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

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Planetary Exploration Using Biomimetics An Entomopter for Flight on Mars where ƒd is the radial component of the relative velocity (positive for decreasing range), ν is the radial component of relative velocity, and λ is the radiated wavelength. For example, were 95 GHz chosen as the radar carrier frequency, the wavelength would be, λ = c ÷ ƒ Equation 4-2 = 3E10 cm/s ÷ 95E9 Hz ˜ 0.3 cm The Doppler shift resulting from rover platform motion when the rover is traveling at 2 m/s is ƒ d (platform) = 2(2m/s)(100cm/m) ÷ 0.3 cm ˜ 1.333 kHz Equation 4-3 A low-pass filter with adequate roll-off below 2 kHz will effectively prevent any platform motion from being detected; however, knowing that 1.333 kHz is the offset due to platform motion, the rover can apply the cosine of this value to all Doppler returns depending on their angle relative to the platform motion. In this way, rover platform motion can be completely eliminated from the measurement of the surrounding terrain and Entomopters. Were the Entomopter to be flying straight and level with one-meter wings (tip-to-tip) flapping at a frequency of 10 Hz over a 180° angle, the returned 95 GHz carrier frequency would be modulated at a 10 Hz rate with the frequency excursion of the Doppler signal depending upon the orientation of the Entomopter to the rover's radar. For example, in the simplest case where the Entomopter is flying parallel to the rover at the moment the radar scans across it, the received Doppler (corrected for rover platform motion) would be: Wing radial advance distance (m) = 2(0.5)sin (45) = 0.35 m Assuming a linear acceleration, a distance of 0.35 m would be covered in 0.025 seconds, yielding a radial velocity of 14.142 m/s. ƒd (45° downbeat) = 2 (14.142m/s)(100cm/m) ÷ 0.3 cm ˜ 9.428 kHz. ƒd (midflap) = 2 (0m/s)(100cm/m) ÷ 0.3 cm= 0 Hz. ƒd (135° downbeat)= 2 (-14.142m/s)(100cm/m) ÷ 0.3 cm ˜ -9.428 kHz. Note that the negative sign on the 135° case is due to the fact that the wing is moving radially away from the radar, and the Doppler shift will be subtracted from the returned carrier. Since all parts of the wing are moving at different radial rates from the root to the tip, the Doppler signature will range from 0 Hz to a maximum of roughly those shown above (assuming that the wing is accelerating linearly as it flaps). Therefore, the demodulated and rectified Doppler return from the Entomopter wing under the specified flight conditions would be a unique (for Mars) frequency modulated (FM) signature that varies from 0 to roughly 9 kHz every 0.5 seconds. Such a signal would be unambiguously that of the Entomopter; which Entomopter is being detected is another question, however. 232 Phase II Final Report
Chapter 4.0 Entomopter Flight Operations 4.2 Rover-centric Entomopter Navigation The problem of which Entomopter is detected by the refueling rover's radar is easily resolved by having each Entomopter respond to the rover's radar interrogation signal with a unique code. This code would contain a vehicle-identification code followed by useful information, such as the Entomopter's measured air speed, fuel remaining, vehicle-health monitoring parameters, and altitude above the planet's surface (which would serve both as sanity check for the rover radar, since it already has an estimate of this value, as well as new data were the Entomopter flying over a canyon, the bottom of which is occluded from the view of the rover's radar). The Entomopter's response to the rover's radar interrogation signal need not be an emission of energy. Rather, the Entomopter can remodulate the radar return by intelligently modulating its own radar cross-section. The choice of frequency for this remodulation must be different than the expected Doppler range presented by the Entomopter (above that expected from the effects of wing-beating) so that the rover can distinguish the Entomopter communication from that of the wing beating. A modulation of the radar cross-section is an amplitude modulation (AM) phenomenon and will not be affected by the Doppler shift. Very low power methods of modulating the radar cross-section of the Entomopter can be achieved by solid state means. A significant advantage to this technique is the obvious frequency deconfliction that results from multiple Entomopters not having to radiate simultaneously. As shown in Figure 4-4, the information about Entomopter locations, rover range, and obstacle locations can be impressed upon the interrogating radar signal as a frequency that is above the expected Doppler due to the skin return. The flapping-induced Doppler will not enter into this because only the radial closing rate of the Entomopter with the refueling rover will contribute to the Doppler shift seen by the Entomopter. For maximum flight speeds on the order of 30 m/s, the Doppler shift seen on the radar carrier by a painted Entomopter will be Figure 4-4: Rover-centric Information Paths Used in Navigation ƒd (platform) = 2(30 m/s)(100 cm/m) ÷ 0.3 cm = 20 kHz. Choosing a frequency modulation for the 95 GHz carrier that is ten times this value (200 kHz) would provide adequate FM information bandwidth while at the same time avoiding any corruption due to Doppler shift. 233
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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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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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