YF-50D
| Manufacturer | CALT |
|---|---|
| Country of origin | China |
| Used on | Long March 3B and Long March 3C fourth stage |
| Associated stages | |
| Comparable | Fregat |
| Launch history | |
| Status | Active |
| Total launches | 4 |
| Successes (stage only) |
4 |
| Failed | 0 |
| Lower stage failed |
0 |
| First flight | 2015-03-30 BDS I1-S Mission |
| Engine details | |
| Engines | 1 YF-50D |
| Thrust | 6.5 kN (1,500 lbf) |
| Specific impulse | 315.5 seconds |
| Fuel | UDMH/N2O4 |
The Yuanzheng-1 (YZ-1) (Chinese: 远征一号; pinyin: Yuǎn Zhēng Yī Hào; literally: "Expedition One") is a restartable rocket upper stage developed by the China Academy of Launch Vehicle Technology (CALT) used as a fourth stage to enable the Long March 3B and Long March 3C launch vehicles to deploy payloads directly to high energy orbits like medium Earth orbit (MEO) and geostationary orbit (GSO). Since the Long March third stage cannot restart, it cannot circularize a GSO orbit from a geostationary transfer orbit. The YZ-1 was designed for restart capability, and to remain operational for more than 6 hours required to reach the transfer orbit apogee for the circularization burn. The YZ-1 enabled the deployment of satellite pairs for the BeiDou Navigation Satellite System and communications satellites directly to their orbits. This eliminates the need for the spacecraft to include a Liquid Apogee Engine or apogee kick motor.
The YZ-1 has a thrust of 6.5 kN (1,500 lbf) 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.
Little is known at the time regarding this stage. Besides the basic characteristics, it is known that there will be a second version specifically designed for the Long March 5 called Yuanzheng-2. It was presented in a 2013 paper. And had its first flight on May 30th, 2015. The debut flight of the Long March 7 included an improved version of the small diameter version called Yuanzheng-1A.
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