Working with students for 15 years has taught awarding-winning high school teacher Ed Galindo that toilet humor is a sure-fire way of getting attention. Thus was born “Fun With Urine,” the wackiest of more than 80 experiments on the space shuttle Columbia’s 16-day science mission scheduled to end on Saturday. The experiment, sponsored by Native American students from the Shoshone-Bannock Indian Reservation in rural Idaho, tackles a serious problem for the future of human space flight: how to combat depression in long-term space voyagers, Galindo said on Tuesday.