Every astronaut reports back to Earth that being in zero gravity and watching our home planet is a fun and extraordinary experience. I envy and agree with them. Until your body overly adjusts to the new environment. That is, your leg muscles weaken, and your bones start to suffer osteoporosis. Earthlings have evolved and adjusted under the 1G environment, after all.
Just behind spacecraft walls is the vast space of vacuum. If space debris or a meteor punctured the thin outer skin, the crew must react quickly, awake or asleep, to avoid a certain death. Extreme heat by the direct Sun light and the extreme low temperature in the shadow also put severe stress on large scale structures.
High energy cosmic rays such as gamma rays, protons and heavy ion nucleus constantly penetrate the spacecraft and threaten the crew.
Supplying oxygen, water, and foods to sustain life does not come easily. Every gram and ounce counts. Space colonies envisioned by O'Neill in 1970s now seem to be facing fundamental challenges.
So what is the point of sending humans to Space?
My personal answer to that question is, to push the realm and the wisdom of human beings to the limit.
Studying the effects of zero gravity to the human body in long duration flights help us understand the mechanism of how life gets old on Earth. Reactions of muscles, circulation system and bones reminds us of the importance of effective physical exercises. Efforts to avoid or repair DNA damages with radiation would give rise to solve the mechanism of cancer or the secrets of cell reproductions for longevity. Observing Earth with multinational crews reminds there's no border seen from space. Developing sophisticated life support systems and building structures would one day revolutionize the living in deserts, jungles, underground or underwater.
Then you might want to ask: at what cost, by when, by whom, for whom?
I don't have the immediate answers for specific projects nor for specific organizations.
But if you look back in the human history, and think forward for the next decades or even centuries ahead, you and I would realize that we are on a same planet!
Our current technologies, economies, business models and civilizations all assume on exponential growth. Take Moore's Law for example. Or energy. Or carbon dioxide. There's an inevitable limit. So there will be a paradigm shift. There must be sustainability built into the system. To better understand the nature of the limit itself, comparing it with another world, or expanding it by visiting another planet, brings us different perspectives.
Space is our final frontier -- to push our wisdom to the limit.
5thstar is a webmaster of a group of people who were the semi-final applicants in NASDA's 1995 astronaut selection. (The National Space Development Agency of Japan or NASDA was merged with two other space agencies to become the Japan Aerospace Exploration Agency or JAXA in 2003.) Going through medical checks and interviews for an incredible week, those forty-some wannabes were tied with a unique bond of friendship. 5thstar reapplied in 1998, and became one of the eight finalists to experience an extensive psychological group survey in NASDA's isolation chamber for a week. The finalists were also interviewed by honorable astronauts at NASA Johnson Space Center in Houston, Texas. He maintains a private blog to advocate space exploration, where he posted English translations of media briefings by JAXA about MUSES-C, a.k.a. Hayabusa, when it touched down on asteroid Itokawa.