Austrian Felix Baumgartner's supersonic plunge to Earth could help determine the spacesuits worn by space tourists.
"This wasn't just a mild penetration of the sound barrier," Baumgartner's doctor, Jonathan Clark, said as the skydiver and his crew celebrated the weekend's record-breaking dive from about 24 miles (39 kilometers) up.
"It was Mach 1.24. Our ground recovery teams on four different locations heard the sonic boom," said Clark, a former high-altitude military parachutist and NASA doctor who worked on escape systems for space shuttle astronauts.
Baumgartner jumped from an altitude of 128,097 feet (39,044 meters) over Roswell, New Mexico, reaching a peak speed of about 833 mph (1,342.8 kph).
The speed of sound at that altitude is about 690 mph (1,110 kph).
His goal was to break records - highest sky dive, fastest free fall, biggest balloon to carry a person into the sky - but the feat was closely followed by doctors, engineers and scientists working to make spaceflight and high-altitude aircraft more survivable in accidents.
Clark knows the dangers firsthand.
He lost his wife, astronaut Laurel Clark, when the damaged shuttle Columbia broke apart more than 200,700 feet (61,173 meters) above ground on Feb. 1, 2003.
Before that, Clark served on a team that investigated the 1986 shuttle Challenger accident, another space disaster that claimed the lives of seven crew members.
Among those interested in data collected during Baumgartner's free fall are NASA doctors and engineers, companies developing space taxis and the Federal Aviation Administration, which oversees the fledgling commercial spaceflight industry and is deciding if spacesuits should be mandatory for space tourists.
During his sky dive, Baumgartner wore a specially made suit similar to the orange pressurised flight suits that space shuttle astronauts began using after the Challenger disaster.
Until Baumgartner's jump, the suits had never been tested in supersonic flight or certified beyond 100,000 feet (30,480 meters), the altitude that previous free-fall record holder Joe Kittinger reached in 1960.
"Felix demonstrated that you can penetrate the sound barrier," Clark said.
"He didn't just go transonic, he went supersonic. Going Mach 1.24 is incredible. That is so much further beyond any limit of human endurance. It's just amazing.
"If you had a breakup of a spacecraft during launch and got lofted to 130,000 feet (39,624 meters) and got out, you could survive and go through the sound barrier.
"Maybe it wouldn't be pretty. You might be unstable, but eventually when you got lower you would have more control."
Future space travellers also could have an emergency drogue chute packed on their suits that would automatically deploy.
"In our case, we wanted to go fast, so to break the sound barrier we didn't want to use a drogue chute," Clark said.
"But if you had a drogue chute, you would go slower, and you would be much more stable and less likely to go into a flat spin."
Sealed inside his pressurised suit, Baumgartner did not feel himself going through the sound barrier, the skydiver said after landing.
"It was like swimming without touching the water. I was fighting all the way down to regain control," he said.
"I had a lot of pressure in my head, but I didn't feel like I was passing out. I felt like I could handle it."
Doctors were not sure what blasting through the sound barrier would do to the human body.
In addition to going into an uncontrollable spin and possibly losing consciousness or worse, Baumgartner's supersonic body could have triggered dangerous shock waves that may have collided with the force of an explosion.
"I'd love to give a special one-finger salute to all those who said he was going to come apart when he went supersonic," quipped Kittinger, who served as an adviser on the project.
For the next six months or so, Clark and his colleagues will be analysing data from the dive.
"Just the physiologic monitoring system that Felix wore generated 50 million data points," Clark said.
"We have a massive amount of data to go through."