Ethanol (C₂H₅OH) is a alcohol fuel propellant used as a fuel. Excellent — stable, storable at ambient temperature. Typical ISP: 250–290 s (with LOX) seconds.
Ethanol is one of the oldest practical rocket fuels in the world. Burned with liquid oxygen, this simple alcohol lifted the first generation of large liquid-fueled rockets and sent the first two Americans into space.
Quick facts
- What it is: ethyl alcohol, chemical formula C2H5OH. It is a fuel, not an oxidizer.
- Partner: almost always paired with liquid oxygen (LOX) as the oxidizer. The combination is called “LOX/alcohol” or “LOX/ethanol.”
- Usual form: diluted with water. The V-2 and early Redstone used roughly 75% ethanol and 25% water; modern mixes range from about 70% up to 99.5% alcohol.
- Performance: specific impulse with LOX is moderate, roughly 224 to 226 seconds in basic configurations, with higher figures cited for some advanced or gelled formulations.
- Best mix: the optimum oxidizer-to-fuel mass ratio is typically around 1.6.
- Sample thrust: the V-2 engine produced about 265 kilonewtons (roughly 56,000 pounds-force) at sea level. The modern DLR/Brazil L75 engine delivers 75 kilonewtons.
What it is and how it works
Ethanol is a bipropellant fuel, meaning it works as one half of a two-part propellant: the fuel is stored in one tank and the oxidizer (liquid oxygen) in another. The fuel is pumped or pressure-fed into a combustion chamber, where it meets the LOX and burns. The hot, high-pressure gas this creates is pushed out through a nozzle to produce thrust, the forward push that drives the rocket.
Pure ethanol burns hot enough to threaten the engine walls, so it is usually mixed with water. The water does not burn; instead it absorbs heat, lowering the flame temperature and making the engine easier to keep cool. Think of it like adding water to a fire to bring its heat down without putting it out entirely. In regeneratively cooled engines, the relatively cool alcohol-and-water fuel is also routed through channels around the chamber and nozzle, carrying away heat before it is finally burned.
Ethanol and LOX are not hypergolic (they do not ignite the moment they touch), so an ignition source is needed to start combustion. The trade-off behind all this is reduced energy per kilogram, which is why ethanol delivers a lower specific impulse than denser, higher-energy fuels like kerosene.
Why it matters
Ethanol with LOX was the propellant combination that made large, controllable liquid-fueled rockets practical at the dawn of the space age. It directly enabled both the world’s first long-range ballistic missile and the first U.S. human spaceflights. It worked because the fuel was cheap and widely available, and because water dilution tamed combustion temperatures enough for early engineers to manage the difficult problem of cooling.
As rocketry matured, ethanol was largely displaced by higher-performance fuels such as kerosene (RP-1), liquid hydrogen, and now methane. In fact, the very rockets descended from the alcohol-burning Redstone soon switched to more powerful fuels: the Jupiter-C and Juno I that launched America’s first satellite, Explorer 1, in 1958 replaced the alcohol with a hydrazine blend called Hydyne for a meaningful thrust boost. But ethanol has since seen a modern revival as a low-cost, low-toxicity “green” propellant. It is favored for student and sounding-rocket programs, experimental and rocket-powered aircraft engines, and small reusable-engine research, where safety, easy handling, and clean combustion matter more than maximum performance.
Notable examples
- V-2 (A-4) missile (Germany, WWII): the world’s first large liquid-fueled ballistic rocket, designed under Wernher von Braun. It burned about 75% ethanol/water with LOX, producing roughly 265 kilonewtons of thrust at sea level.
- Redstone and Mercury-Redstone (USA): a direct V-2 descendant using 75% ethyl alcohol / 25% water with LOX (the Rocketdyne NAA 75-110 engine). Mercury-Redstone launched the first two Americans into space, Alan Shepard and Gus Grissom, in 1961.
- XCOR EZ-Rocket (USA, 2001): an experimental rocket-powered aircraft using twin regeneratively cooled engines on alcohol and LOX, demonstrating quick-turnaround, restartable reusable flight, including the first in-flight engine restarts for a rocket-powered airplane.
- DLR L75 engine and STERN sounding rockets (Germany/Brazil, 2010s): a modern 75-kilonewton LOX/ethanol engine and 500-newton LOX/ethanol student sounding rockets, developed as green-propellant and reusable-engine technology.
Used in V-2 (A-4), Redstone, and early American sounding rockets. Was the primary rocket fuel before kerosene standardization in the 1950s.
Safe, non-toxic, readily available, regeneratively cools well, renewable source possible
Lower Isp and density than RP-1, water content needed for cooling reduces performance
