Terraforming planets/moons

[halfeye]

L 1-3 are enormously unstable to preturbations in the direction of the axis between the two main bodies. Pretty much any push, no matter how small, will eventually push them out of equilibrium. So, our mylar sheet would crash into Venus sooner or later, just from solar wind. (Because if it moves even a tiny bit off L1, the gravity of Venus on it becomes stronger than that on the sun, pulling it further of L1, which increases the imbalance...).

The gravitational field around L1 can be thought of as saddle-shaped:


A small push in either direction makes your body roll off.

Cant' say how long it would take to fall, exactly, though. That probably involves tons of complicated calculations. But it wll probably start moving immediately and constantly accelerate towards venus very slowly.

Yes, I'm sure it will work perfectly, until a micrometeorite hits it and crumples the whole thing up!

Okay, okay. I know a micrometeorite wouldn't do much. Too much inertia in the mylar sheet, and too little momentum in the grain of sand.

Does anyone know how much perturbation it takes to knock something out of a Lagrange 1 point? This sheet of mylar is going to be a pretty fantastic solar sail. Will it stay in place long enough to cool Venus with all that solar radiation hitting it?

As I've said before, the way to do it is a lot of solar sail driven robots orbiting around the L1. I'm a bit perturbed about how heavy that sail is working out to be when made of mylar, because heavy is a problem, and we'll probably need these for Earth (though not so many) before we want them for Venus.

[gomipile]

As I've said before, the way to do it is a lot of solar sail driven robots orbiting around the L1. I'm a bit perturbed about how heavy that sail is working out to be when made of mylar, because heavy is a problem, and we'll probably need these for Earth (though not so many) before we want them for Venus.

Well, it's within about a factor of two of the mass of all plastic humanity has ever produced.

At the same time, it's about the mass of a middling size asteroid. There's plenty of easily accessible mass in the solar system for this sort of project.

Since the time scale for such a project is long, and these satellites would be solar sail driven anyway, we can have them relocate themselves after construction. The delta-v difference from the asteroid belt to Earth-Sun or Venus-Sun L1 is big, but if it all comes from solar sail thrust over a long time, that's not much of an issue. You do need to make sure that these satellites are very durable, but that's a given for their intended application, anyway.

[Rockphed]

Something is wrong with your calculations somewhere. The Earth's radius varies slightly over the surface, but a sphere whose radius is equal to the Earth's minimum (approx 6350km) would have a volume of a bit over 10²¹ cubic metres, which is way higher than the figure you quote there. A cylinder 12,500km in radius and 51 microns thick would have a volume of 1.25 x 10¹² cubic metres.

Seems I both forgot the 4/3 in the sphere volume calculation and used kilometers instead of meters. Ooops.

On the other hand, the shade would have an area of about 4.9 x 10¹⁴, which with a shade thickness of 51 microns would be a total volume of about 2.5 x 10¹⁰ cubic meters.

Also, this would be a shade made of nothing but reflective mylar. A real shade would need to have some sort of structure, both to allow for maintenance and to enable propulsion for station keeping.

[factotum]

On the other hand, the shade would have an area of about 4.9 x 10¹⁴, which with a shade thickness of 51 microns would be a total volume of about 2.5 x 10¹⁰ cubic meters.

...and now I'm wondering where I made the error which resulted in me being a factor of 200 out.