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# Spaceflight and Work

CLMECH-HTFX9E

The force of gravity is usually written as weight, $W = mg$, but if we get very far from the surface of the Earth the force of gravity on an object of mass $m$ is given by:

$$F = G\frac{mM}{R^2}\;$$

A rocket must do

work to lift each kg of payload from the surface to geosynchronous orbit ($R_g=4.2164\times10^7\;m$), neglecting any kinetic energy the satellite has when it gets there.