Liquid rocket booster

Unlike solid rocket boosters, LRBs can be throttled down if the engines are designed to allow it, and can be shut down safely in an emergency for additional escape options in human spaceflight.

[citation needed] By 1926, US scientist Robert Goddard had constructed and successfully tested the first rocket using liquid fuel at Auburn, Massachusetts.

[citation needed] For the Cold War era R-7 Semyorka missile, which later evolved into the Soyuz rocket, this concept was chosen because it allowed all of its many rocket engines to be ignited and checked for function while on the launch pad.

[citation needed] The Soviet Energia rocket of the 1980s used four Zenit liquid fueled boosters to loft both the Buran and the experimental Polyus space battlestation in two separate launches.

[citation needed] Two versions of the Japanese H-IIA space rocket would have used one or two LRBs to be able to carry extra cargo to higher geostationary orbits, but it was replaced by the H-IIB.

[citation needed] After the Space Shuttle retired, Pratt & Whitney Rocketdyne and Dynetics entered the "advanced booster competition" for NASA's next human rated vehicle, the Space Launch System (SLS), with a booster design known as "Pyrios", which would use two more advanced F-1B booster engines derived from the Rocketdyne F-1 LOX/RP-1 engine that powered the first stage of the Saturn V vehicle in the Apollo program.