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

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Planetary Exploration Using Biomimetics An Entomopter for Flight on Mars particles forming, and it must be capable of withstanding the extreme thermal cycling to which it will be subjected. There are two main categories or types of insulation that can be used. The first is a vacuum-jacketed system consisting of layers of Mylar (or a similar type of low-emissivity, high-reflectivity material), separated by thin fiberglass sheets to maintain spacing, surrounded by an outer container able to maintain a low pressure within the insulation layers. The low-pressure environment minimizes the conductivity between the insulation layers, and the layers act as a radiation barrier keeping heat out of the tank. The pressure within the vacuum-jacketed insulation is typically kept at around 0.1 Torr (Mars surface pressure is approximately 4.5 Torr). The main drawback to the vacuum-jacketed insulation is that if the vacuum is lost, the insulation will fail, causing a large and rapid boil-off of propellant. The second type of insulation is a rigid, closed-cell foam that can be applied to the outside of the tank. If needed, a thin metal-walled enclosure can be placed outside the foam to maintain its integrity and protect it from damage. The foam type of insulation is much more resistant to catastrophic failure than the vacuum-jacketed type. However, the densities and thermal conductivity of the foam insulation is greater. Table 3-21 lists a number of different insulation types and the effective conductivity and density [28,126]. Table 3-21: Tank-insulation Properties Insulation Type Density (kg/m3) Thermal Conductivity (W/m o K) Rigid closed cell polymethacrylimide 35.3 0.0096 Rigid open cell polyurethane 32.1 0.0112 Rigid closed cell polyvinalchloride 49.8 0.0046 Rigid closed cell polyurethane and chopped glass fiber 64.2 0.0064 Evacuated aluminum foil separated with fluffy glass mats 40 0.00016 Evacuated aluminum foil and glass paper laminate 120 0.000017 Evacuated silica powder 160 0.00017 The amount of insulation needed on the tank will vary depending on the insulation properties, tank size, allowable boil-off rate, and overall allowable weight. To get an estimate of insulation requirements, a brief analysis on the heat flow into the tank needs to be performed. The analysis is a one-dimensional heat flow from the surroundings to the liquid hydrogen. The heat transfer mechanisms are shown in Figure 3-152. 190 Phase II Final Report
Chapter 3.0 Vehicle Design 3.5 Fuel Storage and Production Figure 3-152: One-dimensional Heat Transfer for Liquid Hydrogen Tank Initially the outside surface temperature of the insulation (T s ) needs to be determined. This wall temperature is based on the heat flow into the insulation from convection and radiation and heat flow to the liquid hydrogen by conduction through the insulation. Q in = Q convection + Q radiation = h(T 8 – T s ) + εσ( T 8 4 – T s 4 ) Equation 3-47 Q out = Q conduction = K (T s – T LH2 ) /t i Equation 3-48 Where ε is the emissivity of the insulation surface, σ is the Stefan-Boltzmann constant (5.67E-8 W/m 2 °K 4 ), h is the convection coefficient for the air surrounding the tank, K is the thermal conductivity of the insulation, and t i is the insulation thickness. It is assumed that the tank is in an isolated environment in which the atmosphere surrounding the tank is still. Therefore, the convection coefficient is based on natural convection of the atmosphere surrounding the tank. This coefficient can be represented by the following equation: h = N UD K g / D Equation 3-49 The thermal conductivity of the carbon dioxide (which composes most of the atmosphere) (K g ) is a property of the fluid at a given temperature and pressure, and D is the tank diameter. The Nusselt number (N UD ) is dependent on the geometry of the tank. Expressions for this are listed for spherical and cylindrical tank shapes [205]. For a sphere: N UD = 2 + 0.589 R ad 1/4 / [1 + (0.469 /PR) 9/16 ] 4/9 Equation 3-50 191
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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 4.0 Entomopter Flight Opera
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Chapter 5.0 Potential Payload Funct
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Chapter 6.0 Media Exposure 6.1 Intr
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Chapter 6.0 Media Exposure 6.3 Onli
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Chapter 6.0 Media Exposure 6.6 Spec
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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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