Greg C Felix
The Lamar Landing Gear Team spent Thursday, October 26, 1995 at NASA with a group of NASA's structural engineers. The team of engineers visited had designed a lunar lander structure with design constraints similar to those proposed for this project. They had developed an optimum lander structure and landing gear. The structure was constructed of graphite composite piping. The energy absorption device used on there design consisted of a system of interference fit washers pressed on a shaft.
The interference fit washers would allow for a fairly constant load for deceleration upon landing. The low weight of this system also gives it an advantage over alternate energy absorption devices. The interference fit washer system has been used previously for other applications. The interference fit washers may be feasible for use on the oxygen plant lunar lander if the load profile can be kept constant enough to limit the necessary "compression length" of the landing gear. The interference fit washer system is designed to discipate vertical loads only. The landing regime may also consist of horizontal velocities requiring energy discipation in the horizontal direction also. The structural design team from NASA indicated that these loading conditions would be the most difficult to account for.
The optimum horizontal energy absorption devices considered by the NASA structural engineers consisted of a yielding bar and a metal foam footpad. The metal foam footpad proved to be wasteful in weight budgeting, and the yielding bar was selected as an optimum design. This design consisted of a metal bar attaching the footpad to the landing gear structure. Upon landing, all horizontal loads on the footpad will be discipated through the deformation of the yielding bar.
In a typical landing gear design, the structure is made up of a material that will absorb the energy generated upon impact. Some possible materials are 7075 and 2219 aluminum alloys. Other landing gear designs have been constructed of titanium alloys. The use of a composite structure may prove to be too rigid and brittle for this application. Due to inconsistencies, the reliability of welded connections was discouraged by NASA's engineers.
The NASA trip helped the landing gear team by increasing our knowledge of typical landing gear designs.