Beyond Helium | Hacker News Reader

Beyond Helium

judegomila.com

164 pointsjudegomila55 comments

The author doesn't understand the concept of a blimp. The only reason for filling it with helium (or hydrogen) is to counter the atmospheric pressure. Since aerographite doesn't do that (it would just collapse under the pressure) there is absolutely no point in filling a blimp with aerographite.

If you found a way to create a hull that withstand the pressure, and prevents the aerographite from being compressed, why fill it with that stuff in the first place? Just use a vacuum inside your superstrong hull!

If hull and mesh together are strong enough, you may have something. But it seems a very difficult, if solvable, problem indeed.

I don't have a lot of engineering knowledge, but I believe they said when evacuated it is about as strong as styrofoam. The latter is able to withstand air pressure. Wouldn't that mean that if you put an airtight hull around it, this stuff would actually hold it up? But yes, probably it will be tricky to evacuate and expand it at the same time...

"As strong as styrofoam" doesn't really mean anything. Are you talking about tensile strength? Or about resistance to shear forces? Compressibility? I haven't found much data on the mechanical properties of aerographite, but the Young modulus given on Wikipedia seems way too low to withstand atmospheric pressure.

Styrofoam doesn't "withstand" air pressure, it has pockets of air inside.

I'm pretty sure aerographite is porous, and the numbers you're quoting don't count the mass of the air permeating the aerographite. You could wrap it in something like mylar, but it'd be less safe than helium. Any break in the skin would be like a hole in a space capsule. This could be ameliorated with smaller cells, but that cuts into your lift. It's also not clear if aerographite is strong enough for the job.

To make something as safe and reliable as you describe, you'd have to build an evacuated closed-cell foam. That material would have to be extremely light while also being able to withstand being crushed by the atmosphere. It's not clear if anything is up to the task.

Sorry to dash your hopes.

Agreed. It would need another material wrapping it or a better aerogel, those materials probably don't exist yet.

Perhaps you could fill it with hydrogen? I'm not sure if that's a joke or not. Hydrogen in a closed-cell matrix seems like it would be a lot better contained and stable than in a bag-of-gas like the Hindenberg.

But this stuff is open-cell, so perhaps seal it into manageable-size beads? Looks like it might hold up to temperature pretty well.

Alternatively, this stuff could be used to produce a lighter-than-air structure in a process that somehow consumes it.

You don't want your hydrogen contained, you want to be able to vent it quickly in case of fire.

Wow - I would have thought that risked an even more exciting event with rocket propulsion. Is venting really the standard way?

During the whole hydrogen car discussion, it was said that hydrogen contained in a matrix was much safer because it would burn in a controlled fire rather than an explosion.

Venting hydrogen quickly into an oxygen-rich atmosphere would be silly.

This is a great idea except for this tricky bit (which they even mention in the article)

"One other limitation will be creating aerographites that can support themselves with the air inside the material “pumped" out of it."

I really can't complain too much though as I too was pretty taken with the idea after reading Diamond Age (which has a variant of this). At some point we might be able to assemble dodecahedrons out of small diamond pentagon sheets while in a vacuum and thus create small, lighter than air, "bubbles". But that time is still quite a ways off. After researching a bit the forces on the materials relative to the amount of air they would have to displace in order to achieve a net density lower than air, at volume. It doesn't look particularly doable yet (perhaps ever but I'm not willing to completely rule it out.)

The idea though is very alluring.

Hey Chuck, I actually replied to your comment on the "Human-Powered Helicopter Wins the $250,000 Sikorsky Prize" thread about a more conventional way we could achieve "permanent points of presence in the air" before we enter the "Diamond Age" :) - and I was curious about your thoughts on it, given that I'm not anything close to an engineer. Anyway, sorry to bug you, just curious if there's anything to it.

=========

I've often wondered if a balloon-based system might be the way that this ("permanent" points of presence in the air) is eventually achieved. As solar energy becomes more and more efficient every year (apparently it's on an exponential price/performance growth curve), you coat the balloon with a light-weight, flexible solar array, and either heat the air like a hot air balloon, or as it becomes cheaper and more efficient to extract hydrogen from water, fill the balloon with hydrogen, and constantly replace the hydrogen that leaks out with hydrogen extracted from water vapor in the air: http://www.technologyreview.com/view/512996/a-cheaper-way-to....

You could use low powered propellers (like a blimp), and take advantage of weather patterns (like Google's Loon project) in order to maintain position or to slowly travel.

The general challenge with balloons is drag, or specifically their response (or lack thereof) in the presence of winds so staying in one place can be problematic. I like the idea of cracking water to get hydrogen to replenish your lift bags, but if you are to fly this over the flyways (say at 60,000') you're not going to get a lot of moisture in the air. The old Zeppelins had gas generators which, while they had to be replenished, could supply plenty of hydrogen during the journey.

Google's balloon system [1] is apparently using quantity to cover holes that appear when winds blow them down range. Also if they get caught in the jet stream the can leave the area in a hurry.

Granted winds are a challenge for any aerial platform but actively flying shapes, seem to out perform lighter than air ideas when staying on station is required [2]. So solving the station keeping question would be a big part of the equation.

That said, the company that proposed the blimp to the Army is continuing to develop it as far as I can tell from their web site [3]. Perhaps it will get additional engineering work on those issues.

[1] http://www.google.com/loon/#utm_source=google&utm_medium=cpc...

[2] http://www.popsci.com/technology/article/2013-02/army-cancel...

[3] http://airshipmanufacturing.com/sentinel-2-airship.html

> It too was scattered with lights; of small towns, villages, individual houses, lanterns on beaches and smaller aircraft, most of them come out to welcome the vacuum dirigible.

> The two slowly revolving gondola sections slid gradually to a halt, preparatory to docking. People in both segments congregated on the sides nearest the island, for the view.

> The airship's system registered the imbalance building up and pumped bubblecarbon spheres full of vacuum from one lot of tanks to another, so maintaining a suitably even keel.

    -- Iain M. Banks, Excession.

Can someone explain why the material isn't floating in the air? I watched the video and it just sits here?

edit: I understand that air is in the space between the nanotube fibers. But I still don't understand why the material doesn't float. Why doesn't the air inside the material average out with the material itself to result in a space with lower density (thus causing it to float) then the surrounding air?

The solid material is denser than air. It does, however, form a structure which when evacuated of air has a lower average density than air.

Letting the air flow in fills in those gaps, raising the interstitial density enough that the average is greater than air.

I keep reading this, but I'm missing what makes it special. If you create a large enough vessel of anything and evacuate all the air, you can make it lighter than air. Is it just that it's rare to find a material strong enough with respect to its density to withstand the necessary vacuum? (ie: would a titanium bubble with a sufficient volume to thickness ratio to be lighter than air implode? Or would it just be too expensive?)

Pretty much, though it's unclear to me whether this material is even strong enough for that. But make it big and strong enough, and you can make even a lead balloon float.

Buckminster Fuller thought that if you built a large enough geodesic dome out of normal midcentury materials, you could get enough lift from sunlight-driven thermal expansion of air to float it. http://www.thirteen.org/bucky/cities.html

> It does, however, form a structure which when evacuated of air has a lower average density than air.

Yet apparently it collapses at that point. Unless that's solved we might as well be talking about birthday balloons here.

The mass of the material with air in the pores is 1.2 times the mass of the equivalent volume of air. Due to buoyancy, if you were to weigh the material in a sea-level atmosphere, you would find that its weight was 0.2 times the mass of an equivalent volume of air (which is where the 5x comes from). The only way to make it float would be to evacuate the air from between the fibers, which would make the mass 0.2 times the air volume, and would allow it to float.

Kudos to Abtinf for being a rare reader here able to identify the obviously misleading claims by a simple thought experiment. The material does not float because it is in fact about 1.2 times heavier than air and the rest is just hyped up nonsense. I am amazed at the number of fools here who are going to build blimps out of it.

Why isn't anyone discussing the one obviously useful application of this, the supercapacitors?

Physics doesn't work that way. The "6x lighter than air" doesn't include the air inside the material.

I'm not sure that "if law of physics X were repealed, we could..." stuff is anything more than science fiction: see the multiple comparisons to Diamond Age in this thread.

They mention that at the end of the article

>One other limitation will be creating aerographites that can support themselves with the air inside the material “pumped" out of it (to truly achieve being lighter than air). In practice, getting a real blimp to work will probably be made out of a future version of aerographite or another aerogel that is super strong and light, one that could self support itself without collapsing in on itself if the air between the meshes of nanotubes is pumped out. A partial vacuum will have to be created inside the aerographite structure without crushing the aerogel. This may be the fatal flaw to the idea or at least the next problem to solve (i.e. given that the material is superhydrophobic, maybe a thin shell of water could be put around the aerogel or some similar exotic solution).

"pumped"

Ionize the air?

Other than giant airships: how about just novelty/party balloons that never out-gas & sink? Re-positionable ceiling decorations? Indoor microblimps?

If such things escape into the atmosphere, you've got a floating-garbage problem... as described in Stephenson's Snow Crash.

> You might ask yourself, how are you going to come back down to earth if you cannot release some of the hydrogen/helium?

If the material can be compressed to 95% it's size and reexpands, you just compress your tanks and lower back down, expand tanks to rise. ( all concerns of other comments having been solved with the standard wave of the hand )

Or you just make it slightly heavier than air, and use it as a very fuel efficient airplane.

The article somehow seems to have a misconception that if you bring material lighter than air aboard, you will float up... Then you could as well just take some vacuum with you.

Maybe that would be even more useful than this material: a balloon filled with vacuum! And some support structure to make it keep its shape :)

Helium 0.1786 g/L

Hydrogen 0.08988 g/L

Air 1.275 g/L

This stuff is six times lighter than air so 0.2 g/L or there about. Both Helium and Hydrogen are lighter than this stuff. Considering the explosive reintroduction of air thing being pretty equivalent to the other two what makes this theoretically better?

Helium is non-renewable and in limited supply.

There's also a greater potential health risk posed by carbon nanotubes. I am completely guessing, but I feel as though the risk of dispersed airborne nanotubes (in this model) would be greater than dispersed helium (from a current blimp.)

The article mentions this would be safer than flammable hydrogen, but wouldn't this stuff burn really well being carbon with a whole lot of surface area?

  how are you going to come back down to earth if you cannot release some of the
  hydrogen/helium?

You compress it.

As others mentioned it, wouldn't air pressure compress it as well and thus make it not be able to take off.

You have to take into account two things:

1. the porosity, meaning air fills the cavities. Can you really talk about open structures and say they're really light? Make an aluminum balloon filled with air and it's probably lighter than air as well.

2. the buoyancy, meaning that the fibers displace air. If a light material is weighed in air, the result does not give the mass of the object.

With normal solids, this does not matter since they are heavy compared to air.

For example, you can weigh wood with a volume of 1 liter in normal air pressure, and get a mass result of 0.500 kg. Then weigh it in a vacuum, you should get a 1 gram difference (air density is about 1 gram per liter) - a weight of 0.499 kg. In practice this is in the noise for normal materials.

Cloced cell extruded foam is about 30 kg per cubic meter. So here the air mass 1 kg per cubic meter already has a 3% effect. I don't know if the weights are usually quoted with buoyancy or not. But this is closed cell, I don't know how well it stands up to a vacuum.

One example of structures that can have a lot of mass but little weight is inflated ones. There have been some human powered aircraft that are really big but light on the scale. Yet they take a lot of time and energy to accelerate since all the air mass inside must be brought up to speed.

Imagine having a landfill of this stuff, blanketing the Earth at 10,000 feet.

Hmmm. :|

Sort of like we have now with satellites + the ISS, which has to move occasionally to avoid the pieces of junk we can track?

How about flying cars?

I've always thought a great idea for a flying car was a van-like vehicle that is either filled with helium or a vacuum, maybe a combination.

A blimp-like vehicle that won't deflate or leak would be even better since it won't need lift to stay up and wouldn't require much power to propel.

That's the point! We don't need materials that are lighter than Helium. We we need nano-materials that are strong enough to keep the vacuum in. Thanks ...

Then suck in air for ballast, it may be similar to ocean going vessels they float when idle but need power or wind for propulsion plus ballast to stabilize.

I'm not too sure if I interpret these right, but wouldn't this material be tailor-made for a weightless sail that can compress itself 20 times?

Wouldn't this be a revolution for boats, lifebuoys or seaplanes?

Also, wouldn't this allow human-size people to carry around weightless wings on their back that expand 20 times from 50cm to 10 meters in span, letting them fly like birds?

Edit: I know these ideas have no scientific basis. I'm just surprised that the only mentioned applications of this material are lithium batteries, waterproof clothing and the likes. Surely there would be a lot of things to create out of an essentially weightless solid.

Cover this new stuff with a balloon and then fill it with helium. Is there any difference to a balloon filled with helium?

I suppose it could keep its shape, which would be a benefit.

When the shape doesn't change there is less wear and tear and tension on the "skin". It could be made of a light, inflexible but strong material, because the shape of "Beyond Helium" unlike with a balloon would not continuously change due to altitude and weather.

> You might ask yourself, how are you going to come back down to earth if you cannot release some of the hydrogen/helium?

So if the aircraft loses power, or loses its hydraulics, the failure results in the aircraft getting stuck in the air? I can see that being promoted as a feature.

On airships of old, this was actually a potential problem as well. They tried to avoid venting lifting gas whenever possible and investigated several techniques to avoid it as much as possible.

Extracting water from the air or weather to use as ballast as your airship becomes lighter and lighter (by consuming fuel for instance) is a particularly clever idea I think.

http://en.wikipedia.org/wiki/Buoyancy_compensator_(aviation)

Great, so airlines have no incentive to get me down and I can wait an age before the flight, after the flight, and now during the flight. Don't give them any reasons to make air transport slower, please.

I've wondered if we could fill a sealed ballon with thin wires. Then put a large electric charge on all the wires so they repel each other and expand the balloon with vacuum.

Why do you guys think?

Actually, I would be more excited about it replacing the non-biodegradable styrofoam. Since it's a simple carbon composite it should be more environmental friendly, no?

What about the effect of 15nm carbon fibres entering your lungs? Are we setting ourselves up for another asbestos-like scenario? Or is this stuff somehow safer?

seems to me like a good styrofoam alternative/competitor, but for floating like properties, it to have vacuums in the tubes right? That is certainly the difficult problem to make this truly be better than helium for some applications. On the other hand, maybe with the structure each small tube is under or is a vacuum.

Idea: how about super-heated air in a balloon lined with aerogels to act as an insulator.

Air at 1000f is a third as dense as air at 200f.

How did this get voted up this high? What? WHAT?

Aerographite is NOT lighter than air. What they mean is that a vacuum-filled cubic cm of aerographite is lighter than a cubic cm of air.

A piece of that material will NOT float up on its own, because it's heavier than air.

Right. Its density that matters, not weight. And as the top posting says, the ability to withstand atmospheric pressure. Since this aerographite stuff actually compresses 20X quite willingly, its useless for balloons etc. because pumping out the air would result in the envelope collapsing.

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