Lighter-Than-Air Bridge Technology
Imagine a very long bridge (Visbi Bridge - named after the designer) across an immense canyon - really almost a wide deep gorge -use on an earth-like world. My concept is that part of the support of the bridge would be a ballon-like, lighter-than-air technology of some kind. The ends of the bridge would use a suspension set-up, with piers and cables. Out toward the middle, the bridge would need additional support
1.I am wondering if this might be feasible, assuming a somewhat more advanced materials technology than we presently have? Gravity and weather would be the similar to our earth.
2.How long could such a bridge be? 1 mile? 2 miles? 5 miles? Assume advanced materials that are at least conceivable today.
3.Would this concept make sense in opposition to flight? In other words it would have more capacity for the energy consumed.
4.Are there other technologies that would realistically allow very long bridge spans?
On this world, the technology is close to what we have. The civilization on this world is less energy intensive than ours, is not car-based and is more sparsely populated. I am ruling out anti-gravity technology or energy bridges, etc. This bridge would not have to bear enormous loads, mainly people in some sort of vehicles and valuable/light cargo. I assume provisions for closing the bridge and/or reconfiguring the bridge structure in unfavorable weather and wind conditions.
This post was sourced from https://worldbuilding.stackexchange.com/q/9247. It is licensed under CC BY-SA 3.0.
1 answer
Air is incredibly light. It's hard to conceive of any materials that are actually lighter than air and sufficiently so to keep lift while under load.
However, it might be possible to use balloons as a lifting device. The gas is a subject of some contention. Helium has a lifting force of 1 gram per litre, which is not very much. Hydrogen is about 8% better but it's very flammable which is why airships no longer use it. Search Hindenburg. Methane can also be used and doesn't escape balloons as easily but it's a much worse lifting gas. So let's go with helium.
Let's also say that we're using nice advanced graphene to build this bridge; although not currently developed enough to do this with, it might well be soon. Graphene has a mass of 0.77mg per square metre, or 21.36 milligrams per cubic metre.
We're building a bridge. How much material does that need? Assuming a span of 1km, width of 10m and average depth just 50cm (which should support enough for your needs), that gives:
$$ 1000 \times 10 \times 0.5 = 5000 \text{ m}^{2} $$ $$ 5000 \times 21.36 = 106800 \text{ milligrams} $$ $$ = 106.8 \text{ grams} $$
Therefore, to lift the bridge alone you need 106.8 litres of helium. You will need extra helium equivalent to the weight of the vehicle in grams when a vehicle crosses (or a person for that matter). Let's say your heaviest vehicle is 1 tonne. That's an extra 1,000,000 litres of helium...
In short, you're going to need a lot of helium. It's fairly impractical.
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