ok, the next...lol...
one of my fellow sent me a link ,I had a quick read and found the article was well written.
https://chinaspacereport.com/2016/07/01/cz-7-payloads-demonstrate-cutting-edge-technologies/
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the third highlight of the LM-7 maiden flight mission...the quote from the article..
Yuan Zheng-1A upper stage
Atop the CZ-7-Y1 launch vehicle was a Yuan Zheng-1A (YZ-1A, “Expedition 1A”) upper stage, which acted as the third-stage of the launch vehicle to deliver the other six payloads into their intended orbits.
Similar to the Russian
Fregat, the Yuan Zheng (YZ) series upper stages are designed to serve as a “space tug” to deliver its payload satellites and spacecraft directly into their intended orbit without the need to use their own propulsion. By employing a combined INS/GPS navigation package, the upper stage can achieve a much higher accuracy in orbit insertion than direct insertion by the launch vehicle. The basic variant YZ-1 was first flown in March 2015 as the fourth-stage of a CZ-3C, delivering a Beidou navigation satellite from the initial low ‘parking’ orbit into a high-altitude orbit.
Compared with the YZ-1, the improved YZ-1A features a number of improvements in performance and capability. It can operate up to
48 hours, as opposed to 6.5 hours of the YZ-1.
Instead of deploying payloads into a single orbit, the YZ-1A can deliver multiple payloads into different orbits. Finally, the YZ-1A can be
restarted up to 20 times.
With its own propulsion, navigation and control systems, the YZ-1A upper stage is capable of flying a complex mission profile autonomously, performing a series of orbital manoeuvres to deploy its payloads at different altitudes and on different orbital planes.
The YZ-1A is powered by a 6.5 kN liquid engine that burns N2O4 as oxidiser and UDMH as fuel. The engine uses a turbo-pump and operates in a gas-generator cycle to allow multiple ignitions and precision control. The upper stage was developed by China Academy of Launch Vehicle Technology (CALT), which also designed and built the CZ-7 launch vehicle.
At T plus 603 seconds, the YZ-1A upper stage and payload stack was separated from the YZ-7’s second-stage and entered a 200 km by 400 km initial parking orbit. At T plus 38 minutes, the upper stage deployed the Aolong 1 robotic spacecraft. At T plus 102 minutes, the upper stage deployed a 12U cubesat named
Aoxiang Zhixing. About 20 hours into the mission, the upper stage lowered to an altitude of 170 km to put the sub-scale capsule into its re-entry trajectory. The upper stage then lowered to an altitude of 130 km, before re-igniting its engine to resume to a higher orbit of 400 km. After orbiting the Earth for
29 times in about 40 hours, the upper stage made a controlled re-entry into the middle Pacific.