ASHINGTON, March 26 (Reuters) - The U.S. Space Force said on Wednesday it has cleared Boeing (BA.N), opens new tab and Lockheed Martin's (LMT.N), opens new tab Vulcan rocket to launch national security satellites for the United States. SpaceX was the first company to handle such missions. "Vulcan certification adds launch capacity, resiliency, and flexibility needed by our nation’s most critical space-based systems," said Brigadier General Kristin Panzenhagen, the program executive officer for assured access to space.