The Battle of Rocket Fuels in Space Exploration: RP-1 vs. Liquid Hydrogen
Sep 25, 2025
Fuel choice is a critical factor when launching rockets into space, affecting everything from cost and efficiency to environmental impact. Two of the most widely used rocket fuels are RP-1 (refined kerosene) combined with liquid oxygen (LOX) and liquid hydrogen (LH₂) combined with LOX. Each fuel has its strengths and trade-offs, and different space agencies and companies have their preferences depending on mission goals and technological priorities. Let’s compare RP-1 + LOX and LH₂ + LOX and explore which fuels major players in the space industry—like NASA, SpaceX, Blue Origin, and ESA—use for their rockets.
Fuel Basics: What Are RP-1 and Liquid Hydrogen?
RP-1 (Refined Kerosene) + LOX
RP-1 is a highly refined version of kerosene, a dense hydrocarbon fuel. Combined with liquid oxygen (LOX), RP-1 delivers a powerful and efficient thrust. It is easier to store and handle compared to cryogenic fuels like hydrogen.
Liquid Hydrogen (LH₂) + LOX
Liquid hydrogen is a cryogenic fuel. To remain in liquid form, it must be kept at extremely low temperatures (-253°C or -423°F). When combined with LOX, it burns cleanly, producing only water vapor as a byproduct. Hydrogen has a higher energy-to-weight ratio than RP-1 but is far less dense, requiring larger fuel tanks.
Comparison: RP-1 + LOX vs. LH₂ + LOX
Factor | RP-1 + LOX | LH₂ + LOX |
|---|---|---|
Thrust | High thrust, ideal for lifting heavy payloads. | High efficiency but lower thrust. |
Energy Density | Higher by volume, requires smaller tanks. | Higher by weight but lower density. |
Storage | Easy to store and handle at room temperature. | Requires cryogenic storage at -253°C. |
Emissions | Produces CO₂ and soot (black carbon). | Produces only water vapor. |
Cost | Cheaper to produce and handle. | More expensive due to cryogenic tech. |
Use Cases | Efficient for first-stage rockets. | Often used for upper stages and deep-space missions. |
Who Uses RP-1 and Why?
SpaceX
Rockets: Falcon 9, Falcon Heavy.
Fuel: RP-1 + LOX.
Why?: SpaceX prioritizes cost efficiency and reusability. RP-1 is easier and cheaper to store and refuel than liquid hydrogen. It also provides high thrust for launching payloads into low Earth orbit (LEO) and beyond.
Roscosmos (Russia)
Rockets: Soyuz and Proton rockets.
Fuel: RP-1 + LOX for Soyuz.
Why?: Russian rockets have a long history of using RP-1 due to its reliability, high thrust, and ease of storage.
China National Space Administration (CNSA)
Rockets: Long March 2, Long March 3.
Fuel: RP-1 for early-stage launches, particularly for heavy payloads.
Why?: RP-1 remains cost-effective and is ideal for China’s growing space program.
Merlin 1D engine undergoes a test at SpaceX's Rocket Development and Test Facility
Who Uses Liquid Hydrogen and Why?
NASA (United States)
Rockets: Space Launch System (SLS), Saturn V (Apollo Program), and Space Shuttle.
Fuel: LH₂ + LOX.
Why?: NASA often prioritizes efficiency and clean combustion for missions that require deep-space travel. Liquid hydrogen provides excellent energy efficiency and burns cleanly, producing only water vapor.
European Space Agency (ESA)
Rockets: Ariane 5 and the upcoming Ariane 6.
Fuel: LH₂ + LOX for core and upper stages.
Why?: ESA uses liquid hydrogen because of its clean-burning properties and high efficiency, especially for launching heavy satellites into geostationary orbit.
Blue Origin
Rockets: New Glenn, New Shepard.
Fuel: LH₂ + LOX for New Shepard (suborbital flights).
Why?: Blue Origin focuses on sustainability and advanced propulsion systems, using
liquid hydrogen for clean combustion and efficiency.
Environmental Impact
RP-1 + LOX: Combusting RP-1 produces carbon dioxide (CO₂) and soot (black carbon), which can have a warming effect in the upper atmosphere. This makes RP-1 less sustainable in the long run.
LH₂ + LOX: Liquid hydrogen produces only water vapor when burned, making it a zero-carbon fuel. However, producing liquid hydrogen can have environmental consequences if derived from fossil fuels (gray hydrogen). Green hydrogen, produced using renewable energy, eliminates this concern.
Future Trends: Hydrogen’s Role in Space Exploration
As technologies advance, liquid hydrogen is increasingly favored for sustainable space travel. With the development of green hydrogen production and improvements in cryogenic storage systems, liquid hydrogen will play a key role in:
Lunar Exploration: Using hydrogen for propulsion and life support during NASA’s Artemis missions.
Mars Missions: Hydrogen can be produced on Mars using water ice and electrolysis, providing fuel for return journeys.
Sustainable Rockets: Companies like Blue Origin champion liquid hydrogen for clean, reusable rocket systems.
While RP-1 remains the practical choice for cost-effective launches, liquid hydrogen represents the future of clean and efficient space exploration.
Conclusion: A Fuel for the Future
While RP-1 has dominated cost-effective rocket launches, liquid hydrogen remains the cleaner and more efficient fuel for deep-space missions. As hydrogen technology evolves, it will be a critical resource for interplanetary travel, lunar bases, and sustainable space systems.
Innovation will power the future of exploration, both on Earth and beyond, and hydrogen is at the heart of it all.
Inspire the Next Generation with the H2GP Foundation
Hydrogen is transforming space exploration and paving the way for a sustainable future here on Earth. At the H2GP Foundation, we’re empowering the next generation of clean energy pioneers to explore hydrogen’s full potential. Through programs like H2GP XPR, Sprint and H2GP PRO, students gain hands-on experience designing, building, and innovating with hydrogen-powered systems. Whether it’s exploring its use in rockets, transportation, or energy production, our programs equip students with the skills to tackle real-world challenges.
Learn more about hydrogen education and get involved at H2GP Foundation.