Viking 1 & 2
NASA sent a series of two spacecraft to Mars, the first of which touched down on July 20, 1976 and the other on September 3, of that same year. The Viking space probe was actually a twin spacecraft. Its mission was to study and survey the Red Planet, Mars. The Viking spacecraft as shown in the pictures below consisted of two distinct sections: the orbiter and the landing module. The landing module initially descended at a speed of 600 mph, when it was about 4 miles above the surface the parachute deployed and the heat shield fell away. Soon after this occurred the lander's legs unfolded and finally separated itself from the parachute at an altitude of 1 mile. There after its descent was controlled by three retro-engines, finally landing on the Martian surface safely.
The orbiter had three main purposes during the mission. First, it was suppose to survey the Martian surface for a suitable place to land. Next, it collected data about the planet's atmosphere, and then it transmitted data from the landing module to Earth. The lander gathered a lot of useful information about the planet's surface. It surveyed the Martian soil, kept track of the wind and climate, and conducted a series of experiments in order to determine if life ever existed on Mars.