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PASADENA — Voyager 1 is heading to the edge of the solar system, but first it must race the sun toward a milestone – a place where the supersonic solar wind backs up in a pressure wave. 

Sometime between early next year and 2003, the spacecraft could reach the “termination shock,” a signpost pointing to the verge of interstellar space, Ed Stone, director of NASA’s Jet Propulsion Laboratory, said Tuesday. 

The spacecraft already is the most distant manmade object in space, at 7 billion miles. 

“Voyager’s really a pathfinder,” Stone said. “It’s the best we have out there.” 

Launched in 1977, Voyager 1 carries scientific instruments and also a gold-plated record with greetings in 55 languages, analog images, music selections and sounds such as a mother’s kiss. 

Voyager is currently about twice as far from the sun as Pluto’s average orbit. It is moving at 38,6111 mph relative to the sun – fast enough that it could race from Los Angeles to New York in under four minutes. 

But that is a snail’s pace compared to the solar wind. The protons, electrons and ionized hydrogen particles that erupt from the sun and surround it in a bubble are blown outward at 1 million mph. 

The termination shock, located about 80 to 90 times the distance of Earth’s orbit, is the place where the solar wind abruptly slows to a fourth of its previous speed, almost as if hitting a wall, Stone said. 

The phenomenon is similar to a ship’s bow wave and the supersonic shockwave in front of a jet, he said. 

Ahead of that region lies the heliopause, where the pressure of the solar wind is counterbalanced by the interstellar wind – particles from exploding stars called supernovae. 

That boundary of interstellar space is believed to be about 120 to 130 times the distance between Earth and the sun, Stone said, but a better estimate will come when Voyager hits the pressure wave. 

“For the first time, we’ll know,” he said. “No one has ever been this far out from the sun before. It will certainly tells us what our local neighborhood is like.” 

There is a problem, however. Voyager must encounter the pressure wave within the next three years. Otherwise, increased solar activity will double or triple the flood of particles, effectively pushing the shock region outward at a speed Voyager can’t begin to match. 

“We probably won’t be able to catch it until it starts moving in again” as part of an 11-year sun cycle, Stone said. 

Both Voyager and its twin, Voyager 2, have enough electricity and attitude control propellant to operate until about 2020. At that time the generators will no longer support the science instruments.