How this calculator works
This circular two-body model uses Earth's standard gravitational parameter, 3.986004418 x 10^14 m3/s2, and a mean spherical radius of 6371000 m. Add altitude to that radius before applying orbital equations. Altitude zero is a mathematical boundary case, not a viable satellite path. Earth rotation, flattening, atmosphere and other gravitating bodies are excluded.
Formula
r = RE + h; v = sqrt(muE/r); T = 2 pi sqrt(r³/muE). Inverse: r = muE/v² or r = cbrt(muE (T/(2 pi))²).
Worked example
At the mean surface radius, the mathematical circular speed is 7909.792 m/s and period is 5060.837 s. At twice that geocentric radius the speed is 5593.068 m/s.
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Frequently asked questions
Is altitude the same as orbital radius?
No. Altitude is measured above the adopted surface; orbital radius is measured from Earth's centre.
Does a higher orbit move faster?
For circular Earth orbits, speed decreases and period increases with radius.
Can this give geostationary altitude?
Enter a sidereal-day period for a circular radius estimate. A geostationary orbit also needs the correct equatorial plane and prograde direction.