The Most Dangerous Rocket Fuels Ever Explored

The book, “Ignition: History of Liquid Rocket Propellants“, by John D. Clark holds a special place among rocketry experts.

It dives into the fascinating chemistry of rocket fuels, covering the post-war period up to the late ’60s.

In this article, we’ll take a peek inside the book and break down some of the extraordinary rocket fuels discussed by the author.

1. The Lethal Lure of Rocket Fuels

Within the pages of “Ignition,” you’ll discover a world of rocket fuels, some of which are vastly more toxic than others.

Let’s start with a well-known but no less hazardous propellant: hydrazine.

Hydrazine-based fuels are infamous for their neurotoxicity, carcinogenic properties, and corrosiveness.

Despite these dangers, they remain in use, primarily in reaction control systems and as first-stage boosters for some Russian and Chinese launch vehicles.

The combination of unsymmetrical dimethyl hydrazine (UDMH) and nitric acid, often referred to as the “devil’s venom” by the Soviets, was used in the ill-fated R-16 ICBM, leading to a tragic accident known as the Nedelin disaster.

This incident serves as a stark reminder of the inherent risks associated with such propellants.

But if you think hydrazine is hazardous, there are even more extreme rocket fuels explored in “Ignition.”

One such example is ozone, a molecule with three oxygen atoms, making it highly unstable and reactive.

While it contains 50% more oxygen than regular oxygen (O2), its propensity to release energy by shedding oxygen atoms makes it toxic at a cellular level.

Ozone, often used in sterilization and purification systems due to its reactivity, can wreak havoc on biological organisms by binding to cellular components and disrupting normal functioning.

It is, in essence, a double-edged sword with the potential for great harm.

2. Liquid Fluorine & Chlorine Trifluoride: Extremes in Reactivity

Chlorine trifluoride

If you thought ozone was reactive, consider the properties of liquid fluorine. Liquid fluorine, when combined with hydrogen instead of oxygen, results in a significant boost in rocket engine performance.

However, this enhanced performance comes at a cost.

The exhaust of such engines consists of hydrofluoric acid, a substance notorious for its corrosiveness, high toxicity, and ability to absorb through the skin.

Handling hydrofluoric acid requires extreme caution, as it can lead to severe burns and health complications.

Liquid fluorine itself poses challenges due to its reactivity with virtually everything, including cloth, wood, metals, and even asbestos.

Engineers who dealt with liquid fluorine often faced difficulties in handling and storage.

Taking reactivity to an even higher level, “Ignition” introduces chlorine trifluoride, a substance hypergolic with virtually every known fuel. This means that it ignites upon contact without requiring an ignition source.

Chlorine trifluoride’s hypergolic nature is so rapid that no ignition delay has ever been measured, making it exceptionally dangerous.

It reacts explosively with various materials, including cloth, wood, sand, and water, posing extreme challenges in handling and storage.

While chlorine trifluoride offers remarkable performance, its extreme reactivity, toxicity, and explosive tendencies make it an impractical choice for most rocket propulsion applications.

3. Mercury: The Heavy Liquid Metal


In the pursuit of higher densities for military applications, researchers explored the use of mercury as a rocket fuel. Mercury, while dense, presented numerous engineering challenges.

Dimethyl mercury, a compound considered for use, is exceptionally toxic and can be absorbed through the skin, causing severe health issues.

Despite the risks, researchers conducted tests with mercury as a propellant, leading to peculiar outcomes.

Mercury’s high density made it an intriguing candidate, but ultimately, concerns over its toxicity and the difficulties in handling and storage limited its feasibility.


“Ignition: An Informal History of Liquid Rocket Propellants” takes readers on a thrilling journey through the world of rocket fuels, highlighting the extreme challenges and complexities associated with developing and utilizing these substances.

From the lethal toxicity of hydrazine to the explosive reactivity of chlorine trifluoride, the book sheds light on the extraordinary lengths to which scientists and engineers have gone in the quest for more potent propulsion.

While some of these rocket fuels have found niche applications, many were set aside due to their impracticality, dangers, or corrosiveness.

“Ignition” stands as a testament to human ingenuity and the willingness to push the boundaries of science, even if it occasionally led to bizarre experiments and unexpected outcomes.

For those interested in rockets, chemistry, or simply an entertaining read on the wild world of science, “Ignition” is a must-read.

It offers a unique glimpse into the history of rocket propellants and the unconventional tales of discovery and experimentation that have shaped the field of rocketry.

So, if you’re looking for an enlightening and humorous journey through the science of propulsion, grab a copy of “Ignition” and prepare to be captivated by the incredible world of rocket fuels.

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