Once you find a dangerous near Earth object, what do you do with it? There are several concepts under study for destroying or deflecting NEOs, the final solution depending on how much warning time exists, plus the size and nature of the objects. These include:Deflection or destruction by stand-off nuclear explosion, most likely an enhanced-radiation device like a neutron bomb. If the NEO has a non-porous surface the explosion is expected to deflect the object, while scientists predict an explosive with a greater energy density would be needed to "evaporate" a porous NEO. Deflection using a spacecraft which attaches to the object and pushes or pulls, using its propulsion system to alter the trajectory. This approach is being proposed by the "Project B612 Foundation" that aims to "substantially" alter the orbit of an asteroid in a controlled manner by 2015. To demonstrate the concept it plans to select a 150m (490ft) diameter asteroid and deflect it by 0.2cm/sec using a spacecraft based on the Prometheus project nuclear-powered vehicle being developed for NASA's exploration of Jupiter's icy moons. The group believes a thrust of 2N would be required over about six months' continuous operation, and would be enough to prevent a collision, given 50 years' warning. Deflection by lasers carried out to rendezvous with the NEO by multi-megawatt nuclear- or plasma-powered spacecraft. These powerplants would provide the electrical power for the lasers that would ablate the surface of the NEO and gradually change its trajectory. Deflection by the creation of artificial gas jets, by focusing a large inflatable mirror keeping station with the NEO. Deflection by mass drivers or thrusters, powered by fuel processed from material mined from the asteroid itself. The concept requires the landing of astronauts to set up the mining equipment and processing systems to fuel the drivers and "de-spin" the asteroid before translational thrusting begins. A "billiards" shot strategy, where a smaller asteroid is deflected to impact and destroy a larger NEO. Proponents of this concept say the kinetic energy of the smaller "striker" is greater than that of any nuclear weapon.
Source: Flight International