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The NK-33 and NK-43 are rocket engines designed and built in the late 1960s and early 1970s by the Kuznetsov Design Bureau. The NK designation is derived from the initials of chief designer Nikolay Kuznetsov. They were intended for the ill-fated Soviet N-1 rocket moon shot. The NK-33 engine is among the highest thrust-to-weight ratio of any Earth-launchable rocket engine, only NPO Energomash RD-253 and SpaceX Merlin 1D engine achieve a higher ratio. The specific impulse of the NK-33 is significantly higher than both these engines. The NK-43 is similar to the NK-33, but is designed for an upper stage, not a first stage. It has a longer nozzle, optimized for operation at altitude, where there is little to no ambient air pressure. This gives it a higher thrust and specific impulse, but makes it longer and heavier. Modified versions of these engines by Aerojet are known as the AJ26-58, AJ26-59 and AJ26-62. In 2010 stockpiled NK-33 engines were successfully tested for use by the Orbital Sciences Antares light-to-medium-lift launcher. However, manufacturing defects in the engine's liquid oxygen turbopump and design flaws in the hydraulic balance assembly and thrust bearings were proposed as two possible causes of the 2014 Antares launch failure. This failure led Orbital Sciences to replace the AJ-26 engines with newly-built RD-181 engines for future launches of the Antares rocket. == Technology == NK-33 and NK-43 are derived from the earlier NK-15 and NK-15V engines, respectively. The engines are high-pressure, regeneratively cooled staged combustion cycle bipropellant rocket engines, and use oxygen-rich preburners to drive the turbopumps. The turbopumps require subcooled liquid oxygen (LOX) to cool the bearings. These kinds of burners are highly unusual, since their hot, oxygen-rich exhaust tends to attack metal, causing burn-through failures. The United States had not much investigated oxygen-rich combustion technologies until the Integrated Powerhead Demonstrator project in the early 2000s.〔(U.S. Air Force-NASA Technology Demonstrator Engine for Future Launch Vehicles Successfully Fired During Initial Full Duration Test )〕 The Soviets, however, perfected the metallurgy behind this method. The nozzle was constructed from corrugated metal, brazed to an outer and inner lining, giving a simple, light, but strong structure. In addition, since the NK-33 uses subcooled LOX and kerosene, which have similar densities, a single rotating shaft could be used for both turbopumps.〔(Astronautix NK-33 entry )〕 Given its longer, heavier nozzle, the NK-43 ratio in vacuum is slightly heavier, with a thrust-to-weight ratio of about 120:1.〔(Astronautix NK-43 entry )〕 The oxygen-rich technology lives on in the RD-170/-171 engines, their RD-180, and recently developed RD-191 derivatives. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「NK-33」の詳細全文を読む スポンサード リンク
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