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Satellite energy
Intermediate
Total energy of a circular orbit is negative.
E = −GMm/2rA circular orbit has K = GMm/2r, U = −GMm/r, so E = −GMm/2r = −K. Losing energy via drag lowers the orbit but speeds the satellite up.
Dragging a satellite makes it faster.
Total energy is negative for bound orbits.
In more detail
A satellite in a circular orbit has total energy equal to −GMm/(2r), which is negative and half its potential energy. Its kinetic energy is GMm/(2r).
Real-world uses
- Satellite operators compute energy needed to change orbits.
- Spacecraft transfers require changes in orbital energy.
- Mission planners use the negative total energy of a circular orbit to see how much energy must be added to raise the orbit.
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Frequently asked questions
Why is the energy negative?
Because the satellite is bound to the planet, so its total energy is less than zero.
Does a satellite need energy to stay in orbit?
No. Once in orbit, it coasts without energy input, except to counter drag.
Why does a satellite speed up when it falls to a lower orbit?
Its potential energy falls, and half of that drop becomes kinetic energy, while its total energy also decreases.
Related topics in Gravitation & Orbits
Escape velocity · Escape velocity of Earth · Orbital velocity · Orbital period · Geostationary satellites · Polar and low Earth orbits