A geocentric orbit or Earth orbit involves any object orbiting the Earth, such as the Moon or artificial satellites. In 1997 NASA estimated there were approximately 2,465 artificial satellite payloads orbiting the Earth and 6,216 pieces of space debris as tracked by the Goddard Space Flight Center.^{[1]} Over 16,291 previously launched objects have decayed into the Earth's atmosphere.^{[1]}
A spacecraft enters orbit when its centripetal acceleration due to gravity is less than or equal to the centrifugal acceleration due to the horizontal component of its velocity. For a low Earth orbit, this velocity is about 7,800 m/s (28,100 km/h; 17,400 mph);^{[2]} by contrast, the fastest manned airplane speed ever achieved (excluding speeds achieved by deorbiting spacecraft) was 2,200 m/s (7,900 km/h; 4,900 mph) in 1967 by the North American X15.^{[3]} The energy required to reach Earth orbital velocity at an altitude of 600 km (370 mi) is about 36 MJ/kg, which is six times the energy needed merely to climb to the corresponding altitude.^{[4]}
Spacecraft with a perigee below about 2,000 km (1,200 mi) are subject to drag from the Earth's atmosphere,^{[5]} which decreases the orbital altitude. The rate of orbital decay depends on the satellite's crosssectional area and mass, as well as variations in the air density of the upper atmosphere. Below about 300 km (190 mi), decay becomes more rapid with lifetimes measured in days. Once a satellite descends to 180 km (110 mi), it has only hours before it vaporizes in the atmosphere.^{[6]} The escape velocity required to pull free of Earth's gravitational field altogether and move into interplanetary space is about 11,200 m/s (40,300 km/h; 25,100 mph).^{[7]}
The following is a list of different geocentric orbit classifications.
Orbit  Centertocenter distance 
Altitude above the Earth's surface 
Speed  Orbital period  Specific orbital energy 

Earth's own rotation at surface (for comparison— not an orbit)  6,378 km  0 km  465.1 m/s (1,674 km/h or 1,040 mph)  23 h 56 min  −62.6 MJ/kg 
Orbiting at Earth's surface (equator) theoretical  6,378 km  0 km  7.9 km/s (28,440 km/h or 17,672 mph)  1 h 24 min 18 sec  −31.2 MJ/kg 
Low Earth orbit  6,600–8,400 km  200–2,000 km 

1 h 29 min – 2 h 8 min  −29.8 MJ/kg 
Molniya orbit  6,900–46,300 km  500–39,900 km  1.5–10.0 km/s (5,400–36,000 km/h or 3,335–22,370 mph) respectively  11 h 58 min  −4.7 MJ/kg 
Geostationary  42,000 km  35,786 km  3.1 km/s (11,600 km/h or 6,935 mph)  23 h 56 min  −4.6 MJ/kg 
Orbit of the Moon  363,000–406,000 km  357,000–399,000 km  0.97–1.08 km/s (3,492–3,888 km/h or 2,170–2,416 mph) respectively  27.3 days  −0.5 MJ/kg 