The NK-33 and NK-43 were rocket engines designed and built in the late 1960s and early 1970s by Kuznetsov. A rocket engine is a Jet engine that uses only Propellant mass for forming its high speed propulsive jet. Kuznetsov ( OKB-276) was a Soviet design bureau for Aircraft engines led by Nikolai Dmitriyevich Kuznetsov. They were intended for the ill-fated Russian N-1 rocket moon shot. N1 or N-1 was the secret Soviet Rocket intended to send Soviet Cosmonauts to the Moon. The NK-33 engine achieves the highest thrust-to-weight ratio of any Earth-launchable rocket engine, whilst achieving a very high specific impulse. Thrust-to-weight ratio is as its name suggests the ratio of instantaneous Thrust to Weight (where weight means weight at the Earth ’s surface
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.
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. The staged combustion cycle is a Thermodynamic cycle of Bipropellant rocket rocket Engines Some of the propellant is burned in a pre-burner and the A bipropellant rocket engine is a Rocket engine that uses two propellants (very often liquid propellants) which are kept separately prior to reacting to form a hot 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. Given its longer, heavier nozzle, the NK-43 ratio in vacuo is slightly heavier with a thrust-to-weight ratio of about 120:1. .
The oxygen-rich technology lives on in the RD-170/-171 engines, and their RD-180 and proposed RD-174/-191 derivatives. The RD-170 is the world's most powerful multi-nozzle multi-chamber liquid Bipropellant rocket engine The RD-180 is a dual- Combustion chamber, dual Nozzle, Russian developed Rocket engine, derived from the RD-170 used in Zenit rockets 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. The RD-107 is a type of Rocket engine initially used to launch R-7 Semyorka missiles
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. The Energia (or Energiya, Энергия in Russian, meaning Energy) Rocket was a Soviet rocket that was designed 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. Aerojet has renamed the NK-33 and NK-43 the AJ26-58 and AJ26-59, respectively. Aerojet is a major Rocket and missile propulsion manufacturer based primarily in Sacramento California with divisions in Redmond WA; Orange VA Kistler Aerospace, now called Rocketplane Kistler (RpK), designed their K-1 rocket around three NK-33s and an NK-43. Rocketplane Kistler (RpK based in Oklahoma City, was a Reusable spacecraft firm formed in 2006 by Rocketplane Limited Inc The K-1 launch vehicle was to be a two-stage fully reusable aerospace vehicle in commercial development by Rocketplane Kistler. On August 18, 2006, NASA announced that RpK had been chosen to develop Commercial Orbital Transportation Services for the International Space Station. Events 293 BC - The oldest known Roman temple to Venus is founded starting the institution of Vinalia Rustica. Year 2006 ( MMVI) was a Common year starting on Sunday of the Gregorian calendar. Commercial Orbital Transportation Services is a NASA program to coordinate the commercial delivery of crew and cargo to 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.  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. Events 1251 BC - A Solar eclipse on this date might mark the birth of legendary Heracles at Thebes Greece. Year 2007 ( MMVII) was a Common year starting on Monday of the Gregorian calendar in the 21st century. Rocketplane Kistler (RpK based in Oklahoma City, was a Reusable spacecraft firm formed in 2006 by Rocketplane Limited Inc 
RSC Energia is proposing an 'Aurora-L. SP Korolev Rocket and Space Corporation Energia ( Russian: ru Ракетно-космическая корпорация "Энергия" им SK' launch vehicle which would use an NK-33 to power the first stage and a Block DM-SL for the second stage. Block D ( Блок Д in Russian is the upper stage of USSR / Russia heavy Expendable launch systems used for the N1 rocket, Proton 
Proposals existed to retrofit the Soyuz launcher with NK-33s. The Soyuz launch vehicle (Western designation A-2 is an Expendable launch system manufactured by TsSKB-Progress in Samara Russia. 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. A solid rocket or a solid-fuel rocket is a Rocket with a motor that uses solid propellants ( Fuel / Oxidizer) A hypergolic propellant is either of the two Rocket propellants used in a hypergolic Rocket engine, which spontaneously ignite when they come into contact However, as a developmental vehicle many parameters may still change.