NASA's Polar satellite meets fate with Sun

NASA this week shut off one of most successful, unexpectedly long-living satellites, Polar, ahead of what NASA called a likely fatal encounter with the sun.

According to NASA the 12 year-old Polar satellite ran out of fuel during its final maneuver in February but continued to maneuver on the cold helium gas that was left in its tank, NASA said. From its current orientation, Polar will drift slowly, allowing the energy from the Sun to quickly overwhelm the satellite. If Polar were left on, first to go would be its radiators, batteries, and transmitters. These would overheat and probably fail. The satellite's planned turn off at the end of April will allow controllers to send the final commands before Polar meets its fate by burning up, NASA said.

When the Polar satellite launched February 24, 1996, the plan was for a two-year science mission to study the lights that form a ring around Earth's north and south magnetic poles, known as the Northern and Southern Lights, or auroras. Polar has exceeded expectations by a decade.

Polar - built by Lockheed Martin - was launched from Vandenberg Air Force Base and was the second element in NASA's Global Geospace Science (GGS) program. Polar orbited from Earth's North Pole to its South Pole to study how solar wind particles and their energy enter Earth's magnetosphere, the area surrounding Earth dominated by its magnetic field. Polar also revealed how those particles and their energy end up in Earth's atmosphere, and how the radiation belts form and dissipate, NASA said.

During its run, the satellite completed an orbit every 17½ hours, passing over one pole at a maximum altitude of about 32,000 miles and diving past Earth's equator to the opposite pole at a minimum distance of about 3,200 miles. As Polar flew over the north and south poles, three of the satellite's 12 instruments captured images of auroras in ultraviolet, X-ray, and visible light. The other nine instruments measured charged particles and Earth's electric and magnetic fields throughout its journey around Earth, NASA said.

The other spacecraft in NASA's GGS program, called Wind, was also built by Lockheed Martin. It was launched on November 1, 1994 and continues to operate in orbit around the L-1 libration point about one one-hundredth of the way from the Earth to the Sun, where the gravitational pull of the Earth and Sun and centrifugal force balance in such a way as to give an orbit of exactly one Earth year. The objectives of the Wind mission are to provide complete plasma, energetic particle, and magnetic field input for magnetospheric and ionospheric studies; determine the magnetospheric output to interplanetary space in the up-stream region: and investigate basic plasma processes occurring in the near-Earth solar wind, NASA said.

The NASA GGS program is part of a larger effort called the International Solar Terrestrial Physics (ISTP) program that was mounted by NASA, the European Space Agency (ESA), and the Japanese Institute of Space and Astronautical Science. The fleet of spacecraft flown represented a collaborative effort to better understand how energy is generated deep within the Sun, how it radiates to the surface, crosses space to eventually reach the near-Earth environment, and, finally, how that energy affects the Earth, NASA said.

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