DART (Double Asteroid Redirection Test) is a spacecraft designed to test a possible strategy for protecting Earth against an asteroid on a collision course. Launched November 23, 2021, it will encounter a double asteroid on September 26, 2022. The larger member of the system, Didymos, is a half-mile in diameter. Its companion, Dimorphos, is only about a tenth of a mile across. DART will hit Dimorphos head on, at a speed of about 15,000 miles (25,000 km) per hour. The impact should change the smaller space rock’s orbit. Astronomers will use several telescopes to track the impact and its aftermath to see how much the orbit changes. The goal is to help determine if we could deflect an asteroid on a collision course with Earth. One way to do so would be to ram objects into it at high speeds. DART is the first test to see how well that might work. It is expected to shorten the length of Dimorphos’s orbit by several minutes.