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scienceguy
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« on: 12/05/2007 06:39 PM » |
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Has anyone ever thought of using a hydrogen balloon to get high into the atmosphere, then burning the hydrogen to get into space?
If you used say a rubber balloon with a volume of 8850 m^3 filled with hydrogen to carry a payload of 10^4 kg (10 tonnes), then the net force would be a lift on the craft as per the following:
Fup = force up
Fb = buoyant force
Fw = force of weight of craft
rhoair = density of air
Vair = volume of air displaced
g = acceleration due to gravity
mH2 = mass of Hydrogen
mpay = mass of payload
Fup = Fb – Fw
= rhoair*Vair*g – (mH2 + mpay)g
= 1.2 kg/m^3*8850 m^3*9.8 m/s^2 – (700 kg + 9300 kg)(9.8 m/s^2)
= 6000 N
I imagine the craft could get as high as run of the mill weather balloons, or 40 km (25 miles). Then you could squeeze the hydrogen out of the balloon to be fuel for an engine.
56% of the payload could be liquid oxygen and 37% of the payload could be the mass of the rest of the craft that you want to get into space (7% of the mass of the craft is hydrogen).
56% of the payload would have to be oxygen because that is how much oxygen (5600 kg) would be needed to burn 8850 m^3 (700 kg) of hydrogen.
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« on: 12/05/2007 06:39 PM » |
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Jim
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« Reply #1 on: 12/05/2007 06:49 PM » |
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Where is the power to "squeeze" the H2 from? What maintains the vehicle's alt while the H2 is squeezed? If there is any velocity generated during this time, what keeps the balloon from tearing?
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scienceguy
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« Reply #2 on: 12/05/2007 07:27 PM » |
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I imagine the power to squeeze out the hydrogen can just come from batteries. The craft can have perhaps a little LH2 stored in the payload to begin thrusting as soon as the balloon is started to be squeezed so it doesn't lose altitude. The shape of the balloon can affect how easily it is squeezed. Here is a picture: !["Balloon"]("<a "\"Balloon\"") http://img233.imageshack.us/img233/5589/balloonapparatus1ks3.jpg" />
Please note diagram is not to scale.
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meiza
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« Reply #3 on: 12/05/2007 07:48 PM » |
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Yeah I think JP aerospace experimented with rolling apparatus to keep the shape of a very high altitude balloon right. They inflate at higher altitude when the ambient pressure is lower. You could fold and roll.  How high could you go with a balloon anyway if you heat the hydrogen? Store a little hypergolics, burn it outside and heat the hydrogen with a small heat exchanger. Or use the solar energy somehow by having the balloon be transparent to visible but blocking to IR on one side and have an absorbing inside surface on the other side.
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neviden
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« Reply #4 on: 12/05/2007 07:52 PM » |
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How and when would you achive 10 km/s speed?
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scienceguy
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« Reply #5 on: 12/05/2007 08:10 PM » |
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Well, I would have to ask the aerospace engineers here how much thrust you can get from burning hydrogen, and if it would be enough force to accelerate 10^4 kg from 0 km/s to 10 km/s in an acceptable time frame.
Also, would 700 kg of hydrogen be enough?
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neviden
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« Reply #6 on: 12/05/2007 08:16 PM » |
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My guess is that 700 kg of hydrogen would be enough only if you would use fusion reactor to get it and 10 mT payload to 10 km/s speed (LEO)..
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Jim
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« Reply #7 on: 12/05/2007 08:23 PM » |
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scienceguy - 5/12/2007 2:27 PM
I imagine the power to squeeze out the hydrogen can just come from batteries. The craft can have perhaps a little LH2 stored in the payload to begin thrusting as soon as the balloon is started to be squeezed so it doesn't lose altitude. The shape of the balloon can affect how easily it is squeezed. Here is a picture: http://img233.imageshack.us/img233/5589/balloonapparatus1ks3.jpg" /> Please note diagram is not to scale. The balloon can't support anything on top of it. Squeezing isn't going to provide enough pressure to operate the engine.
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Propforce
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« Reply #8 on: 12/05/2007 10:42 PM » |
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I think this explains a lot of strange foreign objects found at Rosewell, NM.....
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LEGO Space
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« Reply #9 on: 12/05/2007 11:52 PM » |
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scienceguy - 5/12/2007 12:39 PM
Has anyone ever thought of using a hydrogen balloon to get high into the atmosphere, then burning the hydrogen to get into space?
If you used say a rubber balloon with a volume of 8850 m^3 filled with hydrogen to carry a payload of 10^4 kg (10 tonnes), then the net force would be a lift on the craft as per the following:
Fup = force up
Fb = buoyant force
Fw = force of weight of craft
rhoair = density of air
Vair = volume of air displaced
g = acceleration due to gravity
mH2 = mass of Hydrogen
mpay = mass of payload
Fup = Fb – Fw
= rhoair*Vair*g – (mH2 + mpay)g
= 1.2 kg/m^3*8850 m^3*9.8 m/s^2 – (700 kg + 9300 kg)(9.8 m/s^2)
= 6000 N
I imagine the craft could get as high as run of the mill weather balloons, or 40 km (25 miles). Then you could squeeze the hydrogen out of the balloon to be fuel for an engine.
56% of the payload could be liquid oxygen and 37% of the payload could be the mass of the rest of the craft that you want to get into space (7% of the mass of the craft is hydrogen).
56% of the payload would have to be oxygen because that is how much oxygen (5600 kg) would be needed to burn 8850 m^3 (700 kg) of hydrogen.
Even if this could work, I doubt it would be worth the effort (i.e. money). You'd still have to reach a reasonable LEO altitude and velocity. Your only minor advantage would be that you start some 40 km higher up.
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veedriver22
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« Reply #10 on: 12/06/2007 12:11 AM » |
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Once you started burning the hydrogen, then you need some kind of guidance. Otherwise it will just fly allover the place until the fuel was spent.
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scienceguy
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« Reply #11 on: 12/06/2007 12:17 AM » |
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Thanks for all the responses
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LEGO Space
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« Reply #12 on: 12/06/2007 04:33 PM » |
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veedriver22 - 5/12/2007 6:11 PM
Once you started burning the hydrogen, then you need some kind of guidance. Otherwise it will just fly allover the place until the fuel was spent. LOL, basically like a regular balloon that you pump, not tie its opening and then release.
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shostetler
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« Reply #13 on: 12/06/2007 09:24 PM » |
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speaking of balloons, if hydrogen was able to get something to 25 miles up, what would it take to get it the rest of the way into orbit? I'd like to see a way that instead of trying to use rockets that a slower albiet more effective way of getting a large amount of mass into orbit. I'd consider an entire building, built to be put into orbit. Then to have a blimp of hydrogen lift the mass and eventually at 25 miles pushed into orbit with some other means of lift, what that would be, I don't know. I'm not the rocket scientist here. But once in orbit, to use an ion propulsion engine or something to get the speed required to stay in orbit. Un doable? yeah... a dream? probably, but it's a thought I've often pondered.
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neviden
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« Reply #14 on: 12/06/2007 10:00 PM » |
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You weren’t the first and the last one to think of that idea. But I am afraid that it just isn’t too practical and the reason is simple: How far away from the surface of the Earth you are doesn’t mean one bit of a difference if you don’t have enough speed, that when you fall you continuality miss Earth (=orbital speed). Sure, you might get high with balloon, but you are still in the atmosphere and balloons don’t work in vacuum. They also have huge surface and that means that if you try to move them you soon get to the point where the friction slows you down more then whatever you use to push will make you faster. But if you leave your balloon then you simply fall down.
You could be 1000 km high and you would still fall like a rock to the earth if you are even a little short of 10 km/s. You need a lot of energy to reach the speed of 36.000 km/h. If you don’t have that speed then you will fall to the Earth in few minutes. Rockets much achieve that speed in few minutes. That is why the rockets are made of 95% fuel and oxidizer, they burn it fast as possible and yet they still barely made it into LEO.
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