The Mars 2 and Mars 3 missions consisted of identical spacecraft, each with an orbiter and an attached lander. The orbiters' primary scientific objectives were to image the martian surface and clouds, determine the temperature on Mars, study the topography, composition and physical properties of the surface, measure properties of the atmosphere, monitor the solar wind and the interplanetary and martian magnetic fields, and act as communications relays to send signals from the landers to Earth. Mars 2 and 3 were launched by Tyazheliy Sputniks.
Mars 2 released the descent module 4.5 hours before reaching Mars on November 27 1971. The descent module entered the martian atmosphere at roughly 6.0 km/s at a steeper angle than planned. The descent system malfunctioned and the lander crashed at 45 deg S, 302 deg W, delivering the Soviet Union coat of arms to the surface. Meanwhile, the orbiter engine performed a burn to put the spacecraft into a 1380 x 24,940 km, 18 hour orbit about Mars with an inclination of 48.9 degrees. Scientific instruments were generally turned on for about 30 minutes near periapsis.
Mars 3's descent module was released at 09:14 UT on December 2 1971, 4 hours 35 minutes before reaching Mars. The descent module entered the martian atmosphere at roughly 5.7 km/s. Through aerodynamic braking[?], parachutes, and retro-rockets, the lander achieved a soft landing at 45 S, 158 W and began operations. However, after 20 seconds the instruments stopped working for unknown reasons, perhaps as a result of the massive surface dust storms raging at the time of landing. Meanwhile, the orbiter had suffered from a partial loss of fuel and did not have enough to put itself into a planned 25 hour orbit. The engine instead performed a truncated burn to put the spacecraft into a long 12 day, 19 hour period orbit about Mars with an inclination thought to be similar to that of Mars 2 (48.9 degrees).
The Mars 2 and 3 orbiters sent back a large volume of data covering the period from December 1971 to March 1972, although transmissions continued through August. It was announced that Mars 2 and 3 had completed their missions by 22 August 1972, after 362 orbits completed by Mars 2 and 20 orbits by Mars 3. The probes sent back a total of 60 pictures. The images and data enabled creation of surface relief maps, and gave information on the martian gravity and magnetic fields.
Mars 4 and 5:
Mars 4, 5, 6, and 7 comprised an associated group of Soviet spacecraft launched towards Mars in July and August of 1973. The Mars 4 and 5 automatic stations were designed to orbit Mars and return information on the composition, structure, and properties of the martian atmosphere and surface. The spacecraft were also designed to act as communications links to the Mars 6 and 7 landers. They were launched from Earth by Proton SL-12/D-1-e boosters.
The Mars 4 orbiter reached Mars on February 10 1974. Due to a flaw in the computer chip which resulted in degradation of the chip during the voyage to Mars, the retro-rockets never fired to slow the craft into Mars orbit, and Mars 4 flew by the planet at a range of 2200 km. It returned one swath of pictures and some radio occultation data which constituted the first detection of the nightside ionosphere on Mars. It continued to return interplanetary data from solar orbit after the flyby.
Mars 5 reached Mars on February 12, 1974 at 15:45 UT and was inserted into an elliptical 1755 km x 32,555 km, 24 hr, 53 min. orbit with an inclination of 35.3 degrees. Mars 5 collected data for 22 orbits until a loss of pressurization in the transmitter housing ended the mission. About 60 images were returned over a nine day period showing swaths of the area south of Valles Marineris, from 5 N, 330 W to 20 S, 130 W
Mars 6 successfully lifted off into an intermediate Earth orbit on a Proton SL-12/D-1-e 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 12, 1974. The descent module separated from the bus at a distance of 48,000 km from Mars. The bus continued on into a heliocentric orbit after passing within 1600 km of Mars. The descent module entered the atmosphere at 09:05:53 UT at a speed of 5.6 km/s. The parachute opened at 09:08:32 UT after the module had slowed its speed to 600 m/s by aerobraking. During this time the craft was collecting data and transmitting it directly to the bus for immediate relay to Earth. Contact with the descent module was lost at 09:11:05 UT in "direct proximity to the surface", probably either when the retrorockets fired or when it hit the surface at an estimated 61 m/s. Mars 6 landed at 23.90 S, 19.42 W in the Margaritifer Sinus region of Mars. The landed mass was 635 kg. The descent module transmitted 224 seconds of data before transmissions ceased, the first data returned from the atmosphere of Mars. Unfortunately, much of the data were unreadable due to a flaw in a computer chip which led to degradation of the system during its journey to Mars.
Mars 7 successfully lifted off into an intermediate Earth orbit on a Proton SL-12/D-1-e 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 onboard 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 chip error which resulted in degradation of the systems during the trip to Mars. The intended landing site was 50 S, 28 W. The lander and bus continued on into heliocentric orbits.
An orbiter launched in 1996 by Russia and not directly related to the Soviet series of probes of the same name.
The Mars 96 spacecraft was launched into Earth orbit, but failed to achieve insertion into Mars cruise trajectory and re-entered the Earth's atmosphere at about 00:45 to 01:30 UT on November 17 1996 and crashed within a presumed 320 km by 80 km area which includes parts of the Pacific Ocean, Chile, and Bolivia. The cause of the crash is not known.
The Russian Mars 96 mission was designed to send an orbiter, two small autonomous stations, and two surface penetrators to Mars to investigate the evolution and contemporary physics of the planet by studying the physical and chemical processes which took place in the past and which currently take place. Mars 96 was scheduled to arrive at Mars on September 12, 1997, about 10 months after launch, on a direct trajectory. About 4 to 5 days before arrival the small surface stations would have been released. The orbiter was to go into an elliptical 3-day transfer orbit about Mars, and the two penetrators to descend to the surface during the first month of orbit. The final orbit would have been a 14.77 hour elliptical orbit with a periapsis of 300 km.