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Trade Space Analysis of Mars Surface Explorers

NASA’s Mars Exploration Program seeks to answer the question of whether Mars has ever been a habitable world, through study of how geologic, climatic, and other processes have interacted to shape the Martian environment. Alternating orbiter and lander vehicles are planned for upcoming biannual launch windows, potentially resulting in a surface mission once every four years. This infrequency of surface missions makes it important to maximize the potential for useful science return of each landed mission through carefully directed mission design. The motivation for this project arose from the need for a tool to rapidly create and compare system-level Mars rover designs. Specifically, the project resulted in a trade space design and analysis tool that is able to render rover designs applicable to the architecture and design selection of the 2009 Mars mission – the Mars Science Laboratory (MSL) – and to future robotic surface explorers. Graduate students in the Department of Aeronautics and Astronautics at MIT developed a Mars rover modeling tool as a semester-long project in a space systems engineering course. The project was supported by engineers and scientists from the Jet Propulsion Laboratory (JPL), who provided insight into rover design drivers, information on existing rover designs, and suggestions as to the appropriate scope of the project. The project scope was limited to the design of independent rovers, and emphasis was placed on design drivers that are related to surface operations, disregarding launch and entry/descent/landing. Focus was placed on architectural and system-level trades, rather than on detailed engineering decisions. Active landers were not considered in the trade space, and only a very limited set of prior-to-landing considerations was taken into account. Figure 1 depicts the process followed by the trade space tool in creating a set of rover designs. The process begins with a user-defined mission scenario represented by a set of parameters in the science and design vectors. The science vector includes those parameters that are held constant for all designs in a particular trade space. Examples of science vector parameters include the science payload (instruments and acquisitions tools) and landing site parameters such as rock distribution, latitude, and the expected distance between interesting samples. The design vector includes the set of architectural and system-level parameters that uniquely identify a particular rover design within the trade space. Design vector parameters include mission duration, power system type, wheel diameter, and several indicators of autonomous capability. The user provides a range of allowable values for each parameter in the design vector, and iteration through all allowable instances of the design vector results in a trade space of rover point designs.