It is not a matter of if but when a dangerously large asteroid ends up on a collision course for Earth, and NASA wants to be ready. The Double Asteroid Redirection Test (DART) has been in development for several years, and now it’s got a real launch date with the awarding of a contract to SpaceX. DART will head into space to blast an asteroid in June 2021 aboard a Falcon 9 rocket.
DART, which is part of NASA’s planetary defense research initiative, is under development at the Johns Hopkins University Applied Physics Laboratory. One of the most promising proposals to deflect an asteroid is with a kinetic impactor. If you hit the object with something dense and fast, it may be possible to nudge its trajectory away from an impact. However, there’s a lot we don’t know about asteroids even with recent missions to study them up close. DART aims to learn how asteroids are likely to behave when smacked with a kinetic impactor.
NASA’s deal with SpaceX comes with a much lower price tag than similar launches. It will cost the agency just $ 61 million, including all support and related services. That’s cheap even by the standards of a Falcon 9 launch, which are less expensive than competing rockets because they’re fully reusable. A similar late 2020 SpaceX launch for the Sentinel-6A satellite will cost NASA $ 97 million, for example.
The mission will use a refrigerator-sized impactor against an object called Didymos. Technically, Didymos is two objects that orbit each other. Didymos A is about 2,600 feet (800m) in diameter, while Didymos B (sometimes called Didymoon) is a mere 560 feet (170m) across. The 2021 launch gives the ion thruster-powered DART enough time to rendezvous with Didymos A and B as they pass within a few million miles of Earth in October 2022.
The impactor will collide with Didymos B at a speed of more than six kilometers per second. That should impart a lot of kinetic energy to the small asteroid, allowing scientists to gauge the effect of the impact by observing how its orbit changes.
No one is expecting Didymoon to fly off into deep space, but the best case scenario is that its orbit does change. That would indicate kinetic impactors can deflect an asteroid. However, it’s also possible the asteroid could deform and dissipate much of the kinetic energy, in which case we’d need to focus on other ways to redirect asteroids.