Orbital Lifetime Calculator
Orbital decay time from altitude and ballistic coefficient.
About this calculator
Low orbits decay because even the wispy upper atmosphere still exerts drag on a spacecraft moving at roughly 7-8 km/s, and this calculator estimates how long that process takes using a simplified King-Hele-style model. It first looks up atmospheric density and scale height for your altitude from a piecewise exponential table (based on US Standard Atmosphere / CIRA reference data), then applies a solar activity multiplier — because the thermosphere genuinely expands during solar maximum as increased UV and X-ray output heats and puffs up the upper atmosphere, multiplying effective density up to 5× the average case, versus 0.3× at solar minimum. From mass, cross-sectional area, and drag coefficient it derives the ballistic coefficient (m / (Cd × A)) — a single number capturing how resistant an object is to drag, where a dense, small-cross-section satellite decays far more slowly than an equally massive but draggy one like a deployed solar array or tumbling debris fragment.
The lifetime formula then combines orbital period, atmospheric scale height, semi-major axis, and the area-to-mass ratio into an approximate time to decay, with an explicit escape hatch treating anything above roughly 1500 km as an indefinite (non-decaying on human timescales) orbit. A "complies with 25-year rule" flag checks the estimate against the IADC/FCC orbital debris mitigation guideline requiring LEO objects to re-enter within 25 years of end of mission. Because real atmospheric density fluctuates day-to-day with actual solar flux (F10.7 index) rather than the three discrete levels modeled here, and because this ignores orbital eccentricity and precise satellite attitude, treat the output as an order-of-magnitude estimate for mission planning, not a certified debris-compliance calculation.
Inputs
Results
Orbital lifetime (days)
231
Orbital lifetime (years)
0.63
How to Use This Calculator
- Enter orbital altitude (km), spacecraft mass (kg), and projected cross-section area (m²).
- Set the drag coefficient (typically 2.0–2.5 for most spacecraft shapes).
- Select solar activity level (low, moderate, or high) — solar maximum significantly increases drag.
- Review ballistic coefficient (kg/m²), atmospheric density, orbital period, and lifetime in days and years.
- For debris mitigation compliance, orbital lifetime must be below 25 years for LEO objects.
How the result changes with Orbital altitude (km)
| Orbital altitude (km) | Orbital lifetime (days) | Orbital lifetime (years) |
|---|---|---|
| 200 | 0.6 | 0 |
| 300 | 7.3 | 0.02 |
| 600 | 6,455.6 | 17.67 |
| 1,000 | 2,060,000 | 5,651.77 |
What each input means
- Orbital altitude (km)
- Circular orbit altitude. Below ~300 km decays within weeks. Above ~800 km lasts decades.
- Spacecraft mass (kg)
- Total spacecraft mass including fuel. Heavier = slower decay.
- Cross-section area (m²)
- Average drag cross-sectional area perpendicular to velocity vector.
- Drag coefficient
- Aerodynamic drag coefficient. Typical satellite: 2.0-2.4. Flat plate: 2.2.
- Solar activity
- The solar cycle phase, which affects upper-atmosphere density.
What each result means
- Ballistic coefficient (kg/m²)
- m/(Cd×A). Higher = more resistant to drag.
- Atmospheric density (kg/m³)
- Estimated atmospheric density at the orbit altitude.
- Orbital period (min)
- Time for one complete orbit.
- Orbital lifetime (days)
- Estimated time until re-entry due to atmospheric drag.
- Orbital lifetime (years)
- Same lifetime expressed in years.
- Decay rate (km/day)
- Approximate rate of altitude loss per day.
- Complies with 25-yr rule
- Whether orbital lifetime is under 25 years (IADC debris mitigation guideline).
- Orbital radius (m)
- Semi-major axis: Earth radius (6371 km) plus your orbit altitude, in metres.
- Semi-major axis decay rate (m/s)
- Approximate da/dt from drag: ρ × v² × Cd × (A/m). Not a percentage.
How this is calculated
Worked example, using the default values
- Identify Input Parameters4 parametersOrbital altitude (km) = 400, Spacecraft mass (kg) = 400, Cross-section area (m²) = 10, Drag coefficient = 2.2 = 5 input(s) provided
- Calculate Orbital lifetime231 = 231
- Calculate Orbital lifetime0.63 = 0.63
- Calculate Ballistic coefficientBallistic coefficient = massKg / (dragCoeff * crossSectionM2)18.18 = 18.18
- Calculate Atmospheric densityAtmospheric density = Number(effectiveDensity.toExponential(3))9.12e-13 = 9.12e-13
Figures and sources
- IADC 25-year post-mission disposal guideline for low Earth orbit objects (2020) — Inter-Agency Space Debris Coordination Committee (IADC), Space Debris Mitigation Guidelines — recommends that any spacecraft or orbital stage left in or passing through low Earth orbit be disposed of so that it re-enters the atmosphere, via natural orbital decay or a maneuver to a lower orbit, within 25 years of the end of its mission.
Engine last updated . Checked against 2 independently-derived tests — how we verify calculators. Built by Paul Gunder, a software engineer, not a licensed financial, medical, or legal professional.
Frequently Asked Questions
Why does solar activity change the estimated orbital lifetime so much?
The calculator applies a solarMultiplier directly to atmospheric density — 0.3× at solar minimum, 1.0× average, and 5.0× at solar maximum — because increased solar UV and X-ray output genuinely heats and expands the thermosphere. Since lifetime is inversely proportional to atmospheric density in the underlying formula, that same 0.3x-to-5x density swing across the solar cycle can change estimated lifetime by more than an order of magnitude for the same satellite.
What does the ballistic coefficient measure, and why does a higher value mean a longer lifetime?
Ballistic coefficient is massKg / (dragCoeff × crossSectionM2) — mass per unit of effective drag area. A dense, compact satellite (high mass relative to its drag-facing area) has a high ballistic coefficient and decelerates from drag much more slowly than an equally massive but draggy object like a deployed solar array or tumbling debris fragment, which is why the lifetime formula divides by the area-to-mass ratio rather than multiplying by it.
How does the calculator decide whether an orbit "complies with the 25-year rule"?
It simply checks whether the computed lifetimeYears is less than or equal to 25 and reports Yes or No accordingly. This mirrors the Inter-Agency Space Debris Coordination Committee's (IADC) Space Debris Mitigation Guidelines, which recommend that LEO objects be disposed of so they re-enter the atmosphere within 25 years of the end of their mission — a guideline also referenced by the FCC's own orbital debris rules — though the underlying lifetime estimate itself is simplified and shouldn't be treated as a certified compliance figure.
Why is an orbit above about 1500 km treated as essentially permanent?
The atmosphere model's getAtmosphere function returns a near-zero density (1e-20 kg/m³) for any altitude above 1500 km, and the lifetime formula falls back to an effectively infinite value (1e15 seconds) whenever effective density drops below 1e-25. Physically this reflects that the atmosphere at those altitudes is so thin that drag-driven decay would take far longer than any realistic mission or human timescale to matter.
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