The launch of NASA’s twin GRAIL spacecraft

The next American polar-orbiting weather satellite that will feed long-range forecasts and track environmental trends has slipped into space-like testing ahead of launch.

The nation’s existing Atlas and Delta launch sites are vying for a future when United Launch Alliance completes its modernization with a new rocket system and downsizing to one pad on each coast.

The next-to-last Delta 2 rocket is being stacked at its California launch site to take flight in January to put a civilian weather satellite into polar orbit.