--- title: What Is Used as Fuel in Rockets? url: https://upfuel.online/blog/rocket-fuel-explained topic: Transport & Industry author: Priya Raman (Energy science editor) published: 2026-06-02 updated: 2026-08-20 source: UpFuel — https://upfuel.online --- # What Is Used as Fuel in Rockets? Rockets burn liquid hydrogen, refined kerosene (RP-1) or solid composite propellants — and must carry their own oxidiser, because there is no air in space. ## Summary Liquid hydrogen, refined kerosene (RP-1), hypergolic liquids or solid composite propellant — always paired with an oxidiser the rocket carries itself, because there is no air in space. ## Key takeaways - A rocket carries both fuel and oxidiser; together these are the propellant. - Liquid hydrogen with liquid oxygen gives the highest specific impulse of practical chemical propellants. - RP-1 kerosene is denser than hydrogen, so tanks are smaller — good for first stages. - Solid propellants are simple and storable but cannot be throttled or shut down. - Hypergolic propellants ignite on contact, so they need no ignition system. Rocketry has one constraint that changes everything downstream of it: there is no air in space. An aircraft engine breathes. A rocket cannot, so it has to carry its own oxygen — and once you accept that, almost every strange thing about launch vehicles starts to make sense, including why they are roughly 90% propellant by mass and why the payload is such a small fraction of what leaves the pad. ## Fuel plus oxidiser equals propellant **Propellant = fuel + oxidiser.** Both are carried on board, and together they typically make up around 90% of a launch vehicle's mass at lift-off. The payload is often under 4%. Common pairings: | Fuel | Oxidiser | Where used | | --- | --- | --- | | Liquid hydrogen (LH₂) | Liquid oxygen (LOX) | Upper stages, some core stages | | RP-1 (refined kerosene) | Liquid oxygen | First stages | | UDMH / MMH | Nitrogen tetroxide (N₂O₄) | Storable stages, spacecraft | | Aluminium powder | Ammonium perchlorate | Solid boosters | | Methane | Liquid oxygen | Newer reusable designs | ## The three families ### Cryogenic: liquid hydrogen and liquid oxygen **The highest performance available from chemical propulsion.** Specific impulse around 450 seconds — the standard measure of propellant efficiency, roughly the exhaust velocity divided by g. ``` 2 H2 + O2 -> 2 H2O ``` The exhaust is water vapour. Nothing cleaner exists. The cost is handling. Hydrogen must be kept below −253 °C and oxygen below −183 °C, requiring heavily insulated tanks, continuous boil-off management, and fuelling that can only happen shortly before launch. Liquid hydrogen is also extremely low in density, so tanks are enormous for the mass carried. This is why cryogenic stages dominate upper stages, where efficiency is worth the complexity, while denser propellants often do the heavy lifting lower down. ### Kerosene: RP-1 **RP-1 is highly refined kerosene** — the same petroleum fraction as jet fuel, purified to remove sulphur and unsaturated compounds that would leave deposits. Specific impulse around 350 seconds with liquid oxygen, lower than hydrogen, but RP-1 is far denser. Denser propellant means smaller tanks and a lighter structure, which matters most in the first stage where aerodynamic drag and structural mass dominate. It is also storable at ordinary temperatures and much easier to handle. Saturn V's first stage, Soyuz and Falcon 9 all burn kerosene with liquid oxygen. ### Solid propellants A rubbery composite cast into the motor casing: **aluminium powder** as fuel, **ammonium perchlorate** as oxidiser, bound with **HTPB** (hydroxyl-terminated polybutadiene), which also acts as fuel. Advantages: simplicity, storability for years, very high thrust, and no pumps or plumbing. The decisive limitation: **once lit, a solid motor cannot be throttled or shut down.** It burns until the propellant is gone. That is acceptable for boosters providing brute lift-off thrust, and unacceptable for anything requiring precise control. ### Hypergolic propellants Fuel and oxidiser that **ignite spontaneously on contact** — typically UDMH or MMH with nitrogen tetroxide. No ignition system means no ignition failure, and they are storable as liquids at ordinary temperatures for years. That reliability is why spacecraft thrusters and planetary landers use them: an engine that must restart after months in space cannot depend on an igniter. The drawback is severe toxicity and corrosiveness, requiring protective handling at every stage. ## Chandrayaan-3 as a worked example India's LVM3 launcher demonstrates all three families in one vehicle: | Stage | Propellant | | --- | --- | | S200 strap-on boosters (2) | Solid — HTPB composite | | L110 core stage | UDMH + nitrogen tetroxide, Vikas engines | | C25 upper stage | Liquid hydrogen + liquid oxygen, CE-20 engine | | Propulsion module | Storable liquid bipropellant | | Lander descent engines | Storable liquid bipropellant, throttleable | The logic is visible in the sequence: solid boosters for raw lift-off thrust, storable liquids for the core, cryogenics for the efficient upper stage, and throttleable storable propellant for the landing, where precise control decides success. ## Why the tyranny of mass shapes everything The **Tsiolkovsky rocket equation** governs the whole enterprise: ``` Δv = ve x ln(m0 / mf) ``` Velocity change depends on exhaust velocity and on the *logarithm* of the mass ratio. Because the relationship is logarithmic, adding propellant gives diminishing returns — so improving exhaust velocity, which means better propellant, is far more valuable than simply carrying more. That single equation explains staging, explains why hydrogen's efficiency is worth its handling difficulty, and explains why payload fractions are so small. The kerosene used as RP-1 is the same fraction that fuels [jet aircraft](/blog/what-fuel-do-aeroplanes-use), and hydrogen's role here is the flip side of [why it is not used on the ground](/blog/why-hydrogen-is-not-widely-used-as-fuel). ## The compact answer > Rockets use liquid hydrogen, refined kerosene (RP-1), hypergolic fuels such as UDMH, or solid composite propellants containing aluminium powder. Every rocket must also carry an **oxidiser** — usually liquid oxygen or nitrogen tetroxide — because there is no oxygen in space. Liquid hydrogen with liquid oxygen gives the highest efficiency and produces only water vapour. ## FAQ ### What is used as fuel in rockets? Liquid hydrogen, refined kerosene known as RP-1, hypergolic fuels such as unsymmetrical dimethylhydrazine, and solid composite propellants based on aluminium powder with ammonium perchlorate. Every one of these is paired with an oxidiser carried on board, such as liquid oxygen or nitrogen tetroxide. ### Why do rockets carry their own oxygen? Because combustion needs oxygen and there is none in space. Aircraft engines draw oxygen from the air, which is why they only work within the atmosphere. A rocket must carry its oxidiser, which is why propellant makes up the overwhelming majority of a launch vehicle's mass at lift-off. ### Which fuel was used in Chandrayaan-3? Chandrayaan-3 launched on the LVM3, which uses three propellant types: two S200 solid boosters burning an HTPB-based composite propellant, a liquid core stage with Vikas engines burning UDMH with nitrogen tetroxide, and a cryogenic upper stage burning liquid hydrogen with liquid oxygen. The spacecraft's own propulsion used storable liquid propellant. ### Why is liquid hydrogen used despite being difficult to handle? Because it delivers the highest specific impulse of any practical chemical propellant — roughly 450 seconds with liquid oxygen, against about 350 for kerosene. Specific impulse measures propellant efficiency, and higher values mean more velocity from the same propellant mass, which matters enormously for upper stages. --- Safety note: indoor fuel burning carries carbon monoxide, fire and air-quality risks. Follow your appliance manual and local regulations, fit a certified CO alarm, and use a qualified engineer for installations.