If NASA wants to land astronauts on the Moon again, it's got three problems, and they're all bodies. The space agency just completed the first Cislunar Autonomous Positioning System Technology Operations and Navigation Experiment (CAPSTONE), using two microwave-sized satellites. That makes lunar operations hard enough as it is, but what's really cranked up the difficulty is the plan to land astronauts on the Moon. They went in an Orion spacecraft. So we really, really need to learn how to fly in that environment.