Design of small impact-resistant RTGs for Mars environmental survey (MESUR) mission

Abstract

Ongoing studies by the National Aeronautics and Space Administration (NASA) for the robotic exploration of Mars contemplate a network of about twenty small and relatively inexpensive landers distributed over both low and high latitudes of the Martian globe. They are intended to explore the structural, mineralogical, and chemical characteristics of the Martian soil, search for possible subsurface trapped ice, and collect long‐term seismological and meteorological data over a period of ten years. They can also serve as precursors for later unmanned and manned Mars missions. The collected data will be transmitted periodically, either directly to Earth or indirectly via an orbiting relay. The choice of transmission will determine the required power, which is currently expected to be between 2 and 12 watts(e) per lander. This could be supplied either by solar arrays or by Radioisotope Thermoelectric Generators (RTGs). Solar‐powered landers could only be used for low Martian latitudes, but RTG‐powered landers can be used for both low and high latitudes. Moreover, RTGs are less affected by Martian sandstorms and can be modified to resist high‐g‐load impacts. High impact resistance is a critical goal. It is desired by the mission designers, to minimize the mass and complexity of the system needed to decelerate the landers to a survivable impact velocity. To support the NASA system studies, the U.S. Department of Energy’s Office of Special Applications (DOE/OSA) asked Fairchild to perform RTG design studies for this mission.The key problem in designing these RTGs is how to enable the generators to tolerate substantially higher g‐loads than those encountered on previous RTG missions. The Fairchild studies resulted in designs of compact RTGs based on flight‐proven and safety‐qualified heat source components, with a number of novel features designed to provide the desired high impact tolerance. The present paper describes those designs and their rationale, and a preliminary, quasi‐static impact analysis that yielded very encouraging results. They indicate that these RTGs have sufficient impact resistance to enable survival of landers without retrorockets. This would result in significant cost savings.