Deflection – Nuclear
Nukes effective -- one-size fits all deflector
NASA ’06 (“2006 Near Earth Object Survey and Reflection Study”, Nasa Office of Program Analysis and Evaluation, Pg. 131-132, December 28, 2006, http://www.b612foundation.org/papers/NASA-finalrpt.pdf, TDA)
The use of nuclear explosives was found to be the most effective alternative in the near term. While an explosion on or below the surface of a threatening object is 10-100 times more effective than a detonation above the surface, the standoff detonation would be less likely to fragment the target. Nuclear options require the least amount of detailed information about the threatening object. A nuclear standoff mission could be designed knowing only the orbit and approximate mass of the threat, and most impulsive missions could be carried out incrementally to reach the required amount of deflection. Additional information about the object's mass and physical properties would perhaps increase the effectiveness, but likely would not be required to accomplish the goal. The study examined conventional explosives, but found they were ineffective against most threats.
Nuclear explosions could deflect solid PHOs. For non-solid asteroids, gravity tractors will be used because explosions will have lesser effects.
Bucknam, Mark and Robert Gold in 8 (Former Council Military Fellow, Survival, Asteroid Threat? The Problem of Planetary Defence, http://web.ebscohost.com/ehost/pdfviewer/pdfviewer?sid-4d559d5c-113d-420a-befe-99ff529968a5%40sessionmgr11&vid-6&hid-10, DF)
If two objects are on a collision course, it is necessary only to speed up, or slow down, one of them early enough to prevent the collision. Changing Earth’s orbital velocity would likely be impossible; it is, however, theoretically possible to change the orbital velocity of a smaller PHO. The smaller the PHO, the easier it would be to affect its velocity, and the earlier attempts were made, the smaller the required change would be to avert a collision. NASA’s March 2007 report stated plainly that using stand-off nuclear explosions to deliver an impulsive force to a PHO would be 10–100 times more effective than other means of deflecting PHOs. Nonetheless, other tools and techniques, including kinetic impactors, gravity tractors, focused solar and laser energy, and rockets to change a PHO’s orbital velocity were identified and analysed An asteroid resembling a massive pile of sand and gravel might be impossible to push with a rocket or to affect by slamming into it with a kinetic impactor. However, a gravity tractor could, theoretically, hover nearby and – using the gravitational pull between itself and the rubble pile – fire rockets to gradually pull the pile faster or slower in its orbit. The gravity-tractor scheme is the least efficient and least technologically mature option. Indeed, NASA concluded that a gravity tractor would likely prove useful only for the smallest PHOs, and even then decades would be needed for the tractor to effect the desired change in velocity. However, for cases where only a very small deflection is required – keeping Apophis from hitting the gravitational keyhole in 2029, for example – the gravity tractor may be the simplest solution.
With limited warning time nuclear weapons can destroy a dangerous asteroid
Tyson in 95 (Peter Tyson is the Managing Editor of Earthwatch and a contributor to Technology Reviw, Technology Review vol. 98 iss. 2, Cometbusters, http://proxy.foley.gonzaga.edu/login?url-http://search.ebscohost. com/login.aspx?direct-true&db-a9h&AN-9502076494&site-ehost-live) DF
Physicists agree that the only way to generate enough energy to deal with a large object on short notice would be with a nuclear device. "A nuclear weapon has the highest energy per unit mass, and we're limited right now by the amount of mass we can put in space," says Gregory Canavan, a physicist at Los Alamos National Laboratory who coedited the proceedings of the 1992 NASA interception workshop. Either a U.S. Titan missile or a Proton, which the Russians routinely use to launch military payloads into low-earth orbit, could be used as a booster rocket, he says. To ensure that the object or objects were destroyed and not merely fragmented, with pieces still raining down on earth, Edward Teller, the developer of the hydrogen bomb, says simply that he would send up enough explosives to make sure the job was done right. "In other words," he says, "we are very sick, I have a cure, and my only concern is to achieve overkill."
Early Detection key
Now is key- by developing deflection now, we have time to implement methods to deal asteroids over time rather than in an emergency situation.
Lu and Love ’05 (Lu: B.S. electrical engineering from Cornell University, PhD in applied physics from Stanford University, NASA missions specialist. Love: BS in physics from Harvey Mudd College, masters in scince from University of Washington, PhD in philosophy, NASA astronaut, “A Gravitational Tractor for Towing Asteroids”, 9/20/05, http://arxiv.org/abs/astro-ph/0509595v1, AG)
The mean change in velocity required to deflect an asteroid from an Earth impact trajectory is ~3.5×10−2 /t m/s where t is the lead time in years4. Thus, in the example above, a 20 ton gravitational tractor can deflect a typical 200m asteroid, given a lead 2 time of about 20 years. The thrust and total fuel requirements of this mission are well within the capability of proposed 100kW nuclear-electric propulsion systems2, using about 4 tons of fuel to accomplish the typical 15 km/sec rendezvous and about 400 Kg for the actual deflection. For a given spacecraft mass, the fuel required for the deflection scales linearly with the asteroid mass. Deflecting a larger asteroid requires a heavier spacecraft, longer time spent hovering, or more lead time. However, in the special case where an asteroid has a close Earth approach followed by a later return and impact, the change in velocity needed to prevent an impact can be many orders of magnitude smaller if applied before the close approach5. For example, the asteroid 99942 Apophis (2004 MN4), a 320m asteroid that will swing by the Earth at a distance of ~30000km in 2029, has a small 10−4 probability of returning to strike the Earth in 2035 or 20366. If it indeed is on a return impact trajectory, a deflection ∆v of only ~10−6 m/s a few years before the close approach in 2029 would prevent a later impact (Carusi, personal communication). In this case, a 1 ton gravitational tractor with conventional chemical thrusters could accomplish this deflection mission since only about 0.1 Newtons of thrust are required for a duration of about a month. Should such a deflection mission prove necessary, a gravitational tractor spacecraft offers a viable method of controllably steering asteroid 99942 Apophis away from an Earth impact.