The rocket would then coast on momentum to about 100 miles (160 km) before nosing down for reentry. The second stage engine would then fire before jettisoning and igniting the third and final stage. On April 24, 1957, an X-17 reached a speed of 9,000 miles per hour (14,000 km/h) at Patrick AFB.[1] Ultimately the X-17 would be travelling towards Earth at up to Mach 14.5.