Satellite Visibility Calculator
Calculate horizon slant range, ground coverage distance, central angle, and maximum pass duration for satellite ground station line-of-sight visibility.
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Math
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Related
Enter parameters and click Calculate to view results
Formula & Theory
d_slant = √(Rₑ² + (Rₑ+h)² - 2Rₑ(Rₑ+h)cos ψ), ψ = arccos[(Rₑ/(Rₑ+h)) cos θ] - θThis formula is used to calculate antenna parameters for satellite visibility calculator.
Overview
This satellite visibility calculator determines when and for how long a satellite is within line-of-sight of a ground station, computing the Earth central angle, maximum slant range, ground-track coverage footprint, and pass duration for a given orbital altitude and minimum elevation mask — essential figures for antenna tracking system design, pass scheduling, and link availability planning.
Input Guide
Enter Satellite Altitude, Minimum Elevation Mask exactly in the units shown by this satellite visibility. Check the operating band, unit prefix, and decimal position before calculating; these are the inputs used by the formula.
- Satellite Altitude — use km.
- Minimum Elevation Mask — use °.
Output Guide
The results describe the calculated satellite visibility values for the inputs you entered. Check each value against the available space, selected components, feed system, and operating conditions before making a final design decision.
How This Calculator Works
The Satellite Visibility uses d_slant = √(Rₑ² + (Rₑ+h)² - 2Rₑ(Rₑ+h)cos ψ), ψ = arccos[(Rₑ/(Rₑ+h)) cos θ] - θ. Supply Satellite Altitude (km), Minimum Elevation Mask (°) in the displayed units, then use the calculated values as the first engineering target for this satellite communication design or analysis.
Design Notes
Visibility geometry is governed entirely by two variables: altitude and elevation mask. Altitude sets the orbital period and the size of the visibility footprint on the ground; the elevation mask is a practical design choice, not a physical constraint. A 0° mask represents the theoretical geometric horizon, but real ground stations rarely track that low — terrain, buildings, trees, and rising atmospheric noise floor near the horizon all degrade link margin at low elevation angles. A 5–10° mask is typical for VHF/UHF ground stations, while high-gain X-band or Ka-band tracking antennas often use a 10–15° mask to avoid multipath and tropospheric scintillation, which both worsen sharply below 10°. Raising the mask shrinks the visibility window and shortens every pass, so there's a direct trade-off between usable link margin and total contact time per orbit.
Build and Tuning Notes
This calculator assumes a circular orbit and computes the overhead (zenith) pass case — the longest possible pass at a given altitude, where the satellite's ground track carries it directly over the station. Real passes are almost always shorter than this maximum, since most passes cross the visibility circle off-center rather than through its middle; use this figure as an upper bound when sizing antenna slew rates or scheduling contact windows, not as a typical-case estimate. For LEO constellations, pass duration and slant range both shrink as altitude decreases, which is why very low LEO systems (400–600 km) need faster-slewing tracking antennas and shorter, more frequent contact windows than higher LEO or MEO systems. At GEO altitude (35,786 km) the central angle math still applies, but because the orbital period matches Earth's rotation, a station within the visibility footprint sees the satellite as fixed — no tracking is required at all, only a one-time pointing calculation.
Frequently Asked Questions
What is a ground station elevation mask angle?
An elevation mask angle is the minimum angle above the local horizontal plane required before a ground terminal attempts to track or communicate with a satellite, avoiding physical obstructions and ground RF noise.
How long can a LEO satellite remain visible during a single pass?
Depending on orbit altitude and elevation mask, an overhead zenith pass for LEO satellites (500–1,200 km) lasts between 6 and 15 minutes. Off-center passes that don't cross directly overhead are shorter, sometimes lasting only a minute or two above the elevation mask.
What is the sub-satellite point (nadir)?
The sub-satellite point is the position on Earth directly beneath the satellite where the satellite appears at a local elevation angle of exactly 90° (zenith).
Why does lowering the elevation mask increase pass duration so much?
The visibility footprint grows geometrically as the mask angle decreases, so even a small reduction — say from 10° to 5° — can noticeably extend contact time. The trade-off is signal quality: at low elevation angles, the RF path travels through much more atmosphere, increasing tropospheric attenuation, multipath from ground reflections, and sky noise temperature, all of which reduce the achievable link margin during the very moments of longest contact.
Does this calculator account for Earth's rotation or orbital eccentricity?
No — it assumes a circular orbit and treats the ground station as stationary during the pass, which is accurate enough for first-pass link budgeting and antenna sizing. For precise pass prediction (AOS/LOS times, azimuth/elevation tracking tables), use a full SGP4/TLE-based orbit propagator, which accounts for Earth's rotation, orbital perturbations, and non-circular orbits.
Alex Warren
B.Sc. in Electrical & Electronic Engineering (EEE)
Alex specialises in antenna design and wave propagation. His expertise helps ensure these calculators present practical RF concepts, useful design estimates, and clear engineering guidance for students, HAM operators, and wireless professionals.