I don’t think the human race will survive the next 1,000 years, unless we spread into space. There are too many accidents that can befall life on a single planet. But I’m an optimist. We will reach out to the stars. So said cosmologist Stephen Hawking last year. Optimist or not, it is clear there are many formidable hurdles to clear before we will be able to live for extended periods away from Earth. It may take centuries before we have truly colonized space, but the prospect — especially after the Space Shuttle Atlantis returned to Earth last week — no longer belongs to science fiction.