Terraforming Mars Not as Easy as Once Thought

You mean like a giant ball of fusing gases emitting a few hundred yottawatts of power? Something like that?

No idea where we'd find one of those just floating about.

 

Yeah, that's exactly the point. Even if you had a rigid sphere with a diameter equivalent to Earths orbit then you would need artificial gravity on the surface to stop a resident from floating away the first time they took a single step, unless the sphere itself has many times more mass than our sun.

The gravitational pull of the Sun on the Earth is a mighty 0.00588 ms^2.

edit: My calculations might be off here, but I estimate that if you built a hollow sphere of cast iron with the mass of the sun and a size equivalent to Earths orbit it would have a shell around a kilometre thick.

 

But if the mass of the rigid sphere equals that of the Earth, it's gravitational field on the outer surface would be equal to Earth's would it not? The gravitational field of a shell is the same as the equivalent point mass.

It's been a looong time since I sat in a physics class, but didn't Newton's shell theorem prove that?

 

It sure is, but if this is a Dyson Sphere then it's gonna be a lot bigger than the Earth. While it's overall gravitational footprint is large, the force on its surface would be equivalent to if you were 149.6 million km away from the Earth.

 

yup the radius!

You'd need a lot more mass! Which comes with its own downsides.

Hold on the white dwarf mining, it's neutron stars we need to mine!

 

I want to say - and could be wrong - that if you want to build a megastructure like this, a ringworld is a better choice than a Dyson sphere. Less material, for one thing. You can build multiple ones around a star so that they can have different angles to the plane of the ecliptic. The gravity thing is still an issue but if you get your sums right, you may be able to spin the ring fast enough for centrifugal gravity. Maybe.

 

Nope. A ringworld is unstable.

 

Yup... but if you built a Dyson Sphere around a star where the gravitational pull was 9.8m/s then you'd have earth gravity on the surface of it.

 

Why not live on the inside?

A Dyson Sphere would be so massive, that if you could build it than you could certainly engineer sun blockers that would orbit around the sun and create night on the surface of the sphere.

Edit: Also I think if you've got the ability to actually build a solid sphere around a star you probably have control of gravity because you're going to need that to make the sphere stable around the star. So the gravity on the inside of the sphere will be provided by you using the sun's energy to power the system.

 

Here's some good videos on building huge things like Ringworlds and Dysons.