[CTRL] Skylab 2000 (a)
Compton's Deorbit Puts Jets and Ships at Risk By Mary Motta Senior Business Correspondent posted: 11:02 am ET 02 June 2000 Scientists Prepare to Deorbit Compton Satellite WASHINGTON â If all goes well when NASA deep-sixes its ailing astronomical satellite next week, the bus-size spacecraft will fall harmlessly into the eastern Pacific Ocean. But just in case the 17-ton (15,422-kilogram) Compton Gamma Ray Observatory (CGRO) careens out of control, those vulnerable to its scorching bits of debris -- mariners and pilots -- will have been warned. NASA's Goddard Space Flight Center in Greenbelt, Maryland, has started a plan to inform commercial airlines, the Coast Guard and other federal agencies when and where to expect CRGO to reenter Earthâs atmosphere. "We began dialogue about two months ago," said Preston Burch, deputy associate director for space science operations at Goddard. Because of a failure of one of its guidance systems, NASA has decided to "deorbit" CGRO in an effort to avoid having it fall onto a populated area. The $557 million spacecraft was launched in 1991. Goddard began warning the Air Force, the National Imagery and Mapping Agencyâs World Wide Navigation Warning Services, the Federal Aviation Administration (FAA) and the U.S. Coast Guard in April that CGRO was expected to come in over the east central part of the Pacific Ocean. The agencies received a three-page letter that outlined NASA's plans for nudging the spacecraft out of orbit. "It is of paramount importance to protect life and property from the hazard of CGRO reentry debris. The CGRO debris is a significant potential threat to the safety of any aircraft or surface vessels in the debris impact area," the letter said. The impact zone for the so-called "controlled reentry" of the observatory covers a rectangular area 16.1 miles (26 kilometers) wide and 963.7 miles (1,552 kilometers) long. That area is about 1,100 miles (1,770 kilometers) from any land area. These "hot and fast chunks" will range from paper-thin debris to 15- to 20-pound (7- to 10-kilogram) chunks that will be falling several hundred miles (kilometers) per hour, Burch said. That could cause potentially devastating damage to a jet flying en route in the Pacific. The debris could slice off a wing or drill a hole through an airliner's cabin causing the plane to explode. Big chunks could also put a hole large enough in the hull of a ship to sink it. But the FAA said that the chances of any of that happening are slim. "Over the Pacific there is so much airspace and so few aircraft that the chances of the debris causing harm is narrow," said the FAA's Bill Shuman. The number of flights in the Pacific over an 8-hour period is about 200. That compares to about 1,000 flights over the North Atlantic in the same period. And there are even less commercial flights for the area pinpointed for the Compton deorbit, Shuman said. Still, the agency plans to warn airlines through a "Notice to Airmen," or NOTAM. This message is delivered via satellite, through e-mail and via fax to carriers around the world who will be flying in that area from June 4-6. Each day, Goddard will send out a notice describing the location of the hazard area "to minimize loss of usable airspace and ocean area to aircraft and surface vessels," the warning notice said. There will be a total of eight debris-hazard areas that Goddard will target. These areas will be off limits for about 90 minutes each day, Burch said. The reentry business is an imprecise one at best because objects can survive and make it all the way to the ground, said Bill Ailor, director for the Center for Orbital and Reentry Debris Studies at The Aerospace Corporation in Los Angeles. "Generally speaking, it is not so easy to predict where they are going to come down," Ailor said. Objects typically enter the atmosphere at a blazing 6 miles (9.7 kilometers) per second and are often incinerated by friction with Earth's atmosphere. But materials designed to be heat-resistant often can survive the plunge all the way to the ground. "Typically what we look for are titanium spheres and objects made of stainless steel (to survive)," Ailor said. Glass also can survive. The bus-sized CGRO is made mostly of aluminum, titanium and stainless steel. But there is a positive side to this undertaking. Several U.S. agencies are interested in documenting the fall of the CGRO to better understand such issues in the face of an increasing number of commercial satellite launches. And if the 110-ton (111,760 kilogram) Mir space station doesnât survive commercially and the Russians decide to take it out of orbit, such information will be critical to ground controllers plotting its reentry zone. "Mir has so much stuff on it that the debris field will be so much larger and more dangerous," Ailor said. A HREF="http://www.ctrl.org/"www.ctrl.org/A DECLARATION DISCLAIMER == CTRL is a discussion informational exchange
[CTRL] Skylab 2000
NASA Saying Goodbye to Universe Eye Updated 12:15 PM ET May 27, 2000 By PAUL RECER, AP Science Writer WASHINGTON (AP) - The Compton Gamma Ray Observatory is poised for a suicide plunge to Earth, ending a successful nine-year $670 million space mission that opened a new window on the universe. Starting Tuesday, NASA engineers will send signals to the satellite to perform a series of rocket firings that will drop the Compton from its 317-mile orbit and send it into a final, fiery dive to the Pacific Ocean early on June 4. "It will be like losing a member of the family," said Donald A. Kniffen, a NASA scientist who has worked with the Compton since 1979, when the astronomical observatory was little more than engineering sketches and scientific dreams. Even though the Compton still was capable of collecting science for the world's astronomers, the craft is ailing. After a gyroscope failed, engineers from the National Aeronautics and Space Administration decided to deliberately crash the 17-ton spacecraft while they still could control it. An analysis showed that if NASA did nothing, the craft would eventually fall on its own, with one-in-1,000 chance of killing someone on Earth. The craft's orbit carries it over some of the most populated areas of the world, including Mexico City, Miami and Bangkok, Thailand. Using the remaining guidance and control equipment on Compton reduces that risk of fatality to about one in 29 million. NASA chief scientist Ed Weiler said he chose safety over science. "How much science is worth the risk of even one human life?" Weiler asked when announced his decision. NASA was not eager to repeat the nail-biting experience of Skylab, the 78-ton space station that crashed in 1979. Engineers had no control over the station when it dropped from space and spread hundreds of pounds of hot metal across the Indian Ocean and into a remote section of western Australia. No one was hurt. The Compton will be the largest spacecraft brought down in a deliberate, controlled crash. NASA engineers plan to dump the Compton in a remote part of the Pacific Ocean, 2,500 miles southeast of Hawaii. The impact target is a corridor 16 miles wide and some 1,426 miles long. It angles across the equator, northwest to southeast, and ends about 680 miles south of the Galapagos Islands. A rocket firing to lower the orbit is scheduled for Tuesday night from the space agency's Goddard Space Flight Center in Greenbelt, Md. A second firing is set for Wednesday. That will set the craft up for two final firings June 4. The rocket thrust will slow the Compton enough to drop it into the atmosphere, where friction heat will burn up most of the craft. The main concern is for six 1,800-pound aluminum I-beams that may survive the re-entry and splash into the ocean. Kniffen said he is approaching the end of Compton with a mixture of sadness and pride. Since the craft was launched April 5, 1991, he said, the instruments on the Compton have completely changed the way astronomers view the universe. The instruments were designed to detect gamma rays, an energetic form of light invisible to the eye and hardly detectable on Earth. But in space, the Compton found that the whole universe was bathed in gamma rays, with explosions occurring in distant galaxies almost daily. Before Compton, Kniffen said, astronomers thought gamma ray bursts, the most energetic events in the universe, could be detected only in the Milky Way, the home galaxy of the Earth and Sun. "Within months of its launch, we had proof that gamma ray bursts were coming from all directions in the universe," he said. "We realized that some of them were coming from very early in the history of the universe," which means they were far beyond the Milky Way and were very, very powerful. During its mission, the Compton recorded more 2,500 gamma ray bursts, while only about 300 had been detected previously, NASA said. Some of its detections came quickly enough to alert other observatories which then collected observations in visible light and X-rays. The cause of the gamma ray bursts is still a puzzle, but Kniffen said the libraries of data from Compton may help astronomers find answers. Compton also detected gamma rays streaming from black holes, from exploding stars and from the sun. An analysis of the data has helped astronomers, for the first time, begin to understand how black holes can trigger jets of X-rays and gamma rays that streak outward at velocities approaching the speed of light. The Compton was originally expected to last only two years. But when that time was up, the mission was extended repeatedly. It took its last bit of data - a gamma ray snap shot of the sun - on Friday. "It performed far beyond our expectations," Kniffen said. "Dollar for dollar, it was one of the most successful missions NASA has ever had." A HREF="http://www.ctrl.org/"www.ctrl.org/A DECLARATION DISCLAIMER == CTRL is a discussion informational exchange
