Viking was the first lengthy mission to another planet involving an intensive exploration both on its surface and from orbit. Each Viking spacecraft came in two parts: a soft-landing probe (the "lander") to examine the physical and chemical features of the planet's surface, and the "orbiter", which surveyed the planet from above. The orbiter was also a communications relay between the surface probe and Earth.
Each Viking comprised six systems. Three of these were Earth-based, and all were interdependent. These multipurpose systems have been used for Viking and most other NASA lunar and interplanetary missions.
