UNIVERSITY OF OKLAHOMA GRADUATE COLLEGE ANALYSIS OF REQUIREMENTS OF A MARS ROVER MISSION TO ACTIVE GULLIES A THESIS SUBMITTED TO THE GRADUATE FACULTY in partial fulfillment of the requirements for the Degree of MASTER OF SCIENCE By LISA BILLINGSLEY Norman, Oklahoma 2010 ANALYSIS OF REQUIREMENTS OF A MARS ROVER MISSION TO ACTIVE GULLIES A THESIS APPROVED FOR THE SCHOOL OF AEROSPACE AND MECHANICAL ENGINEERING BY Dr. David Miller, Chair Dr. Alfred Striz Dr. Kyran Mish © Copyright by LISA BILLINGSLEY 2010 All Rights Reserved. This Thesis is dedicated to my parents Leonard and Patricia Billingsley Acknowledgements I would like to express my sincere thanks to Dr. David Miller for mentoring and supporting me through my Master’s program. I am especially indebted to my family for setting me on this path to begin with. My parents, Leonard and Patricia Billingsley, raised me in an environment of math and science. They taught me logical thinking and a love of information and discussion. My older sister, Sarah, blazed the first few steps of the path I’ve walked in college. Finally, I have to thank my younger sister, Deborah, for breaking the serious pattern and providing an atmosphere of fun and relaxation. iv Table of Contents Page Chapter 1: Introduction 1 1.1 The Red Planet 1 1.2 Water: Why We Care 6 1.2.1 Life As We Know It 6 1.2.2 Astrobiology 6 1.2.3 Human Use 10 1.3 Evidence for Water 11 Chapter Two: Gullies on Mars 13 2.1 Gully Detection and Statistics 13 2.2 Dry Granular Theories 18 2.3 Solid or Liquid CO 2 20 2.4 Water/Brine 21 2.4.1 Sources of Water 24 2.5 New Gully Deposits 27 Chapter Three: Planetary Rovers 30 3.1 Lunokhod 30 3.1.1 Lunokhod 1 31 3.1.2 Lunokhod 2 32 3.1.2 Lunokhod 3 34 3.1.2 Lunokhod Mobility 34 3.2 PROP-M Rover 36 3.3 Pathfinder-Sojourner 38 3.4 Mars Exploration Rovers 41 3.5 Mars Science Laboratory 44 3.6 ExoMars 47 3.7 Marsokhod 49 3.8 Nanokhod 52 3.8.1 Nanoknod Mercury 52 Chapter Four: The Martian Environment 54 4.1 Power 54 4.2.1 Solar Power 56 4.1.2 Radioisotope Thermoelectric Generators 59 4.2 Thermal Effects 63 4.2.1 Seasons on Mars 63 4.2.2 Temperature Swings 65 4.3 Atmospheric Conditions 68 4.3.1 Pressure 69 4.3.2 Atmospheric Dust 71 v Chapter Five: Landing and Movement 76 5.1 Landing Methods 76 5.1.1 Powered Descent 76 5.1.2 Airbags 77 5.1.2 Sky Crane 80 5.2 Choosing a Landing Site 82 5.2.1 Altitude Considerations 82 5.2.1 Terrain Considerations 84 5.3 Inside the Crater 89 5.3.1 Slope 89 5.3.2 Surface and Chemicals 91 Chapter Six: Straw Man Mission 93 6.1 Payload 93 6.1.1 Cameras 93 6.1.2 Chemistry 94 6.2 Rover Base 97 6.3 Power 101 6.3.1 Time 102 6.3.2 Battery Calculations 103 6.3.3 Solar Panel Calculations 104 6.4 Entry, Descent, and Landing 107 6.5 Summary 109 6.5.1 Mission Summary 109 6.5.2 Rover Summary 110 Chapter Seven: Summary and Conclusions 112 7.1 Summary 112 7.2 Future Work 115 7.2.1 Information 115 7.2.2 Hardware 116 7.3 Conclusion 117 References 119 vi List of Tables Page 1-1 Physical properties of Earth and Mars 5 3-1 Wheel modes and their uses 51 3-2 Operational analysis of a 7 day mission 53 4-1 Properties of RTG materials 60 4-2 Length of Mars seasons 63 4-3 Solar irradiance at Mars 65 4-4 Mars’s atmospheric information 68 4-5 Mars’s atmospheric composition 69 6-1 Marsokhod specifications 98 6-2 Small Marsokhod specifications 99 6-3 Solar panel size vs. energy generated 106 6-4 Details on the rover 111 vii List of Figures Page 1-1 Two pictures of the planet Mars 2 1-2 Topographical map of Mars 3 1-3 Comparison between Earth and Mars 4 1-4 Map of hydrogen distribution 12 2-1 An example of gullies on Mars 14 2-2 Statistics on gullies 16 2-3 Gullies on Earth and Mars 22 2-4 Gully apron over sand dunes 23 2-5 Pictures of the Barringer Crater 26 2-6 Gully streak in Terra Sirenum 27 2-7 Map showing slope streak and gully locations 28 3-1 Lunokhod 1 31 3-2 Lunokhod 2 34 3-3 Lunokhod Wheels 35 3-4 PROP-M rover 36 3-5 Sojourner rover 38 3-6 Computer model of Sojourner 39 3-7 Sojourner’s wheel 40 3-8 Mars Exploration Rover 41 3-9 Mars Exploration Rover wheel 43 3-10 Mars Science Laboratory 44 3-11 Comparison of Sojourner, MER, MSL, and Phoenix 45 3-12 Wheels from Sojourner, MER, and MSL 45 3-13 Schematic of MSL’s components 46 3-14 Elements of the ESA-NASA ExoMars Program 47 3-15 Marsokhod wheel design and ground clearance 49 3-16 Marsokhod images 50 3-17 Marsokhod wheel walking 50 3-18 Nanokhod with labeled parts 52 4-1 Lifespan versus wattage for various types of power systems 55 4-2 Effects of temperature on voltage and current 57 4-3 Two types of solar concentrators 57 4-4 Cassini’s Radioisotope Thermoelectric Generator 60 4-5 Seasonal images of Mars 64 4-6 Daytime temperature on Mars 66 4-7 Nighttime temperature on Mars 67 4-8 Mars elevation area distribution 70 4-9 Filter and capture magnets on Opportunity 74 4-10 Views of Mars with and without a dust storm 75 5-1 MER airbags 78 5-2 Opportunity with the landing petals partially opened 79 5-3 Proposed decent sequence for Mars Science Laboratory 80 5-4 Curve of atmospheric transmittance by altitude 83 viii 5-5 Altitude map of the Terra Sirenum region 85 5-6 Topographical map of the Terra Sirenum region 86 5-7 Altitude map of the Centauri Montes region 87 5-8 Topographical map of the Centauri Montes region 88 5-9 Model results for the deposit in the Centauri Montes region 90 6-1 One cell from Phoenix’s Wet Chemistry Laboratory 95 6-2 Marsokhod wheel walking 98 6-3 Comparison of Sojourner, MER, MSL, and Phoenix 99 ix Abstract Several rover missions to Mars have been planned and executed, and most have been successful. Still, the area of the planet that has been covered by rovers has been tiny, and there is much more to learn. This thesis covers a possible mission not currently under consideration; that of visiting areas of the surface that might be geologically active at this time. The reasons for planning this mission are covered, as well as information on past rovers. The major problems faced by rovers on Mars are reviewed, from power to atmosphere to landing. Finally, a possible rover that fits the necessary mission parameters is designed using elements of other rovers and Mars missions. Only the physical makeup of the rover is covered; the electronics, including computers and communication, are not addressed. x Chapter 1 Introduction 1.1: The Red Planet Mars is the fourth planet from the Sun. It is commonly regarded as being the most Earthlike of the other planets in the solar system: the nearest planet to Earth, a bit smaller than Earth, and one we might live on some day. Mars is also ‘known’ to be very cold, with lower gravity than Earth, no atmosphere, and water will boil instantly on the surface because it has no atmosphere. That view is not very accurate. Venus is much closer to us and much nearer in size and composition, and it is easier to reach. It is simply ignored because of its high temperature and the crushing atmosphere of the surface, which is just as deadly and is much harder to compensate for than the low pressure and temperature of Mars. Due to those difficulties, Venus has long since been forgotten as anything except a gravity well to slingshot a spacecraft. All efforts towards reaching another planet are aimed at Mars. In reality, Mars is much smaller than Earth and it does have an atmosphere, though it is a very thin one. That atmosphere permits water to stay in liquid form for at least short amounts of time, and in many places the water will freeze before it evaporates. However, some areas near the equator, in summer, do maintain temperatures in the liquid water range, and the possibilities of underground water are vast. While there are a great many difficulties facing any attempt to colonize Mars, it is the easiest other planet for humans to live on and it is expected that the Red Planet will be the first extraterrestrial colony (not counting the Moon). 1 Figure 1-1: Two pictures of the planet Mars. The top picture is centered on the Valles Marineris, while the north pole is visible in the bottom one. 2 Figure 1-2: A topographical altitude map of Mars. The left circle is the south pole, while the right circle is the north pole. Note the elevation differences between the hemispheres. [Picture from NASA JPL website; taken by Mars Global Surveyor.] 3 Figure 1-3: A comparison between Earth and Mars, showing the year, gravity, energy received from the sun, and atmospheric composition.