When the cloud broke, the test was on. The nine rockets behind Stapp came to life. In five seconds he reached 632 miles per hour, which is about Mach 0.9. Kittinger watched at the sled outstripped his T-33. Almost as suddenly as it started, the run ended. From the moment the scoops first dug into the water, it took just 1.4 seconds for the sled to come to a complete stop. This rapid deceleration translated to more than 40 Gs, making Stapp momentarily weigh 6,800 pounds as his body slammed forward. The force of the stop was the same that a driver would feel smashing into a brick wall at 120 miles per hour.