DART will be the first mission to demonstrate and test the effectiveness of slamming a spacecraft into an asteroid to change it orbit. The mission is considered a critical step in planetary defense preparations should the need to deflect an asteroid on a collision course with Earth arise. Per the NASA announcement, the launch contract with SpaceX is worth $69 million and will see SpaceX launch the DART spacecraft on a Falcon 9 rocket from SLC-4E at Vandenberg Air Force Base, California, in June 2021. A launch in that time frame will allow DART to intercept the asteroid Didymos, specifically its small moon, in October 2022 when the asteroid will be within 11 million kilometers of Earth. This intercept time is crucial as ground-based telescopic observations and planetary radar will have to be used to measure the change in momentum imparted into Didymos and its moon to determine the effectiveness of the asteroid kinetic impact deflection technique. Therefore, the mission’s entire purpose is to slam the 500 kg DART spacecraft into Didymos’ small moon at a velocity of approximately 6 kilometers per second. The impact will change Didymos’ moon’s orbital velocity by 0.4 mm/s – which will in turn change the gravitational balance the asteroid system currently enjoys and alter Didymos’ solar orbital velocity by 0.5 mm/s – or 10 minutes per solar orbit. While that may not appear to be much of a change, if the same velocity change were imparted to a hazardous, Earth-bound asteroid, it would mean the difference between the asteroid hitting Earth and missing Earth by tens of thousands of kilometers. For clarity, Didymos is not an Earth-hazardous asteroid, and altering its orbit by such a small amount will not cause it to become a threat. Therefore, it is the perfect target asteroid for this type of kinetic deflection test. Due to its only mission objective being to slam into Didymos’ moon in a mission-ending impact, DART will not carry scientific instruments and will instead only bear a Sun sensor, a star tracker, and a 20 cm aperture camera for autonomous navigation to its impact target. The DART spacecraft. (Credit: NASA/JPL) NASA’s primary DART mission page, which has not yet been updated to reflect the contract award to SpaceX and the new launch date, shows the mission was originally expected to launch between December 2020 and May 2021 as a rideshare on a commercial or military mission where the primary payload was heading to Geostationary Orbit.