N1 rocket

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N1 or N-1 was the Soviet rocket intended to send Soviet cosmonauts to the Moon, preferably ahead of the Americans. It is also known in the west as the G-1e or SL-15. All four attempted launches failed, and the project was officially cancelled in 1976.

History

Development of the N1 began in 1959 under the direction of Sergei Korolev at his OKB-1 Design Bureau. The original design proposed a 50 ton payload intended as a launcher for military space stations and a manned Mars flyby using a nuclear engine upper stage. The N1 was the largest of three proposed designs; the N2 was somewhat smaller and intended to compete with the proposed UR-200, and the much smaller N3, which would replace his "workhorse" R-7 rocket. No actual development was carried out at this point, however; the N-series was strictly a "paper project".

In December 1959 a meeting was called with all of the chief designers, who presented their latest designs to the military. Korolev presented the N-series along with a much more modest series of upgrades to the R-7. Vladimir Chelomei, Korolev's rival, presented his "Universal Rocket" series, which used a common lower stage in various clustered configurations to meet a wide variety of payload requirements. Mikhail Yangel, perhaps the most successful of the three but with little political power, presented the small R-26 intended to replace the R-16, the much larger R-36 ICBM, as well as the SK-100, a space launcher based on a huge cluster of R-16's. In the end the military planners selected Chelomei's UR-100 as the new "light" ICBM, and Yangel's R-36 for the "heavy" role. They saw no need for any of the larger dedicated launchers, but also gave Korolev funding to develop the Molniya (8K78) adaptation of the R-7.

Things changed in 1961. In March, during a meeting at Baikonur, designers discussed the N1 design, along with a competing design, the R-20. In June, Korolev was given a small amount of funding for N1 development between 1961 and 1963. In May 1961 a government report, On Reconsideration of the Plans for Space Vehicles in the Direction of Defense Purposes, set the first test launch of the N1 rocket for 1965.

When the US announced the goal of landing a man on the moon in May 1961, Korolev proposed a lunar mission based on a new spacecraft, eventually known as Soyuz, that was designed for on-orbit rendezvous. Several launches would be used to build up a complete moon package, one for the Soyuz, another for the lunar lander, and additional launches with cislunar engines and fuel. Although this mission profile, "Earth-Orbital Rendezvous", requires the least amount of launch weight of its boosters, the lunar boosters and fuel were simply too large for any existing Soviet launcher. Korolev thus proposed development of the N1 with a 50-ton payload – much smaller than the N1 design that would eventually be delivered.

To power the new design, Valentin Glushko, who then held a near-monopoly on rocket engine design in the Soviet Union, proposed a new engine, the RD-270, running on unsymmetrical dimethylhydrazine (UDMH) and nitrogen tetroxide (N2O4) for Korolev's design. This formula is hypergolic (i.e. its components ignite on contact, reducing the complexity of the combustion system), and was widely used in Glushko's existing engine designs used on various ICBMs. However, the high weight of the UMDH/N2O4 fuel dramatically reduces specific impulse, and Korolev felt that any realistic high-performance design would need to use higher-performance fuels, in his opinion, kerosene with a liquid oxygen oxidizer. Additionally, Korolev felt that the toxic nature of the fuels and their exhaust presented a real safety risk.

The difference of opinions led to a falling out between Korolev and Glushko. In 1962 a committee that was appointed to break the logjam agreed with Korolev. Since Glushko refused to work on such a design, Korolev eventually "gave up" and decided to enlist the help of the Nikolai Kuznetsov's OKB-276, a jet engine designer. Kuznetsov, who had limited experience in rocket design, responded with a fairly small engine known as the NK-15, which would be delivered in several versions tuned to different altitudes. To achieve the required amount of thrust, it was proposed that a large number of NK-15's would be used in a clustered configuration around the outer rim of the lower-stage booster. The "inside" of the ring of engines would be open, with air piped into the hole via inlets near the top of the booster stage. The air would be mixed with the exhaust in order to provide thrust augmentation, as well as additional combustion with the deliberately fuel-rich exhaust. The ring-like arrangement of so many rocket engine nozzles on the N1's first stage could have been an attempt at creating a crude version of a toroidal aerospike engine system; more conventional aerospike engines were also studied.

Meanwhile, Chelomei's OKB-52 proposed an alternate mission, LK-1, with much lower risk. Instead of a manned landing, Chelomei proposed a series of circumlunar missions which he felt would be able to beat the US. He also proposed a new booster for the mission, clustering three of his existing UR-200 designs (known as the SS-11 in the west) to produce a single larger booster, the UR-500. However, these plans were dropped when Glushko offered Chelomei the RD-270, which allowed the construction of a much simpler "monoblock" design, also known as the UR-500.

The Soviet military, specifically the Strategic Missile Forces, was reluctant to support what was essentially a politically-motivated project with little military utility. However, both Korolev and Chelomei pushed for a lunar mission. For some time, between 1961 and 1964, Chelomei's less aggressive proposal was accepted, and development of his UR-500 and the L1 spacecraft were given a high priority. When Gemini missions put the US in the lead in space development, Korolev pressured Nikita Khrushchev into making a lunar landing before the US. Since there were a number of unknowns in the Earth-Orbit-Rendezvous profile that could not be tested in time, a direct-launch profile similar to Apollo was selected. This required much larger boosters.

Korolev proposed a larger N1, combined with a new lunar package known as the L3. The L3 combined the lunar engines, an adapted Soyuz (the LOK) and the new LK lunar lander in a single package. Chelomei responded with a clustered UR-500-derived vehicle, topped with the L1 spacecraft already under development, and a lander of their own design. Korolev's proposal was selected as the winner in August 1964, while Chelomei was told to continue with his circumlunar UR-500/L1 work.

When Khrushchev was overthrown later in 1964, infighting between the two teams started anew. In October 1965 the Soviet government ordered a compromise; the circumlunar mission would be launched on Chelomei's UR-500 using Korolev's Soyuz spacecraft in place of their own Zond design, aiming for a launch in 1967, the 50th anniversary of the Bolshevik Revolution. Korolev, meanwhile, would continue with his original N1-L3 proposal. Korolev had clearly won the argument, but work on the L1 continued anyway, as the Zond.

Korolev died in 1966 due to complications after minor surgery, and the work was taken over by his deputy, Vasily Mishin. Mishin did not have Korolev's political astuteness or power, a problem that helped lead to the eventual downfall of the N1, and of the lunar mission as a whole.

A comparison of the U.S. Saturn V rocket with the Soviet N1. The N1 was slightly shorter yet delivered much more thrust. Even so, due to the Saturn V's use of liquid hydrogen propellant in its upper stages as opposed to the N1's use of kerosene in all stages, the Saturn V could loft heavier payloads into space. A flight history comparison strongly favors the Saturn V: in 13 operational launches, it lost no payloads; the N1 lost all payloads in 4 launches. America spent more money and took longer developing the Saturn V.

Description

The N1 was a very large rocket, standing 105 metres tall (345 feet) — among the world's largest launch vehicles, second only to the Saturn V in height, mass and payload. The N1-L3 consisted of five stages in total, three for immediate boost into orbit (the N1), and another two for the lunar portion (in the L3). Fully loaded and fueled, the N1-L3 weighed 2788 metric tons (6.1 million lb). The lower three stages were shaped to produce a single truncated cone just over 10 m wide at the base, while the L3 section was cylindrical at about 4.4 m wide. The conical shaping of the lower stages was due to the arrangement of the tanks within, a smaller spherical kerosene tank on top of the larger liquid oxygen tank below.

The first stage, Block A, was powered by 30 NK-15 engines arranged in two rings, the main ring of 24 at the outer edge of the booster, the inner of 6 at about half diameter. The engines were the first ever staged combustion cycle engines. The control system was primarily based on differential throttling of the engines, the outer ring for pitch and yaw, the inner six on gimballing mounts for roll. The Block A also included four grid fins, which were later used on Soviet air-to-air missile designs. In total, the Block A produced 4620 metric tons (10 million lbf) of thrust. This far exceeded the 3469 metric ton (7.65 million lbf) thrust of the Saturn V.

The second stage, Block B, was powered by 8 NK-15V engines arranged in a single ring. The only major difference between the NK-15 and -15V was the engine bell and various tunings for air-start and high-altitude performance. The upper stage, Block V, mounted a 4 smaller NK-21 engines in a square.

During the N1's lifetime, a series of improved engines was introduced to replace those used in the original design. The first stage used an adaptation of the NK-15 known as the NK-33, the second stage a similar modification known as the NK-43, and finally the third stage used the NK-31. The resulting modified N1 was known as the N1F, but did not fly before the project's cancellation.

In comparison with the American Saturn V, the N1 is somewhat larger overall – slightly shorter, but much wider at the base. Generally the N1 produced much more thrust than the Saturn V. However, as it used only kerosene fuel in all three of its stages, it had somewhat lesser overall performance than the Saturn; the N1 stack could place about 95 tons of payload into Low Earth orbit, whereas the Saturn V launched about 130 tons. The US's earlier work with liquid hydrogen jet engines allowed them the confidence to use this higher-performance fuel on their upper stages, which dramatically reduced their weight and led to a higher payload mass fraction.

Problems

The plumbing complexity needed to feed fuel and oxidizer into the clustered arrangement proved to be extremely fragile, and was a major factor in the design's launch failures. It is interesting to speculate whether or not the cost of developing the Saturn V's F-1 engine is more or less than the cost of working out the problems in a cluster engine like the N1. On the other hand, Saturn V had its share of plumbing-related development issues while feeding only 5 F-1 engines, so N1's 30-engine cluster was arguably a recipe for disaster.

There was also the factor that the N1's Baikonur launch complex could not be reached by heavy barge, so for transport by rail all the stages had to be broken down and re-assembled. Because of this, the complex and destructive vibrational modes (which ripped apart propellant lines and turbines) as well as exhaust plume fluid dynamic problems (causing vehicle roll, vacuum cavitation, and other problems) were not discovered and worked out before flight.

As a result of its technical difficulties, in turn due to lack of funding for full-up testing, the N1 never successfully completed a test flight. All four unmanned launches out of 12 planned tests ended in failure, each before first-stage separation. The longest flight lasted 107 seconds, just before 1st stage separation. Two test launches occurred in 1969, one in 1971 and the final one in 1972.

Mishin continued with the N1F project after the cancellation of plans for a manned moon landing in the hope that the booster would be used to launch a large space station comparable to the US Skylab. The program was terminated in 1974 when Mishin was replaced, ironically, by Glushko. Two N1F's were being readied for launch, but these plans were cancelled.

The program was followed by the "Vulkan" concept for a huge Proton-like hypergolic-fuelled vehicle, and then in 1976 by the commencement of the Energia/Buran program.

Remains

The two flight-ready N1Fs were scrapped and their remains could be still be found around Baikonur years later used as shelters and storage sheds. The boosters were deliberately broken up in an effort to cover up the USSR's failed moon attempts, which was publicly stated to be a paper project in order to "fool" the US into thinking there was a race going on. This cover story lasted until Glasnost, when the remaining hardware was seen publicly on display.

More interestingly, the advanced engines for the N1F escaped destruction. Although the spacecraft as a whole was unreliable, the NK-33 and NK-43 engines are considered rugged and reliable when used as a standalone unit. About 50 engines survived, and in the mid-1990s, Russia sold 36 engines to Aerojet General for $1.1 million each. This company also acquired a license for the production of new engines.

Supplied through Aerojet, three of the engines were incorporated into Japanese rockets J-1 and J-2. The US company Kistler Aerospace continues to work on incorporating these engines into a new rocket design, with which Kistler seeks to eventually offer commercial launch services. In Russia, N1 engines were not used again until 2004, when the remaining 20 or so engines were incorporated into a new rocket design. As of 2005, the project has been frozen due to the lack of funding.

Launch history

  • February 21, 1969: Explosion at 12,200 m altitude, 69 seconds after liftoff
  • July 3, 1969: At liftoff, a loose bolt sucked into a fuel pump caused Stage 1 explosion, destroying rocket and launch tower in the biggest explosion in the history of rocketry
  • June 24, 1971: Uncontrolled roll immediately after liftoff; vehicle destroyed 51 seconds after liftoff
  • November 22, 1972: Pogo oscillation at stage 1 initial cutoff; vehicle destroyed 107 seconds after liftoff

Note

The overall rocket system actually bore the designation N1-L3: N1 was the booster, while the L3 was mounted on top for the trip to lunar orbit and, it was hoped, lunar landing. There is a great deal of confusion among Russian online sources as to whether it is N1-L3 (Russian: Н1-Л3) or N1-LZ (Russian: Н1-ЛЗ) because of the similarity of the Cyrillic letter Ze for "Z" and the number "3". Sometimes both forms will be used within the same Russian website (or even the same article [1] [2]). However, English sources refer only to N1-L3, and it seems clear it is a number because there were lunar projects with code names from L1 to L5. [3]

See also

References

External links