lemur

Hi Riya,

Welcome. I guess you're into physics since you post your hello message here.

What purpose would this have?

 

Normally, cargo is at the surface of the earth, and has to go somewhere else on the surface of the earth.

What if it could low enough to receive payloads from conventional jets?

It seems like the problem with mediating between the atmosphere and orbit is that orbit is very fast relative to the atmosphere. So if you could have a series of buoyancy-vehicles at progressive speeds, couldn't they "hand off" payloads in sequence and by doing so accelerate the packages up to the speeds needed to maintain orbit?

the payload would first have to slow down first match speeds with and dock with the balloon. it would also have to go quite deep into the atmosphere. altitude =/= orbit

Could a vacuous sphere "bounce and roll" into the atmosphere without burning up?

which would have to make most of the journey by rocket.

 

the big problem with launches is the velocity not the altitude

Isn't the velocity needed dependent on gravity, which is dependent on altitude? Also, what about air pressure/density? Doesn't that make a different in drag?

That is at sea level.

What would happen if you build a vacuum sphere in outer space and sink it in the atmosphere? Would it float?*

 

Constructing a vacuum sphere at sea level looks like constructing a boat in the abyss.

 

* if it does I'll keep the Copyright.

That's a good idea to start from space and work down instead of working from sea-level up. Maybe such vehicles could be used to lower payloads slowly into the atmosphere to avoid re-entry friction and then carry some air up on their way back to space.

I haven't read the whole thread, sorry, but has anyone mentioned economics or general social science?

Free neutrons decay into a proton, electron and anti-neutrino in a half-life of ~15 min. Besides, a single free neutron actually masses more than a hydrogen atom, so hydrogen gas would be less dense and be more buoyant than a free neutron "gas", not to mention the problems of containing such a "gas".

I think the latter would be the major problem. A neutron "gas" would not follow the ideal gas law and tend to leak out of any container.

The only real value I saw in the neutrons was that I assumed they would be non-combustible, unlike hydrogen. I didn't know they decayed. I might have to start a new thread to discuss that. I suppose I'll throw in the discussion about why they don't follow ideal gas laws too. Interesting, thanks for raising these new questions for me.

Moontanman points out the main difficultly in this. When you use a gas, you are equalizing the pressure on the inside and outside, while still having the gas on the inside being of lower density than the outside air. Thus the material from which your container is made does not have to be rigid.

 

If you try to contain a vacuum, you will have a pressure of ~14psi working to crush your container. So let's say that your "balloon" has a 1 foot radius. This gives a surface area of ~1810 in² for a total force of 25334 lbs. This also works out to a volume of 7238 in³. at 20°C, this much dry air weighs about 0.00004 lbs(0.02g). This is the maximum weight that the material of our "vacuum balloon" can have and have even neutral buoyancy.

 

Diamond, for instance, has a density of 3.5g/cm³. A hunk of diamond with a mass of 0.02g would have a volume of 0.006cc. Spread into a shell with a surface area of 1810 in², you get a thickness of 5 nanometers,. This is about 1/40th the thickness of a typical sheet of aluminum foil. Since diamond is 3.6 times harder than aluminum, this hardly seems enough to withstand the 25334 lbs of crushing force exerted by the atmosphere on our balloon.

This may sound naive, but could it be possible to contain and use free neutrons as a lighter than air gas? Of course, I don't know where you can get them except for as a by-product of radioactive decay.

This rings a bell. I think it's been tried before...

 

As I recall, a "vacuum balloon" would be significantly more efficient (in the 7-10% range or so) than a helium or hydrogen balloon, except for the weight penalty incurred by the need for a rigid envelope.

 

Oh, right here on these forums:

http://www.sciencefo...vacuum-balloon/

Good memory. That thread was from @2008 on the posts I checked. I wonder if size somehow makes a difference. It has always baffled me that zeppelins like the Hindenburg appear to have had heavy steel frames and a heavy payload. I suppose that's my subjective impression though, so I should go google it. Thanks for posting the link to the old thread.

Lighter than air ships have been made to float using light gasses such as hydrogen and helium. Hot air balloons reduce the density of air by heating it. I wonder if it would be possible to make an air ship float by emptying the air out of it instead of replacing that air with light gas.