Performance Optimization Technique for the 1975 Mars Viking Lander

Abstract

This paper presents a technique for optimizing the entry-to-touchdown performance of a planetary vehicle. Developed for the 1975 Mars Viking Lander, this technique is characterized by a graphical tradeoff approach including design parameter and atmosphere model variations. From entry (800,000 ft above the mean surface) to touchdown a lifting entry phase provides for deceleration to low supersonic speeds; the terminal phase includes a parachute and terminal propulsion system. Entry lift-to-drag ratio and the parachute diameter are principal design parameters used for performance optimization. Optimum performance is measured in terms of entry flight-path angle corridor, landing terrain elevation, and terminal phase system weight. Chief among the uncertainties with which the design must contend is the atmosphere. Lift is assumed to be generated passively using a lateral center of gravity offset, resulting in a trim angle of attack that produces lift. Entry phase analysis indicates that a hypersonic lift-to-drag ratio of 0.150 results in the maximum entry flightpath angle corridor. The terminal phase analysis indicates that the same LID and a parachute diameter of 53 ft produce minimum terminal phase system weight (i.e., maximum useful landed weight) for a desired terrain elevation capability. Also indicated is that these values are optimum for a significantly heavier entry weight, as well as for the current Viking Lander.