# E < μ/r

Climbing out of the Earth's gravity well requires energy, but a launch loop on the rotating Earth can launch to infinity with less than the classical μ/r gravitational escape energy. The difference is taken from the rotational energy of the Earth itself.

Assume a spherical planet with mass M and surface radius R. The **standard gravitational parameter** \mu for the planet is the product of the gravitational constant G and M : \mu ~=~ G M . The gravity at the surface of the planet is g(R) ~=~ \mu / R^2 , and the gravity at radius r above the surface is g(r) ~=~ \mu / r^2 .

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