Mars 1969A and 1969B

The M-69 project was an attempt to use the Soviet Union's new heavy rocket, the Proton, to do something nobody had done: put a spacecraft into orbit around another planet. Everything sent to Mars before 1969 had been a flyby, a single fast pass giving a few hours of useful observation before the planet fell behind. An orbiter could watch Mars for months. Chief designer Georgy Babakin approved a preliminary design at NPO Lavochkin in November 1967, built around hardware borrowed from the E-8 lunar lander programme, but the borrowed design would not hold. Endurance tests showed the elastic membranes that pushed propellant out of the tanks could leak on a six month cruise, the centre of gravity shifted unpredictably as propellant drained, and the thermal system could not keep the avionics cool. Babakin threw the architecture away and started again roughly thirteen months before the window opened. The replacement was built around a lenticular propellant tank with a metal membrane (NSSDCA's description of the flown vehicle instead calls the tank spherical), with two solar wings totalling seven square metres, a 2.8 metre dish and three pressurised compartments. A 260 kilogram entry capsule survived into the new design, to be released from Mars orbit rather than on approach, but the vehicle kept gaining weight and there was no time left to drop-test the capsule from a high-altitude balloon, so the landing was cut. The approved design carried thirteen instruments weighing 99.5 kilograms in total, 15 of those kilograms on the deleted lander, so what flew was an orbiter with roughly 85 kilograms of instruments, including a film camera that could store 160 pictures.

The first M-69 lifted off from Pad 23 at Site 81, Baikonur, on 27 March 1969 at 10:40:45 UTC, which was 13:40:45 by Moscow time. Loudspeakers at the site called the milestones: pitch, yaw and roll within limits, first stage separated, fairing separated, second stage separated. Then the announcements stopped, and after a pause came two words, no signal. The Proton's third stage had shut down 438.66 seconds into the flight after a fire in its turbopump, traced to an imbalance in the pump rotor, and then exploded. What was left came down in the Altai mountains of southern Siberia. Asif Siddiqi's NASA chronology puts the shutdown at T+438.46 seconds; the figure of 438.66 appears in both NASA's own NSSDCA catalogue and Anatoly Zak's Russian-sourced account, and that is the one used here. The timing was particularly hard to take. Later the same day, at 22:22:01 UTC, NASA launched Mariner 7 from Cape Kennedy, the second American Mars flyby of the season, and it worked; Mariner 6 had already left on 25 February. Had the Soviet craft flown, it would have entered a 1,700 by 34,000 kilometre orbit inclined 40 degrees on 11 September 1969, then lowered its closest approach to between 500 and 700 kilometres for roughly three months of photography.

The second spacecraft went up from Pad 24, a few hundred metres from where the first had left, on 2 April 1969 at 10:33:00 UTC. At T+0.02 seconds one of the six RD-253 engines in the Proton's first stage failed. The investigation found that a drain port in the oxidiser pump cover was missing its hydraulic lock plug, so oxidiser gas rushed into the cavity behind it and set the pump shaft alight. The control system compensated and the rocket climbed on its five surviving engines. Major General Vasily Shirshov, watching, described it rising about a hundred metres and then settling back with the engines still firing, as though trying to carry itself clear of the pad. Perminov, watching from the same site, remembered black smoke from an engine and then a dense, luminous mass of fire. The published accounts diverge on the numbers. NASA's catalogue and the Russian-language record say the vehicle held on for about twenty-five seconds and reached roughly a kilometre before tipping toward the horizontal, that the engines then shut down, and that it struck nose first at T+41 seconds about three kilometres from the pad. Zak has it down at about thirty seconds just outside the fence at the western corner of Site 81, narrowly missing Pad 23. Both agree on the fireball. The complex itself came through essentially undamaged; the nearest real casualty was the glass in the assembly and test building. It was the seventeenth Proton flight.

That ended the 1969 window and the M-69 project. Only two spacecraft had been built, so there was nothing left to launch, and the next chance to reach Mars was two years away. The loss mattered beyond the two vehicles. M-69 was meant to pin down two numbers the Soviet programme badly needed: a precise Martian ephemeris, so a lander could be aimed accurately, and the atmospheric pressure at the surface, so a parachute could be sized. Without them the 1971 missions carried those uncertainties with them. Vladimir Dolgopolov, one of the leading designers, later remembered the pair as, in his words, "examples of how not to make a spacecraft", and Siddiqi records the engineers' own view that even a clean launch would probably not have produced a working mission, given how fast the hardware had been assembled. What survived was the architecture. The lenticular tank, the pressurised instrument compartments and much of the instrument set went into the M-71 series, which flew in 1971 as Kosmos 419, Mars 2 and Mars 3. The first spacecraft actually to orbit Mars turned out to be American: Mariner 9, which arrived on 14 November 1971 UTC, two years and two months after the date M-69 No. 521 had been aiming for.