Mars 4: July 1973 - February 1974
Mars 5: July 1973 - ?

Full resolution image of a Mars 3 model (~154 K)


Mars 4 was launched by the USSR on 21 July 1973 and its twin, Mars 5, was launched 4 days later on 25 July. As Mars 4 approached the red planet on 10 February 1974, its retro-engine malfunctioned. Alas, rather than going into orbit around the planet, it went into a heliocentric orbit. However, in February 1974, the Mars 5 probe was put successfully into orbit around Mars, with apoapsis 32,560 km, periapsis 1760 km. The inclination of the orbit to the equator of the planet was 35 degrees. It took 24 hours 53 minutes to complete one orbit. Both probes contained identical sets of instruments intended to investigate the composition, structure, and properties of the Martian atmosphere and surface.

Instrumentation

Mars 4 & 5 both contained a 256-channel NaI scintillation gamma-ray spectrometer which was 63x63 mm, with charged particle rejection. It covered the energy range 1-9 MeV. The instrument was located on a boom away from the spacecraft body. Its primary objective was to measure the spectral composition of Mars' gamma-radiation. However, a series of measurements of the cosmic gamma-ray background were made during the flight from Earth to Mars. Six measurements sessions were performed at 61.2, 85.4, and 93.8 million miles from Earth.

The Mars 4 & 5 gamma-ray spectrometers found an average cosmic gamma-radiation background flux density of 1.85e4 quanta/sq-m/s. Mars 5 went on to be a great success in its primary studies of Mars.

References

Johnson 1979, Handbook of Soviet Lunar and Planetary Exploration, pp. 198-203.
Surkov, Exploration of Terrestrial Planets from Spacecraft, pp. 184-212.

Mars probe series images

Last modified: Thursday, 02-May-96 18:38:36 EDT
Web page author: Jesse S. Allen

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