A few decades from now, space travelers living on Mars may think the Pilgrims had it easy. The pioneers who make the 80-million-mile, three-year journey to Mars and back will probably not have the just-add-water-and-heat packaged foods that are aboard the international space station, where the crew orbiting Earth will prepare a traditional Thanksgiving dinner today of turkey, mashed potatoes, corn, green beans and cherry-blueberry cobbler. NASA’s Johnson Space Center is working on a project to send humans back to the moon, and from there to Mars.