Since the Viking mission, a number of scientific missions to Mars have ended in failure. One particularly high-profile failure was NASA’s Mars Observer mission. Launched on September 25, 1992, it was a $1 billion mission that had a tremendous amount of scientific capability. Regrettably, on August 21, 1993, three days before it was to enter orbit around Mars, flight engineers lost contact with Mars Observer. It was never heard from again. Investigators suspect that ruptured tubing in the spacecraft’s propulsion system caused it to spin out of control.