Falling space debris: a matter of luck

Text by: Romain Mielcarek Follow

You may not know it, but objects fall almost daily from space on our planet. A large majority are all small and harmless, but sometimes it is satellites or entire rocket stages that descend. Should we worry about it? For 25 years, the international community has bet on increasingly strict standards ... and on luck.

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The Ivorians were entitled to a big surprise in early May, when they found, in several places in the country, the remains of a Chinese Long-March 5 rocket . Huge pieces of scrap metal fallen from the sky and difficult to identify which, if they amazed the inhabitants, did not surprise the specialists: 127 large space objects fell on the earth last year, including 72 complete satellites and 55 launcher stages. This year, there are already a hundred of them, including 15 satellites and 17 stages of launchers.

Like the inhabitants of the N'Guessankro and Béoumi regions, people regularly find this type of debris in the countryside, in their gardens or on the roofs of their house. Many photos have been circulating for many years, showing curious people from around the world with the remains of spacecraft. In most cases, these objects even go completely unnoticed, failing to be identified by any passers-by. And yet: there has never been the slightest death.

Some precautions and a lot of luck

"  The surface of the globe is 71% of seas and oceans, 10% of deserts and savannahs ... The really populated area represents only 3%," explains Christophe Bonnal, expert from the National Center for Space Studies (CNES). This explains why, despite 25,000 atmospheric re-entries to date, there have never been any victims. We know someone, Lottie Williams, who was hit by a tiny bit of debris on his shoulder… that made him laugh more than anything.  "

The story of Lottie Williams in 1997 had gone around the world. This American was walking in Tulsa, Oklahoma, when she saw what looked like a shooting star, before being hit on the shoulder and finding the object on the ground. Quite an improbability: the researchers estimate that approximately a ton of materials built by the man fall on earth every day (for 100 tons of meteorites). Of this volume, only 10 to 30% withstand the heat of the descent on earth, the vast majority of which are tiny components that will fall into the water or that no one will notice.

There are still large objects, several hundred kilograms, which could injure people. Again, a significant portion of the mass will melt. The main concern of States comes from the difficulty in predicting their place of landing: forecasts are made to the tens of thousands of kilometers ... Or several times around the world! Even if the object's orbit passes over a large city, it may as well fall to the other side of the globe. While pieces of the Chinese launcher fell on the Ivory Coast in early May, American media noted that fifteen minutes earlier, they would have fallen on New York. fifteen minutes later, they would have arrived in the ocean and no one would have talked about it.

The designers of spacecraft favor components whose sizes and materials will ensure that they are almost completely consumed when they fall back to earth. "  We give ourselves a probability threshold of causing injuries or worse, which is one chance in 10,000 ," notes Christophe Bonnal. Be careful, it is not a chance in 10,000 to kill someone. It is a 1 in 10,000 chance of having an injury. With our criteria, for example, everyday activities like driving a car or crossing a street would be prohibited. You would not be allowed to play tennis : a ball served in the wrong place can cause a lot of damage.  "

Reinforcing regulations

The risk remains "  significant  ", tempers Christophe Bonnal. This has pushed the international community and the industry to multiply the rules. From 1993, space agencies began to meet within the inter-agency space debris coordination committee (IADC), giving rise in 2002 to common standards. In 2007, the United Nations transformed these rules into a resolution. Finally, in 2010, these are “ISO” standards which are adopted by 130 countries and which are on the way to becoming the operating rule in space. A “label” which is not compulsory but which most countries seek to adopt, complying with significant efforts to minimize the risks of dispersion of space waste and the risks of terrestrial fallout.

This work led, for example, to require operators to control the fallout of any object weighing more than 500 kilos. This is particularly the case for launchers: you must be certain that the falling pieces will not land on inhabited areas. Either they have propulsion systems that allow them to head towards an ocean, or their composition guarantees that they are almost completely consumed.

This raises questions about the famous Longue-Marche 5 rocket pieces found in Côte d'Ivoire. The Chinese work like the others to avoid this type of incident. Have they lost control of this device? This is the question that all specialists ask themselves. While the different countries are particularly discreet about their space programs, no one in Beijing wants to confess a possible difficulty with the machine which must, in the coming years, convey the components of the future Chinese space.

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