LEO Survivability Estimator
User Guide
User Guide — LEO Survivability Estimator
1. Pick a starting point
Choose a form-factor preset (1U / 3U / 6U / 12U CubeSat, or an ESPA-class microsat). The preset fills in typical mass and drag-area ranges so you can get an answer immediately, then refine. Selecting it again or editing any mass/area field switches you to Custom.
2. Enter your ranges (rough is fine)
| Input | Meaning | Tips |
|---|---|---|
| Mass range (kg) | Lower/upper bound of spacecraft mass | Heavier = more drag-resistant |
| Effective drag area (m²) | Time-averaged ram-facing cross-section | A tumbling sat averages higher than a single face; deployed panels increase it |
| Altitude range (km) | Circular-orbit altitudes to sweep | The dominant driver — sweep widely if unsure |
| Drag coefficient C\_d | Free-molecular drag coefficient | ~2.2 is standard; rarely worth tuning early |
| Mission length (months) | Total intended mission duration | Used to compute how much time remains after failure |
| Propulsion fails at | Fraction of the mission elapsed when thrust dies | "Halfway" = 50%; the remaining fraction is what must be survived |
| Solar / space-weather activity | Thermospheric density level | Low (solar min) → Mean → High (solar max) → Severe/storm |
3. Read the results
- Verdict banner — the headline call for your *nominal* satellite (mid mass, mid altitude): comfortably survives, survives with margin, marginal, or does not survive, with the coast time vs. the time still needed.
- Stat cards — nominal coast lifetime, time still needed after failure, the minimum safe start altitude for that satellite, and its ballistic coefficient.
- Survivability window — a heatmap over mass (vertical) and altitude (horizontal). Green cells finish the mission after a failure; red cells reenter first. The black contour is the break-even line — the edge of the survivability window. Drag area is held at its nominal value here.
- Coast lifetime vs. altitude — the shaded band spans your mass range (top edge = heaviest = longest life). Where the band crosses the dashed "time still needed" line is your minimum safe altitude.
- What matters most — a tornado chart ranking inputs by how much they swing the coast lifetime across their plausible range, with a plain-language note for each.
4. Typical readings
- Below ~400 km: a coasting small sat usually reenters within weeks-to-months. Survivability depends heavily on staying near the top of your mass range and quiet space weather.
- ~500–550 km: several years of coast life for typical CubeSats — usually enough to outlast a remaining mission, except at solar max.
- Above ~600 km: a decade or more; propulsion failure rarely threatens orbit survival (though it raises debris-disposal concerns).
5. What the answer is *not*
This is a screening estimate. It does not model attitude/tumbling dynamics in detail, eccentricity growth, third-body or J2 perturbations, drag-coefficient variation with composition, or the exact time-history of solar flux. For a launch-commitment decision, follow up with a dedicated propagator (e.g. an SGP4/NRLMSISE-00 lifetime tool) seeded with the firm specs this tool helps you converge on.