|Mission type||Mars orbiter|
|Start of mission|
|Launch date||21 July 1973, 19:30:59UTC|
|Launch site||Baikonur 81/23|
|End of mission|
|Last contact||30 July 1973|
|Flyby of Mars (failed orbiter)|
|Closest approach||10 February 1974, 15:34 UTC|
|Distance||1,844 km (1,146 mi)|
Mars 4 (Russian: Марс-4), also known as 3MS No.52S was a Soviet spacecraft intended to explore Mars. A 3MS spacecraft launched as part of the Mars programme, it was intended to enter orbit around Mars in 1974. However, computer problems prevented orbital insertion from occurring.
The Mars 4 spacecraft carried an array of instruments to study Mars. In addition to cameras, it was equipped with a radio telescope, an IR radiometer, multiple photometers, polarimeters, a magnetometer, plasma traps, an electrostatic analyzer, a gamma-ray spectrometer, and a radio probe.
Built by Lavochkin, Mars 4 was the first of two 3MS spacecraft launched to Mars in 1973, being followed by Mars 5. A 3MS was also launched during the 1971 launch window as Kosmos 419. However, due to a launch failure, it failed to depart Earth orbit. In addition to the orbiters, two 3MP lander missions, Mars 6 and Mars 7, were launched during the 1973 window.
Mars 4 was launched by a Proton-K carrier rocket, a Blok D upper stage, flying from Baikonur Cosmodrome Site 81/23. The launch occurred at 19:30:59 UTC on 21 July 1973, with the first three stages placing the spacecraft and upper stage into a low Earth parking orbit before the Blok D fired to propel Mars 4 into heliocentric orbit bound for Mars.
Shortly after performing a course correction on 30 July 1973, two onboard computers failed, leaving Mars 4 unable to perform manoeuvres. As a result of this, it was unable to enter orbit around Mars. A small amount of data was returned as the probe flew past Mars on 10 February 1974, with a closest approach of 1,844 kilometres (1,146 mi) at 15:34 UTC.
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