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The Voyager 2 space probe should be crossing another milestone any day now.

Shortly after Voyager 2's 30th anniversary in space, the probe is set to achieve another milestone in its journey; it is expected to cross the termination shock in late 2007 or early 2008. The termination shock is a spherical area that surrounds the solar system where solar winds slow to subsonic speeds.

Though launched 10 days later, Voyager 2's sister craft, Voyager 1 crossed the termination shock in December of 2004, three years ahead of Voyager 2's projected arrival. The earlier crossing was due to a shorter trajectory out of the solar system.

The prediction comes from physicist Haruichi Washimi at University of California, Riverside. Washimi used a global magneto-hydrodynamic simulation in conjunction with data from Voyager 2 to give the window where the probe will likely cross the boundary. The simulation is a "method that allows precise and quantitative predictions of geometric disturbances caused by solar activities," according to a release at UCR.

"This is the first time the termination-shock position has been forecast in this way. After it crosses this boundary, Voyager 2 will be in the outer heliosphere beyond which lies the interstellar medium and galactic space. Our simulations also show that the spacecraft will cross the termination shock again in the middle of 2008. This will happen because of the back and forth movement of the termination-shock boundary. This means Voyager 2 will experience multiple crossings of the termination shock. These crossings will come to an end after the spacecraft escapes into galactic space," explained Washimi.

Launched August 20th, 1977, Voyager 2 has seen four planets -- Jupiter, Saturn, Uranus and Neptune -- and their moons on its way out of the solar system. The original Voyager missions where slated only to visit Jupiter and Saturn, along with their largest moons. The extraordinary success of the missions convinced NASA to extend Voyager 2's mission and use gravitational boosting to propel it towards Uranus and Neptune.

Though still operational, the natural decay of the plutonium fuel on the craft has forced shutdown of several systems to keep it operational. At launch, the Radioisotope Thermoelectric Generator pumped out 470 watts of power, but by 2001, output was down to a meager 319 watts. Both the Voyager crafts are projected to have enough fuel to continue operations until about 2020.





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