Our interview with Steve Jurczyk, NASA’s acting administrator

Nine Merlin engines at the base of SpaceX’s next Falcon 9 rocket fired up Tuesday on a launch pad in Florida, wringing out the booster and ground systems ahead of a planned liftoff Sunday with a top secret payload for the U.S. government’s spy satellite agency.

Europe’s Sentinel 3B environmental satellite was shipped to the Plesetsk Cosmodrome in Russia’s far northern Arkhangelsk region in March for a month-long campaign to prepare the spacecraft for liftoff aboard a Rockot launcher.

Outgoing space station commander Shane Kimbrough and two Russian crewmates returned to Earth on Monday, riding a Soyuz capsule in a bubble of hot plasma to a parachute-assisted landing in Kazakhstan. The trio undocked from the space station at 0757 GMT (3:57 a.m. EDT) and landed on the Kazakh steppe at 1120 GMT (7:20 a.m. EDT) Monday.