Reentry Casualty Risk

Per-material demise screen + debris casualty area DCA = Σ (0.6 + √A)² × footprint population density, checked against the ODMSP / NASA-STD-8719.14 1-in-10,000 threshold. First-order screening - confirm with NASA DAS / ORSAT before filing.

This reentry casualty risk calculator is free and runs in your browser: no sign-up, no install. It screens an uncontrolled reentry in three steps: each component survives or demises by material, the survivors sum to a debris casualty area (DCA) with the standard 0.36 m² human ground-projected cross-section added around each fragment, and DCA times the footprint's population density gives the expected casualties - checked against the 1-in-10,000 threshold of the US Government Orbital Debris Mitigation Standard Practices (ODMSP) and NASA-STD-8719.14. A first-order design-for-demise screen; confirm a filing number with NASA's Debris Assessment Software (DAS) or the Object Reentry Survival Analysis Tool (ORSAT).

When a satellite reenters, atmospheric heating destroys most of it - but dense, refractory, or high-heat-capacity components can survive to the ground. If enough surviving mass lands in a populated area, it is a public-safety problem, so debris-mitigation standards cap the risk. The US Government Orbital Debris Mitigation Standard Practices (ODMSP) and NASA-STD-8719.14 require the expected casualties from an uncontrolled reentry to be below 1 in 10,000. This tool screens your design against that limit.

The calculation has three steps. First, a demise screen: each component is judged to survive or burn up by material - aluminum (low melting point, low heat capacity) reliably demises, while titanium, stainless steel, Inconel, beryllium, glass-ceramics, carbon composite, and copper typically survive. Second, the debris casualty area: DCA = Σ (0.6 + √A_i)² over surviving objects, where 0.6 = √0.36 m² is the standard human ground-projected cross-section - each surviving fragment is effectively enlarged by a human-body radius. Third, the expected casualties E_c = DCA × population density, where the footprint population density comes from the orbit inclination (which sets the latitude band the debris sweeps) and the reentry year (world population grows). Compliance is E_c < 1×10⁻⁴.

Two levers make a failing design compliant. Design for demise - choose materials and geometries that burn up, so the surviving casualty area shrinks toward zero (an all-aluminum bus can screen to zero). Controlled reentry - target a broad-ocean disposal area (the South Pacific Ocean Uninhabited Area, "Point Nemo"), which drops the population exposure by roughly three orders of magnitude; this is how large buses that cannot be made to demise are disposed of.

What this tool does not do: it is a first-order screening model with a binary per-material demise rule and a coarse population estimate. Real compliance uses NASA DAS or ORSAT, which integrate per-component aerothermal ablation - melting, break-up altitude, and fragment-by-fragment survival through the trajectory - and a gridded population model. It also does not model the 15 J lethal-impact- energy screen per fragment, secondary break-up, or the demise benefit of exposing a component only after its housing fails. Treat a marginal verdict as "run DAS/ORSAT to confirm," not as a certified filing number.