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Shuttle Radar Topography Mission STS-99 - Mission OverviewSpace Radar Mission To Detail the Earth's SurfaceAn innovative imaging radar, the first to map the Earth in three dimensions, is the primary payload onboard STS-99, the first Shuttle flight of the new century. Known as the Shuttle Radar Topography Mission, this radar system represents a breakthrough in the science of remote-sensing and will produce topographic maps of Earth 30 times as precise as the best global maps in use today. The information has the potential to produce one of the most comprehensive and accurate maps of Earth ever assembled. Scheduled for launch no earlier than January 31 from the Kennedy Space Center, the Space Shuttle Endeavour will carry the radar into space for an 11-day mission to learn more about the planet's changing landscapes, its environmental health, and many ecosystems. The imaging radar will be able to capture landscapes that have been sculpted through the millennia, with the passage of ice ages and periods of warmer weather. This new imaging system will orbit at 145 miles (233 kilometers) above Earth, with two radar antennas mounted in the Shuttle payload bay and two extended on a 200-foot-long (60-meter) mast. The radar will image vast, barren deserts, frozen tundra, and deep valleys carved by glaciers, such as those found in Alaska, the Andes, and Himalaya mountains. The vestiges of ancient human settlements, such as the Eighth Century Khmer civilization of Angkor, Cambodia, and the habitats of endangered species, such as the mountain gorillas of Central Africa will be mapped. The 13-ton radar system will be able to collect highly accurate, high-resolution images of Earth's crust between 60 degrees north latitude and 56 degrees south latitude. The regions to be mapped are home to about 95 percent of the world's population and will be captured with an accuracy of better than 100 feet (30 meters). The genesis of the Shuttle Radar Topography Mission lies in NASA's 1994 flights of the Spaceborne Imaging Radar C/X-band Radar on STS-59 and STS-68. Several modifications have been made to the radar systems, which give the mission new capabilities compared with its predecessors. The cornerstone of innovation is the addition of a C-band and an X-band antenna at the end of a deployable mast, which will be the longest rigid structure ever flown in space. This will be the first time that a dual-antenna imaging radar is flown, allowing scientists to use a technique called interferometry--which is akin to combining stereo images--to map terrain elevation in a single pass. By using interferometry to combine two images electronically, researchers will be able to generate computer versions of topographic maps, called digital elevation models. With the exception of weather satellite measurements, this topographic information will be the most universally useful data set about the Earth ever produced. The mission is a partnership between NASA and the National Imagery and Mapping Agency, in which the agencies are jointly seeking information with valuable research and operational uses. The Shuttle Radar Topography Mission will provide important information for NASA's Earth Science Enterprise, which is dedicated to understanding the total Earth system and the effects of human activity on the global environment. In addition to NASA and the National Imagery and Mapping Agency (NIMA), the Shuttle Radar Topography Mission is a collaboration of the German Aerospace Center (Deutsches Zentrum fur Luft- und Raumfart) and the Italian Space Agency, which provided the experimental X-SAR radar system. The two agencies are providing science teams for the mission. The Jet Propulsion Laboratory is managing the project for NASA's Earth Sciences program in Washington, D.C. Background The Shuttle Radar Topography Mission (SRTM) provides a platform for mapping vast areas of the Earth in the relatively short time of a Shuttle flight. In addition, the processing of SRTM data will be almost completely automatic, allowing nearly 1 trillion measurements of the Earth's topography to be integrated into a consistent, high-resolution map. Surprisingly, our home planet isn't mapped as well as one might think. A few countries, such as the U.S., much of Europe, Australia, and New Zealand, have digital maps at the 30 m (100 foot) resolution level, but the vast majority of our planet lacks maps at that resolution, and many lack reliable maps altogether. The main reason for this is that much of the globe, the equatorial regions in particular, are cloud-covered much of the time. Thus, optical cameras on satellites or aircraft can't image the areas. SRTM radar, with its long wavelength, will penetrate clouds as well as providing its own illumination, making it independent of daylight. The land area to be mapped by SRTM In the past decade, numerous imaging radar satellites have been lofted to orbit by the European Space Agency, Japan, and Canada. These radar systems have been demonstrated to have the capability to produce digital topographic data in many situations. However, none of these satellites was designed for the production of digital topographic maps, so they lack some important features of SRTM. The most important feature they lack is a second antenna. While it is possible to obtain the second radar image on a subsequent orbit using a single radar system, it is difficult to measure the separation between the two passes to the required millimeter accuracy. If enough control points can be measured in each scene so that the elevation is known for those points, it is possible to solve for the unknown radar positions. Since SRTM will measure the separation and orientation of its two antennas to a high precision, it needs few control points to make its maps. SRTM is the culmination of a broad arc of technological innovation. Starting with the first civilian spaceborne imaging radar, Seasat, in 1978, it was discovered that meaningful radar images of the land could be obtained from space. Subsequent tests using the Shuttle proved the worth of that platform for improving the technology. The third Shuttle Imaging Radar, SIR-C, tested two critical technologies required for the development of SRTM: active, phased array antennas and ScanSAR. The active antenna was required for its ability to steer to any angle through electronic manipulation of the radar beam. No moving parts were required. ScanSAR was derived from that capability. The radar beam is literally scanned back and forth across as the Shuttle orbits, painting out a much wider swath than was possible in ordinary operation. Thus, the earlier swath of 50 km was increased to 225 km. It turns out that 225 km is just enough for an 11-day Shuttle mission to literally "cover the Earth" by painting one swath at a time. Source: NASA
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