The components considered for use on the landing gear structure have been evaluated for performance versus weight for many possible conceptual designs. The optimum design selected consists of three identical rigid landing gear legs with all energy dissipation at the footpad attachments. Each leg will consist of three main members connecting the footpad attachments to the bus structure. Two of these main members will be located on the top level of the leg structure with a pivot joint between the members and the bus structure. The landing gear has been designed to fold upward against the bus structure during the launch phase. The single member on the lower level of the leg structure will lock to the bus srtucture upon deployment.
The optimum energy dissipation device selected for the landing gear is the interference fit washer system. The horizontal loads will be dissipated into heat energy upon landing due to the friction encountered as the washers are forced to slide along the rod with an interference fit between the two. The interference fit washers act as a load limiter in the horizontal direction between the footpad and landing gear leg structure. The major weakness in the interference fit washer design is the short load spikes experienced while the washers are experiencing static friction. These spikes have been taken into account as being the limiting factor for the design values of the interference fit washers in order to maintain a load profile which does not produce accelerations of the bus structure greater than 7 g's. The spikes may later be ignored if the leg structure and bus structure will help damp the load profile on the most sensitive components and the weight of the interference fit washer system may be reduced by shortening the rod.
The horizontal loads will be dissipated through a yielding rod also located at the footpad. With the present impact velocities, it would also take a crushable foam footpad structure to protect the lander. There is definitely a trade- off between landing regime control and landing gear weight. The closer the lander is to a zero velocity upon impact, the lighter the landing gear can be designed.
Sketches of the landing gear structure will be posted soon.