Large scale lightning protection systems (LPS) present designers unique challenges, especially if they are to be built on a rocket launch pad that has been operating for almost four decades and refurbished many times. This is the case of the LPS of Pad LC39B in support to the NASA Constellation Program. This new LPS had to be designed for much taller vehicles, which were still in their conceptual design stages. Pad LC39B contains all the infrastructure required to launch the Space Shuttle, which includes a mesh of tunnels, underground utilities, cross country lines, and cable trays that could not be affected by the design. This paper presents all the challenges and design criteria for the new LPS at Pad LC39B.