An on-orbit demonstration of asteroid deflection is a key test that NASA and other agencies wish to perform before the actual need is present. The DART mission is NASA’s demonstration of a kinetic impact spacecraft – the Double Asteroid Redirection Test (DART).
DART is directed by NASA and undertaken by a team led by Johns Hopkins University Applied Physics Laboratory with support from NASA Goddard Space Flight Center, NASA Johnson Space Center, and the Jet Propulsion Laboratory.
In the joint NASA/ESA AIDA mission, DART is the kinetic impactor while the ESA Asteroid Impact Mission (AIM) provides assessment capabilities. AIM would observe the asteroid before impact to determine its properties and study the effect of the collision on the double asteroid system Didymos. However, if the ESA/AIM mission is not available, the team will use telescopes and radar to assess Didymos pre impact and following the collision.
DART will be the first ever space mission to demonstrate asteroid deflection by kinetic impactor on a binary asteroid target: the smaller asteroid of Didymos, called Didymos B. Didymos is Greek for "twin." DART is planned to intercept the secondary member of the binary Near-Earth Asteroid Didymos binary system in October 2022.
The threat of asteroid impacts on Earth is statistically low, but the potential threat may be large. Recognizing this potential, in 2016, NASA formalized the Planetary Defense Coordination Office (PDCO). The office is managed in the Planetary Science Division of the Science Mission Directorate at NASA Headquarters in Washington, D.C. As a kinetic impactor, DART will demonstrate one of several techniques available for planetary defense.
Earth orbit is a dangerous neighborhood. Astronomers estimate there are about 1,000 near-Earth asteroids larger than 1 kilometer—big enough to cause a global disaster. About 90 percent of them have been identified. Far less is known about smaller asteroids. All told, about 100 tons of extraterrestrial matter falls onto Earth every day, mostly in the form of harmless dust and an occasional meteorite.
Why do we need to test the impact of an asteroid in space? Primarily, scale. An asteroid impact is not easy to replicate on Earth in a laboratory experiment. While we understand some of how craters develop, we have not observed a crater created on an asteroid. The impacts to not only the asteroid's surface structure and geology but also the orbital mechanics are key to understanding the potential success of the kinetic impact technique.
The technology goals of NASA's DART include:
Observing the change in a single asteroid's orbit is very difficult. However, a binary system like Didymos offers two points of reference: Didymos and Didymos B, thus providing more information about the effect of the DART impact on that system. Didymos will pass close by Earth in 2022 and observations of the DART impact and its aftermath by ground- and space-based assets will provide additional data. Scientists also understand Didymos system; it was observed as a radar target in 2003 and there are several observation opportunities before the DART impact in 2022. Didymos has been spectrally classified as an S-type asteroid, suggesting that its composition is similar to very common ordinary chondrite meteorites and that its physical properties are shared by a large fraction of objects classified as Potentially Hazardous Asteroids (PHA).