Photos: Atlas launch seen from press site

One of the largest satellites in the world will launch aboard America’s biggest operational booster Thursday, riding that power to a listening post 22,300 miles above the planet for its clandestine eavesdropping mission, all indications suggest.

A team of United Launch Alliance and NASA engineers worked through Delta 2 launch day fueling procedures during a simulated countdown Wednesday for what should be the second-to-last time before the venerable rocket’s final liftoff next month from California’s Central Coast.

Less than three months after rocketing into space, the commercial WorldView 4 Earth-imagery satellite has finished in-orbit testing and calibration to begin operations for DigitalGlobe.