The "1.5 staging" technique is no longer used, having been discontinued on the Atlas III with the introduction of the Russian RD-180 engine. The main-stage diameter increased from . Centaur upper stage The Centaur upper stage uses a pressure-stabilized propellant-tank design and cryogenic propellants. The Centaur stage for Atlas V is stretched relative to the Atlas IIAS Centaur and is powered by either one or two Aerojet Rocketdyne RL10A-4-2 engines, each engine developing a thrust of . The inertial navigation unit (INU) located on the Centaur provides guidance and navigation for both the Atlas and Centaur and controls both Atlas and Centaur tank pressures and propellant use. The Centaur engines are capable of multiple in-space starts, making possible insertion into low Earth parking orbit, followed by a coast period and then insertion into GTO. A subsequent third burn following a multi-hour coast can permit direct injection of payloads into geostationary orbit. , the Centaur vehicle had the highest proportion of burnable propellant relative to total mass of any modern hydrogen upper stage and hence can deliver substantial payloads to a high-energy state. Star 48 third stage Star 48 is a type of solid rocket motor used by many space propulsion and launch vehicle stages. It was developed primarily by Thiokol Propulsion, and is now, after several mergers, manufactured by Northrop Grumman's Space Systems division. A Star 48B stage is also one of the few man-made items sent on escape trajectories out of the Solar System, although it is derelict since its use. It has been used once on the Atlas V as a third stage for the New Horizons mission. Payload fairing Atlas V payload fairings are available in two diameters, depending on satellite requirements. The diameter fairing, originally designed for the Atlas II booster, comes in three different lengths: the original version and extended versions, first flown respectively on the AV-008/Astra 1KR and AV-004/Inmarsat-4 F1 missions. Fairings of up to diameter and length have been considered but were never implemented. A diameter fairing, with an internally usable diameter of , was developed and built by RUAG Space in Switzerland. The RUAG fairing uses carbon fiber composite construction and is based on a similar flight-proven fairing for the Ariane 5. Three configurations are manufactured to support the Atlas V: , , and long. While the classic fairing covers only the payload, the RUAG fairing is much longer and fully encloses