How fast can you go through the air? Time for a Geek Out! Richard chats with Carl about the challenges of flying in the hypersonic regime - above Mach 5! Lots of experiments were done in the early days of the space race, and died down after Apollo 11. But toward the end of the cold war there was a resurgence that has continued to this day - developing engines and materials to keep flying faster. Most of the technology is focused on military weapons, but there could be a path to space when more of the problems get solved!