What ever happened to Mars Observer?
Mars Observer was a spacecraft that NASA launched in September
1992 with the same scientific instruments carried by Mars Global
Surveyor. On 21 August 1993, several days before arriving at
Mars, contact was lost with Mars Observer.
Because there were no indications of problems aboard the
spacecraft prior to loss of contact, nobody knows for certain
what happened. However, a NASA review board spent several months
investigating the loss and concluded that the most plausible
theory was that a critical failure in the propulsion system
disabled Mars Observer. The board recommended changes to the
design to prevent such an occurrence from happening on Mars
Global Surveyor.
Mars Observer most likely flew past Mars and is now in an orbit
around the Sun with an orbital period of approximately 500 days.