Voyager I is currently traveling at more than 38,000 miles per hour (17 kmps) due to several gravitational sling-shot maneuvers.

Launched on September 5, 1977, the craft did fly-bys of Jupiter, Saturn and Titan. Voyager 1 crossed the heliopause on August 25, 2012, to become the first spacecraft to enter interstellar space and study the interstellar medium. It will keep broadcasting information until 2025 when its radioisotope thermoelectric generators will no longer supply enough electric power to operate any of its scientific instruments.

More Info: en.wikipedia.org