Coming up in the next few minutes, the launch conductor will take a launch readiness poll and give the final go-ahead to controllers to begin loading flight propellants into the Falcon 9. That activity, called tanking, is scheduled to start at about 4:08 p.m.
The two-stage rocket’s Merlin engines — nine of the first stage and one on the second stage — are powered by a combination of liquid oxygen and highly refined kerosene called RP-1.