Rocket Propulsion
What factors made the greatest impact on the development of modern space rockets?
Was it our irrepressible human urge to explore?
Or rockets’ deadly power as weapons of mass destruction?
How much did the far-fetched fantasies of early science fiction writers inspire early rocket scientists?
The evolution of space rocket propulsion.
Hollow bamboo tubes, stuffed with a rudimentary fuel of saltpeter, sulfur, and charcoal dust would’ve made for a cool noisy projectile to show off at parties. Before long some dreadful meanie saw the potential military application. rocket propulsion
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Surviving accounts from the 13th century battle of Kai-Keng report terrifying ‘arrows of flying fire’, basically rudimentary Song Dynasty rockets, raining down on the rampaging Mongol hordes.
In all likelihood these crude missiles sucked. But they struck sufficient fear into Mongol hearts that the nomadic horse-folk crafted their own rival rocket weapon. Which is most likely how the idea eventually made it to Europe. rocket propulsion
By the 17th century, the concept was well enough understood that the term ‘rocket’ was coined, based on the Italian word ‘roquette’ incidentally, a pointy bit for holding the thread on an old-school spinning wheel.
Around the same time, in England, Isaac Newton codified the laws of motion for the first time. Newton’s third law – every action has an equal and opposite reaction – neatly sums up how rockets do their thing. rocket propulsion
Back in Asia, in the late 18th century, the kingdom of Mysore in present-day southern India developed their own rocket weapon, using sturdy iron tubes to launch projectiles an impressive 2km or so.
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So successful was the Mysorean rocket program that an Englishman named William Congreve stole the idea and, by the early 19th century, was cheerfully bombarding the upstart American colonies with his clone rockets in the war of 1812.
Rockets’ utility as a weapon of war faded somewhat after this, as the superior performance and accuracy of guns made smaller-format weapons more effective in battle. Still, these whiz-bang contraptions had captured the popular imagination. rocket propulsion
And it wasn’t long before bold visionaries were positing a very different application for rockets. In 1861 a Scottish priest and amateur astronomer called William Leitch wrote a book called ‘God’s Glory in the Heavens’, in which he advanced the radical idea that mankind might make a new life out among the stars, with the help of this exciting technology.
‘Let us… attempt to escape from the narrow confines of our globe… and see it from a different point of view’, eulogized Leitch. rocket propulsion
‘But what vehicle can we avail ourselves of for our excursion?
The only machine we can conceive of would be one of the principles of the rocket.’ In that same decade, science fiction writer Jules Verne published his uncannily prescient novel ‘From the Earth to the Moon.
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In the book – written 100 years before the Apollo missions, by the way – Verne correctly predicted the cost of a 20th-century space launch, controlled for inflation, and foresaw nifty details like the fact there’d probably be a three-man crew. rocket propulsion
He even correctly guessed it would be launched from Florida. One Jules Verne fan in a particular set even out to make art imitate life.
Konstantin Tsiolkovsky, a mild-mannered Russian high school maths teacher published an early iteration of what’s now known as the ‘rocket equation’ in a 1903 aviation magazine article thrillingly entitled ‘Exploration of Outer Space with Reaction Machines’. rocket propulsion
The rocket equation, since you ask, sets out the relationship between rocket speed and mass, and how quickly gas has to exit the propellant system to achieve lift.
One crucial insight from Konstantin’s work is that the relationship between fuel and speed is exponential. That means it’s non-linear. If you want to double the velocity of your rocket, simply doubling the fuel won’t do. Tsiolkovsky did more than just the math. rocket propulsion
He vividly articulated a vision of what future spacecraft might ultimately look like. ‘Visualize… an elongated metal chamber, the shape of least resistance,’ he wrote, in about 1900 remember. ‘Equipped with electric light, oxygen, and means of absorbing carbon dioxide, doors, and other animal secretions.
‘At the narrow end of the tube,’ he went on, ‘explosives are mixed: this is where the dense, burning gases… explode outward into space at a tremendous relative velocity at the… flared end of the tube. ‘Clearly, under definite conditions, such a projectile will ascend like a rocket.’ rocket propulsion
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Konstantin wasn’t alone in this vision. In the United States, Robert Goddard independently developed his own version of the rocket equation, inspired by yet another science fiction writer, HG Wells. In March of 1926, Goddard made history by launching the first-ever liquid-fuelled rocket in Auburn, Massachusetts. rocket propulsion
Goddard’s contribution to rocketry can’t be overstated, developing the technology behind no fewer than 214 patents. In his experiments he concluded, among other insights, that combustion should happen in small chambers, separate from primary fuel.
Which should, he reckoned, be held in two separate tanks – one containing fuel, typically alcohol based on his early trials, and an oxidizer. He also realized space-bound rockets would need to be arranged in stages. rocket propulsion
As early as the 16th-century German firework maker Johann Schmidlap proposed a "step rocket”, in which a large rocket advances as far as it can, burning all its fuel, before launching its own second projectile to go even higher – the principle behind all modern space missions.
But Goddard made it work for real. He also ascertained that solid rocket fuel burns too unevenly for accurate control, so the liquid was better. He also devised a clever gyroscope to keep things on course, parachutes to bring things safely back to earth, and the use of the de Laval nozzle. rocket propulsion
The de Laval nozzle, since you ask, accelerates the flow of gases through a section of the tube by narrowing it into an asymmetric yet finely calibrated hourglass shape. That might not sound like much, but alchemizing heat energy into kinetic force creates an additional lift without any extra combustion. rocket propulsion
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In 1920 Professor Goddard was so famous for his dream of getting a rocket into space the New York Times published a mocking editorial, suggesting he didn’t properly grasp Newton’s Third Law. He ‘…does not know the relation of action to reaction,’ thundered the paper. ‘Or of the need to have something better than a vacuum against which to react.
‘He seems to lack the knowledge ladled out daily in high schools. The Times subsequently issued an apology to Goddard, 14 years after his death, and about a month before the moon landings. rocket propulsion
Another early giant of the field – one of many scattered across tinkering workshops and amateur societies around the field – was one Hermann Oberth. Born in present-day Romania, Oberth spent much of his life in Germany.
Rather than being inspired by science fiction like Konstantin in Russia and Goddard in the States, Oberth actually inspired science fiction, working as a scientific consultant on legendary film director Fritz Lang’s 1929 film ‘The Woman in the Moon’. rocket propulsion
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Clearly already a big name in rocketry, that same year he wrote a book called "Ways to Spaceflight" and took on as an apprentice a young man named Werner von Braun.
Von Braun took Oberth’s teachings and went on to develop one of the most important rockets in history – the German Aggregat-4, better known as the V2. The V2, used to devastating effect against the allies in World War 2, was the world’s first ballistic missile. rocket propulsion
Stubby by today’s standards at just 14 meters high, it somehow managed phenomenal thrust burning liquid oxygen and alcohol at a rate of around a ton every seven seconds. It was the first man-made object to break the sound barrier, and the first to reach outer space.
Still, it couldn’t win the war for Germany. After the conflict the V2’s senior engineers were lured over to either the US or Soviet Russia, to progress their own nascent rocket programs. Werner Von Braun always preferred the idea of making rockets for space travel, instead of killing civilians.
And his know-how helped drive postwar rocket development in the United States, where NACA, the National Advisory Committee for Aeronautics, a forerunner of NASA, oversaw progress on rocket features from basic structural components, mechanical elements like pump valves, engine cooling systems, clever new direction controls and more. rocket propulsion
‘Blunt Body Theory’, from which it is understood blunt shapes are better at surviving burnup on re-entry than more aerodynamic bodies, was developed by NACA. Experiments in staged rocketry were conducted on captured German V2 rockets upgraded with a smaller rocket as payload to be launched at peak altitude.
Advances in the development of more energetic and stable solid fuels found use in ICBM, or Intercontinental Ballistic Missiles, which in the febrile Cold War climate needed to be ready to fire at a moment’s notice. The Russians, for their part, weren’t hanging around. rocket propulsion
Their own ex-German recruit, Helmut Gröttrup, helped Soviet chief designer Sergei Korolev develop the R-1. This in turn led to the R-7, a two-stage ballistic missile capable of traveling 8,000 km, that became the workhorse of the Russian space program for half a century.
It won some significant early battles in the so-called race for space when, on October 4, 1957, the R-7 hurled the first-ever man-made satellite Sputnik into orbit. A month later, Laika the dog followed suit. In the US President Eisenhower was incensed to have been beaten to the punch, and briskly signed the National Aeronautics and Space Act in July 1958. rocket propulsion
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Despite rapidly developing the Mercury Redstone booster, again based on the basic V-2 outline, Russia again made the running by launching the first human into space, Yuri Gagarin, on a modified version of the classic Soviet R-7 rocket.
The 1960s were a boom time for rocket engineers, with President Kennedy promising a man on the moon by the end of the decade. Humongous injections of state cash drove the evolution of rocketry at this point, and Werner Von Braun’s ultimate vision was realized in the shape of the three-stage Saturn V that in 1969 carried mankind all the way to the moon. rocket propulsion
The Russians, for their part, tried to catch up. But with budget issues and the death of their whizkid Sergei Korolev, it never really happened for them. Meanwhile, an imperious and cash-rich USA developed the Space Shuttle, a visionary re-usable craft that distinctively relied upon two solid-fuel boosters to get to orbit.
The first shuttle was named Enterprise – clearly, sci-fi influencing real science yet again – and the idea may well have caught on, had it not been a wildly expensive means of getting to and from space. Not to mention the sad fallout from the Challenger disaster of 1986, which led to a radical redesign of those solid-fuel boosters we mentioned, and the Columbia tragedy of 2003. rocket propulsion
To be clear, it isn’t just the Russians and Americans sending rockets into space. Inspired by Soviet successes from Sputnik onwards, the Chinese developed their own late 50s rocket program, which continues to this day with the Long March program regularly launching from the tropical island of Hainan.
The deep-pocketed superpower is highly secretive about the program, which earlier this year had a hair-raising moment and attracted international condemnation when an out-of-control rocket came hurtling down to earth, luckily without hurting anybody. rocket propulsion
Still, most of the important ground-breaking work has come out of America. In 2004 president George W Bush announced the retirement of the Shuttle program but the introduction of two new lunar rockets, the Ares I and Ares V.
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For both two-stage rockets, the idea was once again to get to orbit on a first stage using solid fuel boosters, then switching to liquid-fuelled Rocketdyne J-2X engines to make it to the moon and ideally beyond.
However, in 2010, citing the global financial crisis, Barack Obama canceled the Ares program. Still, in the same move, they greenlit the SLS, or Space Launch System, which looks set to put the first woman on the moon in 2024. Thanks, Obama. rocket propulsion
If the history of rockets can be summed up as pretty fireworks, which became weapons, became tools of geopolitical posturing in the late 20th century, these days it’s all about money. Not necessarily in a bad way.
The radical innovations happening under Elon Musk’s watch at SpaceX – not least reusable, landable Falcon 9s – are driven by the profit motive. To get payloads – and indeed, now, astronauts – to orbit in a safe and cost-effective manner. rocket propulsion
This in turn is driving every greater speed of design iteration, like the progression from the throttlable Merlin to the Raptor engines. The latter of which runs on Meth-Ox, a methane-based fuel because it burns clean.
This is obviously great from a re-usability perspective, meaning engines require less maintenance between flights. But also because the Starships currently in development in South Texas should be able to extract their own methane as a fuel source on mars, a concept almost beyond the dreams of science fiction.
If Musk gets his way, the starships will not only be ferrying Mankind to mars but will also be carrying us from point to point here on earth faster than any conventional jet. rocket propulsion
And what does the future hold?
New Zealand startup Rocket Lab is developing a Rutherford Engine that incorporates 3D printed elements with an electric pump-fed engine and should unveil its own heavy-lift Neutron rocket in 2024.
Going forwards, Nuclear fusion reactors may even provide an even more potent fuel source without needing combustion at all. Now the private enterprise is fully engaged, we human beings aren’t flinging rockets at each other (all that much) and space is cool again, one thing we can be sure of is that the future for rockets is looking up. rocket propulsion
Does mankind’s love of sci-fi, or its warmongering instincts, most deserve credit for the revolution in rocketry?
