Study warns satellite megaconstellations could raise the odds of falling debris striking people

A team of researchers in Canada modeled how fragments from uncontrolled reentries of large satellite constellations would behave and quantified the resulting threat to people and aircraft below. Using aggregated scenarios that include tens of thousands of planned satellites, the study shows that while any single spacecraft carries an almost negligible casualty probability, the collective risk scales nonlinearly: if a small remnant from each vehicle survives atmospheric entry, the probability of at least one casualty across the full fleet can become large — the paper’s illustrative model produces a roughly 40% chance under that survivability assumption. Material selection and component design are central drivers of that outcome: low-melting alloys and thin parts tend to ablate fully, whereas tougher metals and ceramics used in tanks, reaction wheels, and certain structural elements are far likelier to survive. The researchers describe how breakup dynamics and aerodynamic dispersion scatter surviving fragments along the flight path, producing footprints that are effectively random over the Earth’s surface unless a controlled deorbit is executed. Importantly, current demisability testing and regulatory assessments typically focus on individual spacecraft and do not account for aggregated, constellation-level casualty probabilities — a gap the authors identify as a policy blind spot. The paper recommends independent verification of demisability claims, regulatory evaluation of constellation-wide casualty risk, and a globally fair controlled-reentry regime to reduce public exposure. It also argues that operational alternatives — fewer, higher-capacity satellites with longer useful lives — would reduce the number of reentries and therefore the cumulative hazard. Complementing the reentry analysis, the researchers note a second, interacting class of systemic threats: large-scale space-weather events or failures that simultaneously degrade navigation and propulsion could prevent many satellites from executing planned, controlled reentries or station-keeping maneuvers. Such simultaneous failures would not only accelerate collision risk in orbit but could also translate into a surge of uncontrolled reentries and unpredictable fragmentation paths, making demisability and emergency-control capabilities even more critical. To address these layered risks the paper urges technical steps (design for demisability, materials choices, hardening and redundancy for avionics) alongside governance measures (independent testing, constellation-level licensing conditions, and international coordination on emergency protocols). The authors stress the window for effective intervention is now, before full deployment of planned constellations; waiting for hard incidents would raise costs and complicate mitigation at a global scale.