Editor's note: Yang Yuguang is vice chair of the Space Transportation Committee of the International Astronautical Federation. The article reflects the author's opinions and not necessarily the views of CGTN.

At 00:23 Beijing Time on October 16, China's crewed spacecraft Shenzhou-13 launched into space.

Shenzhou-12 and Shenzhou-13 space missions are very important for China's manned space program. According to the white paper on space activities released by the State Council Information Office, China hopes to become an advanced country in space. Currently, it is already a major participant. To achieve the goal, China has to reach different milestones. For manned space engineering, accomplishing the construction of China's space station and operating it will be an important benchmark on the way to an advanced country.

Because China is still a developing country, it chose to construct a mid-sized space station. China doesn't compete with any other country in manned space activities; it only performs missions according to its own needs, i.e., to promote China's high technology industry and to benefit its economy and scientific research. Therefore, the configuration of China's space station is a T-shaped modular design, with a core module and two experimental modules. With the Tianzhou cargo spacecraft and up to two docking Shenzhou crewed spaceships, the total mass will be about 100t. In the future, maybe after several years of operation, an additional core module can be added to the space station, which makes it possible to have more docking and berthing ports, and connect more modules to the station. Even at this moment, the whole combination will be about 180t, still less than half of the international space station (ISS).

Although the scale of China's space station is much smaller than that of the ISS and even smaller than the Russian space station Mir, it has gained high efficiency. We chose advanced technologies such as two-dimensional Solar Array Drive Assembly, which was only used by ISS and can provide sufficient power supply to the station.

China's space station is the first one to use the Hall-effect electric propulsion system, which can save a remarkable amount of propellant to raise its orbit. Because of the advanced technologies adopted, it can be categorized as a fourth-generation space station, like ISS.

But we should also realize that before the construction of this space station, China only had a few manned space missions and did not have much experience like the space superpowers, the U.S. and Russia. That is why China decided to have a "technology verification phase" before the formal construction of its space station.

Before this phase, China has mastered crew transportation by its Shenzhou-5 and Shenzhou-6 missions, and mastered extravehicular activity (EVA) on the Shenzhou-7 mission that lasted less than 20 minutes. China also mastered rendezvous and docking technology on the Tiangong-1 and Shenzhou-8, 9, 10 missions, and mastered mid-term residence technology on the Tiangong-2 and Shouzhou-11 mission, in which two astronauts stayed in outer space for about one month, and then mastered refueling technology on the Tiangong-2 and Tianzhou-1 mission in 2017. At this moment, China has mastered all the three fundamental technologies of manned space engineering, but these are not all the technologies necessary to construct a space station.

During the "technology verification phase," there are six launches. By the maiden flight of the Long March-5 carrier rocket, which has the capability of about 25t to low Earth orbit, and with a 5.2m-diameter payload fairing, China now owns the rocket to launch its space station modules. And then, China launched its experimental core module, "Tianhe-1," or "Space Harmony-1" to orbit.

Then comes the Tianzhou-2 and Shenzhou-12 mission, three astronauts stayed in Tianhe for three months, tested critical technologies such as regenerative environmental control and life support system, long-term duration in space, operation of a robotic arm, and performed two EVAs.

Tianzhou-3 has carried all the resupplies for the Shenzhou-13 crew. The three astronauts will stay in the station for half a year. Unlike all other Shenzhou spaceships, Shenzhou-13 will dock at Tianhe's radial port, which also brings some challenges for the crew. After entering the station, the crew will continue to test a regenerative life support system, and perform EVAs during the flight.

We should notice that Wang Yaping, the second female astronaut and the first space teacher of China, is one of the crew members of the Shenzhou-13 mission. To have female astronauts is important for China's crewed space program. It has been proved that female astronauts have advantages in some tasks. Psychological problems can also be solved more easily if you have both male and female astronauts in a very narrow volume. 

Besides, there are some particular tasks for the crew. In the future, the experimental modules, Wentian and Mengtian, should dock first to the front docking port of the core module, and then transposition to the permanent berthing port on the left and right. Given the importance of this step, China has used a robotic arm as a backup measure and will use Tianzhou-2 cargo spacecraft to simulate Wentian and Mengtian modules. This procedure will be well monitored by the Shenzhou-13 crew.

If it succeeds, China will master all the necessary technologies for its space station. After the Shenzhou-13 crew come back to earth, China will have a very strict evaluation procedure. If everything is OK, the name of "Tianhe-1" will be changed from an experimental core module to a formal core module, and then start the construction formally. If it still needs some improvement, China will launch another core module to replace "Tianhe-1."

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