PERISCOPE is an instrument and mission concept with the goal of investigating and mapping lunar skylights from an orbiting platform using photon time-of-flight imaging. A spacecraft in a very low orbit would direct laser pulses into the lunar skylights, detect light returning to the spacecraft after multiple reflections in the cave, and transmit a summary of those data back to the Earth. A team on the ground would process that data to develop a 3d map of the interior void of the skylight that was at all times beyond the direct line of sight of the spacecraft. In phase I we showed the theoretical feasibility of this mission concept with a variety of simulations and analytical tools. In phase II we intend to bring this concept to a level capable of supporting a full mission proposal. We will perform more detailed trade studies, analyses, and experiments using real world materials as analogous to expected lunar subsurface material as possible.