The N1 (from , "Carrier Rocket"; Cyrillic: Н1, GRAU index: 11A52, Sheldon: G-1-e, DoD: SL-15) was a super heavy-lift launch vehicle of the Soviet space program intended for crewed travel to the Moon and beyond. All four launch attempts between 1969 and 1972 failed. Studied and designed by OKB-1 since 1959, it was the counterpart to the US Saturn V.
A five-stage kerolox-fuelled rocket, its Block A was the most powerful rocket stage flown for over 50 years, at 45 meganewtons of thrust, until the SpaceX Super Heavy. Block A's large cluster of thirty NK-15 engines, prone to individual failures, was managed by KORD, an analog computer which shut down engines opposite the failure, to maintain attitude control. Block B and V used eight and four hot staged engines respectively, planned to bring the rocket to low Earth orbit. Dangers of the complex engine cluster and fuel feeder systems were not discovered earlier as static fires were not conducted on the Block A. Its second test flight resulted in one of the largest conventional explosions ever, that disabled its Site 110 launch pad at Baikonur Cosmodrome for 18 months.
The N1-L3 aimed to compete with the US Apollo program for a crewed Moon landing, using a similar lunar orbit rendezvous method. The rocket had three stages, carrying the L3 lunar payload into low Earth orbit with two cosmonauts. The L3 contained the Block G trans-lunar injection stage; Block D for mid-course corrections, lunar orbit insertion, and initial surface descent; single-pilot LK lander; and two-pilot Soyuz 7K-LOK orbital spacecraft for return to Earth.
The N1 started development in October 1965, almost four years after the Saturn V. The project was derailed by the death of its chief designer Sergei Korolev in 1966; the program was suspended in 1974 and canceled in 1976. The TMK project of crewed Mars and Venus flybys also relied on the N1. OKB-1 later developed Energia, the only Soviet super-heavy lift rocket to reach orbit, flying in 1987 and 1988. Details of the Soviet crewed lunar programs were kept secret until the USSR was nearing collapse in 1989. From 2013, the NK-33 engines, built for the N1F improvement cancelled in 1974, were adapted to the smaller US Orbital Sciences Antares 100 rockets and Russian Soyuz 2.1v rockets.
History In 1967 the United States and the Soviet Union were in a race to be first to land a human on the Moon. The N1/L3 program received formal approval in 1964, which required development of the N1 launch vehicle, comparable in size to the American Saturn V.
On 25 November 1967, less than three weeks after the first Saturn V flight during the Apollo 4 mission, the Soviets rolled out an N1 mock-up to the newly constructed launch pad 110R at the Baikonur Cosmodrome in Soviet Kazakhstan. This Facilities Systems Logistic Test and Training Vehicle, designated 1M1, was designed to give engineers valuable experience in the rollout, launch pad integration, and rollback activities, similar to the Saturn V Facilities Integration Vehicle SA-500F testing at the Kennedy Space Center in Florida in mid-1966. While the crawler transported the Saturn V to the pad vertically, the N1 made the trip horizontally and was then raised to the vertical position at the pad, using a purpose built Transporter Erector (TE) named Grasshopper. Using TEs was standard practice in the Soviet space program. On December 11, after completion of various tests, the N1 mockup was lowered and rolled back to the assembly building. The 1M1 was used repeatedly in the following years for additional launchpad integration tests.
Although this test was carried out in secret, a US reconnaissance satellite photographed the N1 on the pad shortly before its rollback to the assembly building. NASA Administrator James Webb had access to this and other similar intelligence that showed that the Russians were seriously planning crewed lunar missions. That knowledge influenced several key US decisions in the coming months. The satellite imagery appeared to show the USSR was close to a flight test of the N1, but did not reveal that this particular rocket was just a mockup and that the USSR was many months behind the US in the race to land a human on the Moon (however, the CIA the NRO, and President Lyndon B. Johnson did know that the rocket was a mock-up per the daily presidential briefing of 27 December 1967). The Soviets were hopeful that they could carry out a test flight of the N1 in the first half of 1968, but for a variety of technical reasons the attempt did not occur for more than a year.
Early Soviet lunar concepts
In May 1961, the US announced the goal of landing a man on the Moon by 1970. During the same month, the 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. In June, Korolev was given a small amount of funding to start N1 development between 1961 and 1963. At the same time, Korolev proposed a lunar flyby mission using the new Soyuz spacecraft using an Earth orbit rendezvous profile, called the A-B-V. Several Soyuz rocket launches would be used to build up a complete Moon mission package, including one for the Soyuz spacecraft, another for the orbital tug, and one for an orbital tanker. This approach, driven by the limited capacity of the Soyuz rocket, meant that a rapid launch rate would be required to assemble the complex before any of the components ran out of consumables on-orbit.
A lunar surface lander concept was to use three N1 rockets: the first would launch the lander, lunar braking stage, and translunar insertion stage into orbit (referred to as the 19K). The two remaining launches would deliver large fuel tankers, known as 21Ks, to refuel the 19K. A final and fourth launch, of a Soyuz rocket, would launch a Soyuz spacecraft to dock with the 19K, which would boost to the Moon for a lunar landing and return. This architecture was not implemented, and instead Korolev proposed that the N1 be enlarged to allow a single-launch lunar mission.
In November–December 1961, Korolev and others tried to further argue that a super heavy lift rocket could deliver ultra heavy nuclear weapons, such as the just tested Tsar Bomba, or many warheads (up to 17) as further justification for the N1 design. Korolev was not inclined to use the rocket for military uses, but wanted to fulfill his space ambitions and saw military support as vital. The military response was lukewarm – they thought the N1 had little military usefulness and was worried it would divert funds away from pure military programs. Korolev's correspondence with military leaders continued until February 1962 with little progress.
Meanwhile, Chelomey's OKB-52 proposed an alternate mission with much lower risk. Instead of a crewed landing, Chelomei proposed a series of circumlunar missions to beat the US to the vicinity of the Moon. He also proposed a new booster for the mission, clustering four of his existing UR-200s (known as the SS-10 in the west) to produce a single larger booster, the UR-500. These plans were dropped when Glushko offered Chelomei the RD-270, which allowed the construction of the UR-500 in a much simpler "monoblock" design. He also proposed adapting an existing spacecraft design for the circumlunar mission, the single-cosmonaut LK-1. Chelomei felt that improvements in early UR-500/LK-1 missions would allow the spacecraft to be adapted for two cosmonauts.
The Strategic Missile Forces of the Soviet military were reluctant to support a politically motivated project with little military utility, but both Korolev and Chelomei pushed for a lunar mission. Between 1961 and 1964, Chelomei's less aggressive proposal was accepted, and development of his UR-500 and the LK-1 were given a relatively high priority.
Lunar N1 development starts Valentin Glushko, who then held a near-monopoly on rocket engine design in the Soviet Union, proposed the RD-270 engine using unsymmetrical dimethylhydrazine (UDMH) and nitrogen tetroxide (N2O4) propellants to power the newly enlarged N1 design. These hypergolic propellants ignite on contact, reducing the complexity of the engine, and were widely used in Glushko's existing engines on various ICBMs. The full flow staged combustion cycle RD-270 was in testing before program cancellation, achieving a higher specific impulse than the gas-generator cycle Rocketdyne F-1 despite the use of UDMH/N2O4 propellants with lower potential impulse. The F-1 engine was five years into its development at the time and still experiencing combustion stability problems. Rocketdyne eventually solved the F-1 instability problems by adding copper dividers as baffles, but the RD-270 still had unsolved instability problems when the N1 program was cancelled in 1974, long after the F-1 problems were solved.
Glushko pointed out that the US Titan II GLV had successfully flown crew with similar hypergolic propellants. Korolev felt that the toxic nature of the fuels and their exhaust presented a safety risk for crewed space flight, and that Kerosene/LOX was a better solution. The disagreement between Korolev and Glushko over the question of fuels ultimately became a major issue that hampered progress.
Personal issues between the two played a role, with Korolev holding Glushko responsible for his incarceration at the Kolyma Gulag in the 1930s and Glushko considering Korolev to be cavalier and autocratic towards things outside his competence. The difference of opinions led to a falling out between Korolev and Glushko. In 1962, a committee was appointed to resolve the dispute and agreed with Korolev. Glushko refused outright to work on LOX/kerosene engines, and with Korolev in general. Korolev eventually gave up and decided to enlist the help of Nikolai Kuznetsov, the OKB-276 jet engine designer, while Glushko teamed up with other rocket designers to build the very successful Proton, Zenit, and later Energia rockets.
Kuznetsov, who had limited experience in rocket design, responded with the NK-15, a fairly small engine that would be delivered in several versions tuned to different altitudes. To achieve the required amount of thrust, it was proposed that 24 NK-15s would be used in a clustered ring configuration. The ring of 24 engines would be separated from the oxidizer tank by an air gap, suspended via struts similar to those on the hot staging rings, with airflow supplied via the gaps in the struts. The air would be mixed with the exhaust in order to provide some degree of thrust augmentation, as well as engine cooling. Later, a ring of 6 inner engines were added, along with the thrust augmentation was dropped. The arrangement of 30 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.
N1-L3 lunar complex
Korolev proposed a larger N1 combined with the new L3 lunar package based on the Soyuz 7K-L3. The L3 combined rocket stages, the modified Soyuz, and the new LK lunar lander were to be launched by a single N1 to conduct a lunar landing. Chelomei responded with a clustered UR-500-derived vehicle, topped with the LK-1 spacecraft already under development, and a lander developed by his design bureau. Korolev's proposal was selected as the winner in August 1964, but Chelomei was told to continue with his circumlunar UR-500/LK-1 work.