Guidance and control system design of the Viking planetary lander

This paper describes the salient features and unique problem solutions for the Viking lander guidance and control system design. Because of the following design requirements imposed, the lander guidance and control function presented stringent design challenges. These requirements were: (1) a completely autonomous operation was required although the on-board computer memory size was limited to solve the descent problem; (2) the lander deorbit maneuver had to be very accurate to achieve a satisfactory planet atmospheric entry and an accurate touchdown at the predicted landing site; (3) the landers had to descend through an unknown atmosphere with a large variation in predicted characteristics, and they had to land at an unknown terrain height; and (4) they had to be as fuel-efficient as possible, particularly in the terminal descent phase. This paper describes how a safe and accurate landing on the surface of Mars while meeting these design requirements was achieved by the guidance and control systems of both Viking landers.