Physicist Stephen Hawking, the wheelchair-bound theorist known for his insights into the nature of black holes and gravity, experienced weightlessness today during an eagerly anticipated airplane ride off Florida's East Coast.

Credit: Zero Gravity Corp.

Attended by a team of physicians, nurses and supporters, Hawking enjoyed 20 to 25 seconds of weightlessness during eight parabolic arcs aboard the Zero Gravity Corp.'s Boeing 727 jet. Passengers on such flights are weightlessness as they "fall" toward Earth inside the plane's foam-padded interior.

At the bottom of each arc, the nose of the plane is pulled up, briefly subjecting the passengers to about 1.5 times the force of gravity. Hawking, who suffers from amyotrophic lateral sclerosis, or ALS - Lou Gehrigs Disease - was closely monitored throughout the afternoon flight. After returning to the Kennedy Space Center's shuttle runway, he was all smiles and officials said he enjoyed the ride.

"Many people have asked me why I am taking this flight," the renowned physicist told reporters earlier today at the Shuttle Landing Facility. "I am doing it for many reasons. First of all, I believe that life on Earth is at an ever increasing risk of being wiped out by a disaster, such as sudden global warming, nuclear war, a genetically engineered virus or other dangers.

"I think the human race has no future if it doesn't go into space. I therefore want to encourage public interest in space," he said, speaking through a computer in his famously robotic "voice." "I have long wanted to go into space and the zero gravity flight is a first step toward space travel. I also want to demonstrate to the public that everyone can participate in this type of weightless experience."

Peter Diamandidis, president of Zero Gravity Corp., said the flight was organized to benefit four charities - Easter Seals, the Starlight Starbright Children's Foundation, Augie's Quest and the X Prize Foundation. Eight seats were auctioned off, raising some $150,000. Rides on the plane normally sell for $3,500 per passenger.

"We're really excited," Diamandis said. "The entire team is pumped and ready to go to fulfill his dream of being weightless."

To ensure's Hawking's safety, the physicist was closely monitored by his personal team of physicians and nurses. During a test flight Wednesday using an eighth grade student as a stand in, the team perfected the way they will gently lower Hawking to the padded floor after each parabola to make sure he remains comfortable during the half-minute or so when he will be subjected to 1.5 times the normal force of gravity.

"We've done a tremendous amount to ensure safety on this flight," Diamandis said. "We feel we have an excellent safety plan."

Diamandis said Hawking's doctors planned to assess blood pressure, oxygen levels and other factors after the first parabola to make sure it is safe to proceed. Diamandis said he would be happy with a single parabola, prompting Hawking to interject a computer-synthesized "no!"

"As you can imagine, I am very excited," Hawking said earlier. "I have been wheelchair bound for almost four decades and the chance to float free in zero G will be wonderful."

Hawking is considered one of the world's leading authorities on quantum black holes and big bang cosmology. Along with his scholarly achievements, Hawking is the author of the popular bestseller "A Brief History of Time."