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The M-69 series of Mars spacecraft was the first of a new generation of Mars probes designed by the Lavochkin design bureau for launch on the heavy Proton booster. Although the 1969 missions were originally meant for both Mars orbit and landing, weight constraints late in mission planning forced engineers to delete the lander and retain only the orbiter. These new probes were designed around a single large spherical tank to which three pressurized compartments were attached.

After two en route mid-course corrections during a six-month flight to Mars, the spacecraft were intended to enter orbit around Mars at roughly 1,056 x 21,127 miles (1,700 × 34,000 kilometers) at 40 degree inclination. After an initial photography mission, the probes would lower their pericenter to about 311 to 435 miles (500 to 700 kilometers) for a second imaging mission. Total mission lifetime would be about three months.

During the launch of the first M-69, the Proton’s third stage stopped firing at T+438.46 seconds after its turbopump caught on fire because of a faulty rotor bearing. The probe, scheduled to reach Mars orbit on Sept. 11, 1969, never reached Earth orbit.

Source

Siddiqi, Asif A. Beyond Earth: A Chronicle of Deep Space Exploration, 1958-2016. NASA History Program Office, 2018.

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