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.
                                                                        
                                                                  Orbiter Construction

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.
                                                                        
                                                               Parachute Deployment 

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.
                                                                        
                                                                        Touchdown

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.
                                                                       
                                                           On the Surface of Mars

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.