The Air Force is to start construction this month of a prototype silo for the Sentinel LGM-35A future ICBM by Northrop Grumman [NOC] in advance of a planned Pentagon engineering and manufacturing development (EMD) re-certification decision on the ballistic missile this year and a first pad-launched flight test next year, the service said on Tuesday. In February, "teams will break ground on a prototype launch silo at Northrop Grumman’s Promontory, Utah, site," the service said. "This crucial effort will allow…