This report discusses development and proof‐of‐concept testing of a new lightweight carbon‐carbon (C‐C) space radiator heat pipe developed under the NASA Civil Spqce Technology Initiative (CSTI) High Capacity Power Program. The heat pipe was filled with potassium working fluid and tested for 11 hours, including startup from ambient temperature with the working fluid initially in the frozen state to near 700 K condenser temperature. Steady‐state heat pipe input power during testing was facility limited to about 300 watts, representing about 50% of the design input power. Post test inspection showed the heat pipe to be in excellent condition after eight thermal cycles from ambient to steady‐state operating temperature. Potential applications, ranging from small spacecraft heat rejection to aircraft and terrestrial uses, are discussed. © 1995American Institute of Physics