The Viking mission to Mars sent twin spacecraft to the Red Planet. This image shows a model of one of the Viking spacecraft, each of which was made of two parts: an orbiter and a lander. The orbiter's initial job was to survey the planet for a suitable landing site. Later the orbiter's instruments studied the planet and its atmosphere, while the orbiter acted as a radio relay station for transmitting lander data. Once on the surface of Mars, the lander surveyed the soil, wind, and atmosphere and conducted numerous experiments to determine the existence of past or present life.
Once the Viking orbiters were attached to their lander pods they were positioned inside the nose cones of Titan Centaur launch vehicles. The landers were folded up inside their pods, which were designed to isolate the landers from biological contamination while on Earth.
In this artist's rendering a Viking lander released its parachute just after entering the Martian atmosphere. When the parachute was deployed, the lander pod was at an altitude of about 6 km (4.0 mi) and traveling at a velocity of 900 kph (600 mph). Soon after, the lower half of the heat shield fell away and the lander's legs unfolded. At an altitude of about 1.5 km (5000 ft) the pod separated from the parachute and using three retro-engines to control its descent, landed safely on the surface of Mars.
Captured here in this rendering is a Viking lander just before it touched down on the Martian surface. The parachute and upper aeroshell can be seen in the upper left corner of the image. At this stage of the descent, the lander's terminal descent propulsion system (three retro-engines) had slowed the craft down so that velocity at landing was about of 2 mps (7 mph). Seconds after the lander reached the surface it began transmitting images back to the orbiter for relay to Earth.
This photograph shows a model of the Viking lander on a simulated Martian surface. The first of the two landers arrived on the surface of Mars July 20, 1976. The second touched down September 3, 1976. Each lander housed instruments that examined the physical and magnetic properties of the soil and analyzed the atmosphere and weather patterns of Mars.
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