Originally Posted by Fred Brackin (Post 2447163)

They need to make the shades out of photovoltaic film so they an absorb that sunshine and use it to power the reactionless drve units that do the stationkeeping.

Originally Posted by Fred Brackin (Post 2447163)

The thrust units also need to be around the edges rather than in the center. You would need a stiff disc for a center mount. There'll be some extremely strong cables involved too.

Originally Posted by Varyon (Post 2447166)

Although I do wonder how Venus would appear in Earth's night sky with such a large, high-albedo "structure" up in its orbit. How bright would that be?

Originally Posted by scc (Post 2447151)

It's not technology that's stopping, it's politics. Europe trying to enforce environmental protection standards in Africa would go down about as well as Russia's current invasion of Ukraine.

Originally Posted by SydneyFreedberg (Post 2447080)

And they can’t spare a couple million robots to clean up Africa? Grumble grumble I’ll stop now.

Originally Posted by Fred Brackin (Post 2446925)

I suspect that for brobdinagian purposes like terraforming you want to keep all of your terraforming machinery working as close to 24/7 as possible.

Originally Posted by scc (Post 2447151)

As for reusing the cargo containers, they're going to need equipment to keep their cargo cool and now drives systems and this is a government program, not throwing away perfectly usable equipment is frowned upon.

Originally Posted by Varyon (Post 2447159)

Most sci-fi also makes heavy use of superscience drives for a similar reason - with or without a human crew, transporting things through space with hard-science drives is boring. Even with superscience, transporting things through space is likely to be boring, unless something goes wrong.

I honestly have no issues with inefficiently using manned ships for this kind of stuff for the service of drama, although I suspect you're either going to either have things be fairly boring or will need to have interesting problems occur with strikingly-unrealistic frequency. If that's the campaign you want, go for it.

Originally Posted by Varyon (Post 2447159)

Ha ha ha ha ha ha ha ha ha ha ha ha ha ha *deep breath* ha ha ha ha ha ha ha ha ha ha ha ha ha ha!

Originally Posted by Varyon (Post 2447159)

Aluminum foil of standard thickness weighs around 4.5 kg per square meter, or 4500 metric tons per square kilometer. 44 million square miles is around 114 million square kilometers, so a sunshade consisting of nothing but that foil would weigh in at 513 Pg (513,000,000,000 metric tons). To put that in perspective, that's roughly 10,000 times the weight of the Great Wall of China. And you're going to have some inefficiencies due to it being made up of separate components, plus you'll need to add in the weight of the attached robots. Even if your reflective plastic is somehow lighter than such an incredibly-thin sheet of aluminum foil, you're talking about an absolutely massive edifice, here.

And, honestly, using some sort of metal may be a better option than plastic. Plastic requires that you either grow plants and turn them into bioplastic, or drill for oil to turn into more traditional plastic. Earth currently generates somewhere north of 340 million metric tons of plastic each year, so you'd need 1,500 years worth of modern plastic production to build your sunshade. Probably better to harvest your needed materials from asteroids - you won't find any oil, but there's plenty of metal to go around.

Originally Posted by Fred Brackin (Post 2447163)

They need to make the shades out of photovoltaic film so they an absorb that sunshine and use it to power the reactionless drve units that do the stationkeeping.

The thrust units also need to be around the edges rather than in the center. You would need a stiff disc for a center mount. There'll be some extremely strong cables involved too.

Originally Posted by DangerousThing (Post 2447207)

Agreed. They have to experiment with terraforming anyway. It should be much easier to terraform the planet we have!

Originally Posted by Varyon (Post 2447166)

I
Depending on what the minimum efficient size is for these reactionless drives, simply having several dozen small ones spread out over the inner surface may be ideal.

Originally Posted by Varyon (Post 2447159)

Aluminum foil of standard thickness weighs around 4.5 kg per square meter, or 4500 metric tons per square kilometer.

Originally Posted by Fred Brackin (Post 2447224)

Nevermind the drives. The disc has to be a weight-bearing structure (it's own weight) and a stiff disc will be either very small or very heavy.

The lightest structure for large sizes (like a mile or even kilometer across) will be a spider web of buckytube cables with a thin layer of either reflective or photovoltaic material transferring its' weight to the cable structure.

For strength and stabiility you "anchor" those loadbearing cables to thrust units at the cables' ends. Putting thrust units in the middle doesn't help.

Originally Posted by Agemegos (Post 2447234)

Standard thickness for what? The density of aluminium is 2 700 kg per cubic metre, so foil that massed 4.5 kg per square metre would be 1.67 mm thick. That's chonk foil.

I weighed a roll of aluminium foil in my kitchen. Net of the box and the cardboard core it's rolled up on, a 30 m by 30 cm roll (9 square metres) massed 343 g. That is 0.038 kg per square metre. 38 tonnes per square kilometre.