On June 1, 1951, US Air Force Colonel John Paul Stapp sat in a sled that was poised on a 610-metre deceleration track. Moments later, rocket thrust blasted him down the track and into a braking system.
For a brief instant, Stapp endured 48 times the force of gravity, or g?s, with a rate of onset at roughly 500 g?s per second.
As his own volunteer subject, the colonel became known as the world's fastest man when on December 10, 1954, he took a bone-and-tissue-punishing 839-metre sled ride at Holloman Air Force Base in the US. In less than a tenth of a second, rockets on back of the sled sent the vehicle at 19 g?s with more than 18,000kg of thrust. Stapp's ride hit 1018 km/h - nearly supersonic speeds - before coming to a dead stop in 1.4 seconds, pushing him to 40 g?s. And, for an instant, his 76kg body weighed over 3 tonnes.
The colonel literally saw red for eight minutes as his eyeballs pushed against upper eyelids, tugging at their attachments. He also suffered double vision for 20 minutes.