Scientists have calculated the probability of space junk falling and killing someone

The risk of someone being killed by space junk falling from the sky may seem ridiculously small. After all, no one has yet died from such an accident, although there have been cases of injuries and property damage.

But as we launch more and more satellites, rockets and probes into space, should we start taking the risk more seriously?

A new study published in natural astronomyestimated the risk of death from falling rocket parts over the next ten years.

Every minute of every day, debris rains down on us from space – a danger we are almost completely unaware of. Microscopic particles from asteroids and comets pass through the atmosphere to settle unnoticed on Earth’s surface, adding up to about 40,000 tons of dust each year.

While not a problem for us, such debris can damage spacecraft – as was recently reported for the James Webb Space Telescope. From time to time, a larger sample arrives as a meteorite, and perhaps once every 100 years or so, a body several tens of meters in diameter manages to cross the atmosphere to dig a crater.

And – fortunately very rarely – objects the size of a kilometer can rise to the surface, causing death and destruction – as shown by the lack of dinosaurs that roam the Earth today. These are examples of natural space debris, the uncontrolled arrival of which is unpredictable and distributed more or less evenly across the globe.

The new study, however, investigated the uncontrolled arrival of man-made space debris, such as spent rocket stages, associated with rocket and satellite launches.

Using mathematical modeling of the inclinations and orbits of rocket parts in space and the population density beneath them, along with 30 years of past satellite data, the authors estimated where rocket debris and other space debris land when they fall back to Earth. .

They found that there is a small, but significant risk of coins being reintroduced within the next decade. But this is more likely to happen at southern latitudes than at northern latitudes.

In fact, the study estimated that rocket bodies are about three times more likely to land at the latitudes of Jakarta in Indonesia, Dhaka in Bangladesh or Lagos in Nigeria than those in New York in the United States, Beijing in China or from Moscow to Russia. .

The authors also calculated a “casualty expectation” – the risk to human life – over the next decade as a result of uncontrolled rocket re-entries. Assuming that each re-entry spreads deadly debris over an area of ​​ten square meters, they found that there is an average 10% chance that one or more victims will be killed over the next decade.

To date, the potential for satellite and rocket debris to cause damage to the Earth’s surface (or in the atmosphere to air traffic) has been considered negligible.

Most of the studies on this space debris have focused on the risk generated in orbit by extinguished satellites which could hamper the safe operation of functioning satellites. Unused fuel and batteries also lead to explosions in orbit which generate additional waste.

But as the number of entries into the rocket launch business grows – and moves from government to private enterprise – it is highly likely that the number of accidents, both in space and on Earth, will like the one that followed the launch of the Chinese long march 5b, will also increase.

The new study warns that the 10% figure is therefore a conservative estimate.

What can be done

There are a variety of technologies that do make it possible to control the re-entry of debris, but they are expensive to implement. For example, spacecraft can be “passivated”, so that unused energy (such as fuel or batteries) is expended rather than stored after the life of the spacecraft is over.

The choice of a satellite’s orbit can also reduce the risk of producing debris. A defunct satellite can be programmed to move into low Earth orbit, where it will burn up.

There are also attempts to launch reusable rockets which, for example, SpaceX has demonstrated and Blue Origin is developing. These create much less debris, although there is some paint and metal shavings, as they return to Earth in a controlled manner.

Many agencies take risk seriously. The European Space Agency is planning a mission to try to capture and dispose of space debris with a four-armed robot. The UN, through its Office for Outer Space Affairs, released a set of space debris mitigation guidelines in 2010, which were strengthened in 2018.

However, as the authors of the new study point out, these are guidelines, not international law, and do not elaborate on how mitigation activities should be implemented or monitored.

The study argues that advanced technologies and more thoughtful mission design would reduce the rate of uncontrolled spacecraft debris re-entry, thereby decreasing the risk of danger across the globe. It states that “uncontrolled rocket body re-entries are a collective action problem; solutions exist, but each launcher state must adopt them”.

The obligation for governments to act together is not unprecedented, as shown by the agreement to ban chlorofluorocarbon chemicals that destroy the ozone layer.

But, unfortunately, this type of action usually requires a major event with significant consequences for the northern hemisphere before acting. And changes to international protocols and conventions take time.

In five years, 70 years will have passed since the launch of the first satellite into space. It would be a fitting celebration of this event if it could be marked by a strengthened and binding international treaty on space debris, ratified by all UN states. Ultimately, all nations would benefit from such an agreement.

Monica Grady, Professor of Planetary and Space Sciences, The Open University.

This article is republished from The Conversation under a Creative Commons license. Read the original article.

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