Fueled segments of the solid rocket boosters that will lift off on the first flight of NASA’s Space Launch System have arrived at the Kennedy Space Center in Florida, but officials will hold off on stacking the boosters until the SLS core stage completes a crucial test-firing later this year.

A Japanese H-2A rocket lifted off from the Tanegashima Space Center at 0017:46 GMT Thursday (8:17:46 p.m. EDT Wednesday) with the Michibiki 2 navigation satellite designed to improve positioning and timing services over Japan.

SpaceX’s next launch of satellites for the company’s Starlink broadband network — planned in the final days of 2019 — will carry one spacecraft with an experimental coating designed to make it less reflective in orbit, a first step in assuaging concerns from scientists who say the deployment of thousands more Starlink stations would impede some astronomical observations.