Development of a lithium/thionyl chloride battery for the Mars Microprobe Program

The Mars Microprobes (2) are secondary payload on the 1998 Mars Surveyor Lander Mission. After an eleven month journey to Mars, the two probes will be released and use a self-orienting, nonablative aeroshell for their single-stage passive entry, decent and landing on Mars. The Microprobes will penetrate through the aeroshell and strike the surface with an impact velocity of approximately 200 m/sec and separate into two sections; a surface (aft-body) module which contains the power source and telecommunication subsystem and a subsurface (fore-body) module which contains most of the scientific instrumentation. The fore-body is expected to penetrate the Martian surface anywhere between 0.3 and 2 m while the aft-body remains on the surface. The two components are connected through a flex cable umbilical. The Microprobe power source is a four-cell lithium/thionyl chloride battery with a second redundant battery in parallel. The eight 2 Ah cells are arranged in a single-layer configuration in the aft-body. The lithium primary cells (and battery configuration) have been designed to survive the maximum landing impact that may reach 80000 G and be operational on the Martian surface to -80°C. Primary lithium batteries were selected for the Microprobes based on high specific energy and promising low temperature performance