“I also want to show,” he said in an e-mail interview, “that people need not be limited by physical handicaps as long as they are not disabled in spirit.”  Coming at a time when human spaceflight is at a crossroads, his trip into space is likely to shine a giant light on the burgeoning and hopeful industry of space tourism.  NASA has redesigned the space program around finishing the International Space Station and sending people to the Moon again and then to Mars, much to the unhappiness of many scientists who fear that the growing costs of human flight will squeeze science out of the program.  Some voices, including Martin Rees, Dr. Hawking’s old friend and president of the Royal Society, have been saying that space may be explored more economically and faster by private entrepreneurs, who can take risks and weather the occasional disaster without having to worry about a Congressional cancellation of financing.  Last summer, at a news conference in Hong Kong, Dr. Hawking said humanity’s ultimate survival depended on colonizing the solar system and beyond.  “Life on Earth,” he said, “is at the ever-increasing risk of being wiped out by a disaster, such as sudden global nuclear war, a genetically engineered virus or other dangers we have not yet thought of.”  At an age when many of his contemporaries are thinking about retirement, Dr. Hawking seems determined to add yet another chapter to a tale of already legendary adventurousness and determination, not to mention scientific achievement.  He was only a graduate student at Cambridge University in the 1960s when he was found to have amyotrophic lateral sclerosis, or Lou Gehrig’s disease, which usually kills its victims in two to five years. He persevered to get his degree and become the world’s reigning expert on black holes, the bottomless pits in which gravity has crushed dead stars, space and time out of existence.  Along the way he has married twice, fathered three children (he is now a grandfather), written the best-selling “A Brief History of Time” among other books, traveled the world and appeared as a guest on “Star Trek: The Next Generation” and “The Simpsons.”  Dr. Hawking has been to the White House, the Great Wall of China and Antarctica, met the Dallas Cowboys Cheerleaders and been lowered into the pit of an underground particle accelerator. Lawrence M. Krauss, a cosmologist from Case Western Reserve University, who once took him down in a submarine, said, “Stephen is a dreamer and an adventurer who enjoys the opportunities his celebrity brings in a way that happily perhaps compensates, although only minuscule-ly, for his physical affliction.”  The image of him floating through the stars in his wheelchair has become a symbol of humanity’s restless curiosity and wonder.  Now it seems that the symbol is about to become the real thing, sans wheelchair.  Dr. Diamandis, a space entrepreneur who is a founder of the $10 million Ansari X Prize, awarded in 2004 for the world’s first private spacecraft, on which the Branson craft is based, said he had offered Dr. Hawking a ride after hearing him express enthusiasm for spaceflight.  There followed long discussions between Dr. Hawking’s doctors and the company’s to make sure that it would be safe. Almost completely paralyzed, and frail after decades in a wheelchair, Dr. Hawking long ago lost the power of speech and communicates with a computerized voice synthesizer that is controlled by his eye movements.  Zero Gravity, founded in 1993 by Dr. Diamandis and Byron K. Lichtenberg, a former astronaut, has flown some 2,500 people, only 1 or 2 percent of whom, Dr. Diamandis said, have become spacesick.  The aircraft has about 35 seats. Once the plane reaches some 24,000 feet, he said, the passengers leave their seats and lie in a large padded open area. As the plane flies its roller-coaster trajectory, they experience repeated swings between feeling heavier than normal, at the dip, and then weightless, at the peak, where they drift gently off the floor in what Dr. Diamandis, who has been on 40 or 50 such flights, described as a “really a joyous experience, almost Zen-like,” lasting about half a minute.  Dr. Hawking’s flight will probably be even shorter, Dr. Diamandis said, with the pilots consulting with Dr. Hawking and his doctors after each cycle.  In the e-mail interview, Dr. Hawking said, “I’m not worried about the zero gravity section, but the high-G part will be difficult.”  Asked what his family thought of the adventure, he replied, “My family say ‘Good on you!’ ”  A version of this article appears in print on , on Page A15 of the New York edition with the headline: Stephen Hawking Plans Prelude to the Ride of His Life. Order Reprints| Today's Paper|Subscribe
Stephen Hawking, the British cosmologist, is to take a zero-gravity ride out of Cape Canaveral on a so-called vomit comet, offering him a chance to get away from his wheelchair.