Mission Type: Lander
Launch Vehicle: Proton booster plus upper stage and escape stages, 8K82K + Blok D (Proton-K no. 281-02)
Launch Site: Tyuratam (Baikonur Cosmodrome), , USSR, NIIP-5 / launch site 81P
Spacecraft Mass: 3,260 kg at launch
Spacecraft Instruments:
Bus: 1) magnetometer; 2) plasma traps; 3) cosmic-ray sensors; 4) micrometeoroid detectors; 5) Zhemo instrument for study of solar proton and electron fluxes and 6) Stereo antenna
Lander: 1) thermometer; 2) barometer; 3) accelerometer; 4) radio-altimeter; 5) mass spectrometer and 6) soil analyzer
References:
Deep Space Chronicle: A Chronology of Deep Space and Planetary Probes 1958-2000, Monographs in Aerospace History No. 24, by Asif A. Siddiqi

National Space Science Data Center, http://nssdc.gsfc.nasa.gov/

Solar System Log by Andrew Wilson, published 1987 by Jane's Publishing Co. Ltd.

Mars 7 was the last of the four Soviet spacecraft sent to Mars in the 1973 launch window (although it arrived at Mars prior to Mars 6). On its way to Mars, the spacecraft performed a single midcourse correction on 16 August 1973. En route to Mars, there were failures in the communications systems, and controllers were forced to maintain contact via the only remaining radio communications complex.

On 9 March 1974, the flyby spacecraft ordered the lander capsule to separate for its entry into the Martian atmosphere. Although the lander initially refused to accept the command to separate, it eventually did accept it. Ultimately, the lander's main retro-rocket engine failed to fire to initiate entry into the Martian atmosphere. As a result, the lander flew by the planet at a range of 1,300 kilometers and eventually entered heliocentric orbit. The flyby probe did, however, manage to collect data during its short encounter with the Red Planet.

The failures on both Mars 4 (computer failure) and Mars 7 (retro-rocket ignition failure) were probably due to the faulty transistors, installed in the circuits of the onboard computer, which were detected prior to launch.