YF-75

YF-75
Name	YF-75
Country	China
Manufacturer	China Academy of Launch Vehicle Technology
First flight	1994
Status	Retired
Predecessor	YF-73
Successor	YF-75D
Type	Cryogenic
Fuel	Liquid hydrogen
Oxidizer	Liquid oxygen
Cycle	Gas-generator
Thrust vac	78.45 kN
Isp vac	440 s
Chamber pressure	5.0 MPa
Burn time	800 s

YF-75 is a Chinese cryogenic rocket engine developed in the late 20th century for upper-stage propulsion of orbital launch vehicles. It was designed to burn liquid hydrogen and liquid oxygen using a gas-generator cycle to produce high specific impulse for geostationary transfer and deep-space missions. The engine entered service on Long March 3 variants and played a role in China's expansion of spaceflight capabilities during the 1990s and 2000s.

Development

The YF-75 program was initiated by the China Aerospace Science and Technology Corporation and executed by the China Academy of Launch Vehicle Technology to replace the earlier YF-73 and to support upgraded variants of the Long March family such as the Long March 3A and Long March 3B. Development teams coordinated with institutions like the Shanghai Academy of Spaceflight Technology and the China National Space Administration to meet payload requirements for commercial and governmental satellites including missions to geostationary orbit and support for the Beidou and communications satellite deployments. The design effort drew on experience from Soviet-era engines and contemporary developments in cryogenics and turbomachinery, with partnerships among industrial groups in Beijing, Xi'an, and Guangzhou to industrialize components.

Design and Technical Characteristics

The YF-75 employed a gas-generator cycle burning liquid hydrogen and liquid oxygen with a regeneratively cooled combustion chamber and nozzle to achieve a vacuum specific impulse around 440 seconds and a vacuum thrust near 78.45 kN. The engine used a single open-cycle gas generator to drive separate turbopumps for fuel and oxidizer, incorporating cryogenic feedlines and insulation developed in facilities in Shanghai and Harbin. Structural materials and welding techniques were developed in collaboration with research centers at Tsinghua University and the China Academy of Engineering Physics to manage thermal stresses and hydrogen embrittlement. Guidance and control integration interfaced with avionics from suppliers in Xi'an Aerospace Propulsion Institution and system tests were conducted at test stands modeled on those used for the YF-73 program.

Variants

The baseline configuration served the third stage of early Long March 3 series. An improved YF-75 variant featured uprated turbomachinery and longer restart capability to support multi-burn profiles for complex geo-transfer missions and dual-satellite injection. The evolutionary YF-75D successor introduced closed-loop control, enhanced restart reliability, and modular mounting designed for Long March 3B and later heavy-lift adaptations. Specialized adaptations were evaluated for upper stages supporting scientific missions similar to those on Chang'e precursor projects, and for commercial satellite operators including ties to Chinese telecommunication providers and international launch customers.

Operational History

YF-75-equipped stages flew on numerous Long March 3A and early Long March 3B missions, enabling placement of communications satellites into geostationary transfer orbits and supporting national programs such as ChinaSat and meteorological satellite deployments. Flight heritage accumulated through launches from Xichang Satellite Launch Center and contributed to the operational reliability improvements that paralleled the maturation of Chinese launch services competing with international providers like Arianespace and partnering agencies. The engine's in-orbit restarts and long-duration burns were instrumental in multi-burn profiles that mirrored techniques used by European Space Agency and NASA upper-stage practices.

Testing and Qualification

Qualification campaigns for the YF-75 included hot-fire tests at facilities near Beijing and high-altitude simulation tests to validate vacuum performance. Test programs involved component-level endurance runs, turbopump spin tests, and integrated stage firings overseen by engineers with ties to Institute of Mechanics, Chinese Academy of Sciences and propulsion groups from Sichuan test ranges. Ground test data supported reliability assessments required for flight certification by the China National Space Administration and for export evaluations when negotiating commercial launch contracts with international satellite operators.

Production and Manufacturers

Production of YF-75 engines was managed by the China Academy of Launch Vehicle Technology with subcontracts to aerospace firms in Shanxi, Sichuan, and industrial partners like the Aero Engine Corporation of China and specialized suppliers for cryogenic turbomachinery. Manufacturing scaled to support series production for Long March vehicles launched from Xichang Satellite Launch Center and logistical coordination with launch services at Jiuquan Satellite Launch Center for test campaigns. As the program transitioned to YF-75D and other successors, production lines were retooled and knowledge transferred across enterprises tied to China's broader space program industrial base.

Category:Chinese rocket engines Category:Cryogenic rocket engines