LEO Survivability Estimator

Estimate whether a small satellite could hold a stable, usable low-Earth orbit if its propulsion system fails halfway through the mission — starting from nothing more than rough mass and altitude ranges. The tool maps the survivability window across mass and altitude, shows how long the satellite would coast before reentry, and ranks the parameters that matter most.

The question it answers

"If thrust dies at T+½, does the orbit last long enough to finish the mission, or does it decay and reenter first?"

Without propulsion a LEO orbit *always* decays eventually — atmospheric drag is relentless. "Survivable" therefore means the coast lifetime after the failure exceeds the time still left in the mission. This tool finds the boundary between those two outcomes and shows where your design sits relative to it.

What you get

• A verdict for your nominal satellite (mid-range mass at mid-range altitude): survives comfortably, survives with margin, marginal, or reenters early — with the numbers behind it.
• A survivability-window heatmap over your mass × altitude ranges, with the break-even contour drawn in.
• A coast-lifetime-vs-altitude band spanning your mass range, against the "time still needed" line — read your minimum safe altitude straight off the crossing.
• A sensitivity (tornado) ranking of which inputs swing the outcome most, with plain-language explanations.

How it works (short version)

A first-order atmospheric-drag decay model for a near-circular orbit:

da/dt = -(Cd · A / m) · ρ(h) · sqrt(μ · a)
lifetime = ∫ da / [ (Cd·A/m) · ρ(h) · sqrt(μ·a) ]   from start altitude down to ~120 km

ρ(h) is a piecewise-exponential atmosphere (US Standard Atmosphere / Vallado) scaled by a solar-activity multiplier — the single largest real-world swing in LEO lifetime. The combined term Cd·A/m is the inverse ballistic coefficient, the design knob that decides how fast you fall.

This is a screening tool: order-of-magnitude answers for early trade studies with rough specs, not a high-fidelity reentry prediction. See user-guide.md for inputs and verification-report.md for how the model is checked against known LEO behaviour.

Use it

• Live tool: open tool.html (published at the outcome's URL).
• Verify the model: node verify.mjs (writes verification-report.json).

Bottom line on the original ask

For a typical 3U-class CubeSat the survivability window is governed first by altitude, then by space-weather (solar) activity, then by the ballistic coefficient (mass ÷ drag area). Below roughly 400 km a coasting small sat reenters within months; near 500–550 km it can survive several years; above ~600 km it persists for a decade or more. The exact line moves with solar activity and how much drag area the satellite presents — both of which the tool lets you sweep.