Most powerful liquid-propellant rocket motor
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- Who
- RD-171M
- What
- 7,256,000 newton(s)
- Where
- Russian Federation (Moscow)
- When
- 15 May 1987
The most powerful liquid-propellant rocket motor is the RD-171M, developed by NPO Energomash (RUS) for the Zenit launch vehicle. The RD-171M consists of four combustion chambers and nozzles connected to shared fuel/oxidizer pump machinery and generates 7,256 kN (1,631,214 lbf) of thrust at sea level. The RD-171M is a modernized version of the RD-170, which first flew on the Soviet Energia rocket on 15 May 1987.
The RD-170/171M is what's called a oxidizer-rich staged combustion motor. In this design, the pumps which feed fuel and oxidizer to the combustion chambers are powered by a "preburner" – essentially a small enclosed rocket engine that drives a turbine. The oxidizer is fed into the preburner, in which it is mixed with a proportionally small amount of fuel. This uneven mixture burns much cooler than the main combustion chamber (and so doesn't melt the engine) and its exhaust is almost entirely oxidizer, which is then fed into the main combustion chamber alongside the rest of the fuel.
Motors such as this one are what's called "closed cycle" systems, as opposed to open-cycle, or "gas generator" designs which vent the exhaust from the preburner separately, wasting significant amounts of energy.
Despite its deliberately incomplete combustion, the preburner/turbine combination provides a massive 189.3 megawatts (253,855 horsepower) of power to the fuel and oxidizer turbopumps. This allows the pumps to force 1,792 kg of liquid oxygen and 732 kg of kerosene into the combustion chambers every second.
Work on the RD-170 started in 1976. It only flew twice because the massive and expensive Energia launch system (which included the Buran spaceplane) was abandoned with the fall of the Soviet Union. The RD-171 flew 54 times on the Zenit rocket between 1985 and 2005, while the RD-171M has flown 30 times on the Zenit 3SL since 2006. The Zenit rocket family is a joint Russian-Ukrainian design, however, and tensions between the two countries mean that this system has only flown twice since 2014.