Video: Orion flight highlights

NASA is gearing up for a milestone unmanned test flight Thursday, the first launch of the agency’s Orion deep space exploration spacecraft intended to one day carry astronauts on missions beyond low-Earth orbit to the vicinity of the moon, one or more nearby asteroids and, eventually, Mars.

A United Launch Alliance Delta 4-Heavy rocket climbed into orbit Monday from a military base northwest of Los Angeles, delivering to space a classified U.S. government spy satellite as large as a school bus and leaving just three Delta rockets left to fly before retirement.

NASA managers Thursday cleared the $1.5 billion Parker Solar Probe for launch early Saturday on a daring mission to “touch the sun,” repeatedly flying through its outer atmosphere to find out why the blazing corona is millions of degrees hotter than our star’s visible surface.