate the threat of mass
destruction posed by these threats with very short warning times, though longer
warning is always preferred. A 20m diameter asteroid ($sim$0.5Mt, similar to
Chelyabinsk) can be mitigated with a 100s prior to impact intercept with a
10m/s disruption. With ~1m/s internal disruption, a 5 hours prior to impact
intercept of a 50m diameter asteroid ($sim$10Mt yield, similar to Tunguska), a
1 day prior to impact intercept of 100m diameter asteroid ($sim$100Mt yield),
or a 10-20 day prior to impact intercept of Apophis ($sim$370m diameter,
$sim$4Gt yield) would mitigate these threats.

We present a practical and effective method of planetary defense that allows
for extremely short mitigation time scales. The method involves an array of
small hypervelocity non-nuclear 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 $sim$10-meter diameter allow the Earth’s atmosphere to
act as a “beam dump” where the fragments burn up and/or air burst, with the
primary channel of energy going into spatially and temporally de-correlated
shock waves. It is the de-correlated blast waves that are the key to why PI
works so well. The effectiveness of the approach depends on the intercept time
and size of the asteroid, but allows for effective defense against asteroids in
the 20-1000m diameter class and could virtually eliminate the threat of mass
destruction posed by these threats with very short warning times, though longer
warning is always preferred. A 20m diameter asteroid ($sim$0.5Mt, similar to
Chelyabinsk) can be mitigated with a 100s prior to impact intercept with a
10m/s disruption. With ~1m/s internal disruption, a 5 hours prior to impact
intercept of a 50m diameter asteroid ($sim$10Mt yield, similar to Tunguska), a
1 day prior to impact intercept of 100m diameter asteroid ($sim$100Mt yield),
or a 10-20 day prior to impact intercept of Apophis ($sim$370m diameter,
$sim$4Gt yield) would mitigate these threats.

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