THE RD-170 ENGINE

The RD-170 (also known as 11D521), designed and manufactured by KB Energo – mash in Khimki near Moscow, was a LOX/kerosene engine employing the staged combustion cycle. Providing 740 tons of thrust and a specific impulse of 308.5 s at ground level, it remains not only the most powerful LOX/kerosene engine built to date, but also the highest-thrust liquid-fuel engine flown on any launch vehicle in the world.

Although Energomash had gained significant experience with staged-combustion cycle engines burning hypergolic propellants, the RD-170 marked the bureau’s first foray into closed-cycle LOX/kerosene engines. The only other closed-cycle LOX/ kerosene engines built in the Soviet Union until then had been much less powerful single-chamber engines such as the ones used on the Blok-L and Blok-D upper stages (built by the OKB-1 Korolyov bureau) and the NK engines for the first three stages of the N-1 rocket (developed by the Kuznetsov bureau in Kuybyshev). The United

States has never built a staged-combustion cycle LOX/kerosene engine. The only powerful LOX/kerosene engine ever flown by the United States was the F-1, five of which powered the first stage of the Saturn V. This was an open-cycle engine inferior in most aspects to the RD-170.

The RD-170 consisted of four combustion chambers, one turbopump assembly, and two gas generators. The turbopump assembly incorporated a single-stage active axial-flow turbine, an oxidizer pump, and a two-stage fuel pump. Connected to the assembly were low-pressure oxidizer and fuel pumps to increase the pressure of the propellant and thereby prevent cavitation of the turbopump assembly. The turbo­pump was driven by two oxidizer-rich gas generators. Originally, it was planned to have a single gas generator consuming 1.5 tons of propellant per second, but this would have been too big. In the RD-170 the entire oxidizer supply and just a small fraction of the kerosene (6% of the overall propellant mass) passed through the gas generators. The turbopump produced about 257,000 horsepower, which the Russians like to compare with the combined horsepower of three of their heavy nuclear icebreakers.

The RD-170 could be throttled down to 50 percent of rated thrust and could be gimbaled about 8° with the help of hydraulic actuators. The engine could be gimbaled in two axes, whereas the Zenit’s RD-171 had only single-axis gimbal capability. Therefore, each RD-170 required a total of eight hydraulic actuators, two for each combustion chamber. Unlike the RD-171 nozzles, those of the RD-170 entered the air stream impinging on the rocket when they were swiveled, requiring the use of more powerful actuators to counter the aerodynamic pressures.

With a nominal flight burn time of 140-150 seconds, the engine was designed to be used at least ten times, a capability confirmed during bench tests. Although the RD-170 was used only for the two Energiya missions in 1987 and 1988, its nearly identical twin (the RD-171) continues to fly today on the two-stage Zenit launch vehicle and its three-stage Sea Launch version. A derived version with just two combustion chambers (the RD-180) now powers America’s Atlas-5 rockets and a single-chamber version (the RD-191) is expected to become the power plant of Russia’s Angara family of launch vehicles (see Chapter 8). [4]