sentences:  While the design is nearly the same, the concept uses the flow of air, rather than water.In the case of the space shuttle, waste water is vented overboard into space, and solid waste is compressed, and removed from the storage area once the shuttle returns to earth.The current toilet model was first flown on STS-54 in 1993, and features an unlimited storage capacity, compared to only 14-day capacity of the original shuttle toilets, and the new model has an odor-free environment.