  The Sun is expected to increase its radiant output by about 10% per billion
years. The rate at which the radius of the Earth's orbit would need to increase
in order to keep the present value of the Sun's radiant flux at the Earth
constant is calculated. The mechanical power required to achieve this is also
calculated. Remarkably, this is a small fraction (2.3%) of the total solar flux
currently intercepted by the Earth. Treating the Earth itself as a rocket, the
thrust required to increase the orbit is found, as well as the rate of mass
ejection. The Earth has sufficient mass to maintain this rate for several
billion years, allowing for the possibility that the Earth could remain
habitable to biological life for billions of years into the future.
