Question:How can a Near Earth Object be prevented from striking the Earth?
There are three main possibilities.
1: Deflect the object onto a new trajectory by using explosives to blow the object slightly to one side. The explosive could be delivered by a missile or by a spacecraft.
2: Place an object (such as a space craft) next to the NEO in space so that the gravity of the object will alter the trajectory of the NEO.
Although the force of gravitational attraction a spacecraft will be very small, if the change of trajectory is accomplished very far from the Earth, only a very small movement is required to cause the object to miss the Earth completely.
NB Nasa has successfully sent space probes to meet comets before - See Nasa's Deep Impact Mission for more details; So these two possibilities are not science fiction.
3. Blow the object up, so that smaller pieces hit the atmosphere that will most likely be burned up by frictional forces as they enter the atmosphere before they can hit the ground. Most of the objects that we are concerned about would be too big to blow us successfully, this is probably the last resort method.