Yuanzheng (Chinese:远征;pinyin:Yuǎn Zhēng;lit. 'Expedition') is a restartableupper stage developed by theChina Academy of Launch Vehicle Technology (CALT) for theLong March rocket family.

The Yuanzheng stage enables the Chineselaunch vehicles to deploypayloads directly to high-energy orbits such asmedium Earth orbit (MEO) andgeosynchronous orbit (GSO). Since the Long March third stage cannot restart, it cannot circularize aGSO orGEO orbit from a geosyncronous transfer orbit (GTO). With its restart capability, Yuanzheng has enabled the deployment of satellite pairs for theBeiDou Navigation Satellite System in MEO and communications satellites in GSO. This eliminates the need for the spacecraft to include aliquid apogee engine or anapogee kick motor.^[3]

Yuanzheng has a thrust of 6.5 kN (1,500 lb_f) with aspecific impulse of 315.5 seconds. It uses the storablehypergolic propellantsunsymmetrical dimethylhydrazine (UDMH) anddinitrogen 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 designatedYZ-1 forLong March 3B and3C,YZ-1A forLong March 7,YZ-1S forLong March 2C,YZ-2 forLong March 5, andYZ-3 forLong March 2D.

Yuanzheng was presented in a 2013 paper^[3] and performed its first mission on 30 May 2015. The debut flight of theLong March 7 in 2016 included an improved version called Yuanzheng-1A that can flexibly deploy multiple payloads into various target orbits.^[5] Further variants were later deployed forLong March 5 (YZ-2) in 2016,Long March 2C (YZ-1S) andLong March 2D (YZ-3) in 2018.

Currently, there is known to be five versions:

• Yuanzheng-1 (AKAYZ-1) (Chinese:远征一号;pinyin:Yuǎn Zhēng Yī Hào;lit. 'Expedition One'): Initial version used with theLong March 3. It could perform missions of 6.5 hours, make two ignitions, perform one spacecraft deployment operation.^[6][7]
• Yuanzheng-1A (AKAYZ-1A) (Chinese:远征一号甲;pinyin:Yuǎn Zhēng Yī Hào Jiǎ;lit. 'Expedition One A'): Improved version used with theLong March 7. Improved version with mission life extended to 48hs, capability to perform at least 9 ignitions and ability to do 7 different separation events. It also includes improved thermal control system, guidance algorithms and orbit planning for multiple payload deployment missions. It will be used as the base system for future deep space propulsion stages, space tugs and orbital servicing and debris removal spacecraft.^[6][8]
• Yuanzheng-1S (AKAYZ-1S) (Chinese:远征一号商业型;pinyin:Yuǎn Zhēng Yī Hào Shāng Yè Xíng;lit. 'Expedition One Commercial Version'): Improved version used with theLong March 2C.
• Yuanzheng-2 (AKAYZ-2) (Chinese:远征二号;pinyin:Yuǎn Zhēng Èr Hào;lit. 'Expedition Two'): New version used with the 5.2 m (17 ft)Long March 5 upper stage.^[9]
• Yuanzheng-3 (AKAYZ-3) (Chinese:远征三号;pinyin:Yuǎn Zhēng Sān Hào;lit. 'Expedition Three'): New version used with theLong March 2D.

• Rocket stages

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