NASA is crashing a spacecraft into an asteroid

NASA is going to launch a spacecraft with a single mission: smash into an asteroid at a speed of 15,000 miles per hour.

The Double Asteroid Redirection Test, or DART, is a mission that will launch early Wednesday from Earth to see if crashing a spacecraft into an asteroid would force it into a different track. If the test is successful, the results will be useful if NASA and other space organizations ever need to deflect an asteroid to rescue Earth from a disastrous collision.

The DART spacecraft is set to launch from the Vandenberg Space Force Base in California on a SpaceX Falcon 9 rocket at 1:20 a.m. Eastern time on Wednesday.

Starting at 12:30 a.m. Wednesday, NASA will provide a webcast of the launch on its YouTube account.

If the launch is delayed due to adverse weather near the Vandenberg launch site, the next opportunity for liftoff will be around 24 hours later.

Why is NASA's satellite crashing into an asteroid?

For the first time, NASA is crashing DART into an asteroid to test a form of planetary defence that could one day spare a city, or even the entire world, from a devastating asteroid impact.

DART "is something of a replay of Bruce Willis' movie, 'Armageddon,' although that was totally fictional," Bill Nelson, NASA's administrator, said in an interview.

DART will be a confirmed weapon in NASA's planetary defence arsenal if everything goes according to plan. Should another asteroid come close to colliding with Earth, the world's space agencies would be confident that an asteroid missile like DART would be able to deflect the space rock.

How will the mission be carried out?

The spacecraft will make nearly one complete circle around the sun after launch before colliding with Dimorphos, a football-field-sized asteroid that orbits a larger asteroid called Didymos every 11 hours and 55 minutes. The two asteroids are known as a binary system because one is a mini-moon to the other. Every two years, the two asteroids complete one full orbit around the sun.

The mission is mainly target practise and presents no threat to Earth. DART will collide with Earth in late September or early October of next year, when the binary asteroids will be 6.8 million miles away from Earth.

The DART spacecraft, formally known as a kinetic impactor, will direct itself right at Dimorphos four hours before impact, for a 15,000 mph head-on crash. Until 20 seconds before impact, an onboard camera will take and broadcast photographs to Earth in real time. A tiny Italian Space Agency spacecraft, launched 10 days before the hit, will fly as near as 34 miles from the asteroid, taking photographs every six seconds in the moments leading up to and following DART's impact.

How will NASA be able to tell if DART was a success?

Earth's telescopes will focus their lenses on the crash location, revealing the two asteroids as tiny reflected sunshine spots. Astronomers will track the period between one flicker of light indicating Dimorphos has passed in front of Didymos and another indicating Dimorphos has orbited behind Didymos to see if DART's collision affected Dimorphos' orbit around Didymos.

DART will have completed its mission if Dimorphos' orbit around Didymos is extended by at least 73 seconds. The impact, however, is expected to lengthen the asteroid's orbit by between 10 and 20 minutes, according to mission organisers.