Credit: Russian Academy of Sciences/Don P. Mitchell
A total of five spacecraft were launched in 1971 with the intention of going to Mars. This post will cover the first four.
On May 8, the US launched Mariner 8. This satellite was to orbit Mars for a minimum of 90 days, during which time the spacecraft would gather data on the composition, density, pressure and temperature of the atmosphere, and the composition, temperature and topography of the surface. However, during liftoff, the upper stage of the Atlas-Centuar rocket began to tumble out of control. The Centaur stage of the rocket and Mariner 8 separated and re-entered the Earth's atmosphere approximately 1500 km downrange, falling into the Atlantic Ocean about 560 km north of Puerto Rico.
Two days later, on May 10th, the Soviet Union launched Cosmos 419. There is uncertainty over whether this spacecraft was to have been a combined orbiter and lander (as the next two spacecraft discussed, Mars 2 and 3, were) or if it was to be a single orbiter like Mariner 8. Regardless, Cosmos 419 failed to separate from the fourth stage of its Proton rocket, and fell back to earth two days later. The stage 4 timer was originally set to fire 1.5 hours after reaching its parking orbit; however, the timer was actually set to fire 1.5 years later.
Mars 2 and Mars 3 represented a partial triumph for the Soviet Union's space program. These two missions to Mars, the 11th and 12th overall that the Soviet Union had attempted, were the most successful of any to that point in time. Both missions used identical spacecraft, consisting of an orbiter and a 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 atmospheric properties, monitor the solar wind and the interplanetary and Martian magnetic fields, and act as communications relays to send signals from the landers to Earth. The landers, which would descend to the surface by parachute and retro-rockets, contained several instruments, including two television cameras and a mass spectrometer. They also contained a small rover that would move about on two wide, flat skis after being placed on the surface by a manipulator arm. The rover was attached to the lander by a 15 meter umbilical.
Mars 2 successfully entered Martian orbit on November 27, 1971, orbiting once every 17.96 hours with a closest approach of 1,380 km. The lander had separated from the orbiter 4.5 hours prior to reaching orbit. While plummeting through the atmosphere, the descent system on the lander malfunctioned, possibly because the angle of entry was too steep. The descent system did not operate as planned and the parachute did not deploy. The lander crashed at 4° North, 47° West (per Wikipedia; according to NASA, the lander crashed at 45° South, 313° West). Mars 2 was the first manmade object to reach the surface of Mars.
Mars 3 was not quite as lucky as Mars 2. By the time of its orbital insertion, the orbiter did not have enough fuel to put itself into a planned 25 hour orbit. As a result, the orbiter swung into a long 12 day, 19 hour orbit. The closest point of the orbit was 1,500 km, but the farthest point was 211,400 km (in comparison to Mars 2's 24,940 km apoapsis). Like the Mars 2 lander, the Mars 3 lander was released about 4.5 hours prior to reaching orbit. However, unlike the other lander, the Mars 3 lander successfully soft-landed onto the Martian surface (45° South, 158° West) and began operations. Unfortunately, 20 seconds later, transmission on both data channels stopped for unknown reasons and no further signals were received from the Martian surface. It is not known whether the fault originated with the lander or the communications relay on the orbiter. A partial panoramic image returned showed no detail and a very low illumination of 50 lux. The cause of the failure may have been related to the extremely powerful Martian dust storm taking place at the time, which may have induced a coronal discharge, damaging the communications system. The dust storm would also explain the poor image lighting.
The two orbiters, however, worked as planned and transmitted most of their data between December 1971 and March 1972, although both orbiters continued transmissions through August 1972. On August 22, the Soviet Union announced that both missions had been completed; Mars 2 had completed 362 orbits, with 20 orbits by Mars 3. A total of 60 photographs were sent back. The images and data revealed mountains as high as 22 km, atomic hydrogen and oxygen in the upper atmosphere, surface temperatures ranging from -110 C to +13 C, surface pressures of 5.5 to 6 mb, water vapor concentrations 5000 times less than in Earth's atmosphere, the base of the ionosphere starting at 80 to 110 km altitude, and grains from dust storms as high as 7 km in the atmosphere. The images and data enabled the creation of surface relief maps, and gave information on the Martian gravity and magnetic fields.
The photo above is a composite image from the Mars-3 52 mm camera, using its program of cycling red, green and blue glass filters.