Antigravity

JohnRoth wrote:If it negates gravitational mass, does it also negate inertial mass? If it does, the lightest breeze would blow people using AG belts around like thistledown. If it doesn't, it's just driven a super-dreadnaught sized hole through General Relativity.

As an aside, if it negated inertial mass, the aircar collision that killed the Havenite Secretary of State wouldn't have. No inertial mass would mean no force of impact; and the aircars would have remained undamaged.

It's the inertial *compensators* that negate inertial mass (and thus the G forces due to acceleration or course changes). They probably require more power than a typical aircar is able to produce.

The interesting thing is that the contra-grav generator must only work on *itself*. It lifts attached objects only by the fact of their attachment, not actually negating their own gravity. Otherwise, the people *inside* an aircar, or a contra-grav supported building, would find themselves weightless, if not "massless". There's no textual reference to such a state occuring, however.

OrlandoNative wrote:It's the inertial *compensators* that negate inertial mass (and thus the G forces due to acceleration or course changes). They probably require more power than a typical aircar is able to produce.

It's not a matter of power. Inertial compensators require a grav wave as a sump into which to dump inertia. Air cars don't create wedges or other grav waves. However, some vehicles (such as Sting ships and shuttles) do use wedges, and probably do have inertial compensators.

Relax wrote:The problem with partial space towers, is that the cost of fuel is the miniscule part of the cost to LEO. The missile is the major cost, not the fuel. Fuel cost, by and large, is inconsequential. Now, if the number of launches dramatically increases and the number of rockets produced dramatically increases, dropping their price tag, then and only then will the price of fuel even make a small blip on the total $$$ to LEO.

Why use fuel at all? If you could do a "partial space tower", why not go for a complete "skyhook"? Anything that can withstand the stress of being 20km high should be able to stand the stress of going all the way to geosynch and being tethered to a captured asteroid. Indeed, once you get *above* 20 or 30 km the stress should actually be *less*; since you don't need to worry about stress from the atmosphere (wind).

True, it would take energy for the vehicles to rise to whatever point spaceships could easily dock at, but you could probably come up with some sort of "reciprocating energy store"; where the going back down produced energy where the going up used it. Then, once you'd "primed" the system, you'd only need to "top off" the energy lost to friction and whatever inherent inefficiency the system couldn't do away with.

Power generation on Earth is much more efficient than any existing rocket motor, after all.

SWM wrote:

OrlandoNative wrote:It's the inertial *compensators* that negate inertial mass (and thus the G forces due to acceleration or course changes). They probably require more power than a typical aircar is able to produce.

It's not a matter of power. Inertial compensators require a grav wave as a sump into which to dump inertia. Air cars don't create wedges or other grav waves. However, some vehicles (such as Sting ships and shuttles) do use wedges, and probably do have inertial compensators.

Sting ships and shuttles are at least near-space capable. So they would *need* some sort of impeller drive, unless they were going to only rely on less efficient thrusters of some sort.

Aircars are not. While I don't believe it's ever been said exactly what motive power aircars use, it's unlikely it would work in a vacuum. They probably use some sort of fan/turbine; possibly electrically driven.

In theory, there's probably no reason a "supercharged" aircar couldn't be made that used some spinoff from a standard impeller drive, but that would probably make driving much more dangerous, as any "near miss" would probably be as bad as an actual collision due to grav band interference, just like what happens when starships get too close to one another.

OrlandoNative wrote:

Relax wrote:The problem with partial space towers, is that the cost of fuel is the miniscule part of the cost to LEO. The missile is the major cost, not the fuel. Fuel cost, by and large, is inconsequential. Now, if the number of launches dramatically increases and the number of rockets produced dramatically increases, dropping their price tag, then and only then will the price of fuel even make a small blip on the total $$$ to LEO.

Why use fuel at all? If you could do a "partial space tower", why not go for a complete "skyhook"? Anything that can withstand the stress of being 20km high should be able to stand the stress of going all the way to geosynch and being tethered to a captured asteroid. Indeed, once you get *above* 20 or 30 km the stress should actually be *less*; since you don't need to worry about stress from the atmosphere (wind).

I think you missed the beginning of the discussion. The partial space tower under discussion does not withstand the stress of its own weight. It is inflated--effectively it is supported by balloons. You can't do that all the way to orbit. You probably can't do that much higher than the 20 km height listed in this particular patent. This particular side topic is not talking about Honorverse technology--we are talking about a real patented proposal in the 21st century.

SWM wrote:

OrlandoNative wrote:Why use fuel at all? If you could do a "partial space tower", why not go for a complete "skyhook"? Anything that can withstand the stress of being 20km high should be able to stand the stress of going all the way to geosynch and being tethered to a captured asteroid. Indeed, once you get *above* 20 or 30 km the stress should actually be *less*; since you don't need to worry about stress from the atmosphere (wind).

I think you missed the beginning of the discussion. The partial space tower under discussion does not withstand the stress of its own weight. It is inflated--effectively it is supported by balloons. You can't do that all the way to orbit. You probably can't do that much higher than the 20 km height listed in this particular patent. This particular side topic is not talking about Honorverse technology--we are talking about a real patented proposal in the 21st century.

Pretty close. A synchronous orbit based skyhook is tensile, and it has been pointed out, that if something chops it in half, the part near the earth wraps itself around the earth, at very high energies. DAMAGE

This partial tower design is compressive, and not supported by inside/outside density differences. Instead, the weight of the containment parts of the tower needed to enclose the pressurized gas are held up by the gas pressure differences, thus transferring the weight to the earth without the high weight of doing it with solids. This is why it needs to vertically segmented, since you don't want the total weight hanging from the top. Instead, each segment as it goes up is at a lower pressure, and the pressure differential holds up that segment. The key factor is that the gasses can hold up quite a bit of weight without adding much weight. Think of how much compression a basketball has when exposed to a very hard bounce , yet it is light weight. Also, since pressures are higher near the earth, the upper segments would have lighter containment weights. It would be possible at the bottom to concentrate on lowest cost/effective enough materials, but the higher parts would likely need more capable (and expensive) materials. A little calculation on the thickness needed for the lowest segments pressure containment shows they would not be thin. It might make sense to have the lower segments larger diameter than those above (slightly conical) also, so that the outer walls of each segment are held up by the direct pressure difference between inside and outside, and not just that between the lower and higher segments. This variation would slightly resemble a skinny giant Eiffel tower.

There would be an optimum design, with each segment's height being different at various tower heights.

As mentioned, radial segmentation would also be needed to compensate for any bending stresses working on that high length/diameter ratio.

Gaseous fuel could also be transferred to the platform by pressure without high weight. It would trade density for height. Actually, the tower doesn't care what gas is used, although using flammables would make any blowouts super spectacular.

Assume bottom pressure is 1,000 PSI. With steel, this could support a thickness of 3,000 inches, (250 feet) average. However, each vertical segment would be supported on the gasses of the one below it, thus not needing as much weight. I'm seeing something like giant, stacked, tires which are also segmented radially to handle the bending problem.

The tensile stresses would be circumferential, only needed for containment of pressure, unlike the sky hook where they are vertical, needing to support the vehicle weight and total cumulative tower material weight.

A blowout would be pretty spectacular, but damage would be less and could be protected from by placing it at the center of a large uninhabited circle. I wonder why airports don't have buildings crowding the runways

My last on the pneumatic space tower, unless someone comes up with something good.

A major disadvantage is the point failure mode possible with all space towers. Unless the price is low enough and traffic high enough to enable many towers to be built, destruction will make a major dent in traffic flow. Remember the situation after the space shuttle Challenger blew up?

The handwavium anti/contra gravity is highly distributed, thus more robust. Recall how microgrids survived Hurricane Sandy better than the major grid? Unless RFC provides something to knockout A/CG like an EMP strike could knock out the major unhardened parts of our electrical grid, major damage is difficult. Oyster Bay was such a something for the space based infrastructure in Manticore.

For anyone interested, given a known gas it would be possible to arrange the slope of the outside surface so that the gas pressure would balance the local weight all the way up unless something changes too much. Thus the primary weight can be carried by one vertical volume without divisions at various heights. I didn't do the math, but suspect a log version of a trumpet bell.

Also, since the rate of pressure change with height is inversely related to the gas molecular weight, filling the primary part of the tower with hydrogen would be optimum. By adding H2 at the bottom, and changing it to LH2 at the top we have rocket fuel. Attached O2 filled vertical segments on the outside can vary pressure to provide needed bending moments along the length and provide LO2 at the top for rocket oxidizer. However, given the leverage of possible wind forces, the foundation must be very carefully designed and built!!!

It might be possible to build it gradually at ground level, using the gas pressure to lift the tower a bit more as each new height is added. Providing good sealing at ground level while this is done is only one of the engineering challenges to be overcome for this to work! If the engineering challenges can be met, this should reduce the cost quite a bit.

Unlikely to be built, but an interesting idea.

DDHvi wrote:My last on the pneumatic space tower, unless someone comes up with something good.

Yea. Try reality of simple math. Will calculate several different iterations to "cover the bases" since we are working with words instead of diagrams and parsing your ideas which I gather you got off of space.com popular mechanics, or its ilk who never bother to do simple math either.

1) Wind Shear
2) Dynamic oscillations caused by #1
3) Diameter required would be immense to solve #2 and #5
4) At such an immense diameter, the tensile properties requires are ginormous and the compressive forces insane.
5) Has to be at least aircraft carrier sized to land/launch.

"assume 1000psi". What a load of....

A 1000psi on a diameter of 500 feet is a tidy 6,000,000lbs per linear dimension. Add very basic safety factor due to defects, wear, very basic fatigue and then on top of that: Now add dynamic loads due to wind shear and this force goes up by at least 2 under best case scenario and quite easily 4X or more. So, 12,000,000lbf at below bare minimum that is not even allowed for jet fighters, let alone pretty much a civilian structure.

12,000,000lbs. Lets see, if the best carbon is used. Currently it has a tensile strength of roughly 400,000psi. Great, wonderful, a thickness of "ONLY" 15inches is required in tensile. Of course the opposite side is in compression and its "best" compression properties is a whopping 150,000psi, so it needs roughly 35 inches thick sides. Lovely. Might have gotten a clue by now, why everyone proposes TENSILE space elevators...

Density of Carbon is roughly ~0.1lbs/in^3. So, great, each inch of height on this 1000psi pressure vessel, weighs in at a tidy 300,000lbs at best and reality would dictate a lot worse per inch of height...

Lets see total weight "suspended" by a 1000psi bag 500 feet in dia is roughly 200million lbs. Height proposed: ~750,000inches. AT 300,000lbs/in = 2.25 Trillion lbs.

Which is larger. 225Trillion or 28Trillion.....

28 Trillion is from 500 dia = (250x12)^2(xPI)

Oh yea, I didn't even calculate the bell ends. One is on the ground so, not a problem and the other is the top. Lets just call it free.

The proposal as proposals go is blatantly stupid and does not even come into range of a power of 10 due to reality.
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Actually, I give up, as trying to envision this a different way simply does not work without resorting to density differentials. You can claim to use multiple hydraulic lines(high pressure), but it comes back to:
1) Compression due to wind shear and
2) Your 1000psi hydraulic lines ability to "HOLD" something up is directly proportional to its area. At 1000psi this is not much meaning that your "diameter" of your hydraulic lines must be GIGANTIC which once again, see the first off the cuff calculation up above.
3) Pressure pushing does not take care of #1 and therefore fails simple logic test let alone a calculation as any such calculation would be pointless.

Relax wrote:

DDHvi wrote:My last on the pneumatic space tower, unless someone comes up with something good.

Yea. Try reality of simple math. Will calculate several different iterations to "cover the bases" since we are working with words instead of diagrams and parsing your ideas which I gather you got off of space.com popular mechanics, or its ilk who never bother to do simple math either.

1) Wind Shear
2) Dynamic oscillations caused by #1

Click for real-life example of #'s 1 and 2: https://youtu.be/j-zczJXSxnw

Oh yea, and if you do a deflection calc on a tower 60,000ft high with a diameter of only 500ft and a wind velocity of 60mph, lets just say, it blew over. Don't know about you, but the wind blows a hell of a lot stronger than 60mph.

The tensile problem only becomes MASSIVELY more pronounced the larger diameter you go. Now if you wish to propose multiple columns of pressurized air 60,000ft high, go for it. Its base is going to be around a mile wide...