The RD-170 () is the world's most powerful and heaviest liquid-fuel rocket engine. It was designed and produced in the Soviet Union by NPO Energomash for use with the Energia launch vehicle. The engine burns kerosene fuel and LOX oxidizer in four combustion chambers, all supplied by one single-shaft, single-turbine turbopump rated at in a staged combustion cycle. Shared turbopump Several Soviet and Russian rocket engines use the approach of clustering small combustion chambers around a single turbine and pump. During the early 1950s, many Soviet engine designers, including Valentin P. Glushko, faced problems of combustion instability while designing bigger thrust chambers. At that time, they solved the problem by using a cluster of smaller thrust chambers. Variants RD-170 The RD-170 engine featured four combustion chambers and was developed for use on the Energia launch vehicle – both the engine and the launch vehicle were in production only for a short time. Energia was launched twice. Each Energia vehicle had a core hydrolox stage, plus 4 Zenit boosters, each powered by one RD-170. The engine was designed for 10 reuses but tests showed they could stand up to 20 burns. RD-171 Building on the technology from the Energia's liquid fuel booster the Zenit (rocket family) was developed, which uses a RD-170 variant, the RD-171. While the RD-170 had nozzles which swiveled on two axes, the RD-171's nozzles only swivel on one axis. RD-171 was intended to be used on Zenit rocket. Models called the RD-172 and RD-173 were proposed, upgrades that would provide additional thrust, and the RD-173 proposal was finalized as the RD-171M upgrade in 2006. RD-171MV A modification of RD-171M being developed for the Irtysh rocket. Unlike RD-171M it's completely made from Russian components and features a new control system. First test sample was manufactured in early 2019 Tests were reported to have been successfully completed in September 2021. Dual-chamber derivative The RD-180 uses only two combustion chambers instead of the four of the RD-170. The RD-180 used on the Atlas V replaced the three engines used on early Atlas rockets with a single engine and achieved significant payload and performance gains. This engine had also been chosen to be the main propulsion system for the first stage of the now cancelled Russian Rus-M rocket. Single-chamber derivative The RD-191 is a single-chamber version used in the Russian Angara rocket. Variants of RD-191 include RD-151 in South Korean Naro-1