Atlas V is an active expendable launch system in the Atlas rocket family. Atlas V was formerly operated by Lockheed Martin, and is now operated by the Lockheed Martin-Boeing joint venture United Launch Alliance. Each Atlas V rocket uses a Russian-built RD-180 engine burning kerosene and liquid oxygen to power its first stage and an American-built RL10 engine burning liquid hydrogen and liquid oxygen to power its Centaur upper stage. The RD-180 engines are provided by RD AMROSS, while Aerojet Rocketdyne provides both the RL10 engines and the strap-on boosters used in some configurations. The standard payload fairing sizes are 4 or 5 meters in diameter and of various lengths, and are made by RUAG Space. Fairings sizes as large as 7.2 m in diameter and up to 32.3 m in length have been considered. The rocket is assembled in Decatur, Alabama; Harlingen, Texas; San Diego, California; and at United Launch Alliance's headquarters near Denver, Colorado.