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Mars 8, the only Soviet/Russian lunar or planetary probe in the 1990s, was an ambitious mission to investigate the evolution of the Martian atmosphere, its surface, and its interior.

Originally planned as two spacecraft, Mars 94 and Mars 96, the missions were delayed and became Mars 96 and Mars 98. Subsequently, Mars 98 was canceled leaving Mars 96 as the first Russian deep space mission beyond Earth orbit since the collapse of the Soviet Union.

The entire spacecraft comprised an orbiter, two small autonomous stations, and two independent penetrators. The three-axis stabilized orbiter carried two platforms for pointing several optical instruments for studying the Martian surface and atmosphere.

After an initial period in low orbit lasting three to four weeks acting as a relay to the landers, the orbiter was designed to spend approximately two Earth years in a 155 x 11,185-mile (250 × 18,000-kilometer) orbit at 101-degree inclination mapping Mars.

The orbiter would have released the two 194-pound (88-kilogram) small autonomous stations (Malaya avtonomnaya stantsiya, MAS), four to five days before entering orbit. The small stations would have landed on the Martian surface, cushioned by an inflatable shell that was to split open after landing. The stations were to have transmitted data daily (initially) and then every three days for about 20 minutes each session. The stations would have also studied soil characteristics and taken photos on the surface.

The two 271-pound (123-kilogram) penetrators, each 7 feet (2.1 meters) long, would have impacted the Martian surface at a velocity of 249 feet per second (76 meters per second) to reach about 20 to 26 feet (6 to 8 meters) in depth. The plan was for the orbiter to release them between 7 and 28 days after entering orbit. During their one-year lifetimes, the penetrators would have served as nodes of a seismic network.

After launch, the Proton-K rocket successfully delivered the payload to Earth orbit after the first firing of the Blok D-2 upper stage. Initial orbit parameters were about 94 x 103 miles (150.8 × 165.7 kilometers) at 51.53-degree inclination.

At that point, the Blok D-2 was to fire once again to place Mars 8 into an elliptical orbit, after which the Fregat propulsion module (with its S5.92 engine) would have sent the spacecraft on a Martian encounter trajectory.

The Blok D-2 was to have fired at 10:57:46 UT Nov. 16 for 528 seconds, but either didn’t fire or shut down very soon after ignition, putting its precious payload into an incorrect and similar orbit of 89 x 105 miles (143.7 × 169.6 kilometers).

Mars 8 and its Fregat module then automatically separated from the Blok D-2. The latter seems to have fired (as planned earlier), placing Mars 8 in a 50 x 932-mile (80 × 1,500-kilometer) orbit that deposited the planetary probe in Earth’s atmosphere, with re-entry between 12:30 and 01:30 UT November 17, probably over southern Chile.

Various parts of the vehicle, including about 7 ounces (200 grams) of plutonium-238, must have survived the re-entry although there have been no reports of detection.

Mars 8 was scheduled to arrive in Mars orbit Sept. 23, 1997.

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