[meteorite-list] New Cosmic Defense Idea: Fight Asteroids with Asteroids

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Tue Jun 20 21:04:39 2006
Message-ID: <200606210102.SAA03964_at_zagami.jpl.nasa.gov>

http://www.space.com/scienceastronomy/060620_science_tuesday.html

New Cosmic Defense Idea: Fight Asteroids with Asteroids
By Robert Roy Britt
space.com
20 June 2006

In a Space Age version of fighting fire with fire, French scientists
have suggested using one asteroid to destroy another rather than letting
Earth get pummeled.

The offbeat plan is intentionally incomplete and would allow the planet
to be showered by fragments. But it might be better than a
civilization-ending whack.

No asteroids are presently known to be on collision courses with Earth.
But existing holes in the ground suggest that inevitably one will
eventually be found. There is no firm plan for how to deflect or destroy
an incoming asteroid, though scientists have pondered firing rockets at
them, moving them gently with solar sails, or nudging them with nuclear
explosions.

Lock and load

The new idea is to capture a relatively small asteroid - perhaps 100 feet
(30 meters) wide - by sending a robot to it.

The robot would heave material from the asteroid's surface into space,
and the reaction force would gradually direct the asteroid to a Lagrange
point, one of a handful of nodes along Earth's orbit where the gravity
of Earth and the Sun balance out. Scientists know that objects can be
kept stable at a Lagrange point with little or no energy.

The captured rocky weapon would be held there, traveling around the Sun
ahead of or behind the Earth, held until needed.

Then, if a large asteroid threatens to hit us, the small one is moved
into its path, using the same heaving technique. The rocks collide, and
the big one is broken into somewhat less harmfull bits.

The collision disperses the fragments of the incoming asteroid, so that
not all of them hit the planet.

But...

Depending on the relative masses of the two objects, between 10 and 20
percent of the incoming asteroid mass would still hit, "but the
fragments would be dispersed all over the Earth and, hopefully, none
would be large enough to reach the ground with a large remaining
destructive power," said Didier Massonnet of the CNES research center in
France.

Massonnet and colleague Benoit Meyssignac say the collision should be
engineered to occur at least 620,000 miles (1 million kilometers) from
Earth and would take about eight months to execute from the Lagrange point.

The plan is detailed in the July-September, 2006 issue of the journal
Acta Astronautica. The researchers first floated it at a scientific
conference last fall.

One small asteroid that could fit the bill already been identified; it
is called 2000 SG344, and Massonnet suspects there are many others that
would work.

Fuel for thought

The researchers admit their entire scheme is not quite ready for prime time.

"We are more confident in our capability to capture the asteroid than in
our capability to redirect it to an incoming body," Massonnet told
SPACE.com. "The scenario of this last stage requires further studies on
the very unstable trajectories which will be required."

Meanwhile, there is another aspect to the plan that could make it appealing.

Material mined from a small, nearby asteroid could provide liquid oxygen
for other space missions more efficiently than mining it from the Moon,
which other researchers have proposed. Liquid oxygen could be used as
fuel at a cosmic gas station that would allow spacecraft to be launched
from Earth with much smaller tanks and therefore more cheaply.

Other researchers have suggesting mining asteroids for their metals.

"Several thousands of tons of oxygen might become available sitting on
the outer rim of Earth's gravity field," the researchers write.
Received on Tue 20 Jun 2006 09:02:20 PM PDT