Huge defunct satellite to plunge to earth soon

NASA's Upper Atmosphere Research Satellite, or UARS, is expected to re-enter Earth's atmosphere late September or early October, almost six years after the end of a productive scientific life, the U.S. space agency announced Thursday. Although the spacecraft will break into pieces during re-entry, not all of it will burn up in the atmosphere. The risk to public safety or property is extremely small, NASA said. NASA scientists estimate a 1-in-3,200 chance a satellite part could hit someone on earth. Therefore, any individual's odds of being struck are about one in 21 trillion. Since the beginning of the Space Age in the late 1950s, there have been no confirmed reports of an injury resulting from re-entering space objects. Nor is there a record of significant property damage resulting from a satellite re-entry. NASA said it is too early to say exactly when UARS will re-enter and what geographic area may be affected, but it is watching the satellite closely. NASA will post updates weekly until four days before the anticipated re-entry, then daily until about 24 hours before re-entry, and then at about 12 hours, six hours and two hours before re-entry. The updates will come from the Joint Space Operations Center of U.S. Strategic Command at Vandenberg Air Force Base, which works around the clock detecting, identifying and tracking all man-made objects in the Earth orbit, including space junk. The actual date of re-entry is difficult to predict because it depends on solar flux and the spacecraft's orientation as its orbit decays. As re-entry draws closer, predictions on the date will become more reliable. As of Thursday, the orbit of UARS was 152 miles by 171 miles (245 km by 275 km) with an inclination of 57 degrees. Because the satellite's orbit is inclined 57 degrees to the equator, any surviving components of UARS will land within a zone between 57 degrees north latitude and 57 degrees south latitude. It is impossible to pinpoint just where in that zone the debris will land, but NASA estimates the debris footprint will be about 500 miles (805 km) long. UARS, launched in 1991 from a space shuttle, was the first multi-instrumented satellite to observe numerous chemical constituents of the atmosphere with a goal of better understanding atmospheric photochemistry and transport.