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Mars 4 was one of four Soviet spacecraft of the 3MS (or M-73) series launched in 1973. Soviet planners were eager to pre-empt the American Viking missions planned for 1976 but were limited by the less advantageous positions of the planets which allowed the Proton-K/Blok D boosters to launch only limited payloads toward Mars. The Soviets thus separated the standard pair of orbiter-lander payload combinations into two orbiters and two landers.

Less than four months prior to launch, ground testing detected a major problem with the 2T312 transistors (developed by the Pulsar Scientific-Research Institute) used on all four vehicles, apparently because the factory that manufactured them used aluminum contacts instead of gold-plated contacts. An analysis showed that the transistors’ failure rate began to increase after 1.5 to two years of operation, i.e., just about when the spacecraft would reach Mars.

Despite the roughly 50 percent odds of success, the government decided to proceed with the missions. The first spacecraft, Mars 4, successfully left Earth orbit and headed toward Mars and accomplished a single midcourse correction on July 30, 1973, but soon two of three channels of the onboard computer failed due to the faulty transistors. As a result, the second midcourse correction by its main 11D425A engine could not be implemented.

With no possibility for Mars orbit insertion, Mars 4 flew by the Red Planet at 15:34 UT Feb. 10, 1974, at a range of 1,146 miles (1,844 kilometers). Ground control was able to command the vehicle to turn on its TV imaging system (Vega-3MSA) two minutes prior to this point (at 15:32:41) to begin a short photography session of the Martian surface during the flyby. (The other TV camera system known as Zufar-2SA was never turned on due to a failure). The TV camera took 12 standard images from ranges of about 1,180 miles to 1,300 miles (1,900 to 2,100 kilometers) distance over a period of six minutes. The other OMS scanner also provided two panoramas of the surface.

The spacecraft eventually entered heliocentric orbit.

Source

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

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