Phase II Final Report - NASA's Institute for Advanced Concepts

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Planetary Exploration Using Biomimetics An Entomopter for Flight on Mars From the estimates of the thin film thermoelectric, sufficient power for the Entomopter's systems should be available whenever the engine is operating. However, the engine will not be operating continuously during the mission. In fact, operation time can be a small fraction of the complete mission time. Therefore an auxiliary source of power would be needed. The best choice for this power source is a rechargeable lithium battery similar to that used with the PV system. The operational time of the thermoelectric is limited to 10 minutes over the 1 hour mission. This would provide a total of 3.33 W-h of energy. If 4 W need to be available to the vehicle while the thermoelectric is running, that leaves 16 W or 2.66 W-h available for storage. Therefore, a battery would need to be used with a storage capacity of 2.43 W-h (3.1 W-h for the total mission - 0.66 W-h provided by the thermoelectric and used during flight). Based on the lithium battery specifications given in Table 3-25, the battery mass would be 0.018 kg, and the thermoelectric conversion unit would be 0.02 kg. Also, a cooling system will be needed to keep the back side of the thermoelectric cool in order to maintain the required temperature difference across it. (This temperature difference is usually on the order of 200°C.) However, within the cool atmosphere of Mars, the cooling system may be nothing more than some convective fins. The mass breakdown for the thermoelectric system is given in Table 3-27. Based on these estimates, the thermoelectric system would be about twice as heavy as the battery system. However, if the mission profile is changed, this type of system may look more attractive and should continue to be considered as a viable alternative to the PV system. Table 3-27: Thermoelectric System Mass Estimate System Component Mass (kg) Thermoelectric Unit 0.020 Battery (based on 100% capacity) 0.023 Cooling Fins 0.010 Contingency (50% for wiring, electronics, etc.) 0.043 Total System Mass 0.096 Another approach to using a thermoelectric is to use a radioisotope heat source instead of the combustion-exhaust gasses. This would eliminate the need for a supplemental battery to provide power when the engine is not running. A standard radioisotope heater unit (RHU) can be used as a baseline for the heat source. The specifications of the RHU are given in Table 3-28. [9] Table 3-28: Specifications for Radioisotope Heater Unit System Component Value Isotope Material Mass (Fuel Source) Operating Temperature Watts (thermal) PU-238 3.02 gm 310 o K 1 Wth 222 Phase II Final Report
Chapter 3.0 Vehicle Design 3.6 Power System To meet mission requirements, the RHU/thermoelectric system would need to produce 3.5 W to meet maximum power needs plus a 0.5 W contingency. This contingency is needed because there is no backup battery or other power source that could compensate for an unexpected power drain. So the total power to be supplied by the RHU/thermoelectric system is 4 W. Assuming the conversion efficiency of the thermoelectric is 15% (about 200% better then the state of the art), the thermal watts required would be 26.6 W thermal. This translates into an isotope mass of 0.08 kg. This isotope mass alone is greater than the PV/battery system mass. Even eliminating the contingency power, the isotope mass (0.07 kg) is still greater then that of the PV/battery system. 3.6.8 Linear Alternator System A linear alternator system uses the motion of the engine to generate electricity directly. Because this will extract work from the exhaust gasses by placing an additional load on the engine, however, it will be less efficient overall than the thermoelectric system that provides power by utilizing the waste heat within the exhaust gasses. Also, the alternator will be operating only when the engine is running and would therefore require a supplemental battery similar to the exhaustpowered thermoelectric. Based on these issues, the linear alternator would not be the best choice for the Entomopter vehicle under the mission conditions that were specified. 223
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Planetary Exploration Using Biomime
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Table of Contents Table of Contents
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List of Tables List of Tables Table
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List of Figures List of Figures Fig
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List of Figures Figure 3-54: Pressu
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List of Figures Figure 3-138: Stere
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List of Figures Figure 4-24: Averag
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List of Contributors List of Contri
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Executive Summary Executive Summary
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Chapter 1.0 Introduction Chapter 1.
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Chapter 1.0 Introduction Figure 1-2
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Chapter 1.0 Introduction 1.1 Histor
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Chapter 1.0 Introduction 1.2 Origin
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Chapter 1.0 Introduction 1.3 Missio
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1.3.3.1 Surface Imaging The Entomop
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Chapter 2.0 Entomopter Configuratio
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Chapter 3.0 Vehicle Design 3.1 Wing
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3. Density: 1.40E-2 kg/m 3 4. Press
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Chapter 3.0 Vehicle Design 3.4 Reci
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Chapter 3.0 Vehicle Design 3.5 Fuel
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Chapter 7.0 Conclusion Chapter 7.0
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Appendix A: Mars Atmosphere Data JP
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Appendix A: Mars Atmosphere Data Ge
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Appendix A: Mars Atmosphere Data Ge
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Appendix A: Mars Atmosphere Data Ma
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Appendix B: Sizing Results Appendix
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Appendix B: Sizing Results 30 Wing
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Appendix B: Sizing Results 16 Wing
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Appendix B: Sizing Results Length 0
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Appendix B: Sizing Results Lenght 0
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Appendix C: List of References Appe
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Appendix C: List of References 41.
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Phase II Final Report - NASA's Institute for Advanced Concepts

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