Propellants are being loaded into the Atlas V rocket, a process known as tanking. It begins with chilldown of the ground equipment and transfer lines prior to the flow of supercool, cryogenic propellants. The Atlas booster’s single RD-180 engine uses 48,860 gallons of liquid oxygen, or LOX, in combination with a refined kerosene fuel called RP-1. The Centaur’s RL10-A-4-2 engine runs on 4,150 gallons of LOX and 12,680 gallons of liquid hydrogen, or LH2. RP-1 is not a cryogenic propellant like the others and was loaded into the first stage yesterday afternoon.
Countdown clocks are at T-1 hour, 39 minutes and counting.