# Enormous cargo net

I'm writing a sci-fi story. Is it possible, using today's tech and materials, to make a net that will support 1 million tonnes of one tonne iron chunks? It must be one-point lift and withstand a couple gees acceleration/de-acceleration.

anorlunda
Staff Emeritus
One million tons is about the weight of the Golden Gate Bridge at 1g. Twice that at 2g.

The largest crane can lift about 20000 tons.

A single point lift needs a shackle and a cable strong enough for the load, so it is more than the net.

I think the answer is no.

One million tons is about the weight of the Golden Gate Bridge at 1g. Twice that at 2g.

The largest crane can lift about 20000 tons.

A single point lift needs a shackle and a cable strong enough for the load, so it is more than the net.

I think the answer is no.
The lift is made by superhero, who can easily bench gigatonnes :). So I suppose the net must be designed to be thin enough to be gathered together and slung over his shoulder, heh.

The iron chunks could be assumed to form a rough sphere 60-70 meters in diameter, if my calculator hasn't let me down.

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jrmichler
Mentor
This calls for a calculation. McMaster-Carr lists ropes made of Spectra and Vectran. Both of these materials list a breaking strength of 20,000 lbs in a 1/2" diameter rope. Your superhero wants to pull 1,000,000 tons X 2 G's = 4,000,000,000 lbs force. Assume a safety factor of 2, then 4,000,000,000 / 10,000 = 400,000 ropes. Each rope has cross sectional area of 0.196 square inches, so the total cross sectional area is 78,500 square inches. If the superhero squeezes the bundle of ropes until each rope is in fully contact with the adjoining ropes, then the rope bundle will be 316 inches (26.4 feet, 8.0 meters) diameter. The superhero will need big hands, will need to squeeze hard enough to pull 4,000,000,000 lbs without slipping, and will need to pull in such a way that the force is distributed equally between each and every rope.

chasrob
26 feet? Whoa, the superguy is human sized and not Mr. Elastic :). Know nothing about Spectra or Vectran, but I wonder if the ropes were arranged in a interconnected matrix, like nets, would it would increase lifting capacity over simply roping them together? (if I understand you correctly) When I was in the USN they had steel ropes. How about Kevlar or carbon fiber (if that's available these days)?

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jrmichler
Mentor
I searched MacWhyte wire rope, and found a 1" diameter rope with rated breaking strength 151,000 lbs. You can do the math from there. Spoiler: The superhero still needs big hands.

chasrob
stefan r
He could stand spread eagle and press his cape against a block/wedge. So long as he is not sinking into the surface he should be able to spread the force out. That might give him 2 m2. A 2 meter concrete column can hold up about 40 to 80 million newtons of force. So at 1g concrete is limited to less than 8,000 1 ton blocks. Porcelain has compressive strength closer to 500 MPa so maybe 100,000 tons.

..The lift is made by superhero, who can easily bench gigatonnes :)...
Try picking up a block of margarine using a toothpick. The problem is a palm smooshing into the steel block. The hydraulic press channel has lots of demonstrations of what happens when you apply too much pressure. Here they do a ball bearing. Here is diamond.

... So I suppose the net must be designed to be thin enough to be gathered together and slung over his shoulder, heh.
...image...
The iron chunks could be assumed to form a rough sphere 60-70 meters in diameter, if my calculator hasn't let me down.

If the net is long and stretchy he could accelerate the cables at several g. If the net has similar mass to the iron payload it could lift it a short distance before falling back down. That would not look very heroic.

Why not throw the iron blocks 1 at a time?

[...]
Why not throw the iron blocks 1 at a time?
There are many trillions of tons of blocks gathered together in low earth orbit (long story) and he wants to transfer the lot earthside as fast as possible; a net seemed obvious, heroic or not. Therefore, million ton parcels. Matter of fact, larger than that would be even better but he has to employ current tech/materials.

stefan r
There are many trillions of tons of blocks gathered together in low earth orbit (long story) and he wants to transfer the lot earthside as fast as possible; a net seemed obvious, heroic or not. Therefore, million ton parcels. Matter of fact, larger than that would be even better but he has to employ current tech/materials.

If they are in low earth orbit the net does not need to accelerate at 1g. He just needs to adjust the orbit so that it intersects the atmosphere.

If you have a trillion tons of iron in orbit you should build an orbital ring system. Here is a paper by Paul Birch published in the 1980s (part 1, part2, part3) and a youtube video by Isaac Arthur.

chasrob
If they are in low earth orbit the net does not need to accelerate at 1g. He just needs to adjust the orbit so that it intersects the atmosphere.
Wouldn't that burn up valuable tons of iron? He planned on dropping the net and its load manually :) to a soft landing earthside, taking less than 5 minutes, and continuing until all the iron is landed. That's when the inertia safety factor comes in (the gees). He would like a billion ton capacity net even more, heh.
Orbital ring system... looks interesting.

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stefan r