How far would a helium balloon rise if it never burst

[tackyattack]

If you released a balloon filled with helium, how high would it go if it never burst from the pressure change?

 

[Nabeshin]

I figure the balloon would stop rising roughly when the ambient mass density is the same as the density inside the balloon. If the balloon were filled with Helium, mass density of ~0.1g/L. Judging from this graph: http://upload.wikimedia.org/wikipedia/commons/d/de/Atmosphere_model.png , that corresponds to a height ~7-8 km.

 

[Antiphon]

Balloons have gone more than 3 times that height.

In the 50's a man was hoisted 85,000 feet and then jumped out and parachuted back to earth.

 

[chroot]

Well, it would rise, expanding as it goes, until it reachs the same density as an equally-sized parcel of air. The height would depend critically on the material used to construct the ballon. A lightweight balloon would go higher.

edit: When not enclosed by a balloon, helium entirely escapes the Earth's atmosphere and goes into space.

- Warren

 

[Nabeshin]

Balloons have gone more than 3 times that height.

In the 50's a man was hoisted 85,000 feet and then jumped out and parachuted back to earth.

Good point. Clearly there's a little more going on here than my simple calculation!

 

[Gnosis]

Balloons have gone more than 3 times that height.

In the 50's a man was hoisted 85,000 feet and then jumped out and parachuted back to earth.

Actually, helium balloons have far exceeded 85,000 feet, as Joseph Kittinger (USAF) made his record parachute jump from a high altitude helium balloon, the Excelsior III, on August 16, 1960 from an altitude of 102,800 feet (19.47 miles). This was the latter of a series of high altitude parachute jumps that he made from high altitude balloons.

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

Unmanned weather balloons (using helium or hydrogen) typically reach between 60,000 and 120,000 feet.

http://en.wikipedia.org/wiki/High-altitude_balloon

 

[ideasrule]

I figure the balloon would stop rising roughly when the ambient mass density is the same as the density inside the balloon. If the balloon were filled with Helium, mass density of ~0.1g/L. Judging from this graph: http://upload.wikimedia.org/wikipedia/commons/d/de/Atmosphere_model.png , that corresponds to a height ~7-8 km.

That doesn't account for the fact that as pressure decreases, the helium's density also decreases. Also, the higher altitudes are colder, which increases density.

 

[pergradus]

The ultimate deciding factor is the elasticity of the balloon...

As the balloon rises it will expand with decreasing air pressure and become less and less dense. This expansion can't continue forever though, so eventually the balloon can't become any less dense and still stop rising.

However, I'm really not sure what would happen if the balloon could expand forever... I assume it has to stop somewhere, but there's always going to be internal pressure which means the balloon will expand to an infinite radius... Interesting to think about.

 

[Jonathan Scott]

The ultimate deciding factor is the elasticity of the balloon...

As the balloon rises it will expand with decreasing air pressure and become less and less dense. This expansion can't continue forever though, so eventually the balloon can't become any less dense and still stop rising.

However, I'm really not sure what would happen if the balloon could expand forever... I assume it has to stop somewhere, but there's always going to be internal pressure which means the balloon will expand to an infinite radius... Interesting to think about.

"Elasticity" isn't really the right word here. Balloons used for this sort of thing are essentially big bags which initially contain an amount of helium that nowhere near fills them at sea level. The bigger the bag, the higher it can go before it starts to pressurize the helium, but the heavier the bag too.

 

[tackyattack]

Here is why I am asking this:

A couple days ago I thought this to my self, what if I put a string on the outside of the balloon on the radius of the balloon attached to a switch so that when the balloon expands bigger it triggers the button. At the "nozzle" of the balloon I would have a solenoid valve that leads to a big, light, plastic bag. So when the balloon expands the button gets pressed which then opens the solenoid, releasing the gas into the bag. Then when the balloon gets back to its original size it closes the solenoid valve so the gas stops flowing into the bag.
So technically the balloon would never burst and the extra bag keeps the helium so there is still lift. So, how high could the helium balloon go and still have lift?

 

[Jonathan Scott]

Here is why I am asking this:

A couple days ago I thought this to my self, what if I put a string on the outside of the balloon on the radius of the balloon attached to a switch so that when the balloon expands bigger it triggers the button. At the "nozzle" of the balloon I would have a solenoid valve that leads to a big, light, plastic bag. So when the balloon expands the button gets pressed which then opens the solenoid, releasing the gas into the bag. Then when the balloon gets back to its original size it closes the solenoid valve so the gas stops flowing into the bag.
So technically the balloon would never burst and the extra bag keeps the helium so there is still lift. So, how high could the helium balloon go and still have lift?

In that case, you don't need the "balloon", only an unpressurized "bag". That is effectively how high altitude balloons work.

However, even a loose bag will have a finite size, and the bigger that size the heavier it has to be.

A fixed amount of helium will continue to have a lower mass than the amount of air it displaces at the same pressure as one ascends, and in theory would continue to have the same lift if it is allowed to expand and remain at the same pressure as the surrounding air and the molecular composition of the air remained approximately constant. However, the volume will increase enormously with the decreasing pressure, so eventually it would be necessary either to increase the pressure or vent helium, both of which would decrease lift. I presume that the practical limit will depend on the characteristics of the balloon material, as the atmosphere does not have any sharp cut-off.

 

[Redbelly98]

I figure the balloon would stop rising roughly when the ambient mass density is the same as the density inside the balloon. If the balloon were filled with Helium, mass density of ~0.1g/L. Judging from this graph: http://upload.wikimedia.org/wikipedia/commons/d/de/Atmosphere_model.png , that corresponds to a height ~7-8 km.

That graph is difficult to read, since they made the gridline spacings all wrong. Note the factor of 1000 per major gridline, yet the minor gridlines are as if it's 10x between major gridlines.

According to http://www.usatoday.com/weather/wstdatmo.htm", the density of air reaches that of helium (assumed 1/7 of air, so 1.2/7=0.17 kg/m^3) at an altitude of 16 km.

The 16 km figure is is in pretty good agreement of http://www.google.com/#sclient=psy&...1&bav=on.2,or.r_gc.r_pw.&fp=38378e84586d88e6", based on assumptions that (1) helium atoms are about 1/7 the mass of air molecules, and (2) air density decreases roughly 20% for every mile in altitude.

Either way, the reports are of helium balloons rising higher than this. This could be possible if, at high altitudes, they release helium from the balloon. At the lower ambient pressures, the balloon would stay inflated, and the density of helium is reduced still further. This only works as long as you're not planning to return to ground in the balloon.

EDIT:
Moderator's note - thread moved to General Physics from Astrophysics.

 

[rcgldr]

If the balloon had no limit on expansion, it should rise until it nears the exoshpere, which is a mixture of helium and hydrogen, with less density than an object containing pure helium at the same pressure. This is 350km -> 800km above the Earth's surface, and higher than low orbit vehicles, such as the space station, which orbits in the thermosphere (it's ranges from 80km to about 350km, space station orbits at 320 km to 380km).

 

[pallidin]

If the balloon had no limit on expansion, it should rise until it nears the exoshpere, which is a mixture of helium and hydrogen, with less density than an object containing pure helium at the same pressure. This is 350km -> 800km above the Earth's surface, and higher than low orbit vehicles, such as the space station, which orbits in the thermosphere (it's ranges from 80km to about 350km, space station orbits at 320 km to 380km).

Don't forget the weight of the balloon itself, regardless of expansion capabilities.

 

[rcgldr]

Don't forget the weight of the balloon itself, regardless of expansion capabilities.

True, I was assuming an ideal massless balloon, since it's already unrealistic to assume the huge rate of expansion required to hold the helium at extreme altitudes. The other issue is no one would want stationary space debris at the same altitudes as low Earth orbit satellites and space stations. All the stuff launched up in low orbits is done with the plan that eventuallly the small amount of atmoshpere up there will slow them down and cause them to re-enter the denser part of the atmosphere and burn up. In the case of the space station, or the Hubble telescope, they rely on occasional oribital boost from shuttles. I think there are no more planned for the Hubble, so it's destined to get burnt up.