A famous astrophysicist (and guitar player) tells all about an ambitious mission to save humanity from asteroids, should one ever threaten Earth.

Brian May — lead guitarist and a songwriter with the band Queen — recently discussed the European Space Agency mission Hera in a new video. Hera — along with a NASA mission called the Double Asteroid Redirect Test (DART), will both visit an a double asteroid called Didymos.

"Imagine a mountain in the sky, with another rock about the size of the Great Pyramid swinging around it," May said in the video. "That's Didymos. Just the seemingly tiny world is big enough to destroy a city."

Related: Humanity Will Slam a Spacecraft into an Asteroid in a Few Years to Help Save Us All

Meanwhile, two spacecraft are examining asteroids up close right now. NASA's OSIRIS-REx (Origins, Spectral Interpretation, Resource Identification, Security, Regolith Explorer) is orbiting asteroid Bennu, while the Japanese spacecraft Hayabusa2 is at asteroid Ryugu. Both spacecraft are expected to bring samples back to Earth for further analysis.

Animations showed the spacecraft zooming by Didymos and its moon, which is temporarily called Didymos B until the International Astronomical Union decides on a name. May said the mission would be "really, really hard," because the goal is for DART to deflect the moon — to change its path in space, which no other mission has ever done before.

The plan calls for DART to launch in 2021, then slam into the moon in September 2022 at more than 13,320 mph (21,440 km/h). Ground telescopes will monitor how much DART changes the orbit of the moon so scientists can compare with their estimates.

Hera will follow, launching in 2024 and arriving in 2026, to examine the impact crater DART leaves behind. The mission would also deploy a couple of small cubesats that will approach the asteroid and eventually land on the surface.

"The scale of this experiment is huge. One day these results could be crucial for saving our planet," May said. "If an asteroid ever poses a real threat to Earth, we'll be ready."

Hera and DART together form the Asteroid Impact and Deflection Assessment (AIDA) mission. The concept has undergone some change over the years. Initially, the Europeans planned to fly a larger spacecraft called the Asteroid Impact Mission (AIM). In late 2016, however, the European Space Agency cancelled AIM to free up more funding for the ExoMars program, which will be launching a Mars rover mission in the summer of 2020.

While AIDA continues through the planning and development stages, astronomers are keeping a close eye on asteroids in other ways. Several ground-survey telescopes monitor the sky for potential threats, and NASA has established a Planetary Defense Coordination Office that would come up with a plan should any asteroid imminently threaten Earth.

Follow Elizabeth Howell on Twitter @howellspace. Follow us on Twitter @Spacedotcom and on Facebook.