NATIONAL HARBOR, MD -- U.S. Transportation Command is ready to move forward with a “proof of principle” demonstration of space cargo transport capabilities, but officials expect it will likely be another year before SpaceX, its current launch vehicle partner, is ready to move forward. “We really are traveling at the speed of industry and the way that they’re developing their systems,” TRANSCOM Deputy Commander Vice Adm. Dee Mewbourne said during a panel today at the National Defense Transportation Association’s annual...