If separated after launch, rocket stages are often left in orbit. Parts of it can still fall back to earth months and years later. A Canadian research team has calculated how great the risk is for humans to become victims of space debris.
With the growing number of rocket launches, there is a greater risk of parts of the rocket falling in an uncontrolled manner and injuring people. Canadian scientists have calculated a ten percent probability that a person will be a victim of such an accident in the next ten years. The study by the research group led by Michael Byers from the University of British Columbia in Vancouver has been published in the journal “Nature Astronomy”. Manuel Metz from the German Aerospace Center (DLR) in Bonn considers the calculated value to be too high.
In May 2020, debris from a Chinese Long March 5B missile struck two villages in the West African country of Ivory Coast. A 12 meter long piece of pipe was also found under the rubble. The space debris damaged several houses, people were not injured. To date, no case has been reported in which garbage from space has harmed a human being, reports Metz. However, due to the increased number of rocket launches and the growing world population, the researchers led by Byers assume that the risk will increase.
For their calculations, they looked at how many rocket parts have an orbit of less than 600 kilometers altitude, there are 651. At this altitude, the air is extremely thin, but it is still able to slow down the parts. As a result, they lose height and eventually enter the denser Earth’s atmosphere, burning up much of the mass. On the other hand, they continued the re-entry of rocket parts into the atmosphere in the past 30 years. Byers’ team assumed a slight annual increase in the risk per square meter of earth’s surface and an annual increase in the world population of one percent.
Both approaches yielded a similar result: “Assuming that each re-entry spreads deadly debris over an area of ??ten square meters, we conclude that current practices have a ten percent probability of one or more casualties over a decade.” write the researchers. However, DLR scientist Metz considers some of the Canadian researchers’ assumptions to be unrealistic. The risk per square meter assumes that the population is evenly distributed over the land surface, which is not the case.
Byers and colleagues write that the risk of being hit by missile debris is greater in poorer countries than in wealthier space nations: “The latitudes of Jakarta, Dhaka, Mexico City, Bogotá and Lagos are at least three times as likely that a body of rockets re-enters above them, as for those of Washington, New York, Beijing and Moscow.” They are calling for worldwide political steps that will get space nations to only allow controlled re-entry of rocket stages, even if this involves additional costs. In this way, the rocket parts can be guided to fall in remote sea regions.
Manuel Metz explains the higher risk for countries near the equator with the fact that many rockets bring satellites into geostationary orbit. This orbit runs over the equator and ensures that the satellites are always in the same place in the sky when viewed from Earth. This is important for many communications, television and weather satellites. Metz welcomes all measures that reduce the creation of space debris and the risk to people on Earth. Since 1997, DLR has been a member of the IADC (Inter-Agency Space Debris Coordination Committee), an international forum of space organizations to coordinate government activities on the subject of space debris.
