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Rocketeers

4 weeks ago

Long March 7: Ice Arrow

The Chinese space agency has lofty plans for the future and their new workhorse, Long March 7, features predominantly in them.

As Wang Xiaojun sat at his table exhausted by the day’s efforts at China Academy of Launch Vehicle Technology (CALT), his eyes were drawn to the plaque with his name on it. Below his name big, bold letters declared “Project Manager”. Since 2008, he had been leading a team on dedicated scientists and designers to working towards making the next workhorse of the chinese space program. The pressure was immense. He and his project deputy manager, Zhang Tao, had put in everything they got to get this project going on the right track. The ask was big and he know his team was up for the challenge. The Long March 7 would be everything the Chinese space program needed and more.

The project started in 2008. It started off as a project to develop a replacement for the Long March 2F, which was the then workhorse of the rocket fleet. It’s replacement would account for almost 70% of all Chinese launches. CALT was charged with the task and owing to their stellae track record there was no reason to be majorly concerned. With the acquisition of the RD-120 technology and development of the YF-100 and YF-115 engines, the original plan was to re-engine the Long March 2F. This would involve a “simple” change of fuel from N2O4/UDMH to a LOX/kerosene propellant and the result would be better thrust engines and improved performance. If only rocket science was that “simple”.

The proposed changes lead to such complexity that the project had to be restructured. Moreover, a parallel project, the Long March 5, was aiming to achieve similar results. Hence, a decision was made to merge the two projects. This meant a marriage of high reliability and flight legacy components of the Long MArch 2F with the new technologies of the Long March 5.

In 2010, the project name was officially changed to Long March 7. The project included many firsts for CALT. It required the implementation of 11 new technologies and was the first time the whole process was developed in digital 3D with CAD and CAM. The project also proved the capability of indigenous avionics.

The Long march 7 or Chang Zheng 7 is a two stage, medium lift, liquid fuelled carrier rocket capable of carrying 13,500 Kg into Low Earth Orbit. The Long March 7 has the modular stages of the original Long March 5 project. In fact, its first stage is the same module as the LM-5 boosters. It also shares tank diameters and engines with the Long March 6, but the design groups were different. The basic Long March 7 can be reconfigured by varying the number of boosters or enhanced by the addition of upper stages. These stages allow more mission flexibility, like direct injection to higher orbits or multiple orbit deployment. The additional stages include the Yuanzheng-1A and a Hydrogen stage

The Long March 7 can use 0, 2 or 4 boosters. They are powered by a single oxidizer-rich staged combustion YF-100 engine. Each boosters supplies 1,200 kN (270,000 lbf) at sea level and 1,340 kN (300,000 lbf) in vacuum of thrust. Its specific impulse is 300 seconds (2.9 km/s) at sea level and 335 seconds (3.29 km/s) in vacuum. Each module has its own single axis thrust vector control, and thus it required a special design in the control systems of the rocket to coordinate all the rocket’s nozzles. The level of customization the LM 7 provides is ideal to use the same vehicle for different launches, hence optimizing costs.

Interestingly, Long March 7 rocket booster created a fireball visible from areas of Utah, Nevada, Colorado, Idaho and California on the evening of July 27, 2016; its disintegration was widely reported on social media, and the uncontrolled re-entry of such a five-ton object was regarded as a rare event.

So far the LM7 has had only 2 launches with both being successful. The Chinese have big plans for the Long March 7 with it playing a critical role in the Chinese Space Station. The Long March 7  was used to launch the Tianzhou robotic cargo spacecraft, as a precursor to the Chinese Space Station plans. Eventually, it will be capable of placing a 5,500-kilogram payload into a sun-synchronous orbit.

As all this flashed before Wang Xiaojun’s eyes, he let out a smile. His eyes moved to a schematic of the Long March 7. He still remembered the day when the team gathered to give the vehicle a nickname. It was inspired by the “simple” fuel change problem they faced. He let out another smile. He liked the name….”Ice Rocket”!

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