From a paper on the NEOShield project...
There is currently no concerted international plan addressing the impact threat and how to organize, prepare and implement mitigation measures. We report on a new international project to address impact hazard mitigation issues, being the subject of a proposal to the European Commission in response to the 2011 FP7 Call “Prevention of impacts from near-Earth objects on our planet”. Our consortium consists of 13 research institutes, universities, and industrial partners and includes leading US and Russian space organizations. The primary aim of the project, NEOShield, is to investigate in detail the three most promising mitigation techniques: the kinetic impactor, blast deflection, and the gravity tractor, and devise feasible demonstration missions. Furthermore, we will investigate options for an international strategy for implementation when an actual impact threat arises.
From one of the articles on the NEOShield project...
In response to these worries, the European Commission recently decided to invest €4 million ($5.3 million) in the NEOShield project. An additional €1.8 million will come from scientific institutions and industry partners. Within three years' time, the experts hope to draw up a blueprint for a test mission. If it can find a financial backer, such as the European Space Agency (ESA), the mission could be launched as early as 2020.
In reality, however, a host of ideas have already been proposed for how to deal with an approaching asteroid. For example, there's the "kinetic impactor" idea, which envisions using a massive projectile to knock an asteroid off course. And there's the "gravity tractor" idea, which entails having a small probe hover near the asteroid and use its gravitational traction to deflect it from its Earth-bound course. Some have even proposed an approach to the problem that would involve launching an all-out attack with nuclear missiles.
"Of course, a lot of things have already been proposed," Harris says. "But, so far, most of them have come from a single institution, perhaps even from a single person. So it has been hard to pursue them." The new project aims to systematically investigate all of the mitigation methods that have already been proposed. "That will take place on paper and in lab experiments, since we don't have the money to do more than that," says Wolfram Lork, who handles the involvement of Astrium, a subsidiary of the European aerospace giant EADS, in the project.
Link: NEOShield paper (PDF)