Despite a vision from top Air Force officers that reusable rockets can play roles in future military missions, a conservative safety culture on launch ranges and institutional bureaucracy are slowing the service on its path to embracing the technology and, accordingly low cost launch, when it is ready in four to five years.The Defense Advanced Research Projects Agency (DARPA) is developing a program with a goal of launching 10 times in 10 days to demonstrate aircraft-like operability, cost efficiency and…