Yuanzheng

Yuanzheng (Chinese: 远征; pinyin: Yuǎn Zhēng; lit. 'Expedition') is a restartable upper stage developed by the China Academy of Launch Vehicle Technology (CALT) for the Long March rocket family.

The Yuanzheng stage enables the Chinese launch vehicles to deploy payloads directly to high-energy orbits such as medium Earth orbit (MEO) and geosynchronous orbit (GSO). Since the Long March third stage cannot restart, it cannot circularize a GSO or GEO orbit from a geosyncronous transfer orbit (GTO). With its restart capability, Yuanzheng has enabled the deployment of satellite pairs for the BeiDou Navigation Satellite System in MEO and communications satellites in GSO. This eliminates the need for the spacecraft to include a liquid apogee engine or an apogee kick motor.^[3]

Yuanzheng has a thrust of 6.5 kN (1,500 lb_f) with a specific impulse of 315.5 seconds. It uses the storable hypergolic propellants unsymmetrical dimethylhydrazine (UDMH) and dinitrogen tetroxide (N₂O₄), and can perform at least two burns within its rated life of 6.5 hours, sufficient to reach the transfer orbit apogee, and perform the circularization burn from there.^[4]

Operational variants are designated YZ-1 for Long March 3B and 3C, YZ-1A for Long March 7, YZ-1S for Long March 2C, YZ-2 for Long March 5, and YZ-3 for Long March 2D.