The first stage uses RP-1 (kerosene) and liquid oxygen (LOX) as propellants, powering two NK-33-derived engines (sold by Aerojet as AJ-26 engines). As Orbital has little experience with large liquid stages and LOX propellant, some of the Antares first stage work was contracted to Yuzhnoye SDO, designers of the Zenit series. One source claims that the contract includes the “main-stage fuel tanks and associated plumbing”.[7] The core provided by Yuzhnoye includes propellant tanks, pressurization tanks, valves, sensors, feed lines, tubing, wiring and other associated hardware.[15] Like Zenit, the Antares vehicle will have a 3.90 m (154 in) diameter. It will have a 3.9 m diameter payload fairing.[2]
Antares (rocket) - Wikipedia, the free encyclopedia

Source: Wikipedia