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In gravitationally bound systems, the orbital speed of an astronomical body or object (e.g. planet, moon, artificial satellite, spacecraft, or star) is the speed at which it orbits around either the barycenter (the combined center of mass) or, if one body is much more massive than the other bodies of the system combined, its speed relative to the center of mass of the most massive body.
A wide variety of sources [5] [6] [7] define LEO in terms of altitude.The altitude of an object in an elliptic orbit can vary significantly along the orbit. Even for circular orbits, the altitude above ground can vary by as much as 30 km (19 mi) (especially for polar orbits) due to the oblateness of Earth's spheroid figure and local topography.
The speed (or the magnitude of velocity) relative to the centre of mass is constant: [1]: 30 = = where: , is the gravitational constant, is the mass of both orbiting bodies (+), although in common practice, if the greater mass is significantly larger, the lesser mass is often neglected, with minimal change in the result.
Orbital velocity may refer to the following: The orbital angular velocity; The orbital speed of a revolving body in a gravitational field. The velocity of particles due to wave motion, such as those in wind waves; The equivalent velocity of a bound electron needed to produce its orbital kinetic energy
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 X/Y plane coincides with Earth's equatorial plane, with the +X axis pointing toward the vernal equinox and the Y axis completing a right-handed set. The ECI reference frame is not truly inertial because of the slow, 26,000 year precession of Earth's axis , so the reference frames defined by Earth's orientation at a standard astronomical ...
6.7 × 10 −7 to 2.5 × 10 −5: 1 × 10 −15 to 3.7 × 10 −14: Calculated speed of an amoeba. [5] 10 −6: 1.52 × 10 −6: 5.4 × 10 −6: 3.4 × 10 −6: 5.1 × 10 −15: Speed of a cellular vesicle propelled by a motor protein. [6] 10 −5: 1.02 × 10 −5: 3.67 × 10 −5: 2.28 × 10 −5: 3.40 × 10 −14: Speed of the tip of a 7 cm ...
Estimates from an IAU question-and-answer press release from 2006, giving 800 km radius and 0.5 × 10 21 kg mass as cut-offs that normally would be enough for hydrostatic equilibrium, while stating that observation would be needed to determine the status of borderline cases. [50]