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NK-33: Wikis


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NK-33 and NK-43 are rocket engines designed and built in the late 1960s and early 1970s by the Kuznetsov Design Bureau. They were intended for the ill-fated Soviet N-1 rocket moon shot. The NK-33 engine achieves the highest thrust-to-weight ratio of any Earth-launchable rocket engine, whilst achieving a very high specific impulse. NK-33 is by most measures the highest performance rocket engine ever created[1].

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 ambient air pressure is low or perhaps zero. This gives it a higher thrust and specific impulse, but makes it longer and heavier.

In 2010 stockpiled NK-33 engines were successfully tested for use by the Orbital Sciences Taurus II light-to-medium-lift launcher.[2]



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. These kinds of burners are highly unusual, since their hot, oxygen-rich exhaust tends to attack metal, causing burn-through failures. Oxygen-rich engines were never successfully built in America. The Russians however perfected the metallurgy behind this trick. 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 LOX and kerosene, which have similar densities, a single rotating shaft could be used for both turbopumps; the resultant engines are extraordinarily lightweight, with the highest vacuum thrust-to-weight ratio of any comparable engine- 136.66:1[3]. Given its longer, heavier nozzle, the NK-43 ratio in vacuo is slightly heavier with a thrust-to-weight ratio of about 120:1.[4].

The oxygen-rich technology lives on in the RD-170/-171 engines, and their RD-180 and recently developed RD-191 derivatives. These engines still use the multiple combustion chamber and nozzle topology like the RD-107/108 engines of Soyuz, thus preventing them from reaching the NK's high thrust-to-weight ratio.

Role: 1st stage multi-engine
Propellants: RP-1/LOX
Development year: 1970's
Overall dimensions
Height 3.7 m (12 ft)
Diameter 2 m (6 ft 7 in)
Weight, dry 1,235 kg (2,720 lb)
Thrust-to-weight ratio 137
Specific impulse, sea level 297 s
Specific impulse, vacuum 331 s
Thrust, sea level 1,505 kN (338,000 lbf)
Thrust, vacuum 1,753.8 kN (394,300 lbf)
Combustion chamber pressure, 145 bar (14,500 kPa)
Manufacturer:  ???
Lead engineer:  ???
Design team: Kuznetsov


NK-33-1 (NK-33 with a nozzle extension) mockup

The N-1 launcher originally used NK-15 engines for its first stage, and a high-altitude modification (NK-15V) in its second stage. After four consecutive launch failures and no successes, the project stood down. While other aspects of the vehicle were being modified or redesigned, Kuznetsov improved his contributions into the NK-33 and NK-43, respectively. The 2nd-generation vehicle was to be called the N-1F. By this point the Moon race was long lost, and the Soviet space program was looking to the Energia as its heavy launcher. No N-1F ever reached the launch pad.

When the N-1 program was shut down, all work on the project was ordered destroyed. A bureaucrat instead took the engines, worth millions of dollars each, and stored them in a warehouse. Word of the engines eventually spread to America. Nearly thirty years after they were built, disbelieving rocket engineers were led to the warehouse. Later, one of the engines was taken to America, and the precise specification of the engine was demonstrated on a test stand.

The question of what to do with the remaining NK-33s occurs frequently. The advanced design means they are still competitive today.

About 150 engines survived, and in the mid-1990s, Russia sold 36 engines to Aerojet General for $1.1 million each. This company also acquired a license for the production of new engines. Aerojet has renamed the NK-33 and NK-43 the AJ26-58 and AJ26-59, respectively.

Kistler Aerospace, now called Rocketplane Kistler (RpK), designed their K-1 rocket around three NK-33s and an NK-43. On August 18, 2006, NASA announced that RpK had been chosen to develop Commercial Orbital Transportation Services for the International Space Station. The plan called for demonstration flights between 2008 and 2010. RpK would have received up to $207 million if they met all NASA milestones,[5][6][7] but on September 7, 2007, NASA issued a default letter warning that it would terminate the COTS agreement with Rocketplane Kistler in 30 days because RpK had not met several contract milestones.[8]

Proposals existed to retrofit the Soyuz launcher with NK-33s. Either one engine would replace the Soyuz's central RD-108, or five NK-33s would replace the RD-108 and four booster RD-107s. The lower weight and greater efficiency would increase payload; the simpler design and use of surplus hardware might actually reduce cost.

Future uses

Orbital Sciences is developing a Taurus II light-to-medium-lift launcher, planned to have two NK-33 (or AJ26-58) in its first stage, a solid second stage and a hypergolic orbit stage.[9][2]

RSC Energia is proposing an 'Aurora-L.SK' launch vehicle which would use an NK-33 to power the first stage and a Block DM-SL for the second stage.[10] TsSKB-Progress also plans to use NK-33 as the main engine of the lightweight version of the successful Soyuz rocket family under development, called Soyuz-1.[11]


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