Ground Station Pass Duration Calculator
Visible pass time from orbit altitude and station latitude.
About this calculator
This calculator estimates how long, and how often, a satellite stays visible to a single ground station, using the same spherical-geometry approach as basic satellite-tracking software. From orbital altitude and your minimum usable elevation angle, it derives the ground-range half-angle (lambda) using an exact spherical relation, then doubles it to get the full central angle swept during a best-case overhead pass — the longest pass geometry allows, when the satellite flies directly over the station. Multiplying that central angle by orbital radius gives the ground track's arc length, and dividing by orbital velocity (from a simple circular-orbit relation) yields maximum pass duration. Because most real passes aren't directly overhead — they clip the edge of the coverage circle instead — the calculator applies a 0.65 factor to derive a more realistic average pass duration; this is a rule-of-thumb correction, not a rigorous statistical average over all possible ground-track geometries.
Passes-per-day comes from dividing a sidereal day (23h56m4s, the time for Earth to complete one true rotation relative to the stars, distinct from the 24-hour solar day) by the orbital period, then scaling by a rough geometric factor that grows for ground stations closer to the equator. Data-per-day multiplies the effective downlink rate by average pass duration and passes per day to estimate daily download volume. Because this uses simplified geometry rather than full ephemeris propagation, real mission planning should validate estimates against actual two-line-element (TLE) pass predictions, especially for stations near the edge of a satellite's inclination-limited coverage where visible passes become rare or brief.
Inputs
Results
Max pass duration (min)
7.94
Passes per day
2
Data per day (MB)
3,871.4
How to Use This Calculator
- Enter orbital altitude (km) and minimum usable elevation angle (degrees, typically 5–15°).
- Set your ground station latitude (degrees) and downlink data rate (Mbps).
- Review maximum and average pass duration (min), passes per day, and orbital period.
- Use data downlinked per pass (GB) to verify the ground station can receive all mission data.
- Multiple ground stations significantly increase daily contact time — model each station separately.
How the result changes with Orbital altitude (km)
| Orbital altitude (km) | Max pass duration (min) | Passes per day | Data per day (MB) |
|---|---|---|---|
| 275 | 4.62 | 1 | 1,126.3 |
| 413 | 6.36 | 2 | 3,100.9 |
| 825 | 10.87 | 3 | 7,946.7 |
| 1,375 | 16.27 | 3 | 11,900 |
What each input means
- Orbital altitude (km)
- Circular orbit altitude above Earth's surface in kilometers.
- Min elevation angle (deg)
- Minimum elevation above the local horizon for a usable pass. Higher = shorter but better quality passes.
- Station latitude (deg)
- Ground station geographic latitude in degrees (absolute value).
- Downlink data rate (Mbps)
- Effective downlink data rate for computing data volume per pass.
What each result means
- Max pass duration (min)
- Duration of a best-case overhead pass.
- Avg pass duration (min)
- Typical average pass (~65% of maximum).
- Passes per day
- Estimated visible passes per day from this ground station.
- Orbital period (min)
- Time for one complete orbit.
- Revolutions per day
- Number of orbits completed in a sidereal day.
- Coverage radius (deg)
- Ground footprint half-angle from the sub-satellite point.
- Data per max pass (MB)
- Maximum data volume downloadable in one best-case pass.
- Data per day (MB)
- Estimated total daily download volume.
How this is calculated
Worked example, using the default values
- Identify Input Parameters4 parametersOrbital altitude (km) = 550, Min elevation angle (deg) = 10, Station latitude (deg) = 40, Downlink data rate (Mbps) = 50 = 4 input(s) provided
- Calculate Max pass durationMax pass duration = maxPassDurationSec / 607.94 = 7.94
- Calculate Passes per dayPasses per day2 = 2
- Calculate Data per dayData per day = dataRateMbps * avgPassDurationMin * 60 * passesPerDay / 83871.4 = 3871.4
- Calculate Avg pass durationAvg pass duration = maxPassDurationMin * 0.655.16 = 5.16
- Calculate Orbital periodOrbital period = periodSec / 6095.5 = 95.5
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 is average pass duration reported as 65% of the maximum instead of a separately calculated value?
Maximum pass duration assumes the best-case geometry — a satellite passing directly overhead — but most real passes clip only part of the coverage circle at a shallower angle and finish sooner. The calculator applies a flat 0.65 multiplier to maxPassDurationMin as a rule-of-thumb correction for that typical off-center geometry, rather than integrating over the full distribution of possible pass geometries, so treat it as an approximation, not a statistical average.
Why does the calculator use a sidereal day instead of a 24-hour day to compute revolutions per day?
Revolutions per day is calculated as the sidereal day (86,164.1 seconds, the time for Earth to rotate once relative to the stars) divided by the orbital period, because that's the rotation rate that actually determines how a satellite's ground track shifts relative to a fixed ground station. The familiar 24-hour solar day is about 4 minutes longer since it also accounts for Earth's motion around the sun, which isn't the relevant reference for orbital repeat geometry.
Why does raising the minimum elevation angle shorten pass duration?
A higher minimum elevation requirement means the satellite must climb closer to directly overhead before the ground station 'sees' it as usable, which shrinks the ground-range half-angle (lambda) used to compute the pass's central angle and arc length. A smaller swept angle at essentially the same orbital velocity means less time above the elevation threshold, so raising minimum elevation trades pass duration for stronger, higher-quality signal during the shorter window that remains.
How accurate is the passes-per-day estimate compared to real mission planning tools?
Passes-per-day here comes from a rough geometric factor that scales with how close the ground station sits to the equator, not a full propagation of the satellite's actual ground track against station geometry. The calculator explicitly recommends validating against real two-line-element (TLE) pass predictions for mission planning, since stations near the edge of a satellite's inclination-limited coverage can see visible passes become far rarer or briefer than this simplified geometric model suggests.
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