Technology Chinese rocket debris: “There is a non-zero risk” that it will do damage, “but that would be really bad luck”, assures an expert at CNES

Chinese rocket debris: “There is a non-zero risk” that it will do damage, “but that would be really bad luck”, assures an expert at CNES





Debris from a Chinese rocket will fall back to Earth, perhaps Saturday, May 8 or this Sunday, without anyone knowing where exactly. The risk of damage to the ground is minimal. Christophe Bonnal, member of CNES (National Center for Space Studies) ensures that the danger is very low.

franceinfo: How can we explain that we cannot precisely calculate the trajectory of this debris?

Christophe Bonnal: An object in orbit experiences what is called atmospheric drag, which is the force exerted on your hand when you put your hand through your car window. It depends on the surface and the shape of the object. It depends on the atmospheric density which itself depends on solar activity. In short, it is extremely difficult to calculate, to predict the date of re-entry and consequently, the place of re-entry. You should know that a one-minute error is roughly the length of France.

What risk does this rocket represent?

It’s a big floor. It weighs around twenty tonnes, mainly in aluminum. However, the aluminum melts when the launcher, this stage will enter the atmosphere. He will undergo a huge brake that will fragment him and especially a very important warm-up. It can go up to 1,200, 1,300, 1,400 degrees celsius. There may be something left. There are elements with refractory materials, like titanium, for example, pieces of engines. There can be one ton, two tons, even three tons that can impact the surface of the globe.

Can that do damage?

We are lucky that geography is with us. The surface of the globe is 70% oceans, plus 10% deserts, savannas. It’s astonishing, but only 3% of the earth’s surface is densely populated. There is a probability, there is a non-zero risk, but that would be a significant bad luck. It’s something that is really very classic. On average, we have a launcher stage or an entire satellite that comes in every week. They can be 1, 2, 3, 4 or 5 tons.

And that rarely causes victims?

Since Sputnik 1 in 1957, 25,000 objects, of which about 10,000 large have entered the atmosphere. For the moment there have never been any casualties, or even injuries. There’s a lady who was shot in the shoulder in Oklahoma. It was almost a dead leaf which, after analysis, turned out to be a piece of a rocket. There are roughly a ton of man-made materials, satellites, debris, entering the atmosphere every day, and roughly 100 tons of meteorites.



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