Mars 7 successfully lifted off on August 9, 1973, into an intermediate Earth orbit on a Proton-K/D booster and then launched into a Mars transfer trajectory. Total fueled launch mass of the lander and bus was 3260 kg. It reached Mars on March 9, 1974. Due to a problem in the operation of one of the on-board systems (attitude control or retro-rockets) the landing probe separated prematurely (4 hours before encounter) and missed the planet by 1300 km. The early separation was probably due to a computer error which resulted from degradation of the systems during the trip to Mars. The intended landing site was . The lander and bus continued on into heliocentric orbits.