🪐 Orbit Basics Calculator

Semi-major axis · eccentricity · period · velocities · energy from perigee/apogee altitude

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Inputs

Results

Semi-major axis a
– km
Eccentricity e
–
Orbital period
– min
Mean motion
– rev/day
Perigee velocity
– km/s
Apogee velocity
– km/s
Escape velocity @ perigee
– km/s
Specific energy
– km²/s²
Angular momentum h
– km²/s
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📖 How to use

  1. Pick a preset or enter perigee and apogee altitude — equal values describe a circular orbit.选一个预设，或输入近地点和远地点高度——两者相等即圆轨道。
  2. Read the period, mean motion (rev/day) and velocities at perigee and apogee.读取轨道周期、平均运动（圈/天）以及近/远地点速度。
  3. Use the period and mean motion as inputs to the Repeat Ground Track and Coverage tools; feed the altitude into the SSO tool for a sun-synchronous inclination.周期与平均运动可作为回归轨道和覆盖分析工具的输入；把高度填入太阳同步轨道工具可得同步倾角。

Two-body orbit equations

Geometry: r_p = R_E + h_p, r_a = R_E + h_a, a = (r_p + r_a)/2, e = (r_a − r_p)/(r_a + r_p)

Period (Kepler): T = 2π·√(a³/μ) with μ = 398 600.4418 km³/s²

Vis-viva: v = √(μ·(2/r − 1/a)) — evaluated at perigee and apogee

Specific energy: ε = −μ/(2a); angular momentum: h = √(μ·a·(1−e²))

These are unperturbed two-body values. Real orbits drift under J2, drag and third-body forces — see the J2 Perturbations tool for secular rates.

All computation runs locally in your browser.

二体轨道公式

几何: r_p = R_E + h_p，r_a = R_E + h_a，a = (r_p + r_a)/2，e = (r_a − r_p)/(r_a + r_p)

周期(开普勒): T = 2π·√(a³/μ)，μ = 398 600.4418 km³/s²

活力公式: v = √(μ·(2/r − 1/a)) —— 分别在近地点与远地点求值

比能量: ε = −μ/(2a)；角动量: h = √(μ·a·(1−e²))

以上为无摄二体值。真实轨道在 J2、大气阻力与三体引力作用下漂移——长期变化率见 J2 摄动 工具。

全部计算在你的浏览器本地完成。