Mars Observer

Mission background

In October 1984, NASA approved a new Mars mission considered high priority by the Solar System Exploration Committee, originally named the Mars Geoscience Climatology Orbiter. The orbiter was intended to expand on Viking program data, providing planetary magnetic field measurements, spectral mineral signatures, surface images at 1 meter/pixel, and global elevation data. The Jet Propulsion Laboratory managed the project, handling mission design, instrument acquisition, and flight operations.

Originally planned for a 1990 Space Shuttle launch, the mission was rescheduled to 1992 due to budget concerns and priority given to other missions after the Space Shuttle Challenger disaster. Budget overruns led to the removal of a mapping spectrometer and substitution of a laser altimeter for a more complex radar altimeter. Finalized primary science objectives included determining global surface elemental and mineralogical character, topography and gravitational field, Martian magnetic field nature, temporal and spatial distribution of volatiles and dust, and atmospheric structure and circulation. The total program cost was estimated at $813 million.

Mission profile

On August 25, 1992, particulate contamination was found within the spacecraft; after inspection, cleaning was performed on August 29, with the suspected cause being measures taken before Hurricane Andrew struck Florida on August 24. Mars Observer launched on September 25, 1992, at 17:05:01 UTC from Space Launch Complex 40 at Cape Canaveral Air Force Station aboard a Commercial Titan III CT-4. A solid propellant Transfer Orbit Stage placed the spacecraft into an 11-month Mars transfer trajectory at a final speed of 5.28 km/s relative to Mars.

Orbital insertion was scheduled for August 24, 1993, but contact was lost on August 21, 1993. The likely failure cause was leakage of fuel and oxidizer vapors through an improperly designed PTFE check valve into the common pressurization system, leading to explosion and rupture after engine restart for course correction. Although primary objectives were unachieved, interplanetary cruise phase data was collected. Instruments developed for Mars Observer flew on Mars Global Surveyor (1996), Mars Climate Orbiter (1998), 2001 Mars Odyssey (2001), and Mars Reconnaissance Orbiter (2005).

The planned insertion sequence would have turned the spacecraft 180 degrees and ignited bipropellant thrusters to enter a highly elliptical orbit, followed by transfer-to-lower-orbit maneuvers over three months to reach an approximately circular, 118-minute orbit.

Communications loss

On August 21, 1993, at 01:00 UTC, three days before scheduled Mars orbital insertion, an inexplicable loss of contact with Mars Observer occurred. New commands were sent every 20 minutes in hopes the spacecraft had drifted off course, but the attempt was unsuccessful.

It is unknown whether the spacecraft followed its automatic programming to enter Mars orbit or flew by and entered a heliocentric orbit. On January 4, 1994, an independent investigation board from the Naval Research Laboratory announced the most probable cause was a rupture of the fuel pressurization tank, with hypergolic fuel leaking past valves and combining prematurely, likely causing a high spin rate that triggered contingency mode and interrupted the stored command sequence. A NASA investigation board suggested over-reliance on hardware designed for fundamentally different operations.

Did You Know?

• The spacecraft carried 1,346 kilograms of propellant for its bipropellant and monopropellant systems.
• Its solar array measured 7.0 meters wide and 3.7 meters tall, providing an average of 1,147 watts in orbit.
• The computing system could store up to 2,000 commands in 64 kilobytes of RAM and operate autonomously for up to sixty days.
• Seven scientific instruments were included, and several were successfully reflown on later missions starting with Mars Global Surveyor in 1996.