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Cargo airships could be big

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Re: Cargo airships could be big

#251

Post by morpheos137 »

oliveshell wrote: post #225
dbrueck wrote: post #222

Probably a very stupid question, but can someone help me understand the following: once you have airships that have a rigid shell, why isn't using a vacuum better than a lifting gas? Isn't the buoyant force simply the result of displacing some volume of air with something less dense? (i.e. any excess lifting force comes from the fact that the mass of the hydrogen or whatever is less than the mass of the displaced air…

I looked into this a while back, and there's simply no feasible way to construct an airship from known materials that could sustain a vacuum of the necessary volume without being crushed by atmospheric pressure. You can keep reinforcing the vacuum chamber, but by the time it's strong enough, it'll be too heavy for the buoyant forces to lift it.

You could make many small vacuums in a honeycomb structure but at that point is just cheaper to use a lifting gas...

Re: Cargo airships could be big

#252

Post by likpok »

lesuorac wrote: post #234
jcranmer wrote: post #178

Earlier quoted context omitted.

The USS Akron, USS Shenandoah, and USS Macon all failed due to bad weather. That's 3 of the US's 4 operational airships. (Another airship was constructed for the US, but was destroyed by poor handling before it was delivered to the US.) Of the British experience with airships, R101 outright failed due to bad weather, and three more were scrapped after suffering accidents during bad weather, out of a total of 16 compl…

I mean if the alternative transports also don't work in bad weather I'm not sure you can use some failures to disqualify airships. So long as they work "more" days of the year it's a better solution. Weather doesn't really sneak up on us anymore.

Aircraft are substantially more resistant to bad weather: you can fly an airplane into a hurricane.

Aircraft are also a lot faster -- it's unlikely that a thunderstorm will catch up with you (max speed of a storm is something like 50-80 mph) and trips are a lot shorter.

Airships are much closer to the storm speed and may need to stay aloft for several days. That makes it more likely that they'll hit unexpected weather and give them fewer options to avoid anything.

It's true that someone could do some shipping with airships and just eat the downtime due to weather. So far nobody has done that. And not for lack of trying: CargoLifter (mentioned elsewhere in this thread) went bankrupt on this idea.

Re: Cargo airships could be big

#253

Post by simonh »

chatmasta wrote: post #171
stopping wrote: post #158

Earlier quoted context omitted.

Or a single tracer bullet, if it's filled with hydrogen.

Surely you could design some redundancy into the hull? It's not like the ship needs to be one giant gas bubble. It can be a mesh of a few hundred bubbles that could each pop without bringing the whole thing down.

So several hundred times the weight of the pressure envelope? Tracer bullets was only an example. Airships would be spectacularly vulnerable to all sorts of modes of attack.

Re: Cargo airships could be big

#254

Post by Tuna-Fish »

Asooka wrote: post #249
lordnacho wrote: post #237

Earlier quoted context omitted.

I think the key is in the wikipedia article: You only gain 14% lift with a vacuum vs helium. The tradeoff is either: - Build a pressure vessel to withstand the differential to the atmosphere - Let the helium do the pushing from the inside but make the thing 14% bigger I don't see how the vacuum ever wins.

I wonder if there is a sweet spot between the two. Have a rigid structure with an internal pressure less than one, but more than zero atmospheres.

There is not. The costs of dealing with pressure differentials are extreme, and there are a lot of small thorny issues.

For one, if you have a pressure differential, you need to care very much about even the tiniest leaks. A surprising fact about airships is that they don't actually have to be very gas-tight to work just fine. As people found to their surprise in both world wars, you can shoot an airship full of small holes and it only very slowly degrades in performance.

Re: Cargo airships could be big

#255

Post by taneq »

Asooka wrote: post #249
lordnacho wrote: post #237

Earlier quoted context omitted.

I think the key is in the wikipedia article: You only gain 14% lift with a vacuum vs helium. The tradeoff is either: - Build a pressure vessel to withstand the differential to the atmosphere - Let the helium do the pushing from the inside but make the thing 14% bigger I don't see how the vacuum ever wins.

I wonder if there is a sweet spot between the two. Have a rigid structure with an internal pressure less than one, but more than zero atmospheres.

At the halfway point you get 7% more lift but still need to withstand ~50kPa of external pressure. I can't see how you'll ever build a rigid structure that can withstand 5 tonnes per square meter and only weighs 7% more than a gas bag which operates only under a tiny fraction of that force and only under tension.

Re: Cargo airships could be big

#256

Post by Retric »

schiffern wrote: post #235
Retric wrote: post #190

Earlier quoted context omitted.

Don’t stop there. Charged particles in the solar wind is mostly alpha and Beta particles. 33feet / 2.5 should stop what 99.9999% ish of them? https://sciencedemonstrations.fas.harvard.edu/presentations/... Absorbing materials and their alpha particle penetration depths. 5.5 MeV alphas: AIR(STP) 3.7 cm 2.3 MeV Beta: air 8.8 m Solar wind is even less energetic. Edit: “Auroral emissions typically occur at altitudes of a…

That's not really relevant. Charged particles from the Sun (SEPs) aren't what determine the design envelope for radiation shielding. Your overall dose will almost entirely come from galactic cosmic radiation (GCR) at much higher energy levels, which is significantly harder to shield against. Those particles are what ultimately determine your shielding thickness requirements. That's true whether you're on Venus, or Ma…

https://ntrs.nasa.gov/api/citations/20205008318/downloads/20...

NASA’s direct comparisons between New Mexico (55) and Antarctica (160) only showing a relatively modest decrease from earths magnetic field when measured by high altitude balloons, but again very little GCR reaches the surface.

To be clear a very small fraction of GCR is extreme high energy particles which penetrate just fine.

Re: Cargo airships could be big

#257

Post by vel0city »

4wsn wrote: post #209
nradov wrote: post #187

Earlier quoted context omitted.

You have it backwards. Cargo railways are more developed in the US than in most of Europe. After the latest round of industry consolidation, most rail companies are highly profitable. Trucks pay most of infrastructure costs through fuel taxes and registration fees.

Fair enough. I conceded I might be totally wrong because my conclusion is based on casual observation of passenger trains and their infrastructure rather than looking into the industry. I could feasibly reach all cities and _most_ large towns by rail in Germany. Sure, it's slow as heck if you're not taking the express train with no transfers and few stops. But the infrastructure is there. Whereas in the US there are…

Most cities and towns in the US aren't too far from some rail line. There probably will not be any passenger service on that rail though. Passenger rail service is practically dead for the majority of the US.

https://www.openrailwaymap.org/

Re: Cargo airships could be big

#258

Post by elihu »

einpoklum wrote: post #229
elihu wrote: post #108

Earlier quoted context omitted.

Tourism, mining high value minerals for Earth, mining low value minerals for construction on Mars, manufacturing rocket fuel so that Mars can be the gas station for ships headed for the asteroid belt (enabling more high value mineral mining), low-gravity retirement communities for people with mobility issues who would be wheelchair-bound on Earth, real estate speculation, movies, sports, manufacturing space infrastru…

If I were living on Mars, I would absolutely not be willing to let the rare minerals get sent up into space then down to Earth. Learn to recycle, damn lazy Earthers.

I mean, sure, how can you expect to live a normal middle-class lifestyle without a few hundred tons of ytterbium? What are they going to want next? Lanthanum? Terbium? Praseodymium? Dysprosium? What else are we supposed to build our palaces out of, plain old ordinary gold? How impractical and gaudy would that be?

Re: Cargo airships could be big

#259

Post by simonh »

schiffern wrote: post #247
marcosdumay wrote: post #54

Earlier quoted context omitted.

It has about as much atmosphere above the point where the pressure is 1ATM as we have on Earth. And no, we don't know if Earth's magnetosphere ever filters most of the incoming radiation (we don't such good measurement of the incoming radiation), what we know is that at sea-level, our atmosphere alone is enough. AFAIK, every time we measure it better, the effectiveness of our magnetosphere decreases. But it can only…

>And no, we don't know if Earth's magnetosphere ever filters most of the incoming radiation (we don't [have] such good measurement of the incoming radiation) Where did you hear that? The space station (and presumably other satellites) is perfectly capable of measuring this. https://www.jpl.nasa.gov/images/pia04258-comparison-of-marti... https://ntrs.nasa.gov/api/citations/20070018244/downloads/20... https://agupubs.o…

The space station is in low Earth orbit, so quite low inside the earth’s magnetic field. That’s why the radiation flux shown in the first chart you linked is so low relative to Mars, even though the earth is much closer to the sun. However we have sent out multiple probes able to measure the radiation environment away from earth. There’s lots more to learn, but we already know a fair bit.

Re: Cargo airships could be big

#260

Post by ranched »

veb wrote: post #245
xg15 wrote: post #230

Earlier quoted context omitted.

Still having a soft spot for some cyber/biopunk future where we'll just eventually become the machines - or be able to bioengineer bodies which will be capable of overcoming those limitations :)

I have a cochlear implant so I'm already half cyborg! Still - I am surprised people aren't building on top of CI research/engineering to do _more_. When my processor is upgraded and I get bluetooth which I'd be able to not have to use headphones anymore during calls and such - I kinda wanna make a "hack" as in have an app on my phone that does some beep beep beep kinda thing when I'm facing north, less beeps south et…

Check out “Livewired” by David Eagleman. It talks about the brain’s adaptability to various inputs and using technology to create new “senses”. I think I remember the directional thing being covered and it working to improve peoples sense of direction.
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