Workers assemble a United Launch Alliance (ULA) Atlas V dual engine Centaur upper stage in ULA’s factory in Decatur, Alabama on March 29, 2019. The dual engine upper stage is being prepared for the first crew rotation mission of Boeing’s CST-100 Starliner to the International Space Station. Starliner and the Atlas V rockets that will launch the spacecraft, are key elements of NASA’s Commercial Crew Program to restore the capability to send astronauts to the space station from U.S. soil.