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Дата: 19 января 1998 (1998-01-19) От: Alexander Bondugin Тема: 1997 - The Year Of Mars Pathfinder Привет всем! Вот, свалилось из Internet... From The "JPL Universe" Special issue: 1997 in review January 9, 1998 1997 - The year of Mars Pathfinder Mission captivates the world while setting new standards in planetary exploration By DIANE AINSWORTH Of all the headline news in 1997, Mars Pathfinder's remarkable landing and performance on the surface of frozen, nearly airless Mars stole the show. Pathfinder became a landmark mission and a catalyst for new and affordable ways of exploring other worlds. Pathfinder's landing marked America's return to the red planet after more than 20 years. In addition to a swift, seven- month cruise to the planet, Pathfinder dived directly into the Martian atmosphere and landed with the aid of a parachute and giant cocoon of airbags. This novel entry technique had never been demonstrated before. Nor had any spacecraft before Pathfinder carried a roving vehicle the size of a small microwave oven to the surface of another planet. Pathfinder's companion rover, named "Sojourner" after Sojourner Truth, a female abolitionist who lived during the American Civil War, was the first robotic vehicle ever to make direct measurements of rocks and soil on Mars. Over the course of three months -- which was three times the design lifetime of the spacecraft -- Mars Pathfinder returned about 2.6 gigabits of data, which included more than 16,000 images of the Martian landscape from the lander camera, 550 images from the rover and about 8.5 million temperature, pressure and wind measurements. All science objectives had been fulfilled when the mission ended, 83 days after a nearly perfect landing on July 4. The only remaining objective was to complete a high-resolution 360-degree image of the landing site called the "Super Pan," of which 83 percent had been received. The last successful data transmission cycle from Pathfinder was completed at 3:23 a.m. Pacific Daylight Time on Sept. 27, 1997. Sojourner, built to last seven days, wound up roaming the floor of an ancient flood basin and exploring about 250 square meters (820 square feet) of the Martian surface. In all, the rover traveled a total of about 100 meters (328 feet) in 230 commanded maneuvers, performed more than 16 in-situ chemical analyses of rocks and soil, and carried out numerous soil mechanics and technology experiments. "The mission demonstrated a reliable and low-cost system for placing science payloads on the surface of Mars," said Project Manager Brian Muirhead. "We've validated NASA's commitment to low-cost planetary exploration, shown the usefulness of sending microrovers to explore Mars, and obtained significant science data to help understand the structure and meteorology of the Martian atmosphere and to understand the composition of the Martian rocks and soil." "Pathfinder was an unequivocal success and has given us phenomenal insights into how to operate future landers and rovers on the surface of Mars," added Dr. Wesley Huntress, associate administrator for science at NASA Headquarters, when the mission was officially declared over. "I congratulate the entire Pathfinder team on their accomplishment, which is a lofty but wonderful standard for future missions to attempt to exceed." Part of NASA's Discovery program of low-cost planetary missions with highly focused science goals, the spacecraft used an innovative method of directly entering the Martian atmosphere. Assisted by an 11-meter (36-foot) diameter parachute, the spacecraft descended to the surface of Mars and landed, using airbags to cushion the impact. This innovative method of diving into the Martian atmosphere worked like a charm. "Every event during the entry, descent and landing (EDL) went almost perfectly," said Mission Manager Richard Cook. "The sequences were executed right on time and well within our margins." Pathfinder's descent through the Martian atmosphere was nearly flawless. After being suspended from a 20-meter (65-foot) bridle and firing its retro rockets, the spacecraft released a 5.8-meter (19-foot) diameter cluster of airbags intended to soften the landing. The entry, descent and landing sequence marked the first time this airbag technique had been used. Pathfinder hit the ground at a speed of about 18 meters per second (40 mph) and bounced about 16 times across the landscape before coming to a halt, Dr. Tim Parker of JPL later reported. The airbag sustained little damage. To top it off, the spacecraft landed on its base petal, consequently allowing a thumb-sized auxiliary antenna to communicate the successful landing just three minutes after impact. Once safely on the surface, Pathfinder opened its solar- powered petals and unveiled the small, 10.5-kilogram (23-pound) rover and science instruments to their new home. Science operations got under way within a day of landing, after the rover had exited the lander using one of two exit ramps. As the rover ventured out into unexplored territory, the lander's camera began to image the surroundings, often taking shots of the rover so that scientists and engineers could monitor the vehicle's progress. A new portrait of the Martian environment began to emerge as the spacecraft started to record weather patterns, atmospheric opacity, winds and a variety of other Martian conditions. The rover's alpha proton X-ray spectrometer began studying rocks and making direct measurements of their chemical compositions, another first in this mission. Some of the rocks near the landing site were rich in silica, or quartz, and some were identified as possible conglomerates, reported Project Scientist Dr. Matthew Golombek and his colleagues. Conglomerates are usually formed by running water, which smoothes and rounds pebbles and cobbles found in the conglomerate. Running water would also be the agent necessary to deposit these rocks in a sand or clay matrix. "If you consider all of the evidence we have at Ares Vallis - - the rounded pebbles and cobbles and the possible conglomerate, the abundant sand- and dust-sized particles and models for their origins, in addition to the high silica rocks," Golombek said, "it suggests a water-rich planet that may have been more Earth- like than previously recognized, with a warmer and wetter past in which liquid water was stable and the atmosphere was thicker." A panoramic view of Pathfinder's Ares Vallis landing site was featured on the cover of the Dec. 5, 1997 issue of Science, showing traces of this warmer, wetter past. The Ares Vallis flood plain was covered with a variety of rock types, boulders, rounded and semi-rounded cobbles and pebbles, deposited by floods which occurred early in Mars' evolution. "Before the Pathfinder mission, knowledge of the kinds of rocks present on Mars was based mostly on the Martian meteorites found on Earth, which are all igneous rocks rich in magnesium and iron and relatively low in silica," Golombek and his colleagues reported in Science. Chemical analyses of more than 16 rocks and studies of different regions of soil--along with spectral imaging of rock colors, textures and structures-- confirmed that these rocks had compositions distinct from those of the Martian meteorites found on Earth. "The rocks that were analyzed by the rover's alpha proton X- ray spectrometer were basaltic or volcanic rocks, with granite- like origins, known as andesitic rocks," Golombek said. "The high silica or quartz content of some rocks suggests that they were formed as the crust of Mars was being recycled, or cooled and heated up, by the underlying mantle. Analyses of rocks with lower silica content appear to be rich in sulfur, implying that they are covered with dust or weathered. Rover images show that some rocks appear to have small air sacks or cavities, which would indicate that they may be volcanic. In addition, the soils are chemically distinct from the rocks measured at the landing site." Golombek noted that the rocky surface and rock types found in Ares Vallis matched the characteristics of a flood plain on Earth, created when a catastrophic flood washed rocks and surface materials from another region into the basin. Ares Vallis was formed in the same way that the 40-kilometer-long (25-mile) Ephrata Fan of the Channeled Scabland in Washington state was formed, and the Pathfinder scientists traveled to that area a year before the landing to study the geology and experiment with rover prototype hardware. Additional data from the Pathfinder landing site revealed that magnetic dust in the Martian atmosphere had been gradually blanketing most of the magnetic targets on the lander over time. "The dust is bright red, with magnetic properties that are similar to that of composite particles," Golombek said. "A small amount of the mineral maghemite has been deposited almost like a stain or cement. These results could be interpreted to mean that the iron was dissolved out of crustal materials in water, suggesting an active hydrologic cycle on Mars. The maghemite stain could be a freeze-dried precipitate." Another team of scientists used daily radio Doppler tracking and less frequent two-way radio ranging techniques during communications sessions with the spacecraft to pinpoint the location of the Pathfinder lander in inertial space and the direction of Mars' rotational axis. Dr. William Folkner, an interdisciplinary scientist at JPL, and co-investigators were able to estimate the Martian polar moment of inertia, which showed that Mars had a dense metallic core surrounded by a lighter mantle. The results implied that the radius of Mars' core was larger than about 1,300 kilometers (807 miles) and less than about 2,400 kilometers (1,490 miles). Mars' core and mantle were probably warmer than Earth's at comparable depths. "Variations in Mars' rotation around its own spin axis are thought to be dominated by mass exchange between the polar caps and the atmosphere," Folkner said. "During winter, part of the atmosphere condenses at the poles. If the southern cap increased symmetrically as the northern cap decreased, then there would not be any change in moment of inertia or rotation rate. However, because of Mars' orbital eccentricity, differences in elevation and albedo, the polar caps are not formed symmetrically. "The unbalanced waxing and waning of the Martian polar ice caps results in seasonal changes in air pressure at the Pathfinder and Viking landing sites," he added. "These changes in air pressure are correlated with changes in Mars' rotation rate, which have been observed in our radio tracking measurements." The season and time of arrival of Mars Pathfinder in the late northern summer resulted in some variations in the temperature of the upper atmosphere compared to Viking data, Dr. Tim Schofield, JPL team leader of the atmospheric structure and meteorology instrument, and colleagues reported. High in the atmosphere, at altitudes of 80 kilometers (50 miles) above the surface, temperatures were cold enough to make carbon dioxide condense and form carbon dioxide clouds. At altitudes of between 60 and 120 kilometers (37 and 75 miles), the Martian atmosphere was an average of 20 degrees colder than Viking measurements, Schofield said. Seasonal variations and Pathfinder's entry at 3 a.m. local solar time, compared with Viking's entry at 4 p.m. local solar time, may account for these variations. On the surface, however, daytime temperatures were typically 10 to 12 degrees warmer than Viking surface temperatures. Pathfinder measured regular pressure fluctuations twice a day, which suggested that a moderate amount of dust was being uniformly mixed in a warm lower atmosphere, as was the case with Viking data. The daily average pressure reached a minimum on the 20th day of the mission (Sol 20), indicating the winter south polar cap had reached its maximum size. Schofield said that surface temperatures followed a regular daily cycle, with a maximum of 15 degrees Fahrenheit during the day and a minimum of minus 105 degrees Fahrenheit at night. The science team also observed rapid daytime temperature fluctuations of up to 30 degrees Fahrenheit in as little as 25 to 30 seconds. These observations suggested that cold air was warmed by the surface and convected upward in small eddies. Among a variety of other science findings, Pathfinder also observed winds that were light and variable compared to the winds encountered by the Viking landers. The winds blew steadily from the south during the Martian nights, but during the day they rotated in a clockwise direction from south to west to north to east. Whirlwinds or dust devils were detected repeatedly from mid-morning through the late afternoons. Additional scientific findings are likely to result in the months ahead as researchers continue to analyze data from this mission. Meanwhile, another mission--Mars Global Surveyor--will be observing the planet from space, while other missions gear up for launches in the near term. As part of a sustained program of exploration, Mars is likely to become a familiar place to everyone over the next decade. ### Hа сегодня все, пока! =SANA=

Дата: 19 января 1998 (1998-01-19) От: Alexander Bondugin Тема: Reconfigured Mars Global Surveyor Ready For Mission Based On New Orbit Subject: Reconfigured Mars Global Surveyor Ready For Mission Based On New Orbit Привет всем! Вот, свалилось из Internet... From The "JPL Universe" Special issue: 1997 in review January 9, 1998 Reconfigured MGS ready for mission based on new orbit By DIANE AINSWORTH 1997 saw the arrival of two spacecraft at Mars and the beginning of an extended program of Mars exploration. Two months after Pathfinder's landing, NASA's Mars Global Surveyor was captured in orbit on Sept. 12, after a 10-month journey through deep space. Global Surveyor was designed to replace Mars Observer, which was lost in August 1993. Ingenuity, teamwork and an exceptionally dedicated group of engineers and scientists quickly went to work to develop and launch the spacecraft within a short amount of time and on a tight budget. The time and cost of the mission broke all the records--26 months to build the spacecraft at a cost of only $148 million, which was well under the cost cap and a fraction of what it cost to build previous spacecraft destined for Mars. Mars Global Surveyor carried six scientific instruments to study Mars' climate, surface topography and subsurface resources. Its primary scientific objective, though, was to map the entire surface of the red planet. The journey to Mars wasn't as smooth as the team had hoped for, but each problem that cropped up was remedied in a creative and swift manner. In mid-November, as the spacecraft began to aerobrake into the upper fringes of the Martian atmosphere, structural damage to the yoke hinge of one of the solar panels, incurred during initial deployment of the panels shortly after launch, caused the unlatched panel to begin flexing during each dip lower into the Martian atmosphere. Mechanical stress analysis tests suggested that the solar panel yoke--a triangular, aluminum honeycomb material sandwiched between two sheets of graphite epoxy--had probably fractured on one surface during initial deployment. The analysis further suggested that the fractured surface, with increased pressure on the panel during aerobraking, began to pull away from the aluminum honeycomb beneath it. The flight team at Lockheed Martin Astronautics in Denver, in collaboration with atmospheric specialists at JPL, decided upon a more gradual aerobraking strategy in which to lower the spacecraft. Aerobraking was reinitiated at 0.2 newtons per square meter (3/100,000 of 1 pound per square inch), about one- third of the original aerobraking level. That level was thought to be safe, but could be adjusted in the event of additional trouble with the panel. Science teams then came up with a new aerobraking strategy and a new mapping orbit. The new mapping orbit would be a mirror image of the original mapping orbit, but it would take an additional year to set up. The spacecraft would have to take a six-month hiatus in the spring of 1998 to allow Mars to move into the proper alignment for mapping. The spacecraft's orbit would take Global Surveyor across Mars' equator at 2 a.m. rather than at 2 p.m., and the side of Mars that would have been dark would now be illuminated by the Sun. "From the perspective of the science instruments, the orbit will look just like the original orbit, except that instead of taking data from north to south on the sunny side of Mars, Global Surveyor will be making its observations in a south to north direction in the sunlight," said Glenn E. Cunningham, Mars Global Surveyor project manager, at a mid-November press briefing at JPL. Rather than reaching its final mapping orbit in mid-January 1998, and beginning the science mission in mid-March 1998, Mars Global Surveyor would achieve its final orbital position in mid-January 1999, and mapping was to begin in mid- March 1999. Apart from the year's delay in beginning mapping, the new mapping orbit would preserve all of the science objectives of the mission. During this year's hiatus, Global Surveyor will remain in a fixed, elliptical orbit in which it will pass much closer to the surface of Mars during each periapsis--or closest part of its orbit around Mars--than it will in the final mapping orbit. These close-range bonus passes will provide superb opportunities for data acquisition. The spacecraft's full suite of instruments, including the laser altimeter, will be turned on during this time to study the planet close up. "We expect to gain some spectacular new data during this time," Cunningham said. "The spacecraft's orbit will still be elliptical during this period, with a duration of between eight to 12 hours, but at periapsis, the surface resolution will be much greater and the lighting angles will be spectacular." If additional problems arise with the aerobraking process, the new mission plan will offer the Surveyor team other opportunities to reach an elliptical orbit that will satisfy many of the mission's science objectives. These so-called "off- ramps" from the aerobraking process will be detailed in a new mission plan to be reviewed by NASA officials in February 1998. With renewed vigor that the science mission had not been compromised, the flight team resumed aerobraking on Nov. 7. Since then, the spacecraft's scientific instruments have performed flawlessly, continuing to return new information about Martian magnetic properties, its atmosphere, surface features, temperatures and mineralogy. Among the most intriguing science discoveries was confirmation that Mars had a weak, non-uniform, planet-wide magnetic field. The discovery continues to baffle scientists, but it was the first time that Mars' magnetic field had, in fact, been studied. The spacecraft's magnetometer, which began making measurements of Mars' magnetic field after its capture in orbit on Sept. 11, detected the magnetic field just four days after the beginning of its orbit around Mars. The existence of a planetary magnetic field has important implications for the geological history of Mars and for the possible development and continued existence of life on Mars. "Preliminary evidence of a stronger than expected magnetic field of planetary origin was collected and is now under detailed study," said Dr. Mario Acuna, principal investigator of the magnetometer/electron reflectometer instrument at NASA's Goddard Space Flight Center, Greenbelt, Md. "This was the first opportunity in the mission to collect close-in magnetic field data. Much additional data will be collected in upcoming orbits during the aerobraking phase of the mission to further characterize the strength and geometry of the field. "The current observations suggest a field with a polarity similar to that of Earth's and opposite that of Jupiter, with a maximum strength not exceeding 1/800 of the magnetic field at the Earth's surface. "This result is the first conclusive evidence of a magnetic field at Mars," Acuna continued. "More distant observations obtained previously by the Russian missions Mars 2,3 and 5 and Phobos 1 and 2 were inconclusive regarding the presence or absence of a magnetic field of internal origin." The magnetic field holds important clues to the evolution of Mars. Planets like Earth, Jupiter and Saturn generate their magnetic fields by means of a dynamo made up of moving molten metal at the core. This metal is a very good conductor of electricity, and the rotation of the planet creates electrical currents deep within the planet, which give rise to the magnetic field. A molten interior suggests the existence of internal heat sources that could give rise to volcanoes and a flowing crust responsible for moving continents over geologic time periods. The latter phenomenon is called plate tectonics. "A magnetic field shields a planet from fast-moving, electrically charged particles from the Sun, which may affect its atmosphere, as well as cosmic rays, which are an impediment to life," Acuna said. "If Mars had a more active dynamo in its past, as we suspected from the existence of ancient volcanoes there, then it may have had a thicker atmosphere and liquid water on its surface." It is not known whether the current weaker field now results from a less active dynamo, or if the dynamo is now extinct and what the scientists are observing is really a remnant of an ancient magnetic field still detectable in the Martian crust. "Whether this weak magnetic field implies that we are observing a fossil crustal magnetic field associated with a now extinct dynamo -- or merely a weak but active dynamo similar to that of Earth, Jupiter, Saturn, Uranus and Neptune -- remains to be seen," Acuna said. Mars Global Surveyor is the first in a sustained program of robotic exploration of Mars. In December 1998, a second pair of spacecraft will be launched toward the red planet, carrying instruments that will augment this new global portrait of Mars. As those spacecraft arrive at Mars, Global Surveyor will be generating a global map of the planet that will aid in the selection of future landing sites. ### Hа сегодня все, пока! =SANA=

Дата: 19 января 1998 (1998-01-19) От: Alexander Bondugin Тема: 97's Challenges Brings Changes To The Deep Space Network Привет всем! Вот, свалилось из Internet... From The "JPL Universe" Special issue: 1997 in review January 9, 1998 '97's challenges bring changes to DSN By SHIRLEY WOLFF, TMOD outreach coordinator 1997 brought many changes to the Deep Space Network (DSN). It was the first full year in which the DSN operated under the management of NASA's Space Operations Management Office. Major organizational changes were introduced within the Telecommunications and Mission Operations Directorate (TMOD) that will result in a truly integrated, end-to-end, multi- mission ground system derived from the DSN and the Advanced Multi-Mission Operations System (AMMOS). It was also a very busy year for tracking activities. The DSN provided communications support for 46 NASA and other missions, including international customers. Cassini was one of 14 launches, and the Mars Global Surveyor orbit insertion one of 12 critical mission events supported during 1997. The DSN continues to track the twin Voyager spacecraft--in space for more than 20 years--and now more than 6 billion miles from Earth. The unique demands of the Mars Pathfinder mission created some special communications challenges. To accommodate the difficulties of communicating with the relatively low-powered lander, a rapid paced, quick-response time was essential, requiring the DSN to