A Long March-5B (LM-5B) rocket launched the second element of the Chinese space station into space on Sunday (July 24th). In the sentence you have just read, the important information seems to be contained in the second part where we understand that Beijing is successfully pursuing the construction of its orbital station. However, the first part of this sentence also contains important information because each takeoff of an LM-5B is accompanied, in the days that follow, by a worrying question for a large part of humans: “And if the rocket fell on my head? “.
This is again the case with the launcher which left on July 24 which, according to estimates, could fall back to Earth between the evening of Saturday July 30 and the early hours of Sunday July 31. That said, a fairly large margin of error, fifteen hours, remains because it is difficult to accurately model the behavior of the main stage of this rocket, a cylinder 33 meters in length weighing more than 20 tons.
Three things are certain: this stage will fall; some of its elements, which will not be completely consumed during re-entry into the atmosphere, will reach the ground; it will happen between the 41e parallel north (the latitude of Madrid or Naples in Europe) and the 41e southern parallel which passes south of Africa. No risk for metropolitan France therefore, but this very vast area, which contains southern Europe, a huge part of America, the entire African continent, southern Asia and almost all of Australia, still has 88% of the world’s population…
A single-stage rocket
Why does this problem not arise with every rocket launch but only with the Long March-5B? Ordinarily, a satellite is put into orbit using a two-stage rocket (possibly with the addition of solid rocket boosters). The first stage provided most of the thrust for a few minutes, but it was quickly detached and fell into an unspecified ocean. The much smaller second stage then takes over to put the satellite into orbit and is then desorbed.
More powerful Chinese launcher, since it is capable of putting 25 tons into low orbit, the Long March in its 5B version does not follow this scenario quite simply because it has only one stage and not two (unlike the version 5 for short). To fulfill its mission, this main stage therefore rises to more than 250 kilometers in altitude and finds itself, as a result, in orbit for a few days.
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