N1 The N1 launcher originally utilized NK-15 engines for its first stage and a high-altitude variant, the NK-15V, for its second stage. The Soviets attempted to launch the N1 four times, but each attempt ended in failure, including one catastrophic explosion. By the time of the fourth failure, the
Moon race was already lost. However, Soviet space program managers hoped a second-generation vehicle, dubbed the N1F, could support their ambitions to construct the proposed
Zvezda Moon base. Kuznetsov refined his engine designs for the N1F, creating the improved NK-33 and NK-43 engines. Despite these advancements, other Soviet space leaders prioritized the
Energia rocket as the nation's heavy launcher, and the N1 program was ultimately canceled before an N1F could reach the launch pad. At the time of cancellation, two flight-ready N1Fs equipped with 30 NK-33 engines each in their Block A stages were complete. When the N1 program was shut down, the Soviet government ordered all related materials and documentation to be destroyed to conceal the USSR's failed Moon program. Officially, the N1 project was dismissed as a mere "paper project" to mislead the United States into believing a Moon race was underway. This cover story persisted until the era of
glasnost, when surviving hardware from the program was publicly displayed. However, a bureaucratic decision spared the destruction of over 60 NK-33 engines, including those from the two completed Block A stages and additional spares. These engines were stored in a warehouse and largely forgotten until their existence became known to engineers in the United States nearly 30 years later. Aerojet conducted the first test fire of a NK-33 engine in nearly 30 years on a test stand in Sacramento, during the test, the engine hit its specifications.
Kistler K-1 Rocketplane Kistler (RpK), designed their
K-1 rocket around three NK-33s and a NK-43. On 18 August 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, but on 7 September 2007, NASA issued a default letter, warning that it would terminate the COTS agreement with RpK because the company had not met several contract milestones.
Antares being rolled out for testing, showing the two NK-33 engines The initial version of the
Orbital Sciences Antares light-to-medium-lift launcher had two modified NK-33 in the first stage, a
solid Castor 30-based second stage and an optional solid or
hypergolic third stage. The NK-33s were imported from Russia to the United States, modified, and re-designated as Aerojet AJ26s. This involved removing some electrical harnessing, adding U.S. electronics, qualifying it for U.S. propellants, and modifying the steering system. The Antares rocket was successfully launched from NASA's Wallops Flight Facility on 21 April 2013. This marked the first successful launch of the NK-33 heritage engines built in early 1970s. Aerojet agreed to recondition sufficient NK-33s to serve Orbital's 16-flight NASA
Commercial Resupply Services contract. Beyond that, it had a stockpile of 23 1960s- and 1970s-era engines. Kuznetsov no longer manufactures the engines, so Orbital sought to buy
RD-180 engines. Because
NPO Energomash's contract with
United Launch Alliance prevented this, Orbital sued ULA, alleging anti-trust violations. Aerojet offered to work with Kuznetsov to restart production of new NK-33 engines, to assure Orbital of an ongoing supply. 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. As announced on 5 November 2014, Orbital decided to drop the AJ-26 first stage from the Antares and source an alternative engine. On 17 December 2014, Orbital Sciences announced that it would use the
NPO Energomash RD-181 on second-generation Antares launch vehicles and had contracted directly with NPO Energomash for up to 60 RD-181 engines. Two engines are used on the
first stage of the Antares 100-series.
Soyuz-2.1v In the early 2010s, the
Soyuz launch vehicle family was retrofitted with the NK-33 engine. This upgrade leveraged the engine's lower weight and greater efficiency to enhance payload capacity, while its simpler design and the use of surplus hardware potentially reduced costs.
RKTs Progress integrated the NK-33 into the first stage of the small-lift Soyuz variant, the
Soyuz-2.1v. On the rocket, a single NK-33 engine replaced the Soyuz's central
RD-108 engine, and the four boosters of the first stage were omitted. The NK-33A, specifically modified for the Soyuz-2.1v, underwent a successful hot-fire test on 15 January 2013, following a series of cold-fire and systems tests of the fully assembled rocket conducted in 2011 and 2012. The rocket completed its maiden flight on 28 December 2013. == Versions ==