Leonard David's INSIDE OUTER SPACE

Artwork depicts Cluster satellite reentry.
Image credit: ESA/David Ducross

Recall those uplifting lyrics from “Raindrops Keep Fallin’ on My Head” crooned by B.J. Thomas in the 1969 film Butch Cassidy and the Sundance Kid?

Consider this 21^st century-style downside.

Due to the increasing number of “megaconstellations” of satellites being tossed into Earth orbit, what are the chances of being conked in the head by re-entering fragments?

Risk of on-ground casualties

A new study of the fiery re-entry into Earth’s atmosphere of eleven megaconstellations finds there’s a 40% collective risk of on-ground casualties if satellites do not burn up entirely. The collective casualty risks modeled took into account well-funded constellations that total some 73,369 satellites.

A main propellant tank of the second stage of a Delta 2 launch vehicle landed near Georgetown, Texas in January 1997.
Image credit: NASA Orbital Debris Program Office

“Risky uncontrolled reentries of space objects should be the exception, rather than the norm,” explains a research team led by Ewan Wright from the University of British Columbia, Vancouver, British Columbia, Canada. Their findings are detailed in an upcoming issue of the Space Policy journal.

Design for demise

The highlights of the research paper – “Satellite megaconstellations and collective casualty risks” – are:

• Megaconstellations of thousands of satellites are being launched, and will reenter the atmosphere at end of life to avoid generating space debris.
• Satellite designers may aim for their satellites to demise entirely, but there is considerable uncertainty in the degree to which total ablation can be achieved.
• If a satellite does not burn up entirely, it creates a casualty risk.
• Many existing casualty risk thresholds are calculated per satellite, while others apply vastly different thresholds to address collective casualty risk.

Break up

When satellites reenter the atmosphere, the Canadian team reports, aerodynamic forces cause them to break up. The intense heat of re-entry ablates their materials into fine particles.

“However, many satellites, particularly large ones, do not burn up entirely,” they explain.

Credit: The Aerospace Corporation/CORDS

Unless satellite operators purposely direct their satellites to reenter over a specific location on Earth in a “controlled re-entry” manner, that fall from space will be uncontrolled and surviving debris will be spread out over an area centered on a random location along the satellite’s orbit.

“This creates a casualty risk to people on the ground and in aircraft in flight, as well as other risks such as infrastructure damage and airspace closures,” Wright and colleagues point out.

Melting points

In this study the researchers ask: “what happens if the minimum lethal amount of debris from each satellite does not burn up and reaches the ground intact?”

Materials used in satellites with lower melting points, such as aluminium, are more likely to demise entirely. However, other materials such as stainless steel, beryllium, titanium, tungsten, and silicon carbide are less likely to do so. These are commonly employed in fuel tanks and reaction wheels.

Chunks of space junk rained down in Australia, later identified as SpaceX leftovers from its Crew-1 Mission that flew in 2020-2021.
Photo courtesy: Brad Tucker

“The demise of another common fuel tank material, carbon fiber reinforced plastic is not yet well understood. The demise of components further depends on how they are nested within the satellite structure, and how it breaks up through the atmosphere.”

Recommendations

In wrapping up their research findings, Wright and colleagues ponder a key question: Do we need so many satellites?

“It is possible to design constellations made up of fewer, higher capacity, higher quality satellites with longer operational lives. This, in turn, would reduce the risk to people on the ground and any damage to the atmosphere,” they report.

Images taken of space debris in Australia found in October 2025.
Image credit: Western Australia Police Force

As for recommendations on casualty risks, the Canadian team offers a set of considerations.

“Due to the large collective risks created by single megaconstellations, and the even larger cumulative risks from all constellations, we recommend that states and their national regulators (1) require independent verification of claims of full demisability; (2) evaluate collective casualty risks from entire constellations; (3) pursue a smooth transition to a fair, equitable, and globally applicable controlled reentry regime.”

To access the research paper – “Satellite megaconstellations and collective casualty risks” – go to:

https://www.sciencedirect.com/science/article/pii/S0265964626000044?via%3Dihub