"Well, in space there is no gravity to direct your urine away from your body when you release it. Same for poop. There is no gravity to pull it away when you release it. Menstrual fluid? At least some of it will exit a woman’s body. You don’t want that traveling around your suit.And don’t forget, you can’t always count on poop being solid, especially if you are up in space and nervous about the fact that your vehicle cabin has depressurized."
Nevertheless, NASA's ponying up a full $30,000 for your toilet thoughts, and you've got until Dec. 20, 2016 to help astronauts boldly go dookie where no one has gone dookie before: into a fancy space john that you invented.