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Lost legacy of the Moon Race comes back to life

A legendary NK-33 (14D15) rocket engine was originally developed to carry Soviet cosmonauts on their way to the Moon onboard a giant N1 rocket. After the ill-fated lunar effort was aborted in 1974, dozens of already manufactured NK-33s ended up in storage. For decades, engine developers searched for a new job for the capable powerplant. Finally, at the end of the first decade of the 21st century, NK-33 had a real chance to fly, this time powering both American and Russian rockets. By 2010, the Russian government reportedly came close to making a decision to jump-start mass production of the NK-33 engine.

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NK-33 engine

The NK-33 became the last upgrade of a similar engine developed during the Moon Race. Like its predecessor -- NK-15 -- the engine would power the first stage of the N1 launch vehicle. Comparing to its predecessor, NK-33 sported simplified pneumatic and hydraulic systems, more advanced controls, upgraded turbo-pumps and combustion chamber. The engine needed only seven interfaces employing explosive pyrotechnic devices, instead of 12 on NK-15. Modified interfaces facilitated replacement of parts during refurbishment.

The development of NK-33 was taking place during 1968-1972, as N1 was going through a disastrous flight test program. Although NK-33 engines had been blamed for N1 failures, it was clear early on that the real culprit in the N1 fiasco had always been inadequate pre-flight testing of a fully integrated first stage carrying 30 such engines and its extremely complex and cumbersome flight control system. NK-33 developers have always insisted that as a stand-alone engine, their creation was very reliable and far ahead of its time. The engine used so-called closed cycle design, which would enable very efficient use of onboard propellant, thus increasing performance. At the same time, a relatively low pressure inside the combustion chamber guaranteed reliable and safe operation of the engine.

With the cancellation of the Soviet lunar landing effort, NK-33 developers continued efforts to "marry" the engine with one of the future rockets.

During the 1970s, the competition for the new-generation launch vehicle conducted under the Podyem (Ascent) project saw first proposals to use NK-33 on the Soyuz, Proton and then yet-to-be-developed 11K77 (Zenit) rocket. During a troubled birth of the RD-171 engine for Zenit, NK-33 was reportedly considered again for the Zenit rocket and its first stage of the super-heavy Energia rocket.

At the beginning of the 1980s, a revision of the NK-33 engine, designed for high performance at high altitude and designated NK-43, was eyed by NPO Molniya for a series of proposed aircraft-launched reusable systems within Project 49, 49M and Bizan. (524)

With the end of the Cold War, NK-33 was actively marketed in the United States, as a possible engine for future versions of the workhorse Atlas and Delta rockets. During 1995, as many as five live firings of the engine had been conducted in the US with the total burn time reaching 411 seconds. Combined with tests in Russia, the engine worked for 492.5 seconds. (145) Unfortunately, during 1990s, all these hopes for NK-33 went nowhere, as did the project of a K-1 commercial reusable booster from Kistler Aerospace, which also eyed the engine.

Eventually, NK-33 was adopted for the US Taurus-2 rocket (later renamed Antares) developed by Orbital Science Corp. Aerojet renamed the engine AJ26-62, planning to install a pair of these powerplants on the first stage of the rocket. Around 80 already manufactured NK-33 engines have been left in storage since the 1970s. In the meantime, Orbital forecasted the need for as many as 100 engines for the Antares (Taurus-2) project until 2020.

At the end of the 1990s, a version of the engine known as NK-39, was also considered for the X-34 space plane and the RASCAL system. Around the same time, NK-33 was also eyed for the Japanese Galaxy Express system. In Russia, a stalled commercial venture Vozdushny Start hoped to use an NK-43 version of the engine for a light-weight Polyot rocket launched from an Antonov-124 Ruslan aircraft.

Return to Soyuz

New proposals to integrate NK-33 into the Soyuz family were jump-started in the second half of the 1990s with renewed efforts to develop the Yamal, Onega, Soyuz-2-3 and Soyuz-3 launch vehicles, as well as their commercial version called Avrora, which would fly from Australian Christmas Island in the Eastern part of the Indian Ocean. The project failed due to lack of private investments and the refusal of the Australian government to bankroll the venture.

With the decision of the Russian Ministry of Defense to develop the Soyuz-1 rocket, which would also employ NK-33, the restart of production had to be considered. By the middle of 2010, Rosoboronprom, a government entity which oversaw the engine manufacturer, committed to restart NK-33 production by 2014-2015, Russian officials said. In November 2013, OAO Kuznetsov inaugurated the construction of a new state-of-the-art building intended to expand the company's production capabilities. The project with a price tag of 732 million rubles, including 502 million provided by Roskosmos was to be completed in November 2015. However unofficial reports at the time still said that ongoing work and immediate plans regarding NK-33 had only involved re-inspection of old engines and necessary upgrades of certifiable hardware.

The funding breakthrough for the Soyuz-1 and follow-on rockets equipped with NK-33 finally came after a successful demo firing of the veteran engine on June 2, 2008. The miraculous revival of a dacades-old NK-33 powerplant was attended by a number of high-ranking government and military officials, including then commander of the Russian space forces General Popovkin. Russian military apparently had potential payloads for Soyuz-1 and wanted to have a backup for Rockot boosters, which were plagued by delays in the production of their upper stage engines. The successful test of NK-33 paved the way to a government decree on the Soyuz-1 signed by Russian Prime-Minister Vladimir Putin, thus bringing the project to a new level of federal support.

NK-33 fires again

On Oct. 1, 2009, the NK-33 engine fired for 220 seconds at a test stand in Samara, demonstrating maximum capabilities of the engine. The test aimed to demonstrate a possibility of using the engine in the US-built Antares (Taurus-2) rocket, whose maiden launch was expected in 2010. Representatives of the US firm Aerojet, responsible for integration of NK-33 into Taurus-2, were present at the test.

Alongside the American delegation, representatives of Samara-based TsSKB Progress also watched the firing. Yet, another test of the same engine was planned within a week, after a replacement of expendable elements. Thus, it would demonstrate the capability of the engine to conduct multiple firings. The future test was to benefit both, Antares (formerly Taurus-2) and Soyuz-1 projects.

A fire during test

Only five days after a previous firing, a new live test of the NK-33 engine took place in Samara on Oct. 6, 2009. As before, Aerojet and TsSKB officials were present. However after 160 seconds of operation, an emergency cutoff had been activated, as the fire broke out on the test stand. According to unofficial reports on the Novosti Kosmonavtiki forum posted four days after the accident, the fire was caused by excessive vibration in the oxidizer line of the test stand, leading to the damage of an oxidizer pump and the fire. The accident did not damage the stand and the engine itself did not apparently experience any technical problems.

A new series of NK-33 tests

The NK-33 engine fired again on March 3, 2010, performing normally during an abbreviated 91-second test, a poster on the Novosti Kosmonavtiki forum said. It was followed on March 6, 2010, by another firing, which lasted for 287 seconds testing the engine's a full-duration cycle. The performance profile included 50 seconds of burn at 108 percent from nominal thrust of the engine. A third test firing in a series took place on March 12, 2010, and lasted 239 seconds.

On Oct. 24, 2011, TsSKB Progress announced that on October 15 OAO Kuznetsov conducted a live test of the NK-33A engine for the Soyuz-2-1v rocket. The firing tested a capability of the engine to withstand foreign particles inside oxidizer supply lines, TsSKB Progress said. A second test in a series was conducted on October 26, 2011. According to OAO Kuznetsov, both tests lasted 220 seconds and particles were added into the oxidizer and fuel supply lines. Yet, another test was planned clearing the way to the engine's certification for inter-agency tests, OAO Kuznetsov said.

What was announced as the fourth and final firing of the NK-33A engine took place at Vintay facility on April 20, 2012. The engine was reportedly operating flawlessly for 157.7 seconds logging a total of 600 seconds during multiple test runs, its manufacturer announced a week later. At the time, the company's representatives promised a decision of the inter-agency commission on the resumption of the engine's mass production within a month and a half.

On Jan. 15, 2013, OAO Kuznetsov announced that it started the year with a successful certification and acceptance test of NK-33A engine intended for flight tests of the Soyuz-2.1v rocket. The engine fired for a scheduled duration at the company's test stand and was then shipped to the assembly factory in preparation for shipment to the customer, OAO Kuznetsov said. Also, on the evening of March 22, the company conducted another firing of NK-33A, aimed to test the emergency shutdown command, which was successful. The third qualification test took place on March 30, 2013.

On August 13, 2014, the Samara Today newspaper reported that the NK-33 engine had undergone a 40-second certification firing before its installation on the third Soyuz-2-1v rocket.

Further upgrades

In mid-2012, a chief designer of OAO Kuznetsov said that the company had planned to boost the performance of the NK-33A engine by 10 percent before 2018 and also considered the possibility of a 20 percent increase in its thrust. However, at the same time, NPO Energomash started active development of the RD-193 engine, as a replacement to NK-33, whose production had not been yet resumed. As of 2013, NPO Energomash claimed that only 20 NK engines had remained available and they could support only around 10 missions of the Soyuz-2-1v rocket. However, in 2014, OAO Kuznetsov claimed that the company had already restored a considerable part of the manufacturing process for the NK-33 engine.

On October 5, 2015, the United Engine Corporation, ODK, announced that it had conducted a successful 40-second test firing of the NK-33 engine to certify it for the use on the Soyuz-2-1v rocket, which at the time was being prepared for its second launch. The firing tested an upgraded combustion chamber and a newly manufactured ignition chamber. (Both components were apparently modified in the wake of an Antares rocket failure in 2014.) The ODK said that the final processing of the fifth NK-33 engine would be completed within next two weeks before its shipment to RKTs Progress, the developer of the Soyuz rocket family.


A Soyuz-2-1v rocket powered by NK-33 engine lifts off successfully on Dec. 5, 2015, carrying Kanopus-ST satellite as its primary payload.


NK-33 characteristics:

Fuel Kerosene*
Oxidizer Liquid oxygen
Thrust on the ground 154 tons (1,509.8 kH)
Thrust in vacuum 167 tons (1,638 kH)
Specific impulse on the ground 297 seconds
Specific impulse in vacuum 331 seconds
Propellant consumption 517.3 kilograms per second
Propellant component ratio 2.62
Combustion chamber pressure 14.83 MPa
Engine mass 1,222 kilograms
Engine diameter 1,490.5 millimeters
Engine length 3,705 millimeters
Turbopump power 46,000 horse power
Turbopump rotation speed 18,500 rotations per minute
Maximum burn time 600 seconds

*An experimental version of the NK-33 engine burning liquid methane fuel was under consideration. It would have a thrust of 154 tons (1,509 kH) and a burn time of 410 seconds.


Chronology of NK-33 engine development:

1968: The development of the NK-33 engine starts.

1970 April: NK-33 is fired at a test stand for the first time.

1972 September: Official "State Test" of the NK-33 engine.

1973 Jan. 10: The NK-33 No. F115026M engine, manufactured in 1972 is used for "control and rollout" tests.

1974 Jan. 10: The NK-33 No. F115026M engine, manufactured in 1972 is used for "control and rollout" tests.

1976: An "Endurance" test of the NK-33 engine takes place at the static stand.

1995 July 12: An NK-33 No. F115026M engine is delivered to the United States after refurbishment in Russia.

1995 Oct. 17-Nov. 15: The NK-33 No. F115026M engine undergoes a series of firing tests at the Aerojet test stand.

1997 August: Several NK-33 engines are shipped to the US. (120)

2008 June 2: The funding breakthrough for the Soyuz-1 and follow-on rockets equipped with NK-33 engines comes after a successful demo firing of the veteran NK-33 engine.

2009 Oct. 1: An NK-33 engine fires for 220 seconds at a test stand in Samara, demonstrating maximum capabilities of the engine.

2009 Oct. 6: Only five days after a previous firing, a new live test of the NK-33 engine takes place in Samara.

2010 March 3: An NK-33 engine fired again, performing normally during an abbreviated 91-second test.

2010 March 6: A firing, which lasts for 287 seconds, tests the engine's a full-duration cycle.

2010 March 12: Third test firing in a series takes place and lasts 239 seconds.

2011 Oct. 15: OAO Kuznetsov conducts the first in a series of 220-second live tests of the NK-33A engine designed for the Soyuz-1 (Soyuz-2-1v) launch vehicle at Vintay test facility.

2011 Oct. 26: OAO Kuznetsov conducts a second in a series of 220-second live tests of the NK-33A engine at Vintay test facility.

2012 April 20: An NK-33A engine fires for 157 seconds at Vintay facility during its forth and last test.

2013 Jan. 15: OAO Kuznetsov announces a successful certification and acceptance test of NK-33A engine.

2013 March 22: During the evening, OAO Kuznetsov conducts a firing of the NK-33A engine aimed to test an emergency protection mechanism of the first stage of the Soyuz–2.1v rocket. According to the company, when readings of the emergency sensor reached critical condition, the firing was discontinued on time.

2013 March 30: The third certification test of an NK-33A engine takes place at OAO Kuznetsov.

2014 Aug. 13: OAO Kuznetsov conducts a successful 40-second certification test of an NK-33 engine for the third Soyuz-2-1v launch vehicle at the Vintay test facility in Russia.

2015 Oct. 5: The ODK corporation conducts a 40-second acceptance test of the fifth NK-33 engine for the Soyuz-2-1v rocket.


Next chapter: RD-193 engine

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Page author: Anatoly Zak; Last update: October 17, 2016

With additions from George H. Chambers (July 2012)

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The NK-33 rocket engine. Click to enlarge. Copyright © 2010 Anatoly Zak


The NK-33-1 engine. Click to enlarge.


A version of the NK-33 engine with an extendable nozzle. Credit: TsSKB Progress

NK-33 firing

Live test firing of the NK-33 engine. Click to enlarge. Credit: SNTK Kuznetsov


A live test of NK-33 engine at Vintay facility, apparently in October 2011. Credit: SNTK Kuznetsov


A photo of NK-33 engine test published on Jan. 15, 2013. Credit: SNTK Kuznetsov


Test of emergency protection system on March 22, 2013. Credit: SNTK Kuznetsov


A photo of the NK-33 engine test published in August 2014. Click to enlarge. Credit: OAO Kuznetsov

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