YF-100

The YF-100 is a powerful Chinese rocket engine that burns liquid oxygen and kerosene to lift China’s newest rockets off the launch pad. It was the first engine the country built using a difficult, high-efficiency design called staged combustion.

Quick facts

• Type: Liquid-propellant rocket engine (it burns liquids rather than solid fuel)
• Propellants: Liquid oxygen, or LOX, as the oxidizer (the substance that lets the fuel burn) plus RP-1, a highly refined kerosene, as the fuel
• Cycle: Oxidizer-rich staged combustion, pump-fed
• Sea-level thrust: about 1,200 kilonewtons (roughly 122 tonnes-force, or about 270,000 pounds of push)
• Vacuum thrust: about 1,340 kilonewtons
• Chamber pressure: about 18 megapascals (around 2,600 psi)
• Dry mass: about 1,920 kilograms
• Developer: Xi’an Aerospace Propulsion Institute, under China’s Programme 863
• First flight: 20 September 2015, aboard the Long March 6

What it is and how it works

The YF-100 is “pump-fed,” meaning powerful pumps force its propellants into the engine at high pressure. A single shaft carries one oxygen pump and a two-stage kerosene pump, and smaller boost pumps feed them first to prevent cavitation (bubbles that form when a liquid’s pressure drops too low and can damage the pump).

The clever part is the cycle. Before the main burn, a small chamber called a preburner mixes nearly all of the liquid oxygen with a little kerosene to make a hot, oxygen-rich gas. That gas spins a turbine, which drives the pumps. In simpler engines, that turbine gas is then dumped overboard and wasted. The YF-100 instead pipes it straight into the main combustion chamber, where it meets the rest of the kerosene and burns completely. Think of it as feeding the campfire’s smoke back into the fire instead of letting it drift away. Recovering that energy gives higher chamber pressure and better efficiency.

The engine can throttle (adjust its thrust up and down) and change its mixture ratio. For steering, it can gimbal, meaning the whole engine pivots to point the thrust in different directions, though some booster versions pivot on just one axis for roll control.

Why it matters

The YF-100 was a turning point for Chinese spaceflight. Earlier Long March rockets relied on hypergolic propellants, a toxic chemical pair (UDMH and N2O4) that ignites on contact. The YF-100 switched to non-toxic, higher-performing LOX and kerosene, often called “green” propellants. It was also China’s first operational staged-combustion engine, a demanding design that, until then, only Russia and the United States had truly mastered.

By roughly tripling the thrust of China’s earlier kerosene engines, the YF-100 made possible the heavy-lift Long March 5 and the flexible new-generation fleet that now flies crew vehicles, supplies a space station, and launches deep-space probes. It remains the most powerful liquid rocket engine China has put into service.

Where it is used

• Long March 6: The engine’s first flight, on 20 September 2015, where it powers the first stage.
• Long March 5: China’s heavy-lift rocket, using YF-100 engines in its four liquid boosters, which launched the Tianwen-1 Mars mission and Chang’e lunar missions.
• Long March 7: A medium-lift rocket using the YF-100 in its core and boosters, including launches of the Tianzhou cargo spacecraft to the Tiangong space station.
• Long March 8: Uses YF-100 engines for commercial and rideshare missions.
• YF-100K: An uprated variant (about eight tonnes more thrust, lower mass near 1,820 kilograms, and a wider 50 to 105 percent throttle range) planned for the next-generation Long March 10 crewed lunar rocket and the Long March 12.

Notable details

Oxidizer-rich staged combustion is hard precisely because hot, high-pressure, oxygen-rich gas is extremely corrosive, eating away at turbine and ducting materials. Conquering it required advanced metallurgy, which is why the cycle was long a Soviet and Russian specialty. The program was bootstrapped after China obtained Russian RD-120 engines in the early 1990s following the collapse of the USSR. Those engines informed the work, but the YF-100 is a clean-sheet Chinese design, not a copy. A smaller sibling, the YF-115, was developed alongside it to power upper stages on the Long March 6 and 7. Variant names differ across sources, so exact per-vehicle designations are worth cross-checking.