Future of Space and Earth Robotic Exploration: Scientific and Technological Challenges and Opportunities

Charles Elachi

NASA Jet Propulsion Laboratory

California Institute of Technology

INTRODUCTION

Throughout the ages humans have explored the world around them to gain more knowledge and apply it to better our physical as well as intellectual life. From the early cave dwellers, to the Phoenicians, Greeks, Ptolemy, Zheng He, Marco Polo, Ibn Battuta, da Gama, Columbus, Magellan, Cartier, Cook, Lewis, Clark, Powell, Sir Hillary, Hubble, Hale, Armstrong, you, me and each one of us have been driven to explore for a variety of reasons, be it economical, intellectual, military, survival, or just the pure joy of expanding our horizon. All of these quests were limited to our planet or using observations of the heavens from Earth bound tools until half a century ago when advances in rocketry freed us to explore beyond our “Blue dot” and to look back at our own world in a whole different way.

Today’s generations take it for granted to “Google™” any location on Earth (and in the sky) and get detailed images acquired by satellites. You can access weather satellites data on the Web. Use digital coding techniques on our cell phone, which have been developed for deep space communications. Apply image enhancement techniques in the doctor’s office which were developed for planetary images analysis. Purchase medical thermometers and scanning devices with infrared detectors developed for orbital telescopes. These are just few examples of technological payoffs which were first developed in our adventure of space exploration, and now are embedded in our daily lives.

Fifty years ago, two small satellites, Sputnik and Explorer 1, changed our world from then to now. As of now, just NASA alone, has more than 58 robotic scientific explorers across the solar system, not counting the Space Station, and satellites developed by other U.S. agencies and other nations. We are in a Golden Age of Exploration, but we have only barely got a glimpse of the first chapter of the “Book of the History and Future of Our Universe.”

EXPLORING OUR SOLAR SYSTEM

Many people are surprised when they hear that the United States has had continuous robotic presence on or around Mars. Since the arrival of the Mars Global Surveyor a decade ago, orbiting scientific spacecraft and surface rovers have been providing us with information about the surface and atmosphere of our neighboring planet in order to better understand its evolution and why it took a different path than our home planet, even though we share the same “solar system neighborhood.” Technological advances in electronics, light weight structures, heat shields, imaging systems, and so on, have enabled us to put “robotic geologists” on another planet to explore on our behalf, and within the next decade we will have “robotic chemists” and “robotic biologists” roving on Mars to enable us to better understand the past, present or future potential habitability of another world which is the same size of the landmass on Earth, and prepare for future human expeditions.

Mars tends to get a lot of public attention due to being a popular topic for science fiction writers, and because of the two long-lived explorers Spirit and Opportunity. But the solar system has a wide variety



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Future of Space and Earth Robotic Exploration: Scientific and Technological Challenges and Opportunities Charles Elachi NASA Jet Propulsion Laboratory California Institute of Technology INTRODUCTION scientific explorers across the solar system, not counting the Space Station, and satellites developed by other U.S. Throughout the ages humans have explored the world agencies and other nations. We are in a Golden Age of around them to gain more knowledge and apply it to Exploration, but we have only barely got a glimpse of better our physical as well as intellectual life. From the the first chapter of the “Book of the History and Future early cave dwellers, to the Phoenicians, Greeks, Ptol- of Our Universe.” emy, Zheng He, Marco Polo, Ibn Battuta, da Gama, Columbus, Magellan, Cartier, Cook, Lewis, Clark, EXPLORING OUR SOLAR SYSTEM Powell, Sir Hillary, Hubble, Hale, Armstrong, you, me and each one of us have been driven to explore Many people are surprised when they hear that the for a variety of reasons, be it economical, intellectual, United States has had continuous robotic presence on military, survival, or just the pure joy of expanding our or around Mars. Since the arrival of the Mars Global horizon. All of these quests were limited to our planet Surveyor a decade ago, orbiting scientific spacecraft and or using observations of the heavens from Earth bound surface rovers have been providing us with information tools until half a century ago when advances in rocketry about the surface and atmosphere of our neighboring freed us to explore beyond our “Blue dot” and to look planet in order to better understand its evolution and back at our own world in a whole different way. why it took a different path than our home planet, Today ’s generations take it for granted to even though we share the same “solar system neigh- “Google™” any location on Earth (and in the sky) borhood.” Technological advances in electronics, light and get detailed images acquired by satellites. You can weight structures, heat shields, imaging systems, and access weather satellites data on the Web. Use digital so on, have enabled us to put “robotic geologists” on coding techniques on our cell phone, which have been another planet to explore on our behalf, and within developed for deep space communications. Apply the next decade we will have “robotic chemists” and image enhancement techniques in the doctor’s office “robotic biologists” roving on Mars to enable us to which were developed for planetary images analysis. better understand the past, present or future potential Purchase medical thermometers and scanning devices habitability of another world which is the same size of with infrared detectors developed for orbital telescopes. the landmass on Earth, and prepare for future human These are just few examples of technological payoffs expeditions. which were first developed in our adventure of space Mars tends to get a lot of public attention due to exploration, and now are embedded in our daily lives. being a popular topic for science fiction writers, and Fifty years ago, two small satellites, Sputnik and because of the two long-lived explorers Spirit and Explorer 1, changed our world from then to now. As Opportunity. But the solar system has a wide variety of now, just NASA alone, has more than 58 robotic 11

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120 FORGING THE FUTURE OF SPACE SCIENCE activities or morphology. Io has present volcanic activ- ity that is reshaping its surface. Titan has a methane cycle similar to our planets’ hydrologic cycle and its North pole has numerous large lakes of hydrocarbon. Enceladus is ejecting water particles from its surface in a geyser-like fashion. We are truly having a first glimpse at a wide variety of other worlds. This was done with a small number of flyby and/or orbiting spacecraft which are the Lewis and Clark of the solar system. Over the next few decades we will be sending more sophisticated orbiters, balloons, landers, penetrators, submarines, and so on, which will explore in depth these new worlds. Every time we send a mission to a new celestial object, we are surprised, and in the process gain new knowledge, be it from the analysis of the particles in comet tails acquired by Stardust, to the unexpected larger ejecta from Tempel 1 Deep Impact encounter. In addition to its eight planets (nine if you count Pluto), and their satellites, the solar system has thousands of FIGURE 8.1 O pportunity tracks in Meridiani Planum. small objects which can give us clues of how we came SOURCE: Courtesy of NASA/JPL. here. These includes active comets, main belt asteroids, dead comets, Trojan objects, Kepler belt objects, Earth of exciting targets to explore and better understand crossing objects, and so on. With our technology we planetary evolution and potential habitability. will be able to encounter, observe, land and possibly The Jovian and Saturnian systems are effectively nudge some of these objects to better decipher the his- miniature planetary systems with disks of particles tory of our solar system, and in some rare but important (rings) and a wide spectrum of satellites which have vol- cases, avoid a major catastrophic impact. canic, tectonics, geyser-like, atmospheric and weather Mercury, Venus, Uranus, Neptune and Pluto are activities, among others. Europa and Enceladus seem also key pieces in the puzzle of the history of our to have subsurface oceans directly expressed in surface FIGURE 8.2 Opportunity tracks at Victoria Crater. SOURCE: Courtesy of NASA/JPL-Caltech/Cornell University.

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121 FUTURE OF SPACE AND EARTH ROBOTIC EXPLORATION FIGURE 8.3 O ppor - tunity Image of Cape Vincent in Victoria Crater. S OURCE: Courtesy of NASA/JPL/Cornell University. neighborhood. For example, why is Venus, a planet as we dramatically increase the amount of greenhouse similar in size to ours, have such a different atmospheric gases in our atmosphere? Missions planned in the next environment and a hellish temperature and pressure decade with sophisticated remote sensing instruments, at its surface? Is our planet heading in that direction balloons, probes, and possible surface stations will hopefully shed more light on its evolution path. NEIGHBORING SOLAR SYSTEMS A decade ago, the topics of the presence and, if so, char- acteristics of planets around other stars was left to few science fiction writers and “fringe” scientists. Today, the field of “Exoplanet” studies is one of the most active and exciting scientific fields of research and has captured the public imagination. Detection of planets around FIGURE 8.4 Methane lakes on Saturn’s moon Titan (Cassini FIGURE 8.5 Geysers on Saturn’s moon Enceladus (from Cassini). Radar). SOURCE: Courtesy of NASA/JPL/USGS. SOURCE: Courtesy of NASA/JPL/Space Science Institute.

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122 FORGING THE FUTURE OF SPACE SCIENCE FIGURE 8.6 Saturn’s rings (Cassini). SOURCE: Courtesy of NASA/JPL/Space Science Institute. other stars with what seems to be exoteric astrometric techniques, makes front cover headlines. More than a hundred planets have been detected and their proper- ties (mass, orbit, composition) are turning upside down our models of how planetary systems look like, showing significant differences from the simple orderly model of our own solar system. Within the next decade, we will be able to get “family portraits” of the neighboring few thousands FIGURE 8.7 Comet Temple 1 before and after Deep Im- planetary systems and statistical assessment of how 8.07a&b combined.eps pact. SOURCE: Courtesy of NASA/JPL-Caltech/University of common they are in our galaxy and beyond. This will Maryland. FIGURE 8.8 Venus surface perspective view (Magellan). SOURCE: Courtesy of NASA/JPL.

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12 FUTURE OF SPACE AND EARTH ROBOTIC EXPLORATION be done through a series of techniques which require continuous advances in technology ranging from very large arrays of detectors (for transit surveys like on Kepler), very high accuracy metrology (for astrometric missions), advanced adaptive optical systems (for direct imaging coronographs), and very accurate formation flying (for interferometric direct imaging). Acquiring significant information about other planets can be done even if we detect them as single points of light. Their mass, orbit, size, temperature, atmospheric composi- tion and some temporal variation can be determined without resolving the planet beyond one pixel. Getting resolvable planet images might be a herculean endeavor, but it is not any more far fetched than having rovers on FIGURE 8.9 K epler will observe transits of exoplanets. Mars as viewed by the technologists of 1958 who were SOURCE: Courtesy of NASA/JPL. working on Sputnik or Explorer 1. FIGURE 8.10 Exoplanet Astrometric Mission (Planet Quest). SOURCE: Courtesy of NASA/JPL.

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12 FORGING THE FUTURE OF SPACE SCIENCE atmosphere. The advent of space telescopes, with large light weight optics, large high sensitivity focal planes across the spectrum, have been a critical element in advancing our knowledge of the universe around us. Images from the Hubble Telescope, Spitzer, Chandra and other space telescopes are now embedded in our textbooks, used by artists and advertisers, and are com- mon front cover news. Over the next decade, the advent of the James Webb Space Telescope ( JWST), Herschel, P lanck, NuSTAR, GLAST, and other telescopes presently under study (Con-X, LISA, JDEM, and so on) will allow us to see back to the early dawn of our universe, trace its evolution, and better understand its composition and detect gravitational waves emanating from violent astronomical events. The recent discovery FIGURE 8.11 James Webb Space Telescope. SOURCE: Cour- that we do not even understand what most of the uni- tesy of NASA/GSFC. verse is made of clearly shows that our quest of space exploration still has many discoveries to be made. ADVANCES IN ASTRONOMY OBSERVING OUR PLANET Advances in astronomy has been always driven by It is hard to believe that only a century ago we could t echnological advances. Getting better resolution only observe to the horizon at any time. Today we simply requires larger optics. Deeper viewing requires routinely can observe, monitor and study our planet on more sensitive detectors. Mitigating the atmospheric a global and continuous basis. We now regularly moni- “ blurring” requires adaptive optics or getting above the FIGURE 8.12 Laser Interferometer Space Antenna (LISA). SOURCE: Courtesy of NASA.

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12 FUTURE OF SPACE AND EARTH ROBOTIC EXPLORATION FIGURE 8.14 Topex/Poseidon and Jason missions ocean elevation monitoring. SOURCE: Courtesy of NASA/JPL. FIGURE 8.13 View of Earth’s gravity field acquired with the Gravity Recovery and Climate Experiment (GRACE). SOURCE: Courtesy of University of Texas Center for Space Research and NASA. tor the ocean temperature and currents, wind patterns under the cloud cover of hurricanes, changes of the ice cover at both poles, the dynamics of the ozone layer that protects life on Earth, the changes in the vegeta- tion cover, among many other environmental elements. Within the next decade we will be able to measure the ocean salinity from space, map in three dimensions the emissions, circulation and absorption of carbon dioxide, the subtle tectonic motion of plates leading to assessment of high risk areas, monitor the changes in biomass and the full inventory of atmospheric gases, detect subtle changes in the surface water (with alti- metric changes), and subsurface water (with gravity changes). Our ability to monitor from space almost all the “health symptoms” of our planet is putting us at the threshold of being able to provide the public and the policymakers with scientifically based knowledge of the present and future impact that we are having on our planet. As we better understand, improve and FIGURE 8.15 Interferometric synthetic aperture radar map- verify our global model, we will then be able to assess ping of earthquake displacement. SOURCE: Courtesy of Andrew the impact of specific actions that are proposed to be a Newman, Georgia Institute of Technology, http://geophysics. better custodian of our home planet. eas.gatech.edu.