NK-33

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

The NK-33 and NK-43 were rocket engines designed and built in the late 1960s and early 1970s by Kuznetsov. They were intended for the ill-fated Russian 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.

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.

1 Technology
2 History
3 Future uses
4 References
5 External links

[edit] Technology

The NK-33 and -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. 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 thrust-to-weight ratio of any comparable engine- over 120:1^[1]. Given its longer, heavier nozzle, the NK-43 ratio in vacuo is slightly heavier with a thrust-to-weight ratio of about 120:1.^[2].

The oxygen-rich technology lives on in the RD-170/-171 engines, and their RD-180 and proposed RD-174/-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.

[edit] History

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.

[edit] Future uses

The question of what to do with the remaining NK-33s occurs frequently. The advanced design means they are still competitive today. 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 calls for demonstration flights between 2008 and 2010. RpK may receive up to $207 million if they meet all NASA milestones.^[3]^[4]^[5] But on September 7, 2007, NASA issued a default letter warning that it would terminiate the COTS agreement with Rocketplane Kistler in 30 days because RpK had not met several contract milestones.^[6]

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.^[7]

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.

These 'Aurora'/'Soyuz-3' proposals have not progressed to actual demonstrations. One possibility is that the number of NK-33s remaining is not enough to be worthwhile, given the high flight rate of Soyuz rockets (typically five to nine launches per year). This is far more likely for the five-NK configuration. The Kistler K-1 is designed to be reusable, making engine supply much less of an issue. A simpler possibility is that funds are not available to integrate and requalify a new design, even if its individual components have shown themselves to be viable.

Orbital is developing a "Taurus II" light-to-medium-lift launcher, planned to have two NK-33 in its first stage, a solid second stage, and a hypergolic orbit stage. However, as a developmental vehicle many parameters may still change.