With the recent renewed interest in manned lunar exploration, it is critical to
revisit the Apollo Moon landings with new analysis tools. Modeling the Moon
landings of the past can help guide the development of new landing vehicles for
the present and the future. One of the critical subsystems to model is the
vehicle’s landing gear. During a landing event, structural loading, energy
absorption, and toppling stability are important factors that drive the design
of landing gear subsystems. These aspects can be studied using models and
simulations in addition to physical testing. This study explores one recent
modeling tool for modeling the landing gear and uses the Apollo 11 Moon landing
as a use case.
A generic model was built using MATLAB®, Simulink®, and
Simscape® Multibody to model the dynamics of a landing event. The
landing gear structure comprising the primary strut, secondary struts, footpads,
and joints was modeled in Simscape® Multibody. Various energy
absorption mechanisms in the struts were modeled based on the relative motions
of the inner and outer cylinders of the leg. Touchdown contact forces, when the
footpads strike the lunar surface, were modeled considering the soil mechanical
properties. Slosh dynamics were modeled using a mechanical pendulum module, and
tip-over controllers were developed using Simulink®. However, neither was
applied in the presented analysis relating to the Apollo lunar module.
After developing the generic landing dynamic model, the Apollo 11 landing was
simulated for validation purposes with results closely matching the historical
measured data. A MATLAB® Graphical User Interface application (app)
also was developed based on this model for usability and better accessibility of
the landing simulation by non-experts on landing dynamics. It offered the
opportunity for landing stability study with and without control, i.e., the max
slope a lander can land without tipping over in 3D realistic landing
situations.