The Mars Observer was based on a commercial Earth-orbiting spacecraft and designed to study and take high-resolution photography of the Martian surface. In 1992, it was to be the United States' first mission to the Red Planet in 17 years.

However, the mission ended prematurly on August 22, 1993 when contact with the spacecraft was lost just before it was to enter orbit around Mars.

Scientific Instrument(s)

- Gamma Ray Spectrometer (GRS)
- Magnetometer/Electron Reflectometer (MAG/ER)
- Mars Observer Laster Altimeter (MOLA)
- Pressure Modulator Infrared Radiometer (PMIRR)
- Thermal Emission Spectrometer (TES)
- Mars Observer Camera (MOC)
- Mars Balloon Relay (MBR)