Key points from article :
NASA and European Space Agency are working to deflect asteroids on collision course with Earth.
Double Asteroid Redirection Test (DART) is their demonstration mission planned to run in 2021.
DART will head up to the asteroid Didymos and its satellite Didymoon and try to deflect their course.
Didymos is 11 million km away and it's definitely not on a collision course with Earth.
Needs NASA's Evolutionary Xenon Thruster - Commercial ion engine (NEXT-C) to reach Didymos.
Using electric propulsion it will not need lots of thrusts to push off against Earth's gravity.