joema said:
The Schweikart paper discussed these:
http://arxiv.org/pdf/physics/0608157
A physicist colleague of mine who works in the field of asteroid deflection was telling
me recently about a debate he had with Schweikart. He was not AT ALL impressed
with Schweikart's understanding of the problems and much of the relevant physics.
I would certainly quibble with Scweikart's contention that only the gravity tractor
deflection scheme can be "fully controlled". I would like to see more of the plans
for the "nuclear - electric" propulsion systems. What I have seen of these have
been pretty lacking in design details.
In those cases a nuclear deflection, probably using a non-fragmenting stand-off detonation, would seem the only option. The lead time to launch could be very short -- possibly months, conceivably weeks, since existing ICBMs could be used.
Many of the schemes, like gravity tractors, etc - work only in one end of the threat
spectrum - the asteroids in low eccentricity orbits that will require many orbits before
they impact Earth - hence a long enough lead time for a relatively weak application of
force to deflect the asteroid.
The gravity schemes don't work when you have asteroids or comets in highly eccentric
orbits that are "way out there"; but are heading for impact on their current orbit. These
are the ones that will offer very short lead times from the time we detect the object to
the time it has to be deflected. Those are the ones that are going to need a big push
since we don't have years for the ultimate effect of the push to accrue.
The stand-off nuclear weapon detonation would seem to be our only hope for these. This
technique will also work for the asteroids that would succumb to the gravity tractor. In
other words, the stand-off nuclear weapon detonation covers a much greater fraction of
the threat spectrum. It's even good for "rubble piles" - an object composed of many
discrete objects held together by mutual gravity. You can't push on a rubble pile with
spacecraft . Only a "body force" like a gravity tractor, or the ablation due to a stand-off
nuke will work well on a "rubble pile".
Dr. Gregory Greenman
Physicist