Voyager-1 is apparently at the edge of the solar system, where it is encountering a rapid increase in galactic cosmic radiation.

http://www.nasa.gov/mission_pages/voyager/voyager20120614.ht...

"The laws of physics say that someday Voyager will become the first human-made object to enter interstellar space, but we still do not know exactly when that someday will be," said Ed Stone, Voyager project scientist at the California Institute of Technology in Pasadena. "The latest data indicate that we are clearly in a new region where things are changing more quickly. It is very exciting. We are approaching the solar system's frontier."
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I would like to point out that the instruments on both Voyager spacecraft are powered by plutonium.

http://en.wikipedia.org/wiki/Radioisotopic_Thermoelectric_Ge...

- Pete