The United Launch Alliance (ULA) is launching the classified USSF-51 mission, for the United States Space Force (USSF). The mission was initially planned to launch on ULAs Vulcan rocket, but the company requested a move to the Atlas V rocket. The Atlas for this mission is in the 551 configuration, meaning 5 SRBs (Solid Rocket Booster), bigger fairing, and a single upper stage engine.