Atlas (rocket family)

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Atlas is a family of US missiles and space launch vehicles. The original Atlas was designed in late 1950s to be used as an intercontinental ballistic missile (ICBM). It was a liquid propellant rocket burning liquid oxygen and RP-1 fuel in 3 engines configured in parallel staging design. In parallel staging several small first stages are strapped into the main stage and they are all ignited. After the smaller ones are burnt out they are discarded and main rocket continues burning and the payload is carried atop the main stage into the orbit. This design was used also for the Space Shuttle.

In 1962 and 1963, Atlas boosters launched the first US astronauts to Earth orbit within Mercury program (remember 2 manned Redstone sub-orbital flights). Atlas II model was launched 63 times (1991-2004), Atlas III was launched 6 times (2000-2005), and Atlas V is still in service planned until 2020. Recently InSight (see article InSight Mars Lander) was launched on Atlas V-401 rocket on May 5, 2018.
Left: Atlas rocket family. Right: Atlas Mercury being prepared for the launch 

The Atlas LV-3B or also Mercury-Atlas Launch Vehicle was used as a part of the Mercury Project (see article Mercury- Original Seven). All together 9 LV-3B were launched: 2 unmanned suborbital flights, 3 unmanned orbital flights, and 4 manned Mercury spaceflights. 

 The Atlas Agena was an expendable launch system derived from the SM-65 Atlas missile used between 1960 and 1978. It was used to launch the first 5 Mariner probes to Mars and Venus, and the Ranger (see article Ranger program) and Lunar Orbiter probes to the Moon. It was used also as a part of the Gemini program (see article Gemini project) as a upper stage of unmanned orbital target vehicle for practising of rendezvous and docking. 
Agena upper stage with docking collar for Gemini spacecraft

 Note: 
An expendable launch system is a launch system that is used only once to carry the payload into space. Their components are not recovered. 
A reusable launch system is a system in which some or all components are recovered. The vehicle typically consists of several rocket stages, discarded one by one. 

 The Atlas Centaur was also an expendable launch system derived from the SM-65D Atlas missile. An enhanced version of the Atlas D to mate with the Centaur stages. Due to large upper stage, the engines needed to be upgraded and structure reinforced.  Atlas Centaur was used mostly for planetary probe programs, especially Surveyor (see article Surveyor program) and Mariner programs.  

 The Atlas V, currently in use, was developed as a part of the evolved expendable launch vehicle program. (see article InSight Mars Lander)

 Note:
An evolved expendable launch vehicle is an expendable launch system program of the US Air Force to make space launches more affordable and reliable. It resulted in Delta IV and Atlas V. 



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