Numerical Modeling of Magnetic Capture of Martian Atmospheric Dust ______
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____________________________________________________________________________ Numerical Modeling of Magnetic Capture of Martian Atmospheric Dust __________________________________________________________________________ Kjartan Kinch Mars Simulation Laboratory Institute of Physics and Astronomy Aarhus University, Denmark Ph.D. Thesis Revised Edition March 2005 III Table of Contents Table of Contents .................................................................................. III List of Publications...............................................................................VII Preface.................................................................................................... IX 1. Introduction.........................................................................................1 1.1. The Mars Exploration Rover mission .................................................................1 1.2. Dust in the Martian Atmosphere .........................................................................2 1.3. Magnetic Properties Experiments .......................................................................3 1.4. The Present Work................................................................................................5 1.4.1. Motivation and Method......................................................................................5 1.4.2. Structure of the Thesis .......................................................................................5 2. The Planet Mars..................................................................................7 2.1. Fundamental Characteristics ...............................................................................7 2.2. Geology ...............................................................................................................8 2.2.1. Morphology .......................................................................................................8 2.2.2. Composition.....................................................................................................10 2.3. Water on Mars...................................................................................................11 2.4. Atmosphere .......................................................................................................15 2.4.1. Aeolian Features ..............................................................................................15 2.4.2. Atmospheric Composition ...............................................................................18 2.5. Dust ...................................................................................................................20 2.5.1. Optical Measurements .....................................................................................20 2.5.2. Formation.........................................................................................................21 3. Spirit and Opportunity.....................................................................25 3.1. The MER Mission .............................................................................................25 3.2. Rover Design.....................................................................................................27 3.2.1. Design Overview .............................................................................................27 3.2.2. Mini-TES .........................................................................................................29 3.2.3. Pancam.............................................................................................................29 3.2.4. Engineering Cameras.......................................................................................32 3.2.5. Microscopic Imager .........................................................................................33 3.2.6. Alpha Particle X-ray Spectrometer..................................................................35 3.2.7. Mössbauer Spectrometer..................................................................................36 3.2.8. Rock Abrasion Tool.........................................................................................37 3.3. MER Operations................................................................................................38 3.3.1. Rover Operations .............................................................................................38 3.3.2. Camera Operations...........................................................................................39 IV 3.4. MER Results .....................................................................................................41 3.4.1. Introduction......................................................................................................41 3.4.2. The Spirit Rover in Gusev Crater ....................................................................41 3.4.3. The Opportunity Rover on the Meridiani Plains..............................................47 3.5. The Magnetic Properties Experiment on MER.................................................54 3.5.1. Purpose.............................................................................................................54 3.5.2. The Sweep Magnet ..........................................................................................55 3.5.3. The RAT Magnets ...........................................................................................56 3.5.4. Design of the Capture and Filter Magnets .......................................................57 3.5.5. Results from the Capture and Filter magnets...................................................60 4. Dynamics of Airborne Dust..............................................................65 4.1. The Reynolds Number ......................................................................................65 4.2. Drag Force.........................................................................................................66 4.3. Terminal Velocity and Characteristic Time ......................................................68 4.4. The Magnetic Force ..........................................................................................69 4.5 Summary ...........................................................................................................71 5. Experimental Method.......................................................................73 5.1. Wind Tunnel Design .........................................................................................73 5.2. The Laser Doppler Anemometer.......................................................................75 5.3. The Salten Skov Mars Analogue Dust ..............................................................76 5.4. Quantification of Amounts of Deposited Dust..................................................77 5.5. Equivalent Pressures .........................................................................................78 5.6. Experimental Geometry ....................................................................................80 6. Charging and Aggregation...............................................................83 6.1. Electrical Charging of Dust Grains ...................................................................83 6.2. Laboratory Simulation Experiments .................................................................84 6.3. Aggregation.......................................................................................................87 6.4. The Dust Cycle on Mars....................................................................................89 7. The CFD Model.................................................................................91 7.1. General Method.................................................................................................91 7.1.1. CFD..................................................................................................................91 7.1.2. Example: Wind Profile Above a Flat Plate......................................................92 7.1.3. The STAR-CD Code........................................................................................92 7.2. Specific Model Conditions................................................................................94 7.2.1. General Considerations....................................................................................94 7.2.2. Model Geometry ..............................................................................................95 7.2.3. Computational Grid .........................................................................................96 7.2.4. Boundary Conditions .......................................................................................98 7.2.5. Fluid Properties................................................................................................99 7.2.6. Dust Properties.................................................................................................99 7.3. Calculated Flow Field Data.............................................................................100 7.3.1. Wind velocity.................................................................................................100 7.3.2. Turbulence and Pressure................................................................................103 V 8. CFD Dust Capture Results.............................................................105 8.1. Introduction .....................................................................................................105