Photos: Atlas 5 rocket powers NROL-52 payload to space

A steel tube built as a stand-in for the core stage of NASA’s Space Launch System has arrived at the Kennedy Space Center for a series of rehearsals to hone the skills of technicians before the real rocket reaches the spaceport, an oft-delayed milestone that could still be a year or more away.

Two U.S. Air Force cargo planes delivered the Mars 2020 rover, cruise stage, descent module and the Mars Helicopter to the Kennedy Space Center in Florida this week for final assembly, fueling and mounting atop a United Launch Alliance Atlas 5 rocket in preparation for liftoff in July.

The nine Merlin main engines at the base of a recycled Falcon 9 rocket booster ignited Thursday night for several seconds during a pre-flight test-firing on a Cape Canaveral launch pad, clearing a major hurdle ahead of a scheduled May 31 liftoff with a high-power communications satellite for SES.