  | ||
|
|
USA in Space, 3rd Edition Mars Exploration Rovers Date: June 10, 2003 Type of Mission: Planetary exploration The Mars Exploration Rovers (MERs), twin robotic expeditions exploring the surface of Mars, landed on different locations on opposite sides of Mars to maximize the scientific return. With the ability to trek the length of a football field each day, they can explore a larger portion of the Martian surface than previous missions. Each rover contains a package of scientific instruments designed to analyze Mars's surface geology to help trace the history of liquid water on Mars. Key Figures Jim Erickson, project manager Joy Crisp, project scientist Albert Haldemann, deputy project scientist Steve Squyres, science instrument principal investigator Summary of the Mission The Mars Exploration Rovers (MERs) were launched about a month apart in the summer of 2003 and reached Mars in early 2004. The first rover, Spirit or MER-A, was launched on June 10 from a Delta II 7925 rocket. The second, Opportunity or MER-B, was launched on July 7 atop a Delta 7925H rocket. The H indicates Heavy and was used because the second mission launched when the relative positions of Earth and Mars required more energy to get to Mars. Both were launched from Cape Canaveral, Florida. Both of these MER missions were timed to take advantage of the closest Mars approach to Earth in approximately sixty thousand years. The probes took the fastest possible trajectories to Mars and arrived in January, 2004. After a seven-month journey, Spirit landed at Gusev Crater on January 3, 2004. Opportunity soon followed by landing on Mars at Meridiani Planum on January 25, 2004. Unfortunately two other missions, the Japanese Nozomi probe and the European Beagle 2 mission, which were planned to arrive at Mars near the same time, did not succeed. The MER mission used a landing system pioneered by the 1997 Pathfinder mission, which used a combination of rockets, parachutes, and airbags to cushion the blow of striking the Martian surface. Because the MERs were heavier than the Pathfinder lander, parachutes that were 40 percent larger were used. After the parachute was opened to provide initial slowing, the rockets fired to bring the landers to a stop about 10 to 15 meters above the surface. Finally the airbags inflated to cushion the remaining fall. The landers bounced several times before finally coming to rest on the Martian surface and deflating the airbags. The lander petals were then free to open, allowing the rovers to deploy their solar arrays and begin exploring Mars. Shortly after landing, the computer on board Spirit experienced some memory difficulties. Mission controllers were able to resolve the problems in a little over a week by purging files and reformatting the flash memory. After this initial difficulty, both rovers performed well for their originally scheduled ninety-day mission and beyond. Each 170-kilogram rover contains a suite of instruments designed to allow it to explore the geology of Mars. These include cameras and instruments designed for detailed studies of the chemical compositions of selected rocks. The nine cameras on each rover include six engineering and three scientific cameras. The four Hazard Avoidance Cameras (Hazcams) are mounted on the front and back of the rovers. Their 120{deg} fields of view are pointed downward to see obstacles that might interfere with the rover's motion. Having two in each direction gives three-dimensional images, just as two eyes give human beings three-dimensional depth perception. The two 45{deg} field of view Navigation Cameras (Navcams) provide a three-dimensional forward view higher than the Hazcams and allow ground controllers to see where the rover is going. The two Panoramic Cameras (Pancams) have the same resolution as the human eye, so they can mimic what a geologist would see standing on the surface of Mars. Because there are two Pancams, they can also provide three-dimensional imaging, like a pair of human eyes. In addition, these cameras have a number of color filters to provide both some basic spectral information and color pictures. A solar filter allows the Pancams to locate the Sun's position in the sky. When combined with the time of Mars's day, the Sun's position provides navigational information. In addition to the large view cameras, the Microscopic Imager (MI) takes extreme close-up pictures. This camera is mounted on a robotic arm that can swing into position very close to the rock of interest. The camera is also mounted behind a microscope, so it provides the equivalent of a human geologist's observations of a rock sample through a microscope. As on most space probes, the cameras provide dramatic images, but the information provided by the other scientific instruments is at least as important. The Miniature Thermal Emission Spectrometer (Mini-TES) provides infrared spectra of the Martian rocks, soil, and atmosphere. These spectra reveal much about the chemical composition and mineral structure of the rocks and soil. The Mini-TES is particularly important in searching for minerals that were produced in the presence of water. Atmospheric spectra taken with the Mini-TES tell mission scientists about the temperature and the presence of dust and water vapor in the atmosphere. Two spectrometers study the chemical composition of the Martian surface. The Mössbauer Spectrometer (MB) is designed specifically to study the iron abundance in the mineral content of Martian rock and soil samples. Because iron is magnetic, the MB also helps scientists study the sample's magnetic properties. Magnet arrays mounted at various positions on the MERs collect magnetic samples for analysis by the MB. Chemical compositions other than iron use the Alpha Proton X-Ray Spectrometer (APXS). Alpha particles emitted during radioactive decay tell mission scientists about the presence and abundance of various radioactive isotopes in the mineral structure of rock samples. The x-ray spectra also provide information about the chemical samples' composition. The Rock Abrasion Tool (RAT), located on the end of the robotic arm, can grind a 4.5-centimeter-diameter hole into a selected rock sample. A half-centimeter hole takes about two hours to grind. Mission scientists use the RAT to expose and study the interior structure of rocks. In late October, 2004, the MER mission passed the 50,000-picture milestone. This number represents more than twice as many pictures as taken by all previous Mars landers. In early November, 2004, the Opportunity solar panels received a mysterious power boost that may have been caused by wind blowing accumulated dust off the solar panels. The MER missions, originally planned for about ninety days, performed so well that on October 1, 2004, the National Aeronautics and Space Administration (NASA) extended the missions for a second time. Some rover components were beginning to show signs of age, but they were still exploring Mars's surface. On April 6, 2005, with both rovers suffering from only minor problems and each covering greater and greater distances during translations across the Martian surface, NASA announced that the MER program was being extended for the third time. This latest extension would run for the coming eighteen months. Few program officials and scientists would have been so optimistic before launch to have expected the rovers to last this long in the severity of the Martian environment. Contributions The primary scientific objective of the MER missions was to find evidence of past water on Mars by looking for signs of past water activity in Martian rocks and soils. Other important scientific goals included understanding the environmental conditions when liquid water was present on Mars; understanding the composition and distribution of minerals, particularly those containing iron, near the landing site; and understanding the geologic processes that formed the minerals and terrain at the landing sites. Finally, the studies on the ground can check the conclusions reached about the local Martian geology from orbiter studies and thereby provide confidence that conclusions reached from orbital studies elsewhere on Mars are correct. The Gusev Crater and Meridiani Planum landing sites were chosen for their potential as sites where water once existed. Gusev Crater, the landing site for the Spirit rover, is an impact basin about the size of the state of Connecticut and was once thought to have been a giant lake. However, during the three-month primary mission Spirit failed to find any lake-related deposits at this site. If they ever existed, they have apparently been disrupted by subsequent impacts. Rocks at the Spirit landing site are olivine-bearing basaltic rocks, a type of volcanic rock not previously seen on Mars. The RAT ground off surface layers on rocks at this site, revealing subsurface veins possibly altered by the presence of water. Rock coatings are also consistent with brief periods of moisture in the past, even if not indicative of a large, long-term lake. Spirit also found evidence that subsurface water percolated to the surface at Gusev Crater. After exploring Gusev Crater, Spirit started the trek for the nearby Columbia Hills, named after the crew of the ill-fated space shuttle flight (destroyed upon reentry on February 1, 2003), to search for clues to the early history of Gusev Crater. Initial indications are that the hills are layers of volcanic ash. Meanwhile, Opportunity found evidence for water at Meridiani Planum inside a crater named Eagle. The rocks, containing sediments from evaporation, appear to have formed in a body of slow-moving salt water, perhaps at the shoreline of a salty sea. The rocks at this site contain high concentrations of hematite, which forms in wet conditions. These rocks provide definite direct evidence of liquid water in Mars's past. Samples collected by the Rovers' magnets indicate that most of the rocks on Mars contain iron. Oxidized iron gives Mars its rusty red color. Studies of patterns on the rocks are also helping mission scientists understand the wind erosion on Mars, currently the most significant source of Martian erosion. Some rocks found on Mars also resemble meteorites found on Earth that are thought to originate from Mars, bolstering the evidence that they truly originated on Mars. Context The MER missions are part of NASA's long-term program to explore Mars. The program has four main scientific goals: (1) to determine if there was ever life on Mars (2) to understand the Martian climate (3) to understand the Martian geology (4) to pave the way for human exploration of Mars In 1976, the first Viking landers on Mars found no direct evidence for life on Mars but did find evidence suggestive of large amounts of liquid water in the past in the form of dry riverbeds. The MER missions found more direct evidence of geologic processes requiring liquid water on the surface of Mars. The first Viking landers on Mars had no mobility. The 1997 Pathfinder mission was the first mobile probe to land on Mars. The MER probes have greater mobility compared with the Pathfinder and were able to trek several kilometers from their impact points. There are also spin-off benefits from the MER mission. Engineers at the Jet Propulsion Laboratory (JPL) are modifying the software used to support the Rovers to create a virtual pediatric intensive care unit. When this work is completed, pediatricians around the world will be able to access this database to find the latest research needed to treat difficult pediatric cases. See Also Jet Propulsion Laboratory; Mariner 3 and 4; Mars Climate Orbiter and Mars Polar Lander; Mars Global Surveyor; Mars Observer; Mars Odyssey; Mars Pathfinder; Mars Reconnaissance Orbiter; Planetary Exploration; Private Industry and Space Exploration; Viking Program; Viking 1 and 2. Further Reading Chaisson, Eric J., and Steve McMillan. Astronomy Today. 5th ed. Upper Saddle River, N.J.: Pearson Prentice Hall, 2004. The chapter on Mars in this introductory astronomy textbook provides background for understanding the exploration of Mars. Godwin, Robert, ed. Mars: The NASA Mission Reports. Vol. 1. Burlington, Ont.: Apogee Books, 2000. A thorough presentation of NASA documents relating to the Mars programs, from Mariner 4 through Mars Global Surveyor. Includes press kits and a CD-ROM filled with special programs and interviews. ____________, ed. Mars: The NASA Mission Reports. Vol. 2. Burlington, Ont.: Apogee Books, 2004. A thorough presentation of NASA documents relating to the Mars programs from Mars Odyssey through the Mars Exploration Rovers. Includes a DVD of NASA data, bonus interviews, and NASA animation. Hartmann, William K. Moons and Planets. 5th ed. Belmont, Calif.: Thomson Brooks/Cole, 2005. Provides detailed information about all objects in the solar system. Suitable for high school students, general readers, and undergraduates studying planetary geology. Mishkin, Andrew. Sojourner: An Insider's View of the Mars Pathfinder Mission. New York: Berkley Books, 2003. A thorough exploration of the Mars Pathfinder mission that provides detailed historical perspective on the exploration of the surface of Mars begun by Viking and continued by the Mars Exploration Rovers. Moomaw, B. "Spirit Lands at Gusev." Astronomy 32, no. 4 (2004): 32. This article tells the inside story of Spirit's landing on Mars. Page 48 of the same issue also has an article titled "Envisioning Mars" with many good images of Mars. Naeye, R. "Red-Letter Days." Sky and Telescope 107, no. 5 (2004): 44. This article describes the MER mission through April, 2004, giving both mission details and scientific results. ____________. "Software Links Pediatric Doctors with New Research." Obesity, Fitness and Wellness Week, October 30, 2004, p. 231. This article describes a virtual pediatric intensive care unit that uses modified software similar to that used by the MER mission. National Aeronautics and Space Administration, Jet Propulsion Laboratory. "Mars Exploration Rovers." http://marsrovers.jpl.nasa.gov. Accessed June, 2005. This official Web site for the Mars Exploration Rovers contains a wealth of information about the mission, including overviews of the program, the science, the people involved, and mission details. Paul A. Heckert |
||||||||||||||||||||||||||||||||||||
If you need help with products and ordering, setting up a new account or working with this website, call or email us:
 |
SALEM PRESS, INC. · 131 North El Molino Avenue · Pasadena · CA 91101 © Salem Press, Inc. All Rights Reserved. |