China’s Green Rocket Propulsion Revolution - The YF-100

This post was originally published on May 6th 2024 to Ko-fi.

YF-100 engines burning during the launch of a Long March 5.

China has been slowly moving away from using hypergolic fuels in its launch vehicles for over a decade, with the YF-100 leading the charge. The YF-100 is a cleaner and more modern engine in use with China's newest, and more capable, launch vehicles.

Despite the common misconception, the YF-100 is not one engine but a series of engines with similar production and performance. It has six versions, with three of those in development. 

Before we get into the versions of the YF-100, we should quickly touch on the 'baseline' engine. The YF-100 burns rocket-grade kerosene and liquid oxygen to produce 122 tons of thrust with a specific impulse of 300 seconds at sea level, or 335 seconds in a vacuum. For dimensions, the engine is said to be 2.991 meters from nozzle to fuel inlets and 1.347 meters in diameter at the widest point, which is the nozzle. The specific cycle used for the engine is an oxygen-rich staged-combustion cycle. The YF-100 is also believed to have a mass of 1,920 kilograms which gives the engine a thurst to weight ratio of 63.7.

In-use Versions

• YF-100F - This version is used in the boosters of the Long March 5, 7, and 8 with single-axis gimbaling, for roll control only.

• YF-100G - This version is used in the first-stages of the Long March 6A/B/C, 7, and 8 with dual-axis gimbaling.

• YF-100GBI - This is a unique version of the YF-100 due to its use in the Long March 6, it still has dual-axis gimbaling but diverts part of the preburner exhaust into a series of small 1000 newton (0.1 ton) force thrusters on the first-stage for roll control.

All three of these engines move the entire engine during gimbaling, including the pumps.

In-development Versions

• YF-100K - This version is intended for use in China's next-generation of launch vehicles, most notable the Long March 10 and 12. The engine boasts a ~5-tons of thrust improvement along with a lower mass (1,820 kilograms) and wider thrust range (50%-105%).

• YF-100L - This version is believed to be a non-gimbaling version of the YF-100K for use on the Long March 10.

• YF-100M - This engine is a high altitude optimized version of the YF-100K and will see use in the second-stage of the Long March 10. The nozzle is believed to be 2160 millimeters in diameter, which is a little over 800 millimeters wider than the current YF-100's.

• YF-100N - This engine is believed to be the reusable first-stage engine for China's reusable launch vehicles, it will also have a little over 130 tons of thrust.

The three in-development engines plan to have only the nozzle gimbal and not the entire engine. This is believed to provide the benefit of lower risk during flight.

Brief History

Studies of what would become the YF-100 started in the 1980s under the 863 plan, which was a response to then President Reagan's 'Star Wars' program. This study would be mostly done by the Academy of Aerospace Liquid Propulsion Technology, based out of Xi'an. To assist in development, the Chinese government bought three RD-120s during the dissolution of the USSR. The thought process behind buying these engines was that Chinese engineers could gain a greater understanding of complex propulsion cycles along with greater benefit long term to their production process and launch vehicles. Further studies and component testing would continue into the year 2000.

In September of 2000, the government of China approved the engineering development of a "120-ton liquid oxygen kerosene engine", which a little over a year later the first prototype developments began. Between October 2001 and December 2005, prototypes conducted firings with two ending in failures which led to the complete loss of the engine prototypes. 

Successful firings of the engine occurred sometime in 2005, with 200 seconds of testing being accumulated. By July of the following year, a 600-second test was completed successfully, and a 300-second gimbaling test was completed in November of 2007. In mid-2008 the YF-100 had reached over 17,700 seconds of ground test firings.

The engine would continue to be tested in the following years until May 28th 2012 when the engine passed "acceptance inspection" by the Chinese government, with the engine passing flight qualification in June of 2014. The first flight of a YF-100 occurred on September 20th 2015 with the debut flight of the Long March 6, the version used was the YF-100GBI.

Statistics for YF-100s

While looking into the YF-100s I've also managed to piece together a few fun statistics, and of course a graph.