Rover egress is the method by which the rover descends from the lander to the lunar surface. If the rover cannot egress, it cannot explore and the mission fails. Therefore, successful rover egress is imperative to the success of the overall mission. Egress is complicated by Lander tilt from unpredictable Lunar terrain and uneven amount of composite “crush” in the Lander legs.
In order to find the optimal mechanical solution, a number of egress designs were considered. This was accomplished by formulating a Pugh Chart with the highest weighted considerations being low mass, deployment reliability, compactness, and ease of manufacture. Concepts ranging from “rope ladder” and “shower curtain” inspired designs to scissors lifts were generated. The top three designs are a dual-direction segmented ramp (one rotatable model), a segmented ramp, and a telescoping ramp.
Closeup of the spring mechanism
Worst-case analysis of the dual-direction ramp indicated that the design was too risky to consider given unpredictable landing conditions. The telescoping concept will be investigated in the future. Therefore the chosen egress design is a two segmented ramp.
The two segmented ramp has relatively reliable deployment capabilities and can be modeled for compactness. It can be optimized for low weight, and can be manufactured using standard methods. Additionally, final iterations of the ramps can be manufactured from composites and space-grade components. A well-designed segmented ramp ensures egress success under worst-case landing conditions and launch dynamics.
The lander with deployed two-segment ramps
