Scientists calculate the risk of someone being killed by space junk
The chances of someone being killed by space junk falling from the sky might seem very slim. After all, no one has died from such accidents yet, although there have been cases of injuries and property damage. But given that we are launching more and more satellites, rockets and probes into space, do we need to start taking more serious risks?
A new study, published in Nature Astronomy, has predicted the possible causality of the 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 scatter downward through the atmosphere to settle on Earth’s surface – adding up to about 40,000 tons of dust each year.
While this is not a problem for us, such debris can damage spacecraft – as recently reported by the James Webb space telescope. Occasionally, larger samples arrive as meteorites, and perhaps once every 100 years or so, objects tens of meters in size make their way through the atmosphere to excavate craters.
And – fortunately very rarely – kilometer-sized objects can surface, causing death and destruction – as the lack of dinosaurs roaming Earth today shows. This is an example of natural space debris, whose uncontrolled arrival is unpredictable and spreads more or less evenly around the world.
The new study, however, investigates the uncontrolled arrival of artificial space debris, such as spent rocket stages, associated with rocket and satellite launches. Using mathematical modeling of the tilt and orbit of the rocket section in space and the population density below, as well as 30 years of past satellite data, the authors estimate where rocket debris and other pieces of space debris land when they fall back to Earth. .
They found that there was a small, but significant, risk of parts re-entering in the coming decade. But this is more likely in southern latitudes than in northern latitudes. In fact, the study estimates that rocket bodies are roughly three times more likely to land at latitudes Jakarta in Indonesia, Dhaka in Bangladesh or Lagos in Nigeria than in New York in the US, Beijing in China or Moscow in Russia.
The authors also calculated the “expected casualties” – the risk to human life – over the next decade as a result of the rocket’s uncontrolled re-entry. Assuming that each reentry spreads lethal debris over an area of ten square meters, they found that there was a 10% chance of one or more casualties over the next decade, on average.
Until recently, the potential for debris from satellites and rockets to cause damage to the Earth’s surface (or in the atmosphere to air traffic) has been considered negligible. Most research on such space debris has focused on the risks posed in orbit by malfunctioning satellites that could hinder the safe operation of functioning satellites. Unused fuel and batteries also cause in-orbit explosions that generate additional waste.
But as the number of entries into the rocket launch business increases – and shifts from governments to private companies – it is likely that the number of accidents, both in space and on Earth, such as those after China’s Long March 5b launch, will also increase. The new study warns that the 10% figure is therefore a conservative estimate.
What can be done
There are various technologies that make it possible to completely control the re-entry of debris, but their implementation is expensive. For example, a spacecraft can be “passivated”, where unused energy (such as fuel or batteries) is discharged rather than stored after the spacecraft’s lifetime ends.
The choice of orbit for the satellite can also reduce the probability of generating debris. A dead satellite can be programmed to move into low-Earth orbit, where it will burn up.
There are also attempts to launch reusable rockets that, for example, SpaceX and Blue Origin have shown are in development. This creates much less debris, although there will be some paint and metal shavings, as they return to Earth in a controlled manner.
Many institutions take the risk seriously. The European Space Agency is planning a mission to try to capture and remove space debris with a four-armed robot. The United Nations, through the Office of Outer Space Affairs, issued a set of Outer Space Waste Mitigation Guidelines in 2010, which was strengthened in 2018. However, as the authors behind the new study point out, these are guidelines, not international law, and in effect do not provide any specifically how mitigation activities should be implemented or controlled.
The study argues that technological advances and wiser mission design will reduce the rate of uncontrolled re-entry of spacecraft debris, reducing the risk of harm worldwide. It states that “uncontrolled re-entry of the rocket body is a matter of collective action; solutions exist, but every launching country should adopt them.”
The requirement for governments to act together is not unprecedented, as indicated by the treaty to ban the ozone-depleting chemical chlorofluor-carbon. Sadly, however, this kind of action usually requires a major event with significant consequences for the Northern Hemisphere before action is taken. And changes to international protocols and conventions take time.
In five years, it will be 70 years since the launch of the first satellite into space. It would be a fitting celebration of the event if it could be marked by a strengthened and mandatory international treaty on space debris, which is ratified by all United Nations states. In the end, all countries would benefit from such a deal.
Monica Grady, Professor of Planetary and Space Sciences, Open University
This article is republished from The Conversation under a Creative Commons license. Read the original article.
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