Stephen Hawking hopes his weightless flight will lead to a suborbital flight some time in the future. ((Zero Gravity Corp./Associated Press))

Free of his wheelchair and tethered only to heart rate and blood pressure monitors, astrophysicist Stephen Hawking on Thursday fulfilled a dream of floating weightless on a zero-gravity jet, a step he hopes will lead to further space adventures.

The modified jet carrying Hawking, a handful of his physicians and nurses, and dozens of others firstclimbed to 7.3 kilometres over the Atlantic Ocean off Florida. Nurses lifted Hawking and carried him to the front of the jet, where they placed him on his back atop a special foam pillow.

The jet then climbed to about 9.7 km and made a parabolic dive back to 7.3 km, allowing Hawking and the other passengers to experience weightlessness for about 25 seconds.

Hawking, a mathematics professor at the University of Cambridge who has done groundbreaking work on black holes and the origins of the universe, has the paralyzing disease ALS, also known as Lou Gehrig's disease. The 65-year-old was the first person with a disability to experience the flight by Zero Gravity Corp., which has flown about 2,700 people out of Florida since late 2004.

"As you can imagine, I'm very excited," Hawking told reporters before the flight. "I have been wheelchair bound for almost four decades. The chance to float free in zero-g will be wonderful."

Unable to talk or move his hands and legs, Hawking can only make tiny facial expressions using the muscles around his eyes, eyebrows, cheek and mouth. He uses a computer attached to his wheelchair to talk for him in a synthesized voice by choosing words on a computer screen through an infrared sensor on a headpiece that detects motion in his cheek.

'I want to demonstrate to the public that anybody can participate in this type of weightless experience.' —Stephen Hawking

He raises an eyebrow to signal "yes" and tenses his mouth to the side to indicate "no."

"I want to demonstrate to the public that anybody can participate in this type of weightless experience," Hawking said Thursday.

The jet's interior is padded to protect the weightless fliers and equipped with cameras to record their adventure. Normally, the plane conducts 10 to 15 plunges for its passengers, who pay $3,750 US for the ride, although that fee was waived for Hawking. On Hawking's flight, the jet made eight parabolic dives.

The astrophysicist hopes the zero-gravity flight is a step toward going on a suborbital flight, which may be offered by private space companies by the end of the decade.

"It's a test to see how well he can handle the g-forces that would be necessary in order to leave the atmosphere," said Sam Blackburn, Hawking's assistant. "That is very much one of the major purposes of this flight."