This is not a question If but if a dangerously large asteroid ends with a collision course for Earth, and NASA wants to be ready. The double asteroid reversal test (DART) has been developed for several years and now has a real starting date from the award of the SpaceX contract. DART will go into space, in June 2021, to launch an asteroid onboard the Falcon 9 rocket.
DART, which is part of the NASA research initiative in the field of planetary defense, is being developed at the Applied Physics Laboratory at Johns Hopkins University. One of the most promising propositions of asteroid deviation is the kinetic impactor. If you hit an object dense and fast, it will be possible to shift its trajectory from the impact. However, we do not know many things about asteroids, even with recent missions, to examine them more closely. DART aims to find out how asteroids can behave when hit by a kinetic impactor.
The NASA deal with SpaceX has a much lower price than similar premieres. It will cost the agency only 61 million dollars, including all support and related services. It's cheap even thanks to Falcon 9 start standards, which are cheaper than competing rockets because they are fully multiple. A similar SpaceX start for the Sentinel-6A satellite from the end of 2020 will, for example, cost NASA 97 million USD.
The mission will use a fridge size impactor on a facility called Didymos. Technically, Didymos are two objects that revolve around each other. Didymos A has a diameter of about 2,600 feet (800 m), while Didymos B (sometimes called Didymoon) has a diameter of only 170 meters. Launching in 2021. It gives drives powered by a DART ion engine enough time to meet with Didymos A and B, because they pass several million miles of Earth in October 2022.
The impactor collides with Didymos B at a speed of more than six kilometers per second. This should convey the high kinetic energy of a small asteroid, allowing the scientists to assess the impact of the impact by watching how its orbit changes.
Nobody expects that Didymoon will fly into space, but the best scenario is that its orbit changes. This would indicate that kinetic impactors can reflect an asteroid. However, it is also possible that the asteroid will deform and dissipate much of the kinetic energy, in which case we will have to focus on other ways of redirecting the asteroids.