up up and away in a: balloon!

[forufes]

you want an object to reach as high as possible in the atmosphere, if it reaches space, even better...

 

how can you do that while attaching it to a balloon?

 

this includes a lot of physics and design, maybe even chemistry, but a LOT of innovation..i have some ideas, but wanna hear yours first.

[Klaynos]

Use a big light weight balloon full of a very low density gas. The lighter the balloon, the bigger the balloon, the lower the density of gas the higher it'll go...

[forufes]

alright, so you propose a balloon made of (insert suitable lightweight material), full of (hydrogen i guess)..right?

 

.....

 

i think you rounded it up nicely..you mentioned the general concepts and how to use them..

 

the engineering part is to USE them..

 

what is the lowest density "gas" we can fill it up with? does it have to be a gas? why not vacuum? or gas in a density lower than its normal one?

 

how can you minimize the balloon's body weight? what material will you use and how?

 

how big can you actually make the balloon? a football field? bigger?

 

how will the balloon deal with the change of density of the surrounding air? make it's material expand?

 

what shape do you think will reduce air resistance the most?

 

you have to give the specifics, because only then will you really deal with how they all relate to each other. and that is the tricky interesting part, the one i'm asking you to give.

 

lets also remember that this balloon's goal is to make an object reach as high as possible, method of fulfilling the goal has to consist of a balloon, but is not limited to it. you can add as much other things or mechanisms as you want..

 

well, any other ideas?

[Sisyphus]

Hydrogen would be the lightest gas. Vacuum, obviously, is lighter, but comes with lots of problems. A gas like hydrogen exerts pressure, supporting the structure of the balloon. Something "filled" with vacuum wouldn't be a "balloon," since it would have to be rigid enough to support its own structure against the outside air pressure. This would be a lot harder to build and, presumably, heavier.

 

As for minimizing weight, that's not really the issue so much as the ratio of overall weight to overall volume, i.e. density. The same shape scaled up has a bigger ratio of volume to surface area (it goes up by the 3/2th power). Since it's the internal volume, filled with hydrogen, that's going to be the lightest, and the surface (the balloon itself) where most of the weight is, you'll decrease density by increasing overall size.

 

I don't see any obvious limits to how big you can make it.

 

Air resistance shouldn't matter at all.

[Klaynos]

Expansion is an issue, the first helium ballon burst due to expansion of the gas in it.

 

Have a look around wikipedia....

 

http://en.wikipedia.org/wiki/QinetiQ_1

 

Their balloon was 381m in height.

[forufes]

Hydrogen would be the lightest gas. Vacuum, obviously, is lighter, but comes with lots of problems. A gas like hydrogen exerts pressure, supporting the structure of the balloon. Something "filled" with vacuum wouldn't be a "balloon," since it would have to be rigid enough to support its own structure against the outside air pressure. This would be a lot harder to build and, presumably, heavier.

right, so that begs the question; will the increase in weight due to altering the balloon structure to support itself when "filled" with vacuum be compensated by vacuum's higher lift value?

 

meaning, which will be lighter, a rigid vacuum balloon or a simple hydrogen filled one?

 

by what fraction is vacuum lighter than hydrogen?

 

and besides, can't you have semi-vacuume, or gas in a pressure lower than the outside one? that would give some support, but won't be as light as total vacuum.

 

As for minimizing weight, that's not really the issue so much as the ratio of overall weight to overall volume, i.e. density. The same shape scaled up has a bigger ratio of volume to surface area (it goes up by the 3/2th power). Since it's the internal volume, filled with hydrogen, that's going to be the lightest, and the surface (the balloon itself) where most of the weight is, you'll decrease density by increasing overall size.

density of volume to surface area or weight to volume?

 

can you give me the formula used for this?

 

 

I don't see any obvious limits to how big you can make it.

great, one less thing to worry about.

 

 

 

Expansion is an issue, the first helium ballon burst due to expansion of the gas in it.

 

Have a look around wikipedia....

 

http://en.wikipedia.org/wiki/QinetiQ_1

 

Their balloon was 381m in height.

the link is interesting, but it says

At around 6.55am with the balloon inflated to a height of 15 metres, helium began to escape from the envelope. An irreparable tear was discovered along one of the seams of the balloon and all efforts for a flight in 2003 were abandoned

[Sisyphus]

right, so that begs the question; will the increase in weight due to altering the balloon structure to support itself when "filled" with vacuum be compensated by vacuum's higher lift value?

 

meaning, which will be lighter, a rigid vacuum balloon or a simple hydrogen filled one?

 

A way to rephrase this question is, do you want to support the balloon against outside pressure with hydrogen gas, or with solid structures? The upper atmosphere is going to be orders of magnitude less dense than any solid, but it can't be less dense than hydrogen gas which is allowed to expand.

 

by what fraction is vacuum lighter than hydrogen?

 

Infinity. Vacuum, by definition, has zero mass. (Although true vacuum isn't going to be attainable.) However, what matters is the total mass of the balloon.

 

and besides, can't you have semi-vacuume, or gas in a pressure lower than the outside one? that would give some support, but won't be as light as total vacuum.

 

Yes, but it's the same question as above. I can't answer for certain without doing a lot of engineering calculations, but it's almost certainly better with just gas.

 

density of volume to surface area or weight to volume?

 

can you give me the formula used for this?

 

Density = mass/volume

 

All of your mass that's heavier than the outside atmosphere is going to be on the surface, the solid balloon itself. Therefore, by increasing the ratio of total volume to surface area, you are decreasing the ratio of mass to volume.

 

Surface area increases with by the square of the length. Volume, however, increases with the cube of the length. Therefore, when increasing the overall size of your balloon, the volume increases faster than the surface area, and the density decreases.

 

All of this, of course, is disregarding any additional structure or thickness you might need to hold together a larger balloon.

[J.C.MacSwell]

OK we get the balloon and Hydrogen up there; how much oxygen is available from the rarified air to burn the hydrogen and propel us further?

[SH3RL0CK]

The bigger problem, IMO, would be how to transfer the hydrogen from the balloon to a tank so it can be compressed for a jet or rocket nozzle without falling to the ground first.

 

You can't just suck it out of the balloon as you go because the balloon will distort such that it is in the jet exhaust and/or becomes a very large drag at any meaningful speed.

 

Of course, since the balloon can be an arbitrary size, just hoist up the fueled rocket with a really big balloon.

[forufes]

A way to rephrase this question is, do you want to support the balloon against outside pressure with hydrogen gas, or with solid structures?

 

exactly. so which would generate more thrust (buoyancy). it seems as you mention afterwards:

 

I can't answer for certain without doing a lot of engineering calculations, but it's almost certainly better with just gas.

and yes, it needs a lot of calculations to determine which is better, filling it with gas is easy to evaluate, but vacuum would depend on the exact method you use to support it. so maybe gas is just better

The upper atmosphere is going to be orders of magnitude less dense than any solid, but it can't be less dense than hydrogen gas which is allowed to expand.

so, what would the pressure of the hydrogen inside the balloon be?

or are you saying to hae the balloon expand so the hydrogen inside changes with the one outside?

 

 

 

Infinity. Vacuum, by definition, has zero mass. (Although true vacuum isn't going to be attainable.) However, what matters is the total mass of the balloon.

 

THAT'S WHAT I THOUGHT!!

 

i thought, then the balloon filled with vacuum should have a thrust infinite times that of a hydrogen balloon..

 

then you said true vacuum isn't attainable, then the fact of density..

 

so i'm wrong, it won't work?

 

 

All of your mass that's heavier than the outside atmosphere is going to be on the surface, the solid balloon itself. Therefore, by increasing the ratio of total volume to surface area, you are decreasing the ratio of mass to volume.

 

Surface area increases with by the square of the length. Volume, however, increases with the cube of the length. Therefore, when increasing the overall size of your balloon, the volume increases faster than the surface area, and the density decreases.

 

All of this, of course, is disregarding any additional structure or thickness you might need to hold together a larger balloon.

 

aaaagh, you're a geniuse, i literally felt tha being absorbed by my brain..

 

i'm talking about the relation of surface area to mass density, and i just relized that this is what seemed useless and impractical when we studied it..: A LAMINA!

 

i'll take note of this relation, thanks a lot.

 

OK we get the balloon and Hydrogen up there; how much oxygen is available from the rarified air to burn the hydrogen and propel us further?

WOW, i was thinking of that too..

The bigger problem, IMO, would be how to transfer the hydrogen from the balloon to a tank so it can be compressed for a jet or rocket nozzle without falling to the ground first.

 

the answer IMO is: QUICKLY!

 

i was looking for ways to liquidize the hydrogen before the balloon starts gaining relevant speed downwards..

 

if not liquidize, then any other chemical reaction, or chain of reactions, with chemicals of small size taken overboard, which result in the hydrogen usable as fuel..it doesn't have to be pure, it an be a compound with something else, as long as it burns or expands or can be used to go UP.

You can't just suck it out of the balloon as you go because the balloon will distort such that it is in the jet exhaust and/or becomes a very large drag at any meaningful speed.

that's why i was thinking of using the hydrogen as fuel when the balloon floats in the atmosphere.

 

the balloon will keep going up because of the lower density inside compared to outside. the atmosphere density decreases as we go up, so the balloon will reach a point where the two densities are equal, and reach a stop. there i propose we start the mechanism of using the hydrogen for fuel.

 

um people, an important question:

so the balloon will reach a point where the two densities are equal,

 

how high will that be? and how far is it from "space"?

 

Of course, since the balloon can be an arbitrary size, just hoist up the fueled rocket with a really big balloon.

AND blow up the balloon in a HUGE fireball to give the rocket a head start..what do you say?

[Sisyphus]

so, what would the pressure of the hydrogen inside the balloon be?

or are you saying to hae the balloon expand so the hydrogen inside changes with the one outside?

 

If it was limitlessly stretchy, the pressure outside and inside would always be equal, and that same quantity of gas would expand into a larger and larger volume the higher up (and the lower pressure) you go. It isn't limitlessly stretchy, so the there's a minimum pressure the same inside gas can have. So, at lower atmospheric pressures, you need less gas to maintain the full volume, which will decrease the total weight, so venting some at high altitude will give you slightly more buoyancy.

 

 

THAT'S WHAT I THOUGHT!!

 

i thought, then the balloon filled with vacuum should have a thrust infinite times that of a hydrogen balloon..

 

then you said true vacuum isn't attainable, then the fact of density..

 

so i'm wrong, it won't work?

 

There is no thrust, it's just buoyancy. Buoyancy is going to be proportional to the difference in mass between the object and an equivalent volume of the fluid surrounding it, in this case, air. Not the ratio between the masses. Regular air is about 14 times as dense as hydrogen gas. So, an enclosed unit volume of hydrogen gas has 14-1=13 buoyancy in air, and an enclosed unit volume of vacuum of has 14-0=14 buoyancy in air. So, not a big difference. And the added structure to contain a volume of vacuum has to weigh less than the difference to be worth it.

 

aaaagh, you're a geniuse, i literally felt tha being absorbed by my brain..

 

i'm talking about the relation of surface area to mass density, and i just relized that this is what seemed useless and impractical when we studied it..: A LAMINA!

 

i'll take note of this relation, thanks a lot.

 

You're welcome. About time I get some actual respect around here.