With no reference points, "you don't know how fast you travel," he said.
Coincidentally, Baumgartner's accomplishment came on the 65th anniversary of the day that U.S. test pilot Chuck Yeager became the first man to officially break the sound barrier in a jet. Yeager, in fact, commemorated that feat on Sunday, flying in the back seat of an F-15 Eagle as it broke the sound barrier at more than 30,000 feet above California's Mojave Desert.
At Baumgartner's insistence, some 30 cameras recorded his stunt. Shortly after launch early Sunday, screens at mission control showed the capsule, dangling from the massive balloon, as it rose gracefully above the New Mexico desert. Baumgartner could be seen on video, calmly checking instruments inside the capsule.
The dive was more than just a stunt. NASA, an onlooker in this case with no involvement, is eager to improve its spacecraft and spacesuits for emergency escape.
Baumgartner's team included Joe Kittinger, who first tried to break the sound barrier from 19.5 miles up in 1960, reaching speeds of 614 mph. With Kittinger inside mission control, the two men could be heard going over technical details during the ascension.
"Our guardian angel will take care of you," Kittinger radioed to Baumgartner around the 100,000-foot mark.
After Baumgartner landed, his sponsor, Red Bull, posted a picture to Facebook of him kneeling on the ground. It generated nearly 216,000 likes, 10,000 comments and more than 29,000 shares in less than 40 minutes.
On Twitter, half the worldwide trending topics had something to do with the jump, pushing past seven NFL football games.
This attempt marked the end of a long road for Baumgartner, a record-setting high-altitude jumper. He already made two preparation jumps in the area, one from 15 miles high and another from 18 miles high. He has said that this was his final jump.
Red Bull has never said how much the long-running, complex project cost.
Although he broke the sound barrier, the highest manned-balloon flight record and became the man to jump from the highest altitude, he failed to break Kittinger's 4 minutes and 36 second longest free fall record. Baumgartner's was timed at 4 minutes and 20 seconds in free fall.
He said he opened his parachute at 5,000 feet because that was the plan.
"I was putting everything out there, and hope for the best and if we left one record for Joe — hey it's fine," he said when asked if he intentionally left the record for Kittinger to hold. "We needed Joe Kittinger to help us break his own record, and that tells the story of how difficult it was and how smart they were in the 60's. He is 84 years old, and he is still so bright and intelligent and enthusiastic".
Baumgartner has said he plans to settle down with his girlfriend and fly helicopters on mountain rescue and firefighting missions in the U.S. and Austria.
Before that, though, he said, "I'll go back to LA to chill out for a few days."
Garcia reported from Honolulu. He can be reached on Twitter at http://twitter.com/oskargarcia .
AP Science Writer Alicia Chang and Associated Press writer Christopher Weber in Los Angeles contributed to this report.