The Zensens' call to missionary service occurred during a missions conference in 1971 at their home church, where TWR founder Dr. Paul Freed presented the needs of TWR.  In 1973, they moved to Bonaire, where George was a transmitter engineer and Joan filled a variety of roles. 

In 1980, the Zensens transferred to the TWR Guam station, where George served as chief engineer.  Joan again served in a number of capacities, including responding to listener letters.  George and Joan relocated to the HCJB Engineering Center in 1997 to help build HC100 high-power shortwave transmitters.

George passed away on April 7, 2020 after long battle with cancer.