Introduction THE WAY OFF THE EARTH Someday, people will live on Titan, the largest moon of Saturn. Their energy will come from burning the unlimited supply of fossil fuels on its surface and their oxygen from the water ice that forms much of Titan''s mass. The nitrogen atmosphere, thicker than the Earth''s, will protect them from space radiation and allow them to live in unpressurized buildings and travel without spacesuits, in very warm clothes with respirators. They will go boating on lakes of liquid methane and fly like birds in the cold, dense atmosphere, with wings on their backs. This will happen because, at a certain point, it will make sense. Today, the cold, gloomy Titan skies are unappealing and impossibly distant. We do not yet have the technology to put people on Titan. But the technology is coming at the same time the prospects for the Earth are getting worse.

In earlier times, human beings struck out for strange and dangerous new places when their homes became intolerable. If humanity doesn''t change course on this planet, a new world free from war and climate upheaval could someday draw colonists to Titan in the same way. The technology required for a space colony is already visible. The largest barriers are institutional. An indifferent political establishment. A space agency, NASA, with a culture that squelches dissent and that lacks a coherent goal for human spaceflight. News media that have sold the public a false understanding of the real challenges of space exploration. Going to another planet will be difficult and, without breakthroughs, unacceptably dangerous.

But the ingredients for a space colony are coming together. Experience building space vehicles has spread to many countries and private industry. An Internet-spawned innovation culture that knows how to make new things fast has turned its attention to space. The concepts needed to get us there have been thought out already. When the moment comes, it won''t be the first time human beings have embarked on a voyage that seemed impossibly difficult, expensive, and technically challenging. Our kind repeatedly built new societies in places so remote as to forbid return. When we do it again, we''ll probably have reasons similar to those they had then. As authors, we have investigated science and technology as well as culture and the environment to construct our scenario about space colonization.

We have pondered the fundamental issues facing humanity: our response to technology; our will to explore, expand, and consume; and how we treat one another and treat the world we already have. The most important ingredient for space colonization is the human animal: our cellular response to cosmic radiation, our psychological ability to travel for years through nothingness, and our ecological fitness for a new landscape where no organism has lived before (at least no organism we know of). What are we? How far can we go? Scientists we interviewed often asked if we were writing science fiction or journalism. We never intended to write a work of imagination, but a skeptic would never have predicted what has already happened. We visited a rocket factory floor where private space industry workers were sewing astronaut suits that Captain James T. Kirk would have been proud to wear. Our scenario is not based on a love of cool inventions and inspiring visions. It relies on our knowledge of people''s tendency for dumb decisions, selfish drives, and messy politics.

Recognizing these predictable truths makes it easier to see how technology could unfold, and more interesting and funnier, too. We''ve had tremendous fun thinking and arguing about how this will happen. The work developed while we laughed together for many hours on Skype, Amanda at her office or kitchen table in Los Angeles and Boulder and Charles in a home office facing his snow-buried boat in Anchorage or in the Alaska wilderness. Amanda works with space technology every day. She has practiced to become an astronaut and has managed equipment to capture the scenery of a world on the other side of the solar system. She has also navigated the bureaucracy of big science, a universe of meetings, travel, and egos like any modern organization. Laboring over the myriad details of new ideas, she has helped make the miracle of space exploration real. Charles spends summers off the grid on an Alaskan beach and in winter he cross-country skis almost every day.

His books seeking to understand the fate of the planet have taken him to the Arctic pack ice with Eskimo whalers and to a Cambridge, England, aviary with supersmart birds. We''re complementary opposites. Amanda brings the science and the wonder, but also an awareness of how technology unsteadily unfolds. Charles brings the skepticism of one who has studied human tragedy on Earth, but also the optimism of one who loves the nature in us all. Amanda would eagerly accept a one-way ticket off the Earth to fulfill her drive for adventure and her vision for the future. Charles can hardly sit still through a red-eye flight and cannot imagine saying good-bye to the snow, sea, and fresh air of this world. We''ll never be rich enough to send everyone off to another celestial body, but it isn''t hard to imagine a day when governments or the very rich begin thinking of a spaceship as a lifeboat--or an ark. People are already thinking that way.

In 2008, the Svalbard Global Seed Vault opened, deep inside a frozen mountain on an island halfway between Norway and the North Pole, to preserve millions of plant lines in case of disaster or apocalypse. An off-world colony would likewise shield a store of human genes out of the way of any earthly harm. But, unlike seeds, human beings don''t stay the same when you put them in safe storage. An extraterrestrial colony might begin as an annex to Earth, preserving our species, but it would develop into a world of its own, with its own culture, government, and future. Within a generation the Earth could be a foreign place to children born under an orange sky. For them, the smell of recycled air, not fresh breezes, would carry the nostalgic sense of home. We envision their sky as orange because our scenario for this future leads us to Titan. Why Titan? We have screened each of the places colonists could go to find one where the requirements of human safety and sustenance can be met without direct support from Earth and without end.

The process of constructing a scenario led us to this wet, energy-rich object in the outer solar system. We aren''t exactly predicting that a colony will be built there, and we certainly don''t know when it will happen. A scenario is a way of organizing an investigation of the future, not a prediction. This powerful exercise generates a thought experiment that anyone can run in his or her own mind, using the hard information we provide. As you come with us through this journey into a possible future, you will find all the facts for your own thought experiment to see if your reasoning brings you to Titan, too. The book''s structure reflects this interplay of hard science and intriguing projections. Alternating sections cover reality and the future scenario. Sections labeled "Present" report the technology and ideas that already exist and tell the stories of the real people bringing space closer.

Sections labeled "Future" project a scenario that responds to forces and opportunities that seem to us likely, as well as some whimsical predictions. The book interweaves these two modes to create an integrated picture of what''s known and where that knowledge could lead. Readers are free to reach their own conclusions. Building a self-sustaining space colony is several decades and technology steps away. But many space scientists and engineers think about it, because it represents the kind of adventure that brought them into the field in the first place. And because it raises fascinating questions about today''s technology, research, and space industry. Indeed, the goal of moving people to a new planet is the strongest justification for a manned U.S.

space program. We''ve started with the current state of space science, then asked how we could get to another celestial body and build a colony there, where we would go, and why it might really happen. To be credible, the scenario must respond to these three questions--how, where, and why--with answers that are based in today''s reality. That''s why the book uses alternating sections: so the present can inform the future for each of the three questions. The question of how addresses the technology of both advanced propulsion and the design of conventional spacecraft as they become commonplace. As the business of spaceflight becomes assimilated into our everyday lives, economics holds the key. The commercial spaceflight industry is transforming our sense of possibility. Using Silicon Valley''s money and innovative confidence, it will soon bring mass space products to the market.

This industry looks something like the computer business did when Steve Jobs and Bill Gates were leaving their garages: ready for a rapid spread beyond the confines of expensive, centralized government projects and into making space travel safe, repeatable, and affordable. As that happens, the cost of lifting materials to weightlessness will fall dramatically, transforming the practicality of every space endeavor. The question of where brings out the many insights of planetary science, as well as space health, psychology, reproductive issues, and the interlocking needs of.