Scientists now know how likely you are to be killed by space junk

The chance of someone being killed by space junk falling from the sky might seem ridiculously tiny. After all, no one has yet died from such an accident, although there have been cases of injuries and damage to property. But given that we are launching an increasing number of satellites, rockets and probes into space, do we need to start taking the risks more seriously?

A new study, published in Natural astronomyhave estimated the chance of causality from falling rocket parts over the next 10 years.

Every minute of every day, debris rains down on us from space – a danger we are hardly aware of. The microscopic particles from asteroids and comets scuttle down through the atmosphere to settle unnoticed on Earth’s surface – adding around 40,000 tonnes of dust each year.

Although this is not a problem for us, such debris can cause damage to spacecraft – as was recently reported for the James Webb Space Telescope. Sometimes a larger sample comes along like a meteorite, and maybe once every 100 years or so a body 10 meters across manages to make its way through the atmosphere to excavate a crater.

And – fortunately, very rarely – kilometer-sized objects can rise to the surface and cause death and destruction – as shown by the lack of dinosaurs roaming the Earth today. These are examples of natural space debris, whose uncontrolled arrival is unpredictable and spread more or less evenly across the globe.

However, the new study examined the uncontrolled arrival of artificial space debris, such as spent rocket stages, associated with rocket launches and satellites. Using mathematical modeling of the slopes and trajectories of rocket parts in space and a population density below them, as well as 30 years of previous satellite data, the authors estimated where rocket debris and other pieces of space debris land when they fall back to Earth.

They found that there is a small but significant risk of parts re-entering over the coming decade. But this is more likely to happen over southern latitudes than northern ones. In fact, the study estimated that missile 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 US, Beijing in China or Moscow in Russia.

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

To date, 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 studies of such space debris have focused on the risks generated in orbit by decommissioned satellites, which can prevent 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 rocket launch applications increases—and moves from government to private enterprise—it is highly likely that the number of accidents, both in space and on Earth, such as the one that followed the launch of the Chinese Long March 5b, will also increase. The new study warns that the figure of 10 percent is therefore a conservative estimate.

Can scientists solve space junk?

Space litter is an increasingly challenging problem. Shutterstock

There are a number of technologies that make it entirely possible to control debris re-entry, but they are expensive to implement. For example, spacecraft can be “passivated,” whereby unused energy (such as fuel or batteries) is used instead of stored when the lifetime of the spacecraft is over.

The choice of orbit for a satellite can also reduce the chance of producing debris. A decommissioned satellite can be programmed to move into low earth orbit, where it will burn up.

There are also attempts to launch reusable rockets, such as SpaceX has demonstrated, and Blue Origin is developing. These create much less debris, although there will be some from paint and metal shavings, when 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 remove space debris with a four-armed robot. The UN, through its Office for Outer Space Affairs, issued a set of guidelines for space debris in 2010, which were reinforced in 2018. But as the authors behind the new study point out, these are guidelines, not international law, and do not provide specific information on how mitigation activities should be implemented or controlled.

The study argues that advanced technology and more thoughtful mission design will reduce the frequency of uncontrolled re-entry of spacecraft debris, reducing hazard risk across the globe. It states that “uncontrolled re-entry of missile bodies poses a collective action problem; There are solutions, but each launching state must adopt them.”

A demand for governments to act together is not unprecedented, as shown by the agreement to ban ozone-depleting chlorofluorocarbons. But, rather sadly, this kind of action usually requires a major event with significant impacts on the Northern Hemisphere before action is taken. And changes in 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 that event if it could be marked by a strengthened and mandatory international treaty on space debris, ratified by all UN states. Ultimately, all nations will benefit from such an agreement.

This article was originally published on The conversation of Monica Grady atthe open university. Read the original article here.

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