## Dropping a Cloud Nine From Orbit

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Kyorinrin
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### Dropping a Cloud Nine From Orbit

I was pondering the construction of a "Cloud Nine" habitat And building it on the ground is pretty much a no go, then i thought it might work if you built it under water to support the frame until you can get it under tension, but the corrosion and depths kind of put that out as well.

So my thought became the following.

using an asteroid for raw material could you build the cloud nine framework in orbit, then slowly deorbit it without breaking up on reentry?

I was mainly thinking of it in story terms as,

In my mind i was thinking of the cloud nine as the bottom most portion of a very short tether system (tether up to the city which serves as the launchpad for rockets) rather than a residential area.

Or as a sort of Mobile Infrastructure facility that you could lower onto a new planet (like venus), Jupiter, story planet x, making an intermediary home for colonists where they can adjust before transitioning to the surface.

I'm not sure on how to figure out the mechanics of deorbiting mile+ diameter hollow spheres

Sandor
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### Re: Dropping a Cloud Nine From Orbit

I'd never heard of a "Cloud Nine" before. Interesting idea. For those that can't be bothered to follow the link, it's "the name Buckminster Fuller gave to his proposed airborne habitats created from giant geodesic spheres, which might be made to levitate by slightly heating the air inside above the ambient temperature", where "giant" means in the order of a mile diameter, and "slightly" means a degree or so.

I don't now if such a structure could in fact support itself. Pretty much all the lifting in force on a balloon is on the top surface, so you might need internal cables to support the bottom and sides.

Getting such a structure (a mile wide and lighter than air) out of orbit would be a big challenge. It's going to have to enter the atmosphere at walking speed so it doesn't rip itself apart, which means you have to get it down form orbital velocity to basically zero in space, then lower it. You will need to keep the point loading down, for example by attaching lots and lots of very big rockets all over the structure. Not impossible, but pretty infeasible.

It's not obvious to me you can't build one on the ground. You can heat the air inside much hotter than it would have in normal operation, you don't have to fill out the lattice at the start (e.g. start with every 4th strut), and you can include temporary internal supports. This allows you to start with a lighter structure, and with more lift plus extra support. It might be enough to allow you to build one on the ground.

I think building one in water could be done, but getting it out of the water is going to present similar difficulties to building one on land. Imagine (for example) one three-quarters in the water, and a quarter out of the water. The quarter out of the water has exactly the same support problems as a quarter build dome on dry land would have.

One thing to bear in mind is that the major force that has to be resisted in mega-skyscrapers isn't gravity, but wind loading. If your Cloud Nine is tethered, its going to need a lot of well anchored tethers. It might have to be free floating, in which case I don't have any idea what kind of wind forces will be acting on it.

I made all this up, so some/most of it is probably wrong:)

p1t1o
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### Re: Dropping a Cloud Nine From Orbit

There is no "slowly down from orbit" without tremendous expenditure of energy, no matter how you want to do it.

Can you not build it on land in such a way that you start with the uppermost part and seal it against the ground, then build it up from the edges, see what I'm getting at? So that at each partially built stage (for example, halfway through, it would resemble a hemisphere, with construction occurring at the "equator"), it is sealed and supported at the edges against the ground. In this way it can be supported with warm air and tension in the same way as a full sphere as you build it.

lorb
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### Re: Dropping a Cloud Nine From Orbit

I'd also vote for assemble on ground. As an alternative, maybe it can be assembled in situ? We already have balloons and zeppelins. We can make bigger and better versions of them and use them to lift the pieces of the cloud nine into the air where they are to be assembled. Once you are done with the first one you can use it to aid in the construction of further/bigger objects by making the air inside even a little warmer and having the construction take place hanging from it.
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### Re: Dropping a Cloud Nine From Orbit

Could you build much smaller versions of it, float them to the necessary altitudes, link them together and build your full-size structure around them, incorporating them as you go?
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Neil_Boekend
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### Re: Dropping a Cloud Nine From Orbit

lorb wrote:I'd also vote for assemble on ground. As an alternative, maybe it can be assembled in situ? We already have balloons and zeppelins. We can make bigger and better versions of them and use them to lift the pieces of the cloud nine into the air where they are to be assembled. Once you are done with the first one you can use it to aid in the construction of further/bigger objects by making the air inside even a little warmer and having the construction take place hanging from it.

One of the limits is building the beginning big enough to be supported by the air it encloses without having to heat the air in it to a temperature that damages the structure.
What may be feasible is building the early beginning hanging from lots and lots of balloons. Once it gets big enough to lift the section by heating the air under it you add that lifting method. As you increase it's size the balloons become less and less important.
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jewish_scientist
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### Re: Dropping a Cloud Nine From Orbit

Maybe instead of building it underwater, you could build it from the bottom up at the water's surface. The idea is *mumble mumble* buoyancy force *mumble mumble*. Also, you should build it in a lake because salt water is VERY corrosive and lakes do not have a current.

The other REALLY big problem is how much energy is required to heat that much air by 1oF*. Using hyperphysics and wolframalpha I got an energy requirement of 7.974 * 1015 joules**.

** http://hyperphysics.phy-astr.gsu.edu/hb ... /spht.html
http://www.wolframalpha.com/input/?i=%2 ... 8879+miles^3+of+air%29+*%28+21+degrees+celcius+-+20+degrees+celcius%29[/url]
http://www.wolframalpha.com/input/?i=20 ... fahrenheit
http://www.wolframalpha.com/input/?i=vo ... ile+sphere
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ijuin
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### Re: Dropping a Cloud Nine From Orbit

Ouch. If you have that figure right, then it's equivalent to the energy output of a 1.5 MEGATON nuke, or the total sunlight on a square kilometer of land for three whole YEARS.

Hmm, something seems off here, because the air in the sphere described should only mass six or seven million metric tonnes per cubic mile. Even allowing its specific heat capacity to be as high as that for water (air has lower heat capacity than water), I only get a heat requirement on the order of 2 * 10^12 Joules per cubic mile per degree Farenheit (within a factor of two).

p1t1o
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### Re: Dropping a Cloud Nine From Orbit

jewish_scientist wrote:
The other REALLY big problem is how much energy is required to heat that much air by 1oF*. Using hyperphysics and wolframalpha I got an energy requirement of 7.974 * 1015 joules**.

Unless you want to get it done all at once in a few seconds, heating it shouldn't be that difficult. 10^16J only requires the output of a 1GW power station for 3-4 months, since we are talking of building a miles-wide floating city here, thats not all that much to ask for.

Interesting thought, 1GW is roughly the body heat output of around 10 million people, i doubt that would be a good way of getting it up to temperature, and you might not be able to get 10M folks inside (or could you? What exactly *is* supposed to be inside?), but that combined with the heat waste from all of the other internal infrastructure might be enough to keep it aloft indefinitely without having to worry about further heating it.

DanD
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### Re: Dropping a Cloud Nine From Orbit

ijuin wrote:Ouch. If you have that figure right, then it's equivalent to the energy output of a 1.5 MEGATON nuke, or the total sunlight on a square kilometer of land for three whole YEARS.

Hmm, something seems off here, because the air in the sphere described should only mass six or seven million metric tonnes per cubic mile. Even allowing its specific heat capacity to be as high as that for water (air has lower heat capacity than water), I only get a heat requirement on the order of 2 * 10^12 Joules per cubic mile per degree Farenheit (within a factor of two).

But what is it in in terms of the sun's output over a diametral mile? Remember, that the concept is essentially a giant greenhouse. You leave the top clear and paint the bottom black, and it will warm up on it's own, no active heating required.

And given that, I do suspect his numbers are high, because the sun can very obviously warm air more than a degree or two over a given volume of air. (Case in point, the inside of a car on a cool, sunny day).

ETA: and yes, I know the cube/square thing works against us in terms of volume of air to be heated versus sunlight intercepted, but I don't believe it's that much. And the volume to surface area ratio for heat loss through the skin is in our favor, so meh.

EATA: This is not original to me. The assumption that these structures could be self sustaining in flight due to solar heating is part of the original concept, or developed early on, not sure which. And things like cooling overnight don't matter, as long as the net cooling of the sphere is less than the cooling of the atmosphere around it.

ijuin
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### Re: Dropping a Cloud Nine From Orbit

The specific heat capacity of air is about one joule per gram per Kelvin. It may be that JS had kilojoules instead, given that the figure seems to be off by about a factor of a thousand--either that or the density was miscalculated.

DanD
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### Re: Dropping a Cloud Nine From Orbit

jewish_scientist wrote:Maybe instead of building it underwater, you could build it from the bottom up at the water's surface. The idea is *mumble mumble* buoyancy force *mumble mumble*. Also, you should build it in a lake because salt water is VERY corrosive and lakes do not have a current.

Finding a big enough lake would be a problem though. The great lakes are only 1,300 feet deep at the deepest. Lake Baikal or Lake Tanganyika are deep enough, admittedly.

And of course, once you get past the midpoint, it's mostly self supporting. Although if it came to rest on the bottom of a lake at that point, adhesion with mud can be surprisingly strong.

On the same note, there are a couple of pit mines that get deep enough to go halfway up.

PM 2Ring
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### Re: Dropping a Cloud Nine From Orbit

Maybe I'm missing something here, but I don't see what the big problem is with just constructing the dome on the ground.

Of course, it's not going to support its own weight when it's partly built, but why does it need to do that? It's a tensegrity structure, so you just build it flat, with plenty of slack in the cables. As individual sections of the structure are completed you can partly tighten them, and when everything's connected you bring the whole structure up to full tension so that the structure pops up into its dome configuration. Sure, you may need to man-handle the struts to prevent stuff getting tangled, but that shouldn't be too difficult if you're careful.

But I Am Not An Engineer, so please feel free to point out my naive misconceptions.

jewish_scientist
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### Re: Dropping a Cloud Nine From Orbit

I had a lot of problems working with Wolfram Alpha, but I went over my calculations and found a few mistakes. If X temperature / temperature difference is X unit-less, than my new calculation is 780 MWh. This is equal to the amount of electricity used by 65 US households annually. That is pretty reasonable.
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ijuin
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### Re: Dropping a Cloud Nine From Orbit

That sounds about right. The energy should be on the order of terajoules, not petajoules.

gmalivuk
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### Re: Dropping a Cloud Nine From Orbit

Wolfram|Alpha treated (21ºC - 20ºC) as 1ºC = 274.15K (a specific temperature rather than a temperature difference).

If you just type "(specific heat of air) * (mass of 4.18879 miles^3 of air)", it gives a result of 1.598e13 J/K, which is just 1.598e13 J for the 1K change you're considering. Which is 4440MWh

What other mistake did you make, jewish_scientist, to change that to 780MWh?
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ijuin
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### Re: Dropping a Cloud Nine From Orbit

For starters, the temperature difference was (IIRC) one degree Farenheit, not Kelvin.

jewish_scientist
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### Re: Dropping a Cloud Nine From Orbit

My mistake that I think was the most significant is that I accidentally used the volume of a sphere with a radius of 1 mile, instead of diameter of 1 mile. Another mistake was that Wolfram Alpha could not do all the calculations at once, so I needed to do the calculation in 1 tab and then copy that information over to a second. The last mistake was the one ijuin pointed out; I calculated it in Celsius, then gave the answer in Fahrenheit and forgot to convert it first.
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gmalivuk
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### Re: Dropping a Cloud Nine From Orbit

Then I think there's something else wrong with your calculation.

One mile diameter is 1/8 the volume of one mile radius, and one degree Fahrenheit is 5/9 K, so your new result shluld be a bit less than 1/14 as much as mine, rather than a bit more than 1/6 as much.
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jewish_scientist
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### Re: Dropping a Cloud Nine From Orbit

PM 2Ring wrote:Maybe I'm missing something here, but I don't see what the big problem is with just constructing the dome on the ground.

Of course, it's not going to support its own weight when it's partly built, but why does it need to do that? It's a tensegrity structure, so you just build it flat, with plenty of slack in the cables. As individual sections of the structure are completed you can partly tighten them, and when everything's connected you bring the whole structure up to full tension so that the structure pops up into its dome configuration. Sure, you may need to man-handle the struts to prevent stuff getting tangled, but that shouldn't be too difficult if you're careful.

But I Am Not An Engineer, so please feel free to point out my naive misconceptions.

The problem with this idea is the same one talked about in this What-If: Sure, the math says it should work, but we all know that it won't. Also, tensegrity structures are like arches in that they immediately fail when all outside support is removed and the structure is not finished yet.
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Kyorinrin
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### Re: Dropping a Cloud Nine From Orbit

I guess the best option is (damn it) tethers.

I suppose if you had a geosynchronous counterweight you could lower the completed structure at a slow enough pace, but at that point why would you. (Unless youre dropping facilities onto a gas giant or other "hostile surface / survivable cloud layer situation)

Tyndmyr
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### Re: Dropping a Cloud Nine From Orbit

jewish_scientist wrote:The problem with this idea is the same one talked about in this What-If: Sure, the math says it should work, but we all know that it won't. Also, tensegrity structures are like arches in that they immediately fail when all outside support is removed and the structure is not finished yet.

Essentially, both are engineering problems. Using cheap hobby rockets en masse may work under an idealized, theoretical issue that discounts timing, failures, etc, but once you start factoring those elements in, the issues become here.

Likewise, you could, probably, do tensegrity megastructures, but a failure in one cable is going to overstress ajoining cables, and a cascading failure is totally possible. Given ludicrous size, forces, and the vagrancies of the atmosphere, plus the practical construction difficulties, I can totally envision a cable being damaged and popping at an unfortunate time. It's cool, but Fuller tended to dream bigger than was practical. And *really* liked tensegrity stuff.

Doing it flat and then cinching up the cables in a slow inflation process is probably *most* practical, but anytime you start using dimensions in miles, things start getting expensive and difficult.

ijuin
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### Re: Dropping a Cloud Nine From Orbit

In that case, perhaps we can scale it down a bit. What is the smallest that such a structure can be and still generate adequate lift with the expected temperature differential?

Tyndmyr
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### Re: Dropping a Cloud Nine From Orbit

Well, strictly speaking, a hot hair balloon is working off similar principles. Exact minimum will depend on details, like heat differential and material, but...you can get fairly small and still have a viable hot-air lifting mechanism.

DanD
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### Re: Dropping a Cloud Nine From Orbit

Tyndmyr wrote:Well, strictly speaking, a hot hair balloon is working off similar principles. Exact minimum will depend on details, like heat differential and material, but...you can get fairly small and still have a viable hot-air lifting mechanism.

It's not so much hot air, as passive hot air, combined with livable conditions inside the hot air chamber. A lot depends on what you're placing inside. If it's your helium storage tank, no problem. If it's a company of M1 tanks, you're going to need to be a bit bigger.

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### Re: Dropping a Cloud Nine From Orbit

Rather than trying to heat it up to increase buoyancy what about reducing the oxygen content and increasing the nitrogen content to use it as a lifting gas? Sea level oxygen is about 21% of air but at higher altitudes which we can condition for it's only 12% or so. It's unclear to what would be more difficult - creating the energy to heat the air or creating a higher nitrogen lower oxygen mix. I would assume it would be easier to contain the lifting gas then insulate the energy which would bleed out of the structure but I really don't know much about the engineering challenges each task would face. In addition nitrogen might also reduce the need for mechanical circulation within the sphere to keep the temperature relatively uniform throughout.
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ijuin
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### Re: Dropping a Cloud Nine From Orbit

Doing it that way would reduce the altitude at which you could fly the structure, since its internal pressure will drop with higher altitude in order to maintain bouyancy. Also, if you are going to maintain a gas mix different from the exterior, then you may as well just go whole hog and have a gasbag of some lightweight gas such as hydrogen, helium, or methane.

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### Re: Dropping a Cloud Nine From Orbit

Cleverbeans wrote:Rather than trying to heat it up to increase buoyancy what about reducing the oxygen content and increasing the nitrogen content to use it as a lifting gas? Sea level oxygen is about 21% of air but at higher altitudes which we can condition for it's only 12% or so. It's unclear to what would be more difficult - creating the energy to heat the air or creating a higher nitrogen lower oxygen mix. I would assume it would be easier to contain the lifting gas then insulate the energy which would bleed out of the structure but I really don't know much about the engineering challenges each task would face. In addition nitrogen might also reduce the need for mechanical circulation within the sphere to keep the temperature relatively uniform throughout.

I think the idea is that it would be large enough to contain a community of a size sufficient that its own waste heat would be enough to provide the heat required.
That and the difference in density between nitrogen and air is quite small, even 100% nitrogen is only going to be a few percent less dense than air. And having oxygen present has its uses...

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### Re: Dropping a Cloud Nine From Orbit

If you're going to play with the gas mixture to create lift I'd replace a part of the nitrogen with helium. Helium is extensively used as a breathing gas in diving so I'd hazard a guess that it's relatively safe (actual expertise and more testing required, of course).
AFAIK you wouldn't need much. Your voice would change to a similar degree as heating the air would, because the pitch changed is a result of the density and a couple of degrees of increased air temperature doesn't really increase the pitch of your voice very much.
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### Re: Dropping a Cloud Nine From Orbit

Neil_Boekend wrote:Helium is extensively used as a breathing gas in diving so I'd hazard a guess that it's relatively safe (actual expertise and more testing required, of course).

I believe there is a helium shortage so I discounted the possibility.
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Neil_Boekend
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### Re: Dropping a Cloud Nine From Orbit

Those reports are highly overblown. Helium is the element that is being produced the most naturally. It's Alpha radiation that has found a couple of electrons.
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### Re: Dropping a Cloud Nine From Orbit

Yeah, and we don't actually generate all that much of it. Stick some alpha-shedding nuclear rods in a gasproof chamber and you'll get helium, sure, but *very* slowly. And most of what is generated naturally leaks into the atmosphere, and from there to space as it's too light to be held onto.

I don't recall who said it (someone was clueful about this stuff), but if helium were priced in a free market, a single helium party balloon would cost \$100. Instead we massively control the market and keep prices super-low for some reason.
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### Re: Dropping a Cloud Nine From Orbit

/goes off to work out a better method of alphageneic nucleosynthesis, thenceforth to float my business on the stock exchange and at twenty-thousand feet...

Tyndmyr
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### Re: Dropping a Cloud Nine From Orbit

Xanthir wrote:I don't recall who said it (someone was clueful about this stuff), but if helium were priced in a free market, a single helium party balloon would cost \$100. Instead we massively control the market and keep prices super-low for some reason.

Because we used to have a Strategic Helium Reserve, and then we decided to sell that off, which was sufficiently huge to skew the shit out of the market, so they tried to compensate with MORE price controls, and...yeah, it's a shitshow.

It definitely wouldn't cost \$100 for a party balloon, though. Commercial production does happen, and while it's naturally kind of chained to the auction prices in what they can ask, it's still apparently profitable at the market price of roughly \$84 bucks for a thousand cubic feet.

Once the reserve auctions end, probably some volatility, but eventually it'll stabilize at some level where it makes sense to manufacture more.

ijuin
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### Re: Dropping a Cloud Nine From Orbit

Practically speaking, if helium becomes too expensive, then people will use hydrogen in flame-retardant sacs. The reason for the notorious hydrogen airship fires (e.g. Hindenberg) was because their hydrogen bags and outer skin were made of flammable material, which allowed a spark on the outside to burn through to reach the hydrogen.

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### Re: Dropping a Cloud Nine From Orbit

ijuin wrote:Practically speaking, if helium becomes too expensive, then people will use hydrogen in flame-retardant sacs. The reason for the notorious hydrogen airship fires (e.g. Hindenberg) was because their hydrogen bags and outer skin were made of flammable material, which allowed a spark on the outside to burn through to reach the hydrogen.

The problems is that for certain uses, hydrogen isn't appropriate. About 32% of annual use is for cryogenic uses, mostly cooling NMR spectrometers and MRI scanners. The non-reactive nature of helium is critical for this.

ijuin
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### Re: Dropping a Cloud Nine From Orbit

Yes, but in the context of the current conversation, I was speaking of the use of Hydrogen and Helium as bouyant lifting gases, for which purpose Hydrogen can indeed substitute readily for Helium, provided that appropriate fire-prevention practices are observed.

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### Re: Dropping a Cloud Nine From Orbit

You can also blend the gasses together to get some of the advantages/disadvantages of each. Not sure how efficiently they'd remain blended in balloon of this size, because offhand, not sure how strong the air movement, etc would be in a such a colony, but if we're talking about party balloons, individual balloons of hydrogen aren't all *that* bad. But people have balloons in clusters sometimes, and accidentally lighting them off could maybe be bad.

Even a 50/50 mix should get you significant savings(presuming a world where helium is significantly more expensive than hydrogen), and fairly minor risk from flammability, though.

I'd imagine that companies eager to make a buck will quickly explore such options if it becomes profitable to do so.

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### Re: Dropping a Cloud Nine From Orbit

Hydrogen is in some shielding gasses in welding. If you have the percentages right it's safe.
Under 5% it's not flammable in STP air.
But, it will collect in the top of the cloud unless the air in the cloud is mixed well. In the top is the most dangerous place for a hydrogen explosion too: a large hole there drops the entire cloud.
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