In this SBIR Phase II program Advanced Cooling Technologies, Inc. (ACT) proposes to develop titanium/water heat pipes suitable for Spacecraft Fission Power applications. NASA is currently examining small fission power reactors design, such as the Kilopower, which aims to provide roughly 1 kW of electric power. Kilopower plans to use titanium/water heat pipes to remove the waste heat from the cold end of the convertors. Previous water heat pipe designs for space fission power are not suitable, since they cannot operated in a vertical orientation, which is necessary for ground testing of Kilopower. The overall objective of the Phase I and II programs is to develop a titanium/water heat pipe radiator suitable for Spacecraft Fission Power, such as Kilopower. To meet this objective, the following items must be achieved: demonstrate the ability to transport heat over a long distance from the Stirling cold end to the radiator, design and fabricate a heat pipe radiator for integration into the Kilopower system and identify the best wick design for the varied operating conditions of the Kilopower system. The principle objective of the Phase II project will be to develop full-scale titanium water heat pipes that will be suitable for testing in the Kilopower demonstration unit.