Stephen Hawking to go weightless in April

Concerns about medical condition
Hawking's safety is the top concern for the flight aboard Zero Gravity's jet, Diamandis said.

Parabolic flights can pose a risk of motion sickness or more serious health effects, but Zero Gravity's flights have been structured to minimize the risk. During a typical flight, Zero Gravity's "G-Force One" jet makes a gradual transition to weightless parabolas, and provides significantly fewer bouts of weightlessness than NASA's "Vomit Comet" jet.

Hawking would board the plane in his wheelchair, just as he boards any commercial jet. When the jet reaches about 20,000 feet in altitude, "his assistants will carry him from his seat into the float zone," Diamandis said. He would lie down with medical attendants at his side and coaches at each of his four limbs, then wait for the weightlessness to take effect.

"He will be floating free of his wheelchair — I assume in his flight suit," Diamandis said.

Hawking would be closely monitored during each parabola, and would have to signal his go-ahead for each succeeding bout of weightlessness, Diamandis said. "Our goal is to do three — and if he ends up doing more, so be it," he said.

When the parabolas end, Hawking would be returned to his seat for a normal airplane landing.

This chart shows the flight profile for the Zero Gravity parabolas. Each peak provides 25 seconds of weightlessness, but each valley makes you feel 1.8 times heavier than you do on the ground.

Jay Buckey, a physician and former astronaut who is now a professor at Dartmouth Medical School, said Hawking would face a "good side and a bad side" during a zero-G flight.

"Being weightless like that doesn't require you to have that much strength in your limbs, so in that sense it would be freeing," he told MSNBC.com. However, the fluctuations between weightlessness and a double dose of gravity could put extra stress on Hawking's cardiovascular system, he said.

The potential for injury would be another concern, said Jon Clark, space medicine liaison at the Houston-based National Space Biomedical Research Institute. Clark, who has flown on Zero Gravity's plane as well as NASA's zero-G jet, said fliers are prone to crash into things, particularly when gravity returns at the end of each parabola. That could pose a special threat for Hawking. "You do have to wonder how fragile his bones are, having been in that condition for so many years," Clark told MSNBC.com.

Looking beyond the immediate health concerns, Clark said Hawking's flight could contribute to the field of space medicine.

"There's so little insight into these kinds of issues," he said. "I hope they thoroughly study him, because it's breaking new ground."

A model for people with disabilities
When the possibility of a zero-G adventure first came up in November, McMahon told MSNBC.com that his company would be honored to provide a free flight in recognition of Hawking's "unique contribution" to science. The Cambridge professor has focused on the farthest frontiers of cosmological theory, addressing the nature of black holes and our quantum universe.

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McMahon said Hawking's flight also could serve as a model for accommodating other people with disabilities, on zero-gravity airplane flights as well as future space trips. "If you're bound to a wheelchair, there's nothing more exciting than being able to float free," he said back in November.

Andrew Imparato, president and chief executive officer of the American Association of People with Disabilities, said a successful zero-gravity flight would send a positive message not only to wheelchair-users, but to society at large.

"There are parallels to having the first woman in space, or the first African-American in space," Imparato told MSNBC.com this week. "For somebody who has a significant disability to do that, pushing the boundaries of the human experience ... it can certainly expand the way people think about disabilities."

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