Stephen Hawking floats freely aboard Boeing 727 jet sponsored by Zero Gravity Corporation

The British astrophysicist Stephen Hawking is renowned for his exploration of the mysteries of the cosmos, from the frontiers of outer space to the nature of black holes. He is also a strong advocate for a manned space program that can take humans into the outer reaches of our solar system.

Stephen Hawking is trapped in his paralyzed body. But about a year ago, the 66-year old scientist, who suffers from a degenerative neurological disease, left his wheel chair, and, dressed in a dark blue flight suit, embarked as a passenger on a memorable plane ride. As the aircraft climbed to 9100 meters and carved parabolic arcs in the sky, Hawking floated free in zero gravity. "It was amazing. The zero part was wonderful. I could have gone on and on. Space, here I come!"

University of Cambridge professor Stephen Hawking delivers speech in honor of NASA's 50th Anniversary at George Washington University

Hawking brought that enthusiasm to an audience at George Washington University on the 50th anniversary of the U.S. space agency, NASA. Speaking through a computer-driven voice synthesizer, he called for a new era in space exploration that he likened to the European discovery of the New World in 1492. "It will completely change the future of the human race and maybe determine whether we have any future at all."

Hawking proposes establishing a base on the Moon within 30 years, reaching Mars within 50 years and traveling to the moons of outer planets within 200 years. He says these efforts would give the space program a new sense of purpose. "The low esteem in which science and scientists are held is having serious consequences. We live in a society that is increasingly governed by science and technology, yet fewer and fewer young people long to go into science."

"George's Secret Key to the Universe"

Known for his insatiable curiosity about the cosmos, Hawking wonders whether or not we are alone in the universe. He considers three possibilities:

One is that there are no suitable planets on which even primitive life could evolve.

Another is that primitive life might have evolved, but not intelligent life.

Or third, that intelligent life developed but then wound up destroying itself.

"Let's hope that this [third possibility] is not the reason we have not heard from anyone," he jokes. He says he favors the possibility that primitive life is relatively common, but that intelligent life is very rare. "Some would say it has yet to occur on Earth."

Stephen Hawking and daughter Lucy collaborate on new children 's book "George's Secret Key to the Universe"

Human survival in the solar system, Hawking says, requires that we have access to such vitals as air and water and energy. He adds that a significant fraction of stars have planets around them and some may have liquid water on their surfaces. "There are around 1000 stars within 30 light years of Earth. If one percent of each had Earth-size planets in the zone, we would have 10 candidate new worlds."

Hawking says interstellar exploration should be the long-term goal of the next 500 years, a brief period compared to the two million year history of human life on earth. "Civilization began about 10,000 years ago, and the rate of development has been steadily increasing. If the human race is to continue for another million years, we will have to boldly go where no one has gone before."

Hawking says that while the search for new worlds may not solve any immediate problems on earth, "It would give us a new perspective on them and cause us to look inwards and outwards," as we face our common challenges.