Orbit

Perigee and apogee speed

Altitudes in kilometres. Speeds in km/h, ECI or ECEF.

ECI · Earth

km/h

Perigee

28,421.1

7.895 km/s

Apogee

27,694.3

7.693 km/s

ECEF perigee 26,720.5 km/h, apogee 25,949.1 km/h. Drifts east relative to the surface at perigee.

Perigee is below about 160 km, where drag pulls an Earth orbit down quickly. These are ideal vacuum speeds.

Period
1 h 28 m 11 s
Loops per 24 h
16.33
Eccentricity
0.012951
Semi-major axis
6,563.1 km
Path length
41,236 kmRamanujan approximation of the ellipse.
Escape at perigee radius
39,935.7 km/hLocal escape speed. Not the orbit speed above.
Drawn to scale. The body sits at one focus. Perigee is the near side.

Calculation

vp = √( μ (2/rp − 1/a) )

va = √( μ (2/ra − 1/a) )

μ = 398,600.4418 km³/s²

R = 6,378.137 km · Earth

hp = 100 km · ha = 270 km

rp = R + hp = 6,478.137 km

ra = R + ha = 6,648.137 km

a = (rp + ra) / 2 = 6,563.137 km

e = (ra − rp) / (ra + rp) = 0.012951

vp = 7.89474 km/s = 28,421.1 km/h ECI

va = 7.69287 km/s = 27,694.3 km/h ECI

v_ECEF = v − ωr → perigee 26,720.5 km/h, apogee 25,949.1 km/h

km/s is shown to 5 decimals. km/h is that speed times 3,600, rounded to 0.1. ECEF assumes an equatorial prograde path.

Model

  • Point mass, spherical body, vacuum. The path is an ellipse with the body at one focus. Equal altitudes are a circle, and the speed does not change.
  • Perigee is the lowest altitude. Apogee is the highest. Both are kilometres above the stated radius.
  • ECI is the inertial speed. ECEF subtracts that body's spin at the local radius, for an equatorial prograde orbit. Speed is fastest at perigee.
  • ECI stands for Earth-Centered Inertial. ECEF stands for Earth-Centered, Earth-Fixed.
  • Equatorial radius 6,378.137 km, so altitude matches the usual satellite figure. μ is 398,600.4418 km³/s². One sidereal day is 86,164.0905 s.