N1: The Soviet Moon Rocket

The final N1

The fourth N1 launched, as configured. The N1 itself is the angled portions to the left as far as 65 meters. To the right is the L3, the Russian lunar spacecraft, and an escape tower that could pull the craft free of the N1 in case of a launch emergency. Public domain image derived from an image created by NASA. Click for a larger version.

What it was:  A Soviet super-heavy orbital launcher with three stages, designed to take a manned spacecraft and lander to the Moon and back. It was a behemoth, comparable to only a few other rockets like the Saturn V, and the twice-flown Russian Energia. It was designed to lift to low Earth orbit more than four times the payload of the largest currently operational rocket, the Delta IV-H. It was never discussed by the USSR during its lifetime, though it was known to the West through espionage—particularly spy satellite photos of the Russian launch facilities at Baikonur. Official recognition of its existence didn’t come until 1989.

Details: If you are going to the Moon, you need a capable spacecraft. The more capable your spacecraft, though, the heavier it will be: getting it to the Moon and back is a problem.  In theory you could spread the weight over multiple launches and assemble your craft in orbit, but space docking was in its infancy in the 1960s and the fewer the maneuvers, the better.

Both the Americans and Russians independently came to the conclusion that the best way to pull off the trick was by Lunar Orbit Rendezvous: send a craft out in one piece, then leave the lunar lander portion behind and return in the other half. This reduces the weight that has to be lifted back off of the Moon and also reduces the weight returning to Earth, and so they could radically reduce the amount of fuel needed to get the whole works off the ground during the initial launch. With this in mind, the magic number for a rocket needed to pull this off could be calculated: it had to be able to lift about 100,000 kilograms to low earth orbit.

This was a problem, as the rockets developed in the late 1950s and early 1960s were far less powerful than that. The Russian launchers based on the R-7 topped out at about 6500 kilograms, while even the most capable American rocket in 1965, the Air Force’s Titan IIIC, could loft only 13,100.

Faced with this the US began work on a much bigger rocket as far back as 1959, which would eventually lead to the successful Saturn V that took Apollo spacecraft to the Moon. Russia’s answer to this was the N1, which they began in earnest in 1964.

The most unusual thing about the N1 was its first stage, which was very wide at its base—the rocket more closely resembled a flying cone than the sharp spire of its contemporaries. In the Saturn V there were only five engines used to give the entire stack its initial boost, and accordingly they had to be monsters by previous standards (and even by today’s: the F-1’s, as they were called, are still the most powerful liquid-fuelled rocket engines ever built). The designers of the N1 didn’t think they could pull off an engine that big and so approached the problem from another angle. Their rocket was so broad in the beam because they used a smaller engine, the NK-33, but more of them: 24 of them in the initial design, to be precise, though as we will see even that needed to be changed.

The difficulty was that with so many engines, there was a much higher chance that one or more of them would fail on every launch, as opposed to the American launcher where at least there were only five of them to keep happy. To overcome this, the N1’s lowest stage was designed with more thrust than was necessary: 50,655 kilonewtons of force, as compared again with the Saturn V’s 38,703. Even if as many as four engines cut out, there would still be enough strength left to reach orbit. The only wrinkle with this approach was that if the failed engine was off-centre from the rocket’s main axis (as it almost certainly would be) the N1 would start listing toward that side and go off course. The engineered solution to this problem was to place the engines symmetrically. A system named KORD—the acronym for “Engine Operation Control”, in Russian— would detect an engine failure and then automatically cut off the mirror-image engine on the other side, thus restoring balance.

More cleverness was required when it became clear that the Russian spacecraft capable of going to the moon (the Soyuz 7K-LOK mated with the LK Lunar Lander) was going to ring in at 95,000 kilograms instead of what the N1 was originally designed to loft, 75,000. Rather than go back to the drawing board, the N1’s designers tried a variety of tricks to come up with the extra 20 tonnes. Its fuels were supercooled, each engine was revved up to 2% over its design specs and, most fatefully, the already extreme number of engines in the first stage was upped from 24 to 30.

The Russians first looked to fly the N1 in May 1968, but cracks were found in the first stage after the whole thing had been assembled on the launch pad. The only solution was to pull it back down and repair the cracks, and this took much longer than expected. 1969 rolled around before they were ready to go again.

The N1′s first flight took place on February 21, 1969, and at first looked OK. It got off the pad and flew correctly for almost a minute, but as it turned out there were tiny bits of metallic debris in the turbine of one of the engines, fouling it, and the rocket started oscillating rapidly. The extra stress on the rocket’s components caused a fuel leak, which caused a fire, and then the KORD sent an incorrect signal that shut down all the engines. Seventy seconds into the flight, the N1 was dead in the air 30 kilometers up, and had to be destroyed by remote control from the ground to prevent it from crashing back into the launch site.

This flight was actually the N1′s first full-scale test; usually a few of a new rocket’s stages are clamped to the ground and static-tested first before you let one loose into the air; the Saturn V’s first stage had been tested this way as far back as 1965. So even though the N1 was “flying” some six months before Neil Armstrong stepped on the Moon, the Soviets were actually well behind the Americans. On this basis the Russian space program’s leadership had come to the conclusion that, barring some kind of accident happening to the Apollo program, they were going to lose the Moon race. So when the first N1 blew up it was a disaster for any further progress and morale dropped through the floor. More N1′s would be sent up, but the Soviets’ already-spotty standard for quality control slipped even further.

The second N1 flight sealed the Russian space program’s fate for some time. An unmanned version of the Russian lunar landing craft was to be launched on July 2, 1969, and sent into a looping orbit around the Moon. This was a bit more than two weeks before the Apollo 11 landing and would give the Soviets some kind of laurels prior to that event, but instead it just made things far worse. Something—either a piece of slag in the fuel tanks or debris from a faulty fuel pump that disintegrated—was ingested by one of the engines a quarter of a second after launch and the rocket caught fire just as it cleared its launch tower. 200 meters up the KORD decided to shut off all of the engines, except one. The second N1 collapsed back onto the launch pad at a 45-degree angle—tipped by the one remaining engine. The fully fuelled rocket then exploded, destroying the launch pad and damaging the second N1 pad nearby. It would take 18 months to rebuild, and the Russians were forced to wait until June 26, 1971 for the next test flight.

The third N1 had filters attached to the engine intakes so as to prevent the problems of the first two flights, and this time all the engines worked correctly. Unfortunately the exhaust from the engines began interacting with the slipstream of air passing the rocket and it began twisting as it rose. This rotation became so bad that the rocket began breaking up from the centrifugal force, so once again the N1 was blown up by remote to prevent another pad disaster. This time the flight lasted 50.2 seconds.

The relative success of the third launch showed that the N1’s designers were getting a hold of the rocket’s problems even if it had failed in the end. Now they were in a race to fix them all before their program was cancelled. As it turned out, there was just one more flight and one more chance.

The launch on November 23, 1972 would be the most successful of all of the N1’s flights. The first stage burned for 106.9 seconds, only seven seconds short of its scheduled burnout. Though early, if the first stage had simply been shut down and cut loose so that the second stage had ignited, the mission could have continued. But while KORD did its job, something after the main stage shutdown led to an explosion—this time no-one ever determined what, as the investigation became embroiled in politics between the rocket’s designers and the designers of its engines.

The N1 was done. The Soviet lunar landing program had been cancelled a few months previously, on June 1, and no-one in power had any interest in a proposed space station or an automated Mars soil sample mission that would re-establish Russian prestige in space. After a period of infighting further launches were cancelled on May 19, 1974, and then development as a whole on June 24 of the same year. A fifth rocket, heavily upgraded and which its engineers reportedly felt was finally finished, was dismantled rather than launched as planned in August.

What happened to make it fail: Putting aside the sloppy construction techniques that caused two of the crashes, the proximate reason was its innovative lowest stage. The pipes needed to get fuel to the many engines had to be numerous and so small and less robust than turned out to be necessary. As the N1 rumbled and vibrated through the ascent to orbit, something was bound to break. This was compounded by the too-clever plan to automatically counterbalance one failed engine by turning off another—as the launches proved, KORD had a nasty habit of turning off all the engines in short order. The various cheese-paring techniques used to get the N1 from a 75,000 kilogram payload to a 95,000 kilogram payload also meant that it was skirting disaster in a variety of other ways. Too many things could go wrong, and did, even when the first stage otherwise worked as it should.

More generally the N1 had a problem in leadership and technique. After the death of Sergei Korolev his lieutenant Vasili Mishin proved unequal to the task of continuing Korolev’s work—most of the major projects he headed failed dramatically, which is to say not only the N1, but the first Soyuz capsule and the first Soviet space station (with both failures costing the lives of cosmonauts). Essentially he kept his job only because by the time it became obvious he needed to be replaced (1967 or 1968) no-one was willing to take over from him when it was also obvious that the Americans were going to win the race to the Moon. He was the perfect fall guy while others maneuvered behind the scenes to take over once the Soviet space program was ready to regroup from that psychological blow.

When Mishin was finally replaced by Valentin Glushko, Glushko took revenge on him and Korolev for past slights. Both had worked tirelessly to centralize the Soviet space effort in their department, OKB-1, and Glushko’s alternative rockets were driven out of the picture. So before taking over Glushko had convinced the Soviet leadership (particularly Dmitri Ustinov, the Russian minister in charge of the space program) that the N1 was a white elephant—admittedly not hard. With their blessing, Glushko’s first official act was to cancel the N1 that had been so dear to his predecessors, notwithstanding that there were already two others ready to fly and four more in various stages of completion behind them. A new super-heavy launcher was begun, which would eventually lead to the Energia—the third of the three most powerful rockets to ever fly along with the Saturn V and its ill-starred Russian counterpart.

What was necessary for it to succeed: Better quality control and more money.

Peak annual spending on the N1 was about US$1.5 billion, as compared with Saturn V at $3 billion, and the contrast in total spending on the two rockets was worse, about 4:1 in favour of the Americans. Furthermore the N1 was competing for money, time, and personnel with no less than three other Moon programs (the Zond orbiter, a proposal to build the UR-700 rocket with its associated lander, and the Luna robotic sample return mission). As a result, the N1’s design and testing facilities were much less extensive than Saturn’s. Literally the first time the first stage was fired as a unit was for the rocket’s first flight, which was beyond foolish if somewhat typical of the Soviet space program at times.

With more money, they could have afforded static tests on the ground like the Saturn V got to its benefit. With better quality control, they’d likely have worked out the kinks with the fuel pipes and the temperamental KORD system. The N1 was also due to have upgraded engines on its next launch before it was cancelled, which would have made the various other shortcuts to extra lift less necessary.

That also leads to another possible route to success: more time. Unlike a lot of other items on this blog the N1 was approaching completion; what really killed it was the quickly waning interest of the Soviet government in the wake of their loss of the race to the Moon—they had no more patience for it when that was what it needed. Mishin needed to go, but if Glushko had supported the N1 in 1974 and given it a few more years, it likely could have been turned into a workable launcher.

Evidence for this can be gleaned from the fate of the NK-33 engine. While 30 of them may have been problematic in tandem, the engine itself has been suggested for several rockets since—including the Space Launch System which is being developed by the United States to replace the Space Shuttle. The fate of the Russian Proton-K, a smaller contemporary of the N1, is also informative. It too had bad teething problems (though nothing can match its big sister’s four-for-four failures), but it eventually became one of the most reliable launch vehicles in history. A variation of it is still being used in the modern day.

Video of the final N1 flight

Google Maps satellite images of the remains of the two N1 launch pads, in modern-day Kazakhstan

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11 thoughts on “N1: The Soviet Moon Rocket

  1. I think it’s notable that the many-small-engines idea hasn’t been tried since the failure of the N1. I won’t argue that it couldn’t have been made to work, but even in the 75t version I don’t think it would ever have ended up reliable; vibration is the killer here, and the more you fix that the more weight you add. If the Soviets had had better alloys, they could have built bigger engines with the higher chamber pressures they’d have needed, and they’d have ended up with something looking a lot more like… well… every successful rocket.

    • I think that reliability would always be a problem too, but the more I looked at it the more I came to the conclusion that it could have been made reliable *enough*, say to the one failure in 30 level — which is very low for a rocket launching frangible people as opposed to replaceable satellites, but this is the Russians we’re talking about here. Ultimately it came down to a lot of circumstantial evidence pointing in the same direction, most of which is mentioned in the article. I think one more is “trust Sergei Korolev”. He thought it would work, and he had a good record for that sort of thing.

      The conservatism of rockets since is, I think, conservatism in the “Not broke don’t fix” mode. They did have the alloys needed, so there was no need to continue to explore the MMORPG (massive multi-engine orbital rocket propulsion gambit).

      But of course we’ll never know for sure, at least for this particular rocket.

  2. “It was designed to lift to low Earth orbit more than four times the largest currently operational rocket, the Delta IV-H.”

    Should this say, “…four times the payload of…” ?

  3. Note that the N-1 never flew with the NK-33 engines in the first stage; all four flights were made with NK-15 engines. The fifth flight (never flown) was planned to be the first with NK-33s, and upgrade/redesign of the NK-15.

  4. Very good article!Just one thing Glushko nevery very confident about LOX Kerosene engines then had proposed RD 270 a engine with comparable thrust and higher sfc than the F1 which korolev vetoed.Had Korolev agreed to Glushko’s proposal and with Glushko and Korolov as a team everyone would have to fall in line the USSR may well have beaten the US to the moon. N1 would have required only six RD 270s which were infact ground tested.

    • If I remember correctly, the RD 270 uses highly toxic fuels that are known to make people very sick, if not kill them if they are exposed to the fuel. I think that is why Korolev decided not to use that motor. I remember reading that he was very concerned about the fuels.

      • He was very much concerned by toxic fuels, yes. It was the proximate cause of the falling-out between Korolev and Glushko, and echoed down through the history of Soviet spaceflight until 1989.

      • The propellants, both the fuel (UDMH, a form of hydrazine) and the oxidizer (N2O4, nitrogen tetroxide), ARE toxic, but not ridiculously so (though you don’t particularly want to touch, breathe, or let them come into contact with each other since they will ignite, albeit not explosively). The US launched 10 manned Gemini missions using these propellants, the Chinese use them on most of their launchers today, including the crew-carrying Shenzhou. Not to mention Protons, and Russian Briz upper stages,

  5. Did any crew die on any of the N1 flight tests? I would emagine the Russians would want to do a few unmanned tests but they were in competition with America for a flag & boots on the moon so I would think they would try to rush a crewed flight as early as possible. I can’t seem to find any info on crew fatalities regarding the N1 falures.

    • No, there was no-one aboard. When not forced by political pressure, the Soviets were quite conservative about their testing and wouldn’t dream of putting a man on board any of their spacecraft until they were confident that it would work. For example, Buran’s sole flight was completely automated, while Komarov’s death aboard Soyuz 1 was due to higher-ups in the government insisting that it be launched to coincide with Lenin’s birthday anniversary in 1967 — the 50th anniversary year of the Russian Revolution.

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