Atlas V (401), No. AV-021, with SDO on board before arriving at Launch Pad 41.jpg

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 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.
* 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 both the Centaur upper stage and the payload.

Upgrades

Many systems on the Atlas V have been the subject of upgrade and enhancement both prior to the first Atlas V flight and since that time. Work on a new Fault Tolerant Inertial Navigation Unit (FTINU) started in 2001 to enhance mission reliability for Atlas vehicles by replacing the existing non-redundant navigation and computing equipment with a fault-tolerant unit. The upgraded FTINU first flew in 2006, and in 2010 a follow-on order for more FTINU units was awarded.

In 2015, ULA announced that the Aerojet Rocketdyne-produced AJ-60A solid rocket boosters (SRBs) then in use on Atlas V would be superseded by new GEM 63 boosters produced by Northrop Grumman Innovation Systems. The extended GEM 63XL boosters will also be used on the Vulcan Centaur launch vehicle that will replace the Atlas V. The first Atlas V launch with GEM 63 boosters happened on 13 November 2020.

Human-rating certification

Proposals and design work to human-rate the Atlas V began as early as 2006, with ULA's parent company Lockheed Martin reporting an agreement with Bigelow Aerospace that was intended to lead to commercial private trips to low Earth orbit (LEO).

Human-rating design and simulation work began in earnest in 2010, with the award of US$6.7 million in the first phase of the NASA Commercial Crew Program (CCP) to develop an Emergency Detection System (EDS).

As of February 2011, ULA had received an extension to April 2011 from NASA and was finishing up work on the EDS.

NASA solicited proposals for CCP phase 2 in October 2010, and ULA proposed to complete design work on the EDS. At the time, NASA's goal was to get astronauts to orbit by 2015. Then-ULA President and CEO Michael Gass stated that a schedule acceleration to 2014 was possible if funded. Other than the addition of the Emergency Detection System, no major changes were expected to the Atlas V rocket, but ground infrastructure modifications were planned. The most likely candidate for the human-rating was the N02 configuration, with no fairing, no solid rocket boosters, and dual RL10 engines on the Centaur upper stage.

On 18 July 2011, NASA and ULA announced an agreement on the possibility of certifying the Atlas V to NASA's standards for human spaceflight. ULA agreed to provide NASA with data on the Atlas V, while NASA would provide ULA with draft human certification requirements. In 2011, the human-rated Atlas V was also still under consideration to carry spaceflight participants to the proposed Bigelow Commercial Space Station.

In 2011, Sierra Nevada Corporation (SNC) picked the Atlas V to be the booster for its still-under-development Dream Chaser crewed spaceplane. The Dream Chaser was intended to launch on an Atlas V, fly a crew to the ISS, and landing horizontally following a lifting-body reentry. However, in late 2014 NASA did not select the Dream Chaser to be one of the two vehicles selected under the Commercial Crew competition.

On 4 August 2011, Boeing announced that it would use the Atlas V as the initial launch vehicle for its CST-100 (ISS) and was also intended to service the proposed Bigelow Commercial Space Station. A three-flight test program was projected to be completed by 2015, certifying the Atlas V/CST-100 combination for human spaceflight operations. The first flight was expected to include an Atlas V rocket integrated with an uncrewed CST-100 capsule, the second flight an in-flight launch abort system demonstration in the middle of that year, and the third flight a crewed mission carrying two Boeing test-pilot astronauts into LEO and returning them safely at the end of 2015. These plans did not materialize.

In 2014, NASA selected the Boeing CST-100