RENO, Nev. (CBSDFW.COM/AP) — NASA has launched the final stage of a four-year effort to develop a national traffic management system for drones, testing them in cities for the first time beyond the operator’s line of sight.

Drone

(Credit: Joern Haufe/Getty Images)

Multiple drones took to the air at the same time above downtown Reno this week in a series of simulations testing emerging technology that someday will be used to manage hundreds of thousands of small unmanned commercial aircraft.

NASA officials say it’s the most complicated technical challenge they’ve faced since the simulations began in 2015.

Similar tests have been conducted in remote and rural areas. The Federal Aviation Administration has authorized individual test flights in cities before but never for multiple drones or outside the sight of the operator.

Located in Houston, the Lyndon B. Johnson Space Center is the training base and home for America’s astronauts and the site of Mission Control, where a cadre of flight controllers monitors the work of our women and men in space.