A SpaceX Falcon 9 carrying NASA’s first planetary defense test mission, the Double Asteroid Redirection Test (DART), launches from Space Launch Complex-4 at Vandenberg Space Force Base, CA, Nov. 23, 2021, at 10:21 p.m. Pacific Time. The DART spacecraft is designed to direct itself to impact an asteroid while traveling at a speed of roughly 15,000 miles per hour (24,000 kilometers per hour). Its target is the asteroid moonlet Dimorphos (Greek for “two forms”), which orbits a larger asteroid named Didymos (Greek for “twin”). In fall 2022, DART is projected to impact Dimorphos to change its orbit within the Didymos binary asteroid system. The Didymos system is the ideal candidate for DART because it poses no actual impact threat to Earth, and scientists can measure the change in Dimorphos’ orbit with ground-based telescopes. (U.S. Space Force photo by Michael Peterson)