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

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Planetary Exploration Using Biomimetics An Entomopter for Flight on Mars As an example, two SAR images of the Mars terrain are obtained with antennas displaced along the cross-track direction from one another using one or two Entomopters. The two-way distance from each antenna to a resolution cell on the ground will differ by an amount ∆d. By subtracting the phases between the two images, a phase difference map can be produced, and this resolution cell will have a phase corresponding to ∆d. Now consider a resolution cell containing a raised structure, such as a rock or other terrain feature. Depending on the height of the feature, the difference in distance from the two antennas to the terrain feature will be some other value ∆d´. Thus, the phase difference map encodes information about the third dimension of elevation, which is unobtainable using a single SAR image. Figure 5-2: Possible Flight Configuration for 3D Mapping ISAR has all weather capability, allowing functionality in dust storms where the ground would be obscured under theses conditions using laser radar or electro-optic sensors. However, it is sometimes limited in imaging steep slopes and high depression angles [2] such as Mars caverns. ISAR maps can also readily detect change, which shows up as a random mismatch of phases between the before and after ISAR maps. In this manner, changes in the Mars terrain can be monitored over time. 5.3 Digital Terrain System A digital terrain system (DTS) as described in [97] uses a stored map of terrain elevation with aircraft dynamics and measured height above the ground to provide navigation and terrain reference cues. DTS could provide terrain referenced navigation, terrain following, predictive ground collision avoidance, obstruction warning, and cueing and ranging. If DTS proves to be feasible for the Entomopter mission, a digital terrain system could be used to store a digital map of the terrain for navigation and collision avoidance, potentially resulting in significant savings in 262 Phase II Final Report
Chapter 5.0 Potential Payload Functions Using a Communication/ Control Subsystem power and flight hardware. Prior knowledge of the exploration terrain could obviate the need for constant radar readings for collision avoidance and provide an optimum flight pattern. A single Entomopter could be tasked with this digital terrain mapping of a designated area using ISAR as described above. Upon its return to the refueling rover, the digital map could be uploaded to the rover and this information transferred to the other Entomopters. Once the terrain map has been uploaded, it could then be used by the Entomopters to calculate optimum flight patterns. Accurate knowledge of aircraft position relative to the terrain and the terrain ahead will lead to a flight pattern based on the required clearance height and collision avoidance. This terrain-following feature would avoid energy-consuming maneuvers to avoid obstacles and allow the Entomopter to fly at the minimum required clearance height. The reduction in required mass and power on the other Entomopters would allow additional payload functions to be accomplished. This procedure could be repeated for each exploration area. Alternatively, the Entomopters could have modular payload, where the payload is switched for the desired exploratory function. In this manner, each Entomopter would create a digital map of the terrain for a designated area. Upon completion, it would return to the refueling rover and shed its mapping gear to be replaced by additional payload, such as video equipment. The first method seems to be a more realistic alternative. Switching complex payload equipment might sacrifice reliability. The key capability of a DTS is terrain-referenced navigation. A combination of the stored digital map of terrain elevation and real-time measurements of the aircraft height above the ground allows highly accurate navigation referenced to the terrain without external signals. Typically, this terrain-referenced navigation includes processing and combining data from a dead reckoning system, radar altimetry to give the height above ground, and the digital terrain elevation data map. Generally, there are two modes of operation: Acquisition mode, where the system is initialized by identifying the initial position of the aircraft, and Track mode, where navigation data is provided at a rate of about 2 Hz to 4 Hz. Acquisition mode involves processing a number of altimetry readings to identify aircraft position relative to the terrain map database. This approach relies on the uniqueness of ground profiles within the map. The Acquisition mode will likely be unnecessary for the Entomopter mission, because its initial position relative to the refueling rover will always be known. Thus, the Track mode can immediately be executed. In Track mode, the aircraft has an estimated position at some point in time (update N). Based on the aircraft dynamics, a Kalman filter is used to propagate ahead (Update N+1) to provide a prediction of the height above ground level from the map database. To account for uncertainties in position, a batch of altimetry measurements can be processed to calculate the location of the aircraft within the map database. The difference between the actual position and the predicted position can be used to correct the Kalman filter estimates. Again, the operation relies upon the uniqueness of the terrain to identify the unique position in the map database. If the Mars terrain is relatively flat, performance will be degraded. Whether a DTS would be used for the proposed Entomopter mission would be highly dependent on the specific mission goals. Perhaps a terrain map could be uploaded to the rover and transmitted to Earth for review. Based on that information, an Earth-bound mission planner could communicate back to the rover that the Entomopters should explore certain areas. 263
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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 3.0 Vehicle Design 3.6 Powe
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Chapter 3.0 Vehicle Design 3.6 Powe
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Page 291 and 292: Chapter 7.0 Conclusion Chapter 7.0
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Page 307 and 308: Appendix B: Sizing Results Appendix
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Phase II Final Report - NASA's Institute for Advanced Concepts

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