NASA broke ground Monday on a state-of-the-art research facility intended to revolutionize 21st century space propulsion, helping to power future space vehicles on journeys to the farthest reaches of the solar system — and, eventually, beyond it. The Propulsion Research Laboratory — part of NASA’s Marshall Space Flight Center — will be housed on a 21-acre site on Redstone Arsenal in Huntsville, Ala. It will be occupied primarily by propulsion scientists and technologists from the Marshall Center’s existing Propulsion Research Center.