If humans ever colonize Mars, they won’t be able to fly back to Earth for a quick shopping trip. Instead, as “Tech Live” reports tonight, space settlers will need to live in self-sustaining environments, where everything from the air they breathe to the food they eat will have to be recycled. “The food these astronauts are going to eat has to be made out of something,” said Purdue University professor James Alleman. “And that something will in fact be the waste that they’re going to generate.” Pondering how to turn garbage in space into palatable meals is what Alleman, an environmental engineering professor, does full time. He’s the co-director of the NASA Specialized Center of Research and Training for Advanced Life Support at Purdue.