If a satellite is brought into a stable orbit around another body, it should keep orbiting, right?
In: Physics
Well, first, there’s no such thing as a perfectly stable orbit. *All* orbits decay eventually, even if it takes billions or trillions of years.
The second is that a 2 body system isn’t doing any work. A perpetual motion machine is one that can *do work* indefinitely without an energy source or without depleting an energy source, but a planet orbiting a star isn’t doing any work, If you tried to extract that energy to do work, you’d be reducing the specific orbital energy of the system. Reduce that energy enough and your orbit decays and your bodies collide. There’s no free lunch (or energy) in physics.
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