Nobody likes thinking about the environmental impact of space travel. The environmental movement is admirable, but it’s tied to unstinting realism—you can’t have everything. You have to moderate packaging, energy use, living space, and modes of travel. Everything has a cost, and that cost has to be minimized, even though it can’t be eliminated. Meanwhile, space travel lends itself to the excesses of the imagination. It’s an endless universe full of new worlds and possibilities. One of those possibilities—tourists heading off into space—seems close to coming true.