We live in the Golden Age of space exploration. Humanity's achievements include the continued operation of the International Space Station, rapid advancements in reusable rockets, and soon, a return to the Moon. Within our lifetime, we might have human outposts on the lunar surface and flags flying on the plains of Mars. These strides are not just about reaching new frontiers. They have profound implications for life on Earth. The data from climate satellites overhead, innovative materials and recycling systems designed for space habitats, and emerging space-based energy solutions are essential to addressing Earth's conservation challenges. Space enables the understanding of Earth as much as Earth enables the exploration of space. This bright tomorrow is not assured, however. Space junk, international conflicts and fiscal calamities loom as threats to all that might be accomplished. For the human adventure to continue beyond the Earth's atmosphere, the time is now to reconsider the nature of sustainability.