NASA's mission to deflect an asteroid has taken a step forward with the space agency moving the mission from concept development to the preliminary design phase. Though still awaiting funding by the US Congress, the Double Asteroid Redirection Test (DART) aims to demonstrate the ability to alter the trajectory of a potentially dangerous asteroid by impacting it with an unmanned spacecraft.

The chances of a large asteroid striking the Earth are tiny, but the fate of the dinosaurs shows that it's an event worth avoiding. Since 2016, NASA's Planetary Defense Coordination Office (PDCO) has been seeking, tracking, and characterizing asteroids that might be dangerous, but the agency wants to take more proactive steps than issuing warnings and advisories.

Part of the Asteroid Impact & Deflection Assessment (AIDA) mission that includes ESA's Asteroid Impact Mission (AIM) that will act as an observation platform, DART is designed to travel to the binary asteroid Didymos, named after the Greek word for "twin." It consists of a large, rocky, S-type asteroid called Didymos A with a diameter of about 780 m (2,500 ft) and the smaller Didymos B of unknown composition that's about 160 m (530 ft) across.

The idea is to use DART to test how the impact from refrigerator-sized spacecraft can deflect intermediate-sized asteroids like Didymos B. After autonomously targeting the body, DART will zero in and strike Didymos B. Meanwhile, AIM will orbit Didymos A, where it will record the impact, which will also be observed from Earth.

"A binary asteroid is the perfect natural laboratory for this test," says Tom Statler, program scientist for DART. "The fact that Didymos B is in orbit around Didymos A makes it easier to see the results of the impact, and ensures that the experiment doesn't change the orbit of the pair around the sun."

By measuring how much DART is able to alter the orbit of Didymos B, scientists will be able to assess the effectiveness of such a kinetic impact and how to improve upon it. DART's impact velocity of 13,420 mph (21,600 km/h) may not seem like much, but the idea is that by deflecting an asteroid by only a fraction of a degree while far from Earth, it will shift its path enough to miss the planet entirely.

"DART is a critical step in demonstrating we can protect our planet from a future asteroid impact," says Andy Cheng of The Johns Hopkins Applied Physics Laboratory in Laurel, Maryland, the DART investigation co-lead. "Since we don't know that much about their internal structure or composition, we need to perform this experiment on a real asteroid. With DART, we can show how to protect Earth from an asteroid strike with a kinetic impactor by knocking the hazardous object into a different flight path that would not threaten the planet."

This animation below shows how DART works.

Source: NASA