J-2 engines powered the second and third stages of the Saturn V. In stage 2, a cluster of five J-2 engines took over at an altitude of about 38 miles and boosted the rocket to 114.5 miles, increasing its speed from 6,000 miles to 15,300 miles per hour. Unlike other liquid-fueled engines used in the Apollo program, J-2 engines could be restarted, a capability used on the Saturn V third stage. A single J-2 engine boosted the spacecraft into low-Earth orbit, and after performance checks it was reignited for translunar injection, a 6.5-minute burn that accelerated the vehicle onto a course for the Moon. J-2 engines were used on the Saturn IB and Saturn V rockets for launches from the late 1960s through the mid-1970s, including Apollo spacecraft tests, the three Skylab missions, and the Apollo-Soyuz Test Project.