British physicist Stephen Hawking is wheeled by the people who took part in a ZERO-G flight with him at Kennedy Space Center in Cape Canaveral, Florida April 26, 2007. [Photo: Reuters]

British physicist Stephen Hawking has taken a flight that gave the renowned scientist, who is confined to a wheelchair, a taste of the weightlessness of space.

Hawking, 65, and an entourage of caretakers and other thrill-seekers took off from the space shuttle's runway at the Kennedy Space Centre in a specially modified jet that dives through the sky to give passengers an experience of zero gravity.

They returned to the space centre in Florida about two hours later after doing eight of the dives, giving him four minutes of weightlessness.

"It was amazing," Hawking said afterwards.

"Space here I come," he said, referring to his hope that the experience will prepare him for a real sub-orbital space flight in the future.

Hawking acknowledged before the flight that experiencing weightlessness, even for a few seconds, would be sweet relief from the bondage of a daily life immobilised by a debilitating and irreversible neuromuscular disorder.

"I have been wheelchair-bound for almost four decades and the chance to float free in zero G will be wonderful," Hawking told a pre-flight news conference.

The acclaimed cosmologist and best-selling author of "A Brief History of Time," who has posited theories to help explain black holes and other celestial phenomena, lost his ability for natural speech after a tracheotomy that followed a bout of pneumonia in 1985.

He speaks with the aid of a computer-controlled voice synthesizer.

Hawking said in an interview with Reuters on Wednesday that he feared that the human race did not have a future if it didn't go into space.

"I therefore want to encourage public interest in space. A zero-gravity flight is the first step towards space travel," he said.

"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," Hawking added at the news conference.

In a reference to his affliction, amyotrophic lateral sclerosis, or Lou Gehrig's disease, Hawking noted that his flight also would serve as a demonstration that "everybody can participate in this type of experience."

During these flights, participants experience at least one free-fall, lasting about 25 seconds, where they float up from the floor. The manoeuvre is accomplished as the plane flies toward the ground following a steep climb.

The ride, which normally costs $US3500 ($NZ4801), was courtesy of Florida-based Zero Gravity Corp, which operates a commercial zero-gravity service similar to what NASA uses to train astronauts.

Hawking hopes to make a suborbital spaceflight aboard a new passenger service being developed by Virgin Atlantic Airway's offshoot, Virgin Galactic, expected to begin in 2009.

Hawking's insights about black holes have opened new avenues of thinking about the nature of the universe and helped resolve troubling areas of physics where the laws of nature appear to break down.

Of all the universe's mysteries, Hawking said he would most like to know how it is that humans have come into existence.

"The universe is so big, so smooth and yet just right enough for us to exist," Hawking said in the interview.

Speaking with Hawking is a slow, meditative experience. He twitches one of the few muscles still in his control – his cheek – to scroll through word lists stored in his computer. Constructing a 35-word sentence takes 15 minutes and leaves him fatigued.

Still, Hawking doesn't wait for a question to converse.

A quip about Hawking's robotic voice having a nice British accent, prompts him to reply, "Most people think my accent is American."

Later, when asked about the prospects of intelligent life beyond Earth, Hawking said he hopes it exists.

"There is not much sign of it on Earth," he said.