From the California coast, a Falcon 9 rocket rose into the sky above Vandenberg Space Force Base on a Thursday afternoon, carrying a payload whose purpose the U.S. Space Force has chosen to keep from public view. The launch is one of many classified missions that have quietly made SpaceX indispensable to American military power in orbit — a partnership visible only in the rocket's ascent and the sonic boom it leaves behind. In an era when space has become a domain of strategic competition, what cannot be seen may matter most.