Q&A with Keith Gendreau, principal investigator of the first X-ray space communications experiment (members only)

SpaceX’s first Falcon Heavy rocket fired up 27 main engines Wednesday on launch pad 39A at NASA’s Kennedy Space Center in Florida, sending a crackling rumble across the swampy spaceport and moving the heavy-lifter a step closer to its oft-delayed maiden flight as soon as next week.

An Atlas 5 rocket and a Starliner crew capsule stand at pad 41 in these images taken at sunset Dec. 18.

Two communications satellites owned by SES are booked to fly into orbit — possibly from South Texas — on a pair of Falcon 9 rockets in 2017, giving SpaceX two payloads that could be assigned to launch from the new commercial spaceport, officials said Wednesday.