Debris mitigation
Reentry Casualty Risk
Not everything burns up. Screen what survives reentry against the 1-in-10,000 casualty limit — and see whether design-for-demise or a controlled reentry is what gets you compliant.
// 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 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).
How this model works & what it omits
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.
// pick a scenario, then edit the component list and reentry conditions.
Surviving-candidate components
// material sets the demise screen; cross-section drives the casualty area.
columns: name · material · mass (kg) · cross-section (m²) · verdict
Reentry conditions
// inclination + year set the footprint population exposure.
Disposal mode
// a targeted ocean reentry collapses exposure ~1000x.
Places the footprint over the South Pacific Ocean Uninhabited Area ("Point Nemo").
Threshold
// US Government ODMSP / NASA-STD-8719.14.
Casualty risk limit
< 1 in 10,000
E_c < 1×10⁻⁴ expected casualties per reentry
ODMSP / NASA-STD-8719.14 · < 1 in 10,000
Exceeds limit
1 in 5.3k
E_c = 1.89e-4
2.76 m²
Debris casualty area
3
Surviving parts
22 kg
Surviving mass
1 in 5.3k
Casualty risk
// how to get under the limit
- Design for demise — swap surviving components (titanium tanks, steel wheels, glass optics) for demisable materials or geometries so they burn up. An all-aluminum bus screens to zero.
- Controlled reentry — target a broad-ocean disposal area; exposure drops ~1000×, which almost always clears the limit for a large bus.
// screening only
First-order model: a binary per-material demise rule and a population estimate from inclination + year. Real compliance uses NASA DAS or ORSAT, which integrate per-component aerothermal ablation. Confirm a marginal verdict there before filing.
// shareable URL encodes every input. no backend.
// casualty area by component — grey = demised
// ai-generated breakdown of what these numbers mean — with diagrams.
Common questions
What is the 1-in-10,000 reentry rule?
The requirement that the expected number of casualties from an uncontrolled reentry stay below 1×10⁻⁴ — one in ten thousand — set by the US Government Orbital Debris Mitigation Standard Practices and NASA-STD-8719.14, and the number every orbital-debris assessment has to beat. It is an expectation over the whole footprint, not a probability for one fragment: total surviving casualty area multiplied by the population density under the orbit's ground track at the reentry epoch.
Which satellite components survive reentry?
The dense and refractory ones: titanium propellant tanks, stainless-steel reaction wheels, glass-ceramic optics, Inconel, beryllium, and copper masses typically reach the ground, while aluminum structure and battery boxes reliably burn up. In the default smallsat preset, 3 of 5 components survive (22 kg of titanium, steel, and glass), producing ~2.8 m² of casualty area and an expected-casualty figure of ~1.9×10⁻⁴ — about 1 in 5,300, a factor of ~2 over the limit. The material column is the whole verdict.
What is design for demise?
Choosing materials and geometries so components burn up instead of surviving — the cheapest path to compliance because it removes casualty area at the source. The default preset's titanium tank alone contributes ~1.3 m² of its ~2.8 m² total, so swapping it for a demisable aluminum-lined design moves the verdict most of the way on its own; the all-aluminum CubeSat preset screens to zero surviving area and is compliant by construction.
When is a controlled reentry required?
When demise cannot get the number under the limit — typically large buses full of tanks and wheels. Targeting the burn at a broad-ocean disposal area (the South Pacific Ocean Uninhabited Area around "Point Nemo") cuts the population exposure by roughly three orders of magnitude: the large-bus preset still lands 114 kg of surviving hardware (~5.2 m² of casualty area) yet scores ~3.9×10⁻⁷ — about 1 in 2.6 million — comfortably compliant because almost nobody is underneath.
Does the orbit affect reentry casualty risk?
Yes, through inclination: it sets the latitude band the debris can fall into, and mid-inclination orbits (~30–55°, including the default 51.6°) sweep the most-populated latitudes. The reentry year matters too — the model scales world population, so the same design scores worse the later it comes down. When it comes down is the other half of the standard: screen the post-mission lifetime with the deorbit & lifetime compliance tool.
References
- // U.S. Government Orbital Debris Mitigation Standard Practices (ODMSP, 2019 update) — the 1-in-10,000 casualty limit.
- // NASA-STD-8719.14C (2021). Process for Limiting Orbital Debris, reentry casualty-risk requirements.
- // NSS 1740.14 — origin of the 0.36 m² human ground-projected cross-section.
- // NASA ODPO. Object Reentry Survival Analysis Tool (ORSAT) and Debris Assessment Software (DAS).
- // Ostrom, C. et al. Debris Assessment Software (DAS) Reentry Risk Analysis. NASA/JSC.
- // Lips, T. & Fritsche, B. (2005). A comparison of commonly used re-entry analysis tools. Acta Astronautica 57.
- // UN World Population Prospects (2024) + Gridded Population of the World v4 (CIESIN/NASA) for the population model.
