Engineering Considerations in Design of High Temperature Electronics for Planetary Probes
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Low weight and high reliability are primary goals in scientific exploration space missions. Many mission concepts involve probes operating at high ambient temperatures for various lengths of time. In these cases, high-temperature electronics can simplify the system design and reduce overall mass, resulting in higher reliability of the overall system. High temperature electronics can be improve performance measuring instrumentation for Thermal Protection Systems (TPS), integrated in embedded sensor plugs, to perform front-end signal conditioning and acquisition during atmospheric entry and descent. Thermal Protection System thickness and material characteristics affect the thermal exposure seen by such embedded electronics. The analysis in our examples illustrates scenarios from 150 deg C ambient, up to 260 deg C, with operating time ranging from 15 minutes to several hours. Venus in-situ environment poses different technical challenges, with ambient temperatures of 480 deg C and high pressures. The desired operating times in this environment are much longer, up to 90 days. Our presentation focuses on two of the technologies applied in our group: SiGe (silicon-germanium) for TPS applications, and GaN (gallium nitride) towards a Venus Lander. SiGe electronics for extreme environments (cryogenic temperatures) is being developed by a team led by Prof. Cressler from Georgia Tech, under the NASA RHESE (Radiation Hardened Electronics for Space Environments) program directed by Dr. Andrew Keys. GaN electronics for high temperatures are being developed by HRL. Summing up the numbers, these two technologies together are capable of spanning a range of temperatures of over 700 deg C. Examples from our recent validation tests in harsh environments illustrate the performance of the electronic components and modules. In addition to the SiGe or GaN-based semiconductor material, the characteristics, reliability and viability of the electronics is affected by constituent materials (metallization, dielectric layers) and by the packaging (die attach, wire bonding).