Communication with the spacecraft was lost on August 21, 1993. / Wearbeard
The Mars Observer spacecraft, also known as the Mars Geoscience/Climatology Orbiter, was a 1,018-kilogram robotic space probe launched by NASA on September 25, 1992 to study the Martian surface, atmosphere, climate and magnetic field.
The Martian orbiter was planned to expand on the vast information already gathered by the Viking program in 1975 and 1976.
During the interplanetary cruise phase, communication with the spacecraft was lost on August 21, 1993, three days prior to orbital insertion. Attempts to re-establish communication with the spacecraft were unsuccessful.
Reserve instruments flying on Mars Observer would end being used in other NASA’s mission such as Mars Global Surveyor, Mars Odyssey and Mars Reconnaissance Orbiter.
Investigations to determine the cause of the accident were not conclusive, since communication was never recovered, but suspicion focused on the failure of a valve that would have caused a fuel leak and a pressurizing failure. This would have led to a number of problems, all potentially fatal.