Mars Observer was a failed NASA mission to study the surface, atmosphere, interior and magnetic field of Mars from orbit. The mission was designed to operate for one full martian year (687 Earth days) to allow observations of the planet through its four seasons. However, communication with the spacecraft was lost on 22 August 1993, as it was preparing to enter orbit and no significant data was returned. Later investigation pointed to an explosion in the propulsion system caused by propellant leaking past faulty valves.