Drive systems

aairfccha wrote:This supply of hydrogen would have an impractically low density (that's the point of lighter-than-air), resulting in relatively high structual mass fractions for a given strength and considerable drag.

Completely agree. The lifting capability is very firmly connected with the air pressure, and with additional height... the ammount of lifting gase needed to lift is enormous.

Dilandu wrote:

aairfccha wrote:This supply of hydrogen would have an impractically low density (that's the point of lighter-than-air), resulting in relatively high structual mass fractions for a given strength and considerable drag.

Completely agree. The lifting capability is very firmly connected with the air pressure, and with additional height... the ammount of lifting gase needed to lift is enormous.

Thinking about what you are saying that seems counter intuitive. Less gas would make the lifting work better, the counter pressure on the lifting balloon would decrease with altitude. The balloon would need less pressure to keep it inflated, which is why balloons look empty and deflated when close to the surface. You don't need more gas you need more space for the limited amount of gas.

Lord Skimper wrote:

aairfccha wrote:This supply of hydrogen would have an impractically low density (that's the point of lighter-than-air), resulting in relatively high structual mass fractions for a given strength and considerable drag.

Dilandu wrote:Completely agree. The lifting capability is very firmly connected with the air pressure, and with additional height... the ammount of lifting gase needed to lift is enormous.

Thinking about what you are saying that seems counter intuitive. Less gas would make the lifting work better, the counter pressure on the lifting balloon would decrease with altitude. The balloon would need less pressure to keep it inflated, which is why balloons look empty and deflated when close to the surface. You don't need more gas you need more space for the limited amount of gas.

The nature of buoyancy is that the lift is the difference between the weight of the lifting gas( and the containing envelope) and the weight of the material displaced. Th problem is that at extreme altitudes (low pressure), the weight of the atmosphere per unit volume is very low, so you are going to require an enormous volume to provide the same amount of lift. You are correct that lower amounts of lifting gas is more desirable, and that the lower pressure at altitude will allow for less lifting gas, but the volumes required are still going to be enormous.

As i recall, the average density of air on the heights:

Sea level - 1,225 kg/m3

1 km - 1,112 kg/m3

5 km - 0,736 kg/m3

10 km - 0,414 kg/m3

20 km - 0,089 kg/m3

50 km - 0,00102 kg/m3

About 70-80 km, the density of air fall below the density of hydrogen, so the lift would stop.

As you could see, even to reach the 10 km you need more than triple volume of hydrogen for the same lifting power. For the 20 km, you need 13,7 times more. And for 50 km - more than thousand times more!

Dilandu wrote:About 70-80 km, the density of air fall below the density of hydrogen, so the lift would stop.

The pressure drop decreases the Hydrogen's density as well, is there really a condition where H2 has a higher density than an N2/O2 mix? OTOH lift capacity per volume definitely goes asymptotically down to zero, following the absolute density differences.

Dilandu wrote:As i recall, the average density of air on the heights:

Sea level - 1,225 kg/m3

1 km - 1,112 kg/m3

5 km - 0,736 kg/m3

10 km - 0,414 kg/m3

20 km - 0,089 kg/m3

50 km - 0,00102 kg/m3

About 70-80 km, the density of air fall below the density of hydrogen, so the lift would stop.

As you could see, even to reach the 10 km you need more than triple volume of hydrogen for the same lifting power. For the 20 km, you need 13,7 times more. And for 50 km - more than thousand times more!

WTF is this business of using commas for radix points? What idiot started it, and WHY did anybody copy it? If I see 123,456,789 - HOW am I supposed to tell if it means 123 million 456 thousand 7 hundred and eighty-nine, or 123 thousand 4 hundred and fifty-six and almost 8/10ths? THOU SHALT NOT PUNCTUATE NUMBERS IN AN AMBIGUOUS MANNER! (/rant)
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Gentlemen! You can't fight in here - this is the War Room!

Imaginos1892 wrote:

Dilandu wrote:As i recall, the average density of air on the heights:

Sea level - 1,225 kg/m3

1 km - 1,112 kg/m3

5 km - 0,736 kg/m3

10 km - 0,414 kg/m3

20 km - 0,089 kg/m3

50 km - 0,00102 kg/m3

About 70-80 km, the density of air fall below the density of hydrogen, so the lift would stop.

As you could see, even to reach the 10 km you need more than triple volume of hydrogen for the same lifting power. For the 20 km, you need 13,7 times more. And for 50 km - more than thousand times more!

WTF is this business of using commas for radix points? What idiot started it, and WHY did anybody copy it? If I see 123,456,789 - HOW am I supposed to tell if it means 123 million 456 thousand 7 hundred and eighty-nine, or 123 thousand 4 hundred and fifty-six and almost 8/10ths? THOU SHALT NOT PUNCTUATE NUMBERS IN AN AMBIGUOUS MANNER! (/rant)
---------------
Gentlemen! You can't fight in here - this is the War Room!

I really hate to point this out to you, but the Europeans have been doing it that way longer than the Americans have been doing it our way.

Imaginos1892 wrote:WTF is this business of using commas for radix points? What idiot started it, and WHY did anybody copy it? If I see 123,456,789 - HOW am I supposed to tell if it means 123 million 456 thousand 7 hundred and eighty-nine, or 123 thousand 4 hundred and fifty-six and almost 8/10ths? THOU SHALT NOT PUNCTUATE NUMBERS IN AN AMBIGUOUS MANNER!

Is that a thing? I always just thought it was a typo because they put the "." & "," keys too close together.

Eagleone 55 wrote:I think a Space elevator would be a good Idea. I have read that a Penn State Professor has come up with a benzene process that is harder than a Diamond. http://www.extremetech.com/extreme/1906 ... e-elevator
If you turned this benzene process into a cable like they do with suspension bridges (wind them into a large cable) I believe that would make a great elevator cable. The Cable could be wrapped around a type of benzene tube it would contain Liquid oxygen Or water that could be split into its basic components (hydrogen and Oxygen) use the Oxygen for the facility at a Geo-sync orbit. Store the Hydrogen for use as fuel for the ship.

Build a orbital assembly plant for ship design/ launching. The type of ship that could be built in space would be less restricted than having to have it launch from earth. One would not have to take Launch stresses into account when designing the ship.

The problem is that you can't use any kind of "Fiber Rope" no matter how strong each fiber is. As with a chain being only as strong as it's weakest link, each strand would have to be just that, a single strand, ALL the way down from space. To use shorter strands woven together would mean that the WHOLE thing is held together with the friction between fibers. With the length we're talking to get into space, the weight/mass of all the fibers below pulling down on the fibers above would cause the line to snap before it reached space. So each strand has to be made as 1 single piece and the strands woven together along their entire 50+ mile length. Also remember that the Earth's atmosphere doesn't abruptly end at 50 miles, it extends beyond 5,000 miles and any object (including a length of rope) swinging around will be subject to the forces of drag caused by these thin but present particles. The ISS is constantly having to apply course correction thrust to compensate for the thin atmospheric particles slowing it down. A giant rope hanging from it would be like a Drag racers Drag-chute deployed.