Live coverage: Space station crew safely returns to Earth

A solid-fueled rocket motor mounted horizontally on a Utah hillside ignited and powered up to more than 3 million pounds of thrust Tuesday in a final full-up test-firing before a similar booster helps propel NASA’s huge Space Launch System away from Earth on a demonstration flight in 2018.

A towering mobile platform for the agency’s Space Launch System arrived at launch pad 39B Friday at the Kennedy Space Center in Florida for a sequence of water and propellant flow tests, swing arm checkouts and other rehearsals that should conclude with managers declaring the spaceport’s ground systems ready to support the first SLS launch campaign by the end of the year.

A 139-foot-tall Antares rocket is slated for a predawn launch Monday from the Mid-Atlantic Regional Spaceport on Virginia’s Eastern Shore, carrying a Cygnus supply ship heading for the International Space Station.