NASA Thruster Achieves World-Record 5+ Years of Operation

A NASA advanced ion propulsion engine has successfully operated for more than 48,000 hours, or 5 and a half years, making it the longest test duration of any type of space propulsion system demonstration project ever.

via NASA Breaking News

http://www.nasa.gov/home/hqnews/2013/jun/HQ_13-193_Ion_Thruster_Record.html