Out of control, a Chinese rocket lands on Earth

This weekend, an entire stage of the Chinese Long March 5B rocket, launched at the end of April to put the central body of a future space station into orbit, will fall back to Earth.

Problem: the object is the equivalent of 10 stories high and weighs about 20 tons, and no one can say at what time or where it will fall.

Beijing promises that the probability of damage to Earth is

"extremely low".

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Friday, the European Space Agency (ESA) planned a re-entry into the night from Saturday to Sunday around 5 am (French time), with a still very large uncertainty, of several hours.

"The only certainty is that the object's trajectory will not be able to take it outside a band between latitudes 41o south and 41o north

," explains Nicolas Bobrinsky, head of the engineering and innovation department at the space operations center. from ESA.

For Europe, this band stops south of the Pyrenees, and therefore concerns Spain, Portugal, southern Italy and Greece. "

It also includes all of Africa and much of Asia and the Americas.

As the Earth is 70% covered by oceans and 10% by deserts, the risk of falling in an inhabited area is estimated at 0.1%.

 "The majority of the components will be burned and destroyed when re-

entering

the atmosphere"

(at several thousand km / h), said Wang Wenbin, a spokesman for the Chinese Ministry of Foreign Affairs.

"Of the 20 tonnes of the floor, it is estimated that around 10%, the most solid elements, such as engines, will not burn and will reach the ground"

, specifies Christophe Bonnal, specialist in space debris at Cnes, the French space agency.

A particularly bulky launcher

When the same model was first launched in May 2020, large metal debris fell on fortunately uninhabited areas in Côte d'Ivoire, without causing any injuries. Like last year, China used a model of its rocket without an upper stage.

"It is the large central body, 30 meters high and 5 meters in diameter, to which 4 boosters are attached, which puts its charge directly into orbit",

explains Philippe Coué, author and independent researcher on the Chinese space program. Like its cargo, it finds itself circling the Earth. But with each orbit, its altitude drops well below 200 km, giving it a lifespan of less than two weeks. This inexorable descent is caused by the fact that there is no clear border between the atmosphere and the vacuum of space: even at a few hundred kilometers of altitude, there are still a few molecules of air which will end up slowing down the air. 'object and bring it down. Space stations and satellites turn on their engines at regular intervals to stay in their orbit.

"Almost all of the last stages of launchers that arrive in orbit end up one day or another by falling back to Earth, even if it is still very large

," explains Christophe Bonnal.

Since the start of the space conquest, it is estimated that 25,000 objects larger than the fist, half of which are large whole objects, have already returned to Earth

.

Luckily there have been no known victims in the world to date, but the risk is not zero. At the initiative of NASA, Japan and France at the end of the 1990s, good practice rules have been in place since 2010 to prevent uncontrolled re-entry. ”

But they are much less restrictive than the law adopted by France in 2011, the only country to have legislated on the subject.

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The Long March 5 rocket, which made its first flight in 2016, should theoretically comply with international recommendations which require that the re-entry of the stage be carried out in a controlled manner, preferably over an ocean, to avoid any accident. .

But for one reason or another, this was not done for the flights of the Long March 5B… It is true that the installation which allows to control the reentry is expensive, and reduces the performance of the launcher.