Author Topic: Space cannons & mass drivers, launching into specific orbital planes?  (Read 2644 times)

Offline KelvinZero

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Fortunately, there's no such thing as wind, so nothing could possibly go wrong with a 50 km tall string of airships piled on top of one another.
Again with the strange strawmen. There are many ways you could design this, and we haven't even discussed how wide. I think the wind is potentially a huge resource, as I mentioned.

Since 50km is the limit of what we can do, aiming for specifically that height is probably extreme. Whatever.

Online ChrisWilson68

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Fortunately, there's no such thing as wind, so nothing could possibly go wrong with a 50 km tall string of airships piled on top of one another.
Again with the strange strawmen. There are many ways you could design this, and we haven't even discussed how wide. I think the wind is potentially a huge resource, as I mentioned.

Since 50km is the limit of what we can do, aiming for specifically that height is probably extreme. Whatever.

Strawman?  Are you claiming you weren't talking about a 50km lighter-than-air tower?  Because you were replying to a post about a 50km tower, you talked about liking the idea of lighter-than-air skyscrapers, and you mentioned that the record for balloons is 50km.  Any reasonable reader would conclude you were talking about a 50km lighter-than-air tower.

Online Nilof

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A pair of parallel wires carrying currents I1 and I2 at distance d from each other repel each other with a force per unit length of μo I1 I2 / 2*pi*d

In SI units, this becomes F/L = (2*10^-7 N / A^2) I1 I2 / d

A YBCO superconducting wire can achieve current densities on the order of a megaAmpere per cm/2, so fairly compact MegaAmpere wires are doable. If the tunnel to be elevated carries 10 MA, and the ground wire carries 50 MA, at a distance of 50 km, and we can lift 2 tonnes per meter. No need for lighter-than-air structures.

You can scale up the lifted weight straightforwardly by increasing the currents. Because the force scales quadratically with the current but only a linearly with the distance, it's actually fairly easy to scale up.
« Last Edit: 04/20/2017 10:29 AM by Nilof »
For a variable Isp spacecraft running at constant power and constant acceleration, the mass ratio is linear in delta-v.   Δv = ve0(MR-1). Or equivalently: Δv = vef PMF. Also, this is energy-optimal for a fixed delta-v and mass ratio.

Offline KelvinZero

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Fortunately, there's no such thing as wind, so nothing could possibly go wrong with a 50 km tall string of airships piled on top of one another.
Again with the strange strawmen. There are many ways you could design this, and we haven't even discussed how wide. I think the wind is potentially a huge resource, as I mentioned.

Since 50km is the limit of what we can do, aiming for specifically that height is probably extreme. Whatever.

Strawman?  Are you claiming you weren't talking about a 50km lighter-than-air tower?  Because you were replying to a post about a 50km tower, you talked about liking the idea of lighter-than-air skyscrapers, and you mentioned that the record for balloons is 50km.  Any reasonable reader would conclude you were talking about a 50km lighter-than-air tower.
No I was just clarifying that what I said implied 50km was the upper limit, rather than what you would sensibly aim at.

Your strawman was to introduce a specific presumably very narrow design, but not a tether. Something simultaneously prone to twisting and vulnerable to it. Do you actually have an argument that a lighter than air structure cannot be 50km high due to wind?

You would have to argue from basic principles that cellular inflatable structures do not scale up. Perhaps something to do with the well known area/volume problem of scaling an ant up to the size of an elephant. Something along those lines.

You can't just make up silly implementations and then mock that. That is a straw-man.

Offline Robotbeat

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You can make a heavier than air structure higher than 50km. 50km isn't the upper limit.
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

To the maximum extent practicable, the Federal Government shall plan missions to accommodate the space transportation services capabilities of United States commercial providers. US law http://goo.gl/YZYNt0

Online ChrisWilson68

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Fortunately, there's no such thing as wind, so nothing could possibly go wrong with a 50 km tall string of airships piled on top of one another.
Again with the strange strawmen. There are many ways you could design this, and we haven't even discussed how wide. I think the wind is potentially a huge resource, as I mentioned.

Since 50km is the limit of what we can do, aiming for specifically that height is probably extreme. Whatever.

Strawman?  Are you claiming you weren't talking about a 50km lighter-than-air tower?  Because you were replying to a post about a 50km tower, you talked about liking the idea of lighter-than-air skyscrapers, and you mentioned that the record for balloons is 50km.  Any reasonable reader would conclude you were talking about a 50km lighter-than-air tower.
No I was just clarifying that what I said implied 50km was the upper limit, rather than what you would sensibly aim at.

Your strawman was to introduce a specific presumably very narrow design, but not a tether. Something simultaneously prone to twisting and vulnerable to it. Do you actually have an argument that a lighter than air structure cannot be 50km high due to wind?

You would have to argue from basic principles that cellular inflatable structures do not scale up. Perhaps something to do with the well known area/volume problem of scaling an ant up to the size of an elephant. Something along those lines.

You can't just make up silly implementations and then mock that. That is a straw-man.

The irony here is that while I didn't make up a strawman to argue against, you just did to argue against me.

You said "skyscraper", "lighter than air", and "50km".  I said "50 km tall string of airships piled on top of one another", which is simply adding some humor to the characterization of a 50km tall lighter-than-air skyscraper.  Obviously it doesn't mean you're literally going to take ordinary airships and put them one on top of another.  It just means that any sort of 50km tall skyscraper is going to be roughly similar in some important ways to airships piled one on top of another.  The idea that I was limiting what you said to a particular design is just silly.

And I never said that it can't be done because of wind.  I was just pointing out that wind is going to be a big, big problem for a lighter-than-air tower that tall.

Offline Hanelyp

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... If the tunnel to be elevated carries 10 MA, and the ground wire carries 50 MA, ...
... You have a logistic problem of 40MA return current for the ground wire that has to take a long path around to not significantly detract from the lift magnetic field.  I'm thinking it'll be easier to work if elevated and ground wires carry the same current.

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