Half a croissant, on a plate, with a sign in front of it saying '50c'
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Internal flame hydrogen balloon

Hydrogen is light. Hot hydrogen is lighter.
  [vote for,

Picture if you will, a standard issue rockoon, climbing its way into the sky. Expanding as the atmosphere thins around it. Eventually expanding to the limits of your (initially crumpled and raisinlike) balloon. But yet there is more atmosphere to be traversed. What to do?

One could shrug, ignite the rockets, fire the cannons and hope for the best. One could burn off hydrogen released from the expanding balloon to generate a puny rocket of sorts - probably not much compared to the bloated balloon it is trying to lift. Plus, all of that heat is wasted as the hot gas shoots from the rocket.

I propose that excess hydrogen be burned inside the balloon. In a controlled fashion, of course. This would be analogous to a low altitude hot air baloon where a jet of hot gas is shot up into a shell to provide lift.

Here, excess hydrogen (excess because of expansion at altitude) would be burned to heat the remainer of the hydrogen within the balloon, making it more buoyant. Burn control would be achieved by limiting the oxygen available. Oxygen could be carried with and released as a function of internal balloon pressure. Or, to save weight, ambient air could be used - producing a less vigorous combustion at high altitude but contaminating the baloon interior with worthless nitrogen.

The hot balloon would be even liftier and could gain more altitude than a cold balloon. Energy from burning lift hydrogen would be put to good use as captured heat. Water produced from the burn would condense on the balloon interior and run the the bottom of the balloon and out a special valve, from which it would trickle gently from the skies onto the gathered families of less talented N-prize competitors.

bungston, Jan 23 2009

Big band to outer space Big_20Bang_20to_20Outer_20Space
My inspiration. This one blows up real good. Real good! [bungston, Jan 23 2009]


       I think the advantages are small, but I'm bunning for "liftier". You'd have to carry a good bit of O2 to burn the H2 and that's going to eat up the small gains. I was wondering if there was a light smoke that you could blow into the hydrogen to allow solar heating of the gas.
MisterQED, Jan 23 2009

       AC Clarke's "A meeting wih Medusa" describes a hot hydrogen balloon, albeit in the atmosphere of Jupiter.
AbsintheWithoutLeave, Jan 23 2009

       //was wondering if there was a light smoke// I don't think there'd be any advantage over a simple black envelope.
FlyingToaster, Jan 24 2009

       It would be tricky to balance everything. Heating hydrogen would expand it and increase the pressure, which would cause more hydrogen to be burned, which would heat the hydrogen, etc. After all of that burning you'd still have a lot of water vapor mixed in that hasn't condensed yet - once it condenses the balloon will shrink.   

       I say keep the hydrogen pure. Have a tube run through the center of the balloon, acting as a propulsion jet, a burning chamber, and a heat exchanger. Air enters from the top, hydrogen is introduced and both are ignited firing downward. The products of combustion transfer their heat to the balloon as the travel downward, and are jetted out the bottom for upward lift. No useless nitrogen, no heavy water vapor, and less balloon collapsing once you reach your peak.
Worldgineer, Jan 24 2009

       //Big band to outer space // Tommy Dorsey?
csea, Jan 24 2009

       Good thoughts World. I am wondering about the water vapor as a physics problem. What has more lift, a balloon of gas and water vapor a temperature x or the same balloon now with only the hydrogen at temperature x - y?   

       Of course, reacting away your lift gas is not a good way to maintain lift in the long term, which was your point.
bungston, Jan 25 2009

       Instead of creating a fire by sending air/oxygen into the envelope, with combustion happening as the air diffuses into the hydrogen, take the hydrogen out of the envelope, mix it with ambient air, burn it, send it through a heat exchanger, which heats hydrogen being circulated from the envelope, then expell the air/water vapor exhaust out to the atmosphere.
goldbb, Jan 25 2009

       I'm considering entering the N-Prize with a team of mentally acute people who will hold hands around the satellite and will it into space.
wagster, Jan 25 2009

       I have been pondering the change suggested by World and goldbb. Of course, they dispense with the beauty of an open flame surrounded by hydrogen. They would however be much more practical.   

       As World suggests, a chamber inside the balloon connects with the outside via a coiled tube within the balloon. A rubber valve on the chamber allows H2 to fart in as the balloon rises and with it its internal pressure. A 9V battery is rigged so that it sparks every few seconds. When there is combustion, atmospheric gas that has come up the tube (and supported combustion in the chamber) is propelled back out. Water vapor within the tube then condenses on the walls, delivering its heat, and drips out.
bungston, Jan 26 2009

//Hydrogen is light. Hot hydrogen is lighter//

       Yeah, but not much. Hydrogen already has 93% the lifting power of a vacuum. If you heat it 100K from a stratospheric temp of 270K, then that takes you to 95%, a 2% increase. The effect is much less than you'd get with a hot air balloon because hydrogen weighs so little to begin with. And when you add in the weight of your burner and condenser, and you'll probably have a net loss in lift.
ldischler, Jan 26 2009

       [ldischer], your calculation are for atmospheric pressure, but in a near vacuum at alitude it would be a much higher percentage change.   

       Also, to get enough hydrogen to reach the moon you need about 200l of H2 per kg and 100l of oxygen which gives more than enough lift.
miasere, Jan 26 2009

       <to music> Captain: See Marlene, sun shines through the rain
Marlene: No, that's an airship, why don't you come around again?
Captain: It must be at its ceiling...
Marlene: Is it burning, an internal flame?
zen_tom, Jan 26 2009

       //Also, to get enough hydrogen to reach the moon you need about 200l of H2 per kg and 100l of oxygen which gives more than enough lift.//   

       Ah! Miasere is really Dr Andrew Grant, travelling companion of Sir John Herschel.
ldischler, Jan 26 2009


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