It was so cold on February 20, 1969, that the launch was delayed; even the biggest of all Soviet rockets wasn’t immune to the frigid winters in Kazakstan. Conditions had warmed enough the next day, and at 3:18pm the mammoth N-1 rocket left the Earth for the first time. The combined thrust of the 30 engines powering the first stage shook the ground, and the fire pouring from the bottom of the rocket was an awe inspiring sight for the people who had spent years bringing the rocket to life. Then, just 70 seconds later, all 30 engines shut down. Momentum carried the N-1 to about 17 miles before gravity brought it crashing back to Earth. The escape system separated the modified lunar spacecraft that was its payload, sending it about 21 miles away from the launch pad. The rest of the rocket landed some 10 miles further. In less than two minutes, the Soviets’ last valiant effort to beat America to the Moon was reduced to piles of twisted and burnt metal.
Two N-1s on launch pads
Genesis of the Mega Booster
Like so many large-scale programs of the space age, the N-1 rocket has its roots before the space age formally began with the launch of Sputnik. As was happening in the United States in the mid-1950s, Soviet scientists and planners were beginning to turn their attention towards space. In 1954, one mission up for consideration was a manned flyby of Mars or Venus, something simpler than a landing mission but not a mission that could be done with the existing R-7 rocket. To get to our planetary neighbours, the Soviets would need something much bigger.
This need begat proposals to chiefs of design bureaus in military and research institutions in July of 1957, one of which was a heavy lift interplanetary rocket called TMK, a transliteration of the Russian for Heavy Interplanetary Ship. It ultimately fell to the OKB-1 design bureau at the NII-88 research centre, which was part of the Space Technology Institute, to build this rocket. As the chief designer and head of OKB-1, the program fell specifically to Sergei Korolev.
The Mars/Venus flyby mission parameters dictated specifics for the rocket.Mission planners figured the minimum payload for these missions would be 75 tons. Only 15 tons of that would be the interplanetary spacecraft; the remaining 60 tons would be the mass of the rocket. Don’t forget: rockets have to lift themselves off the Earth along with their payload.
A rocket with this much lift capacity was going to need powerful engines, so Korolev when to the man with the most experience with big rockets: Valentin Glushko, the head of the OKB-456 design bureau. Glushko presented a plan using nitric acid and UDMH in the first stage engines, and Korolev flat out refused. He didn’t want to further complicate the already challenging N-1 by using toxic chemicals. Glushko was unwavering, and this disagreement over engines began a long-standing conflict between the engineers and their design bureaus, and also Glushko’s campaign to stop the N-1 from flying.
With Glushko out, Korolev turned to OKB-276 with Nikolay Kuznetstov at the head to develop the N-1’s engines. Kuznetstov didn’t have Glushko’s experience with big engines, so his solution was crude: get the necessary power by using more smaller engines. The solution suited Korolev and the N-1 started the slow process of moving from concept to reality.
From Venus to the Moon
Korolev’s mega booster program moved steadily forward until 1964 when a strange Soviet decision suddenly derailed years of work. To this point in the space race, the Soviets had been in the lead — it had launched the first satellite, the first animal, the first man into orbit, the first woman, and done the first spacewalk. But the United States was starting to pull ahead with promises from the Gemini program, and Apollo was (metaphorically) already on its way to the Moon. NASA was, effectively, racing against itself to the Moon. But then on August 3, the Soviet Union decided to take on the American challenge of landing a man on the Moon by the end of the decade. Three years after the America officially started its lunar landing program, Soviet leadership endorsed its own.
To spare the N-1 being cancelled in light of this new goal, OKB-1 presented a proposal to go to the Moon with this rocket rather than build a new one. The plan was ultimately accepted and in 1965 the burden of getting a cosmonaut to the Moon before the Americans fell to Korolev and his N-1.
But there was a problem. The N-1 was powerful enough the launch a Mars or Venus flyby mission, but it couldn’t send a landing mission to the Moon. A landing mission is heavier than a flyby mission, especially a free-return trajectory mission. With a flyby, you don’t need to carry fuel for an orbit insertion burn, for a transearth injection burn, and you certainly don’t need a landing vehicle with its own complicated life support and propulsion systems. But these are all things you absolutely need on a landing mission.
So by design the N-1 was a poor Moon rocket. Consider as a comparison the Saturn V, which was honed for Apollo’s lunar orbit rendezvous mission architecture. The Saturn V could put 130 tons into low Earth orbit, enough for even the long-duration Apollo missions that took rovers to the Moon. The N-1 was limited to 75 tons.
This left Korolev’s bureau with a choice: either assemble the lunar spacecraft in orbit with multiple launches or make the N-1 more powerful. They chose the latter to avoid losing a mission from a launch failure. The solution was to decrease the temperature of the Kerosene and overcool the liquid oxygen to store more in the existing tanks, upgrade all the rocket engines, and add six more to the first stage. To get to the Moon the N-1 would have 30 engine powering its first stage, but it could still only take 95 tons into orbit.
The N-1 rolling to the launch pad
**Structure of the N-1 **
The final arrangement of the N-1 emerged after this decision. At the bottom of the stack was Block A, the first stage powered by 30 engines, all of which were managed by a system called KORD. This was a realtime diagnostics system that monitored the crucial parameters for all the engines that was also capable of making the decision to shut down individual engine should it show signs of pending catastrophic failure. This took advantage of the redundancy of a rocket with 30 engines; losing one engine or even two wouldn’t completely ruin a launch. The others could compensate.
But power isn’t all you need for a launch. That rocket also has to be directed in flight. Pitch and yaw control in the N-1 were achieved through differential thrust. Rather than use a complicated and heavy system to swivel the engines, the N-1 was used differential thrust; less power from one side of the rocket would tilt it in the desired direction of flight. Roll control came from six small nozzles outside the main engine cluster could swivel to move the stack around it’s vertical axis.
Like the Saturn V, the N-1 was a multistage rocket. There were two stages above Block A. The second stage was Block B, powered by eight engines. Block V was the third stage and ti was powered by four engines.
On top of Block V was the payload, and for the lunar mission this was the L-3 complex consisting of four parts. Block G sat directly above Block V, and this was the translunar injection stage that would send the crew to the Moon. Above that was Block D, the stage that would perform any midcourse correction burns, the lunar orbit insertion burn, and the burn to start the crew’s descent to the lunar surface. And then there were the two spacecraft, the Block I LOK lunar orbiter and Block E LK lunar lander.
Leaving Earth
When Korolev died in 1966, the N1-L3 program was transferred to his successor Vasiliy Mishin, and under new leadership the rocket got ready for its first flight. A directive called for the N-1 to fly in the second half of 1967 to keep pace with the Americans, but this proved impossible. The rocket was eventually erected on the pad in May of 1968, and everything was finally ready in February of 1969. By this time Apollo 8 had already orbited the Moon but NASA still had a ways to go before attempting the landing. There was hope that the Soviets could still beat the Americans if this first N-1 launch was trouble-free.
N1-3L — the third N-1 rocket not to be confused with L-3 as the lunar spacecraft — left the Earth at 3:18pm on February 21, 1969. At T+70 seconds, all the engines shut down, and within another minutes it was in burning heaps on the ground.
Preliminary data said engines 12 and 24 hd shut down, and instead of firing longer to compensate the remaining 28 had all shut down early. The investigation deepened to focus on KORD. It turned out that electrical interference manifested as an erroneous signal from KORD to shut down engine 12, triggering shutdown of its opposite, engine 24, to retain symmetry. As the rocket flew higher, vibrations tore off a gas pressure-measuring pipe in the turbo pump and broke a fuel pressure pipe in engine number 2. This sent hot kerosene flowing into the base of the rocket, triggering a rise in temperature in engines 3, 21, 22, 23, and 14. The fire destroyed insulation covering power supply cables. This was interpreted by KORD as pulses in the turbo pumps, which sent the command to shut down all engines. The signal traveled up the rocket to freeze the engines in Blocks B and V, too.
Finding the root of the problem didn’t mean it was easy to fix. KORD’s designed admitted that a fire could result in KORD sending faulty commands, and it wasn’t an easy fix. This team was eventually told to keep this matter to themselves as the Soviets hurried to prepare a second N-1 before America landed on the Moon.
The N-1 takes flight
The Second Failure
At 2:18 in the morning on July 4, 1969, the second N-1 rocket left the earth. In an attempt to avoid a second round of premature engine shutdowns, new thermal insulation covered KORD’s wires and transmission lines were isolated from one another to prevent erroneous signals. There were also more sensors in each engine, so more data points for engineers, and KORD, to read.
The rocket began to rise, but just 10.5 seconds later bright pieces could be seen falling from the tail section. The stack seemed to hover, then tilt, then it fell back to the launch pad and collapsed, triggering a series of explosions that engulfed the whole area in flames. It was the largest disaster on a launch pad the Soviet program had experienced, and amazingly no one was killed.
The accident investigation studied telemetry, photos, and film to find that all 30 Blovk A rockets had been firing with the rocket still on the launch pad.Then, a turbopump supplying liquid oxygen to engine number 8 had exploded just before liftoff. The other engines kept working, but just 650 feet above the launch pad engines started shutting down. Within 12 seconds, every engine but number 18 was shut down, and that lone engine pitched the rocket on its side, sending it crashing nearly broadside and adding to its destructive power.
It seemed debris in the turbo pump for engine 8 was the root of the problem. It caused an explosion, the force of which severed feedlines to other the engines and started a fire. This sent a signal to KORD that the pressure and turbopump rotation rates were dangerously high in engines 7, 19, 20, and 21, and it shut them down, followed by the rest, except 18. Debris, a problem with an oxygen sensor, and erroneous signals from KORD had brought down another N-1.
Lost Moon
While the Soviet space program was picking up the literal and metaphorical pieces of the second N-1 disaster, Apollo 11 landed on the Moon. The rocket that had been ripped from its interplanetary program and forced into a lunar mission was now without application. But the program wasn’t cancelled. Changes were made and the directive came from national leadership to ready another N-1 for launch.
A little more than two years later, the third N-1 left the launch pad on June 27, 1971. This rocket started off better than any other launch but quickly developed roll stabilization problems. This put strong torque forces on the rocket, damaging and ultimately destroying Block B. Then at T-51 seconds KORD sent a signal to all 30 first stage engines to shut down. The rocket broke apart in the air and crashed down to Earth. The final flight of the N-1 came on November 23, 1972. For the first 77 seconds, the rocket actually behaved as designed. As it flew further than any of its predecessors, KORD shut down the central cluster of six engines right on time at T+90 seconds,. But fourteen seconds later an explosion erupted in the tail of the Block A, and the mission was over.
This was the last hurrah for the N-1 program. After more than a decade of development and eight years of high priority as a lunar landing program, the N-1 mega booster was cancelled by decree of the Central Committee of the Communist Party of the Soviet Union in 1974.
SpaceX’s Interplanetary Transport System first stage
SpaceX’s Modern Incarnation
SpaceX recently announced an audacious plan to send a crew of 100 humans to Mars to start a colony, and the rocket to launch this massive mission bears some striking similarities to the N-1. Namely in the number of engines powering its first stage. SpaceX’s Interplanetary Transport System — exactly what the N-1 started life as — has 42 engines in its first stage. The core is seven gimbaling engines surrounded by a ring of 14 fixed engines in the middle then another 21 fixed engines in the outer ring.
It’s obviously not exactly the same. The inner engines gimbaling is something the N-1 couldn’t do, and this rocket is designed to carry far more mass into low Earth orbit — 606 tons compared to the N-1’s 95 tons or the Saturn V’s 130 tons. And there is something to be said for the redundancy of so many engines. With 42, the rocket could stand to lose one or possibly two without having the lost thrust badly affect its launch; the others could fire longer to compensate.
But a lesson learned from the N-1 comes to mind: with 42 engines there are 42 complex systems in which one small mishap can break down the entire stage. SpaceX obviously won’t be using the antiquated Soviet KORD system to manage feedback from all its engines. So we can only hope — especially the 100 volunteers for the first mission! — that it comes up with a far more successful way of managing the data from that many engines firing at the same time. Because 42 engines is a lot of places for something to go wrong enough to take down a rocket.
Sources: SpaceX; “The Soviet Space Race With Apollo” by Asif Siddiqi; NASA; “Russia in Space” by Anatoly Zak; Russian Space Web.
