Exploration of Extreme Terrain Using a Polyhedral Rover

The terrains of different celestial bodies are often extreme and vary wildly; their surfaces can be icy, rocky, or sandy. In these extreme environments, traditional rovers with wheels are not the most effective means of exploring the surfaces, as seen with the NASA rover, Spirit. The 400 million-dollar rover got stuck in deep sand on the surface of Mars. After unsuccessful attempts to free it, the rover’s useful lifetime ended, because it was unable to charge its batteries. Had the rover had different means of mobility, its mission to gather scientific data may not have ended prematurely. To avoid such problems, I am developing a polyhedral rover that does not use wheels, but instead steps by rolling around from side to side. The rover is called Polyhedral Extreme Terrain Exploration Rover (PETER). To locomote, PETER uses a control moment gyroscope (CMG) array, which provides two key benefits. First, due to a phenomenon called torque amplification, small CMGs can produce large torques, enabling PETER to navigate bodies with a wide range of terrains and gravitational field strengths. Second, the CMG array is internal to the chassis, so there is no interaction between the actuators and the environment, eliminating the risk of actuator failure from terrain interaction, which occurred to Spirit’s right front wheel. PETER can be used for missions to moons and planets with extreme terrains in our solar system, like Mars, Europa, or Enceladus. Figure 1. PETER navigating Mars. To date, there has been little research on polyhedral rovers. NASA’s JPL developed one such rover called Hedgehog, which has many of the polyhedral rover traits described above. It has gripping pads at the corners and rolls from side to side. However, unlike PETER, Hedgehog uses a reaction wheel system to create movement. The MINERVA rovers are also polyhedral and roll for locomotion. However, like Hedgehog, these rovers use reaction wheels for locomotion. To expand upon the previous research, my research investigated using CMGs as the rover’s actuator. Specifically, I developed a general method for controlling PETER that enables the rover to locomote over extreme terrain with a wide array of system architectures. Additionally, I developed design principles for the rover, informing the development of a rover capable of exploring extreme terrain efficiently and predictably. In conjunction, the design principles and general control architecture enable researchers to quickly adapt PETER’s design to enable exploration of various environments and complete a wide array of missions. PETER will be able to explore extreme terrain on many celestial bodies, including Mars, Enceladus, and Europa. Furthermore, PETER could explore currently unexplored craters, valleys, and crags on Mars, which are believed to contain valuable water content information. PETER enables the exploration and gathering of scientific data from icy terrains like Europa and Enceladus. Additionally, the rover could be scaled easily to support future manned missions. It could help explore future landing areas before manned missions arrive, and carry supplies across the extreme terrains on these celestial bodies. Because bodies like these are rich with scientific potential, NASA regards terrain-adaptable rovers as an important piece of technology development (TA 4.2.1 – TA 4.2.4). This research also expands NASA’s use of CMGs beyond large spacecraft momentum control. NASA has used CMGs in two of its previous largest missions, Skylabs and the International Space Station. The general control methodologies that I have developed are applicable to a wide array of applications, including spacecraft and robotics systems, enabling higher performance control of these systems than is possible with contemporary methods.