Your flight to Mars, cosseted inside a “pod,” costs at the most $18.50. Children and seniors will be able to traipse across the red rock for only $14. “Space: A Journey to Our Future” opens today at the Pacific Science Center in Seattle. And it is a trip. At the Mars “base camp,” you meet Beth, an Earthling. She tells visitors she spent six months traveling 450 million miles to reach Earth’s neighbor. She hangs out in the base camp, which is equipped with sleeping shelves and computers (will there be e-mail on the Red Planet?) and decorated with snapshots of Beth’s pets and relatives back home. She and her comrades grow their own food in a greenhouse.