Date of Award
Doctor of Philosophy (PhD)
Biggers, Sherrill B
Joseph , Paul F
Summers , Joshua D
The All-Terrain Hex-Limbed Extra-Terrestrial Explorer (ATHLETE) is a mobile lunar lander under development by the National Aeronautics and Space Administration's Lunar Architecture Team. While previous lunar missions have lasted only a few days, the ATHLETE is designed to last for 10 years, which will enable a sustained U.S. presence on the moon and exploration of the more treacherous regions which are not suitable for landing. Because the ATHLETE will carry entire astronaut habitats, its six wheels must be carefully designed to support a large load on soft lunar soil efficiently.
The purpose of this thesis is to develop a finite element model that will allow designers to examine how the tractive performance of the lunar wheel is affected by changes in the wheel geometry through numerical analysis. It has been shown in the literature that a wheel rolling on soil is not suited to a plane strain analysis. Two different three-dimensional deformable wheel models are explored, a single-part shell model and a multi-part solid-shell model. For the purposes of this research, the shell model offers sufficient detail with less computational expense. The key to obtaining a smooth pressure distribution is in careful selection of the contact stiffness. For the soil model, a set of parameters to represent a pressure-dependent elasto-plastic cap hardening lunar soil was assembled. Two different methods of selecting an appropriate soil bed size are compared. A holistic method that determines all dimensions at once was found to be quick and reliable. Finally, the wheel and soil models were integrated into one finite element model in the commercial code, AbaqusTM, and three small studies were conducted to demonstrate the utility of the model in predicting changes in traction dues to change in wheel design and operation. For example, the model can help determine how quickly the wheel can accelerate without significant slippage. The model can also inform design decisions. The pilot tests suggested that softening the cylinders and/or the spokes could improve traction, but softening the cylinders too much can lead to structural failure.
Orr, Marisa, "DEVELOPMENT OF A FINITE ELEMENT MODEL TO PREDICT THE BEHAVIOR OF A PROTOTYPE WHEEL ON LUNAR SOIL" (2010). All Dissertations. 579.