The N1 booster had the highest lift-off thrust of any rocket in the history of space exploration

On a clear, cold day in February 1969, five months before Apollo 11 left with the first men to walk on the Moon, a gigantic rocket stood on the launch pad at Baikonur. It was from this fabled cosmodrome, now in Kazakhstan, that the Soviet Union launched Sputnik, the world's first artificial satellite, and sent Yuri Gagarin on a journey that made him the first human to venture into space. Those achievements spurred a space race, and U.S. President John F. Kennedy responded by vowing to land men on the Moon by the end of the 1960s.

In order to have any chance at all in that race, the Soviet Union needed a powerful rocket like America's Saturn V that would carry the Apollo missions. That rocket was the N1. Its huge first stage was driven by no fewer than 30 liquid-fuelled engines. Together, those engines could generate 4,620 tonnes of thrust. “The Soviet N1 booster had the highest lift-off thrust of any rocket built in the history of space exploration,” observed space historian Asif A. Siddiqi in his book 'Challenge to Apollo: The Soviet Union and the Space Race, 1945-1974'.

On February 21, 1969, the N1, as tall as a 35-storey building and weighing over 2,700 tonnes, lifted off on its maiden flight. But, shortly afterwards, the rocket's onboard system shut down two engines of the first stage and then the remaining ones as well, sending it crashing to the ground. Three subsequent launches of the N1 were equally disastrous and ended Soviet hopes of sending its cosmonauts to the Moon.

Now, four decades later, an American launch vehicle, carrying improved versions of the N1's first-stage liquid engines, is poised for its first flight. Orbital Sciences Corporation's Antares rocket, with a first stage powered by just two of those engines, is scheduled to lift-off from NASA's Wallops Flight Facility on April 17. The Antares is intended to take cargo to the International Space Station on commercial terms.

Behind the development of those engines lay a tale of bitter rivalry that went on behind the impenetrable iron curtain of the Soviet space programme. It was an animosity that very nearly resulted in the engines being destroyed for good after the N1 programme was terminated.

Friction between Sergey Korolev, the legendary Soviet rocket designer who was responsible for the country's space programme, and Valentin Glushko, the country's pre-eminent designer of liquid engines, had been mounting. Their disagreements came to a head over how the N1 should be built.

Korolev wanted Glushko to develop high-powered engines using liquid oxygen (LOX) and kerosene for the lower stages of the rocket. But Glushko refused, arguing that it was easier to develop high-thrust engines running on a different propellant combination (nitrogen tetroxide and unsymmetrical dimethyl hydrazine). He was, in any case, developing such an engine for what became the Proton rocket.

Low thrust

The resulting rupture in relations between the two men led to Korolev turning to a far less experienced design bureau headed by Nikolay Kuznetsov for the N1's LOX-kerosene engines. The Saturn V's first stage too used LOX-kerosene engines – just five of them. However, each of those huge F-1 engines could produce 690 tonnes of thrust.

By contrast, the NK-15 engines from the Kuznetsov design bureau, which were used in the N1's first stage, could each generate only 154 tonnes of thrust. The result was that 30 NK-15s were needed to get N1 off the ground.

After the Soviet government decided to terminate the N1 programme in 1974, eight years after Korolev's death, there was a dramatic reorganisation of the space industry. Control of Korolev's design bureau was handed over to his rival, Glushko. The first thing the latter did on taking over was to order the destruction of all N1 rockets that were being assembled as well as all related materials and technical documentation.

Despite receiving such an instruction, Kuznetsov managed to preserve a large number of engines that his design bureau had produced for the N1. That included an improved version of the NK-15 engine, designated as NK-33, which had been extensively tested on the ground but not flown.

In the mid-1990s, after the disintegration of the Soviet Union, a U.S company, Aerojet, purchased about 40 NK-33 engines. It modified the engines for use on the Orbital Sciences' rocket, giving them the designation AJ26.

Thus, in a tale with many twists, the NK-33 engines, intended for a massive Soviet Moon rocket, will instead get their first flight in a much smaller American launcher.