Wengtian, the third and final module of China’s space station, successfully entered orbit and docked with the Tianhe Central Module just 13 hours after launch, but the first stage of the Chang Zheng 5B rocket that carried it to space remained in orbit and will soon return through the atmosphere . Why does this happen every time the Chang Zheng 5B rocket launches?

But first, let’s get to know the rocket: Chang Zheng 5 is the pride of China’s space program, the most advanced and powerful rocket ever built by China: it can launch 14 tons into geostationary orbit or 25 tons into low Earth orbit, and it does so with two YF-77 engines running on hydrogen and liquid oxygen. This makes it more powerful than the European Ariane rocket, but inferior to the performance of the American Delta IV Heavy and Falcon Heavy rockets. Chang Zheng 5 has two variants: a two-stage or three-stage, which can launch satellites into geostationary orbit of the Moon or Mars, and a complex variant 5B, which is used exclusively for launching into low Earth orbit and uses only one stage (on top of which were installed modules that now form the Chinese space station).

In addition to the main stage and possible secondary stages, the rocket is assisted in the early stages of flight by four liquid-fuel (kerosene) side boosters. They detach after running out of fuel and fall into the ocean a few minutes after launch without causing any problems. In fact, China has even built a new space center on Wenchang Island, from where it launches new-generation missiles (Chang Zheng 5, 6 and 7), precisely to avoid problems with the old-generation missiles that are still launched at the mainland, and whose debris often lands on populated areas areas of China (this is because, due to Cold War secrecy, all Chinese space centers were built in isolated areas within China). Somehow a problem at home was solved, but a global one was created.

Why is the Chinese missile a problem?

For all other rockets, the reentry of the primary stage (the most massive of the rocket stages) is not a problem: the controls create a flight path, and after the fuel runs out, the primary stage detaches and falls into the ocean, and Flight continues with the upper stages. to get the payload into orbit. Thus, the primary stage does not reach enough speed to enter orbit, so it goes ballistic and falls into the ocean waters without bothering anyone. Spectacular re-entries of the secondaries have also been observed, but the Falcon 9 second stage is about 4 tons and starts to burn up completely, while the Chang Zheng 5 main stage is 22 tons (only 4 other objects have uncontrolled re-entries). due to the atmosphere were heavier, and one of them was the space shuttle Columbia during its last mission).

Because the Wengtian module (like the others so far) must reach orbit, and because it is directly attached to the main stage, by the time the rocket and module detach, the main stage is already at orbital velocity and remains in orbit following the module. But unlike the modification, the primary stage has no ability to adjust its orbit, and all the fuel has been used to squeeze out the maximum possible performance, so even if it had attitude control, it still wouldn’t stall (that is, if the YF-77 engines could be rerun under unimportant conditions). Thus, the Chang Zheng 5B rocket in this configuration is the only one capable of involuntarily launching its main stage into orbit. Due to interaction with the atmosphere, the orbit is not stable, and within a few days after launch, the rocket partially disintegrates, and its debris returns to Earth.

Romania is safe

It must be said that the territory of Romania is safe: since the Chinese space station is at an orbital inclination of 41.5 degrees, this means that the debris of the rocket cannot fall outside the belt that stretches around the equator, between 41.5 degrees south latitude and 41 .5 degrees. degrees of north latitude. Given the fact that the southernmost point of our country is at 43 degrees north latitude, it is physically impossible to get under the debris of Chinese missiles. However, the strip I was talking about covers the area where 88% of the Earth’s population lives, and the probability that this uncontrolled return will lead to losses is estimated by the specialists of the Aerospace Corporation to be somewhere between 1:230 and 1:1000, above the permissible threshold for 1:10000.

When is the event?

In addition, because the interaction of the rocket with the upper atmosphere is difficult to model, it is difficult to calculate when the rocket will complete its final orbit. We can only make predictions and at the moment we have three agencies that have put forward the following estimates: EU Space Surveillance and Tracking (EUSST) estimates that the re-event will occur today, November 4, at 10:49 UTC ± 223 minutes, in while Aerospace Corporation advances at 12:24 UTC ± 4 hours.

China’s position

China refuses to admit that its rocket is dangerous: In a broadcast dedicated to the launch of the Wengtian module, Chinese officials said that the first stage would make a destructive return through the atmosphere after the mission, although in the three previous flights Chang Zheng Variant 5B, the fragments of the rocket survived the passage through the atmosphere. reaching Ivory Coast, the Indian Ocean and more recently Borneo, within a few hundred meters of human habitation.

Will there be more Chang Zheng 5B launches in the future?

I said that the assembly of the Chinese space station is complete, but there are still a few modules on the ground, built as backups, in case one of the launches fails yet. This did not happen, so it is possible that in the future they will be used to expand the space station. By this time next year, China plans to launch the space telescope using a Chang Zheng 5B rocket, but the good news is that all other rocket flights planned for the near future will use versions with upper stages, meaning separation from the main stage will happen faster, and it will no longer reach orbit. And who knows, maybe by the time the modules of the future space stations are launched, China will have found a way to use the rocket without creating a shower of metal debris over random areas of the Earth’s surface.

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