A Chinese rocket’s main stage will fall back to Earth uncontrollably

The Long March-5B (LM-5B) rocket launched the second element of the Chinese space station on Sunday (July 24). The sentence you just read seems to contain important information in the second part, which we understand is that Beijing is successfully continuing the construction of its orbital station. However, the first part of this sentence also contains important information, because each departure of the LM-5B, in the following days, is accompanied by an anxious question for most people: “What if the rocket falls on my head?”.

This will happen again with the launcher that took off on July 24, which, according to estimates, could return to Earth sometime between the evening of Saturday, July 30 and the early hours of Sunday, July 31. Fifteen hours is because it is difficult to accurately model the behavior of the main stage of this 33-meter-long rocket weighing more than 20 tons.

Three things are certain: this state will collapse; Some elements that are not fully consumed reach the ground when re-entering the atmosphere; Happens between 41^e parallel north (latitude of Madrid or Naples in Europe) and 41^e The Southern Parallel runs south of Africa. So there is no danger to metropolitan France, but this very large area, which includes southern Europe, much of the Americas, the entire African continent, southern Asia, and almost all of Australia, still contains 88% of the world’s population.

Single stage rocket

Why doesn’t this problem occur with every rocket launch, but only with the Long March-5B? Normally, a satellite is placed into orbit using a two-stage rocket (perhaps with the addition of solid rocket boosters). The first stage provided high thrust for a few minutes, but it quickly separated and fell into an uncharted sea. A much smaller second stage carries the satellite into orbit and then disengages.

Since the more powerful Chinese launcher is capable of thrusting 25 tons into a low orbit, the Long March in its 5B version does not follow this scenario quite simply, since it has only one stage and not two (unlike version 5 in short). To accomplish its mission, this main stage rises to an altitude of more than 250 kilometers and as a result, finds itself in orbit for a few days.

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