The Discovery Urine-cicle
During a 1984 mission on the space shuttle Discovery, the aircraft's waste water venting system failed, leading to the formation of a very large icicle made of urine on the outside of the shuttle. Realizing that the urine-cicle could break free during re-entry and damage the protective heat tiles on the shuttle, the crew used the shuttle's robot arm to break it off. The tiles were saved, but the crew had no choice but to shut the urine collection system down. The crisis was averted, but the problem left the crew without a working toilet for the rest of the six-day mission.