Video: Falcon 9 stands at the launch pad

Nine Merlin main engines at the base of a SpaceX Falcon 9 rocket fired at launch pad 39A Saturday, passing a major test before the company’s next launch, a secretive mission slated for liftoff Wednesday night.

Mostly clear skies and brisk westerly winds are forecast at launch time Friday afternoon for SpaceX’s first resupply mission to the International Space Station in nearly a year.

When SpaceX’s Falcon 9 rocket takes off with 64 small satellites — a payload cache representing 34 customers in 17 nations — it will be just the first act in a nearly five-hour sequence to deftly deploy each of the spacecraft, which range in size from a Rubik’s cube to a refrigerator.