The sun’s luminosity will rise by around 300X as it turns into a giant. If we wish to keep the same energy flux onto the earth at that point, we must increase the earth’s orbit a factor of sqrt(300) = 17X. The total energy of the earth’s current orbit is 2.65E33 J. We must reduce this to 1⁄17 of its current value. or reduce it by (16/17)*2.65E33 J = 2.5E33 J. The current total annual energy production in the world is about 5E17 J. The sun will be a red giant in about 7.6E9 years. So we would need about a million times current global energy production running full time into rocket motors to push the earth out to a safe orbit by the time the sun has expanded.
But it is worse than that. The Sun actually expands over a scant 5 million years near the end of that 7.6E9 years. So to avoid freezing for billions of years because we have started moving away from the sun too soon, we essentially will need a billion times current energy production running into rocket engines for those 5 million years of solar expansion. But the good news is we have 7.6E9 billion years to figure out how to do that.
If we use plasma rockets which push reaction mass out at 1% the speed of light, then we will need a total of about 6E16 kg reaction mass, or about 0.000001% of the earth’s total mass. The total mass of water on the earth is about 1E21 kg so we could do all of this using water as reaction mass and still have 99.99% of the water left when we are done.
I wonder what the exhaust plume of an engine like that would look like, and how far away from it you’d have to be standing to still be capable of looking at anything after a second or two.
The sun’s luminosity will rise by around 300X as it turns into a giant. If we wish to keep the same energy flux onto the earth at that point, we must increase the earth’s orbit a factor of sqrt(300) = 17X. The total energy of the earth’s current orbit is 2.65E33 J. We must reduce this to 1⁄17 of its current value. or reduce it by (16/17)*2.65E33 J = 2.5E33 J. The current total annual energy production in the world is about 5E17 J. The sun will be a red giant in about 7.6E9 years. So we would need about a million times current global energy production running full time into rocket motors to push the earth out to a safe orbit by the time the sun has expanded.
But it is worse than that. The Sun actually expands over a scant 5 million years near the end of that 7.6E9 years. So to avoid freezing for billions of years because we have started moving away from the sun too soon, we essentially will need a billion times current energy production running into rocket engines for those 5 million years of solar expansion. But the good news is we have 7.6E9 billion years to figure out how to do that.
If we use plasma rockets which push reaction mass out at 1% the speed of light, then we will need a total of about 6E16 kg reaction mass, or about 0.000001% of the earth’s total mass. The total mass of water on the earth is about 1E21 kg so we could do all of this using water as reaction mass and still have 99.99% of the water left when we are done.
I wonder what the exhaust plume of an engine like that would look like, and how far away from it you’d have to be standing to still be capable of looking at anything after a second or two.