NK-33
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The NK-33 and NK-43 were the rocket engines designed and built in the 1960s 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.
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.
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 a thrust to weight ratio of over 136:1[1].
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. Aerojet has renamed the NK-33 and NK-43 the AJ26-58 and AJ26-59, respectively. Kistler Aerospace designed their K-1 rocket around three NK-33s and an NK-43. On August 18, 2006, NASA announced that Kistler, now a unit of Rocketplane Kistler, had been chosen to develop Commercial Orbital Transportation Services for the International Space Station. The plan calls for demonstration flights between 2008 and 2010. Rocketplane Kistler may receive up to $207 million if they meet all NASA milestones.[2][3][4]
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.
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 chambers and nozzles like used on RD-107/108 engines of Soyuz, however, preventing them from reaching the NK's high thrust-to-weight ratio.
[edit] References
- ^ Astronautix NK-33 entry
- ^ NASA selects crew, cargo launch partners. Spaceflight Now (August 18, 2006).
- ^ NASA Selects Crew and Cargo Transportation to Orbit Partners. SpaceRef (August 18, 2006).
- ^ Alan Boyle. "SpaceX, Rocketplane win spaceship contest", MSNBC, August 18, 2006.
