Deorbit rule check
Estimate how long a satellite without a disposal burn stays in orbit from atmospheric drag alone, and compare it with the FCC rule that low-Earth-orbit satellites re-enter within 5 years after their mission ends.
Example: a 3U CubeSat at 525 km decays in about 4.0 yr (range 1.6 yr–10 yr).
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The FCC 5-year rule
For satellites ending their mission in, or passing through, low Earth orbit below 2,000 km, the FCC defines successful disposal as atmospheric re-entry “as soon as practicable, but no later than five years following completion of the mission” (47 CFR 25.114(d)(14)(vii)(D)(1); 5.64(b)(7)(iv)(A) for experimental licenses). It was adopted in the FCC's Second Report and Order, FCC 22-74 (29 Sep 2022), and applies to satellites launched from 29 Sep 2024. It replaced the old 25-year guideline for FCC-authorized satellites.
FCC 22-74 (PDF) ↗ · Federal Register 2024-17093 ↗ · FCC orbital debris FAQ ↗
How the estimate works
- Model: a circular orbit shrinking under drag, da/dt = −ρ·√(μa)·Cd·A/m, stepped in 0.5 km increments down to 100 km. Cd = 2.2 (a common value for small satellites).
- Density: exponential atmosphere table from Vallado, Fundamentals of Astrodynamics and Applications (4th ed., 2013), Table 8-4 (CIRA-72 based), 100–1,000 km; above 1,000 km the last layer is extended. Table values as published in pyatmos ↗
- Solar activity: the table is a single average. Drag rises a lot when the Sun is active: NOAA's Space Weather Prediction Center notes LEO satellites reboost about four times a year at quiet sun but every 2–3 weeks at solar maximum (SWPC ↗). The range uses density × 2.5 (active sun) to × 0.4 (quiet sun), our assumption sized from that 4–6× difference. Real decay averages over the 11-year cycle, so the middle value is the best single guess.
- Elliptical orbits: drag acts mostly at perigee, so the range runs from a circular orbit at perigee (active sun) to a circular orbit at the mean altitude (quiet sun); the middle value is the geometric mean of the two average-sun results.
- CubeSat presets: maximum mass and area-to-mass ratio from NASA ODPO's “Orbital Debris Mitigation and CubeSats” (2021), Table 1 (NTRS ↗). Tumbling, deployables and attitude change the real area.
- After the mission = lifetime minus mission length, assuming the satellite drifts from the start (no station-keeping).
Check against published figures
| Case | Model (range) | Reference | Agrees? |
|---|---|---|---|
| 1U at 400 km | 6 mo (2 mo–1.3 yr) | NASA SST: smallsats around 400 km “naturally decay in under five years” | agrees |
| 12U at 400 km | 1.2 yr (6 mo–2.9 yr) | NASA SST: smallsats around 400 km “naturally decay in under five years” | agrees |
| 1U at 550 km | 7.1 yr (2.8 yr–18 yr) | NASA ODPO Fig. 1: about 10 years (read from chart) | agrees |
| 1U at 575 km | 11 yr (4.3 yr–27 yr) | NASA ODPO Fig. 1: about 16 years (read from chart) | agrees |
| 1U at 600 km | 16 yr (6.3 yr–40 yr) | NASA ODPO Fig. 1: about 25 years (read from chart) | agrees |
| 6U at 550 km | 12 yr (4.7 yr–29 yr) | NASA ODPO Fig. 1: about 14 years (read from chart) | agrees |
| 6U at 575 km | 17 yr (7.0 yr–44 yr) | NASA ODPO Fig. 1: about 22 years (read from chart) | agrees |
| 3U at 650 km | 29 yr (12 yr–73 yr) | NASA ODPO: CubeSats deployed above about 600 km “typically will not be compliant” with 25 years | agrees |
References: NASA Small Spacecraft Technology State of the Art, ch. 13 Deorbit Systems (nasa.gov ↗); Ostrom, NASA ODPO, “Orbital Debris Mitigation and CubeSats” (2021), Fig. 1 DAS lifetimes, read from the chart to about ±2 years (NTRS ↗). Our average-sun value runs about 20–35% shorter than the DAS curves at 550–600 km, but every DAS reading falls inside our range. Built 19 Oct 2026, 18:59 PT.
