Inputs

Orbit altitudekm, circular

Constrain bywhat limits the footprint

Min elevation εdeg — user/ground constraint

Results

Earth central angle λ

– deg

Swath width

– km

Footprint area

– km²

Fraction of Earth

– %

Slant range @ edge

– km

Nadir angle @ edge

– deg

Elevation @ edge

– deg

Horizon limit λ_max

– deg

Sats for equatorial ring

–

📖 How to use

Enter the altitude and choose what limits the footprint: a minimum elevation seen from the ground (comms), or the payload's half-cone angle off nadir (imaging/SAR).输入高度并选择限制足迹的因素：地面看到的最低仰角（通信），或载荷偏离星下点的半锥角（成像/SAR）。

Read the swath width, footprint area and slant range at the edge — slant range drives the link budget at edge of coverage.读取幅宽、足迹面积与边缘斜距——边缘斜距决定覆盖边缘处的链路预算。

Compare the swath with the equator spacing from the Repeat Ground Track tool to confirm gap-free coverage within one repeat cycle.把幅宽与回归轨道工具给出的赤道条带间距对比，确认一个回归周期内无缝覆盖。

"Sats for equatorial ring" is a quick constellation sizing hint: how many satellites of this footprint are needed side by side around the equator."赤道环所需卫星数"是星座规模的快速提示：绕赤道一圈并排需要多少颗这样足迹的卫星。

Coverage geometry

With r = R_E + h, for a minimum elevation ε the geometry gives

sin η = (R_E/r)·cos ε and λ = 90° − ε − η

Swath width = 2·λ·R_E (great-circle arc); footprint area = 2π·R_E²·(1 − cos λ) (spherical cap); slant range = R_E·sin λ / sin η.

When constrained by a sensor half-cone η instead, the same triangle is solved for ε: cos ε = (r/R_E)·sin η. If that exceeds 1 the sensor looks past the horizon and the footprint is horizon-limited at λ_max = acos(R_E/r).

All computation runs locally in your browser.

覆盖几何

令 r = R_E + h，给定最低仰角 ε 时：

sin η = (R_E/r)·cos ε 且 λ = 90° − ε − η

幅宽 = 2·λ·R_E（大圆弧长）；足迹面积 = 2π·R_E²·(1 − cos λ)（球冠）；斜距 = R_E·sin λ / sin η。

改由传感器半锥角 η 限制时，对同一三角形解 ε：cos ε = (r/R_E)·sin η。若该值大于 1，说明传感器视线越过地平线，足迹受地平线限制，λ_max = acos(R_E/r)。

全部计算在你的浏览器本地完成。