Atlas V is an expendable launch system and the fifth major version in the Atlas launch vehicle family. It was originally designed by Lockheed Martin, now being operated by United Launch Alliance (ULA), a joint venture between Lockheed Martin and Boeing. Atlas V is also a major NASA launch vehicle. It is America's longest-serving active rocket. In August 2021, ULA announced that Atlas V would be retired, and all 29 remaining launches had been sold. , 19 launches remain. Each Atlas V launch vehicle consists of two main stages. The first stage is powered by a Russian RD-180 engine manufactured by Energomash and burning kerosene and liquid oxygen. The Centaur upper stage is powered by one or two American RL10 engine(s) manufactured by Aerojet Rocketdyne and burns liquid hydrogen and liquid oxygen. The Star 48 upper stage was used on the New Horizons mission as a third stage. Strap-on solid rocket boosters (SRBs) are used in most configurations. AJ-60A SRBs were used originally, but they were replaced in November 2020 by Graphite-Epoxy Motor (GEM 63) SRBs. The standard payload fairings are in diameter with various lengths. Vehicle description The Atlas V was developed by Lockheed Martin Commercial Launch Services (LMCLS) as part of the U.S. Air Force Evolved Expendable Launch Vehicle (EELV) program and made its inaugural flight on 21 August 2002. The vehicle operates from SLC-41 at Cape Canaveral Space Force Station (CCSFS) and SLC-3E at Vandenberg Space Force Base. LMCLS continued to market the Atlas V to commercial customers worldwide until January 2018, when United Launch Alliance (ULA) assumed control of commercial marketing and sales. Atlas V first stage The Atlas V first stage, the Common Core Booster (CCB), is in diameter and in length. It is powered by one NPO Energomash RD-180 main engine burning of liquid oxygen and RP-1. The booster operates for about four minutes, providing about of thrust. Thrust can be augmented with up to five Aerojet AJ-60A or Northrop Grumman GEM 63 strap-on solid rocket boosters, each providing an additional of thrust for 94 seconds. The main differences between the Atlas V and earlier Atlas I and II family launch vehicles are: The first stage tanks no longer use stainless steel monocoque pressure stabilized "balloon" construction. The tanks are isogrid aluminum and are structurally stable when unpressurized. Accommodation points for parallel stages, both smaller solids and identical liquids, are built into first-stage structures.