h a l f b a k e r yWhy on earth would you want that many gazelles anyway?
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Think of a long tube with steam generators spaced evenly down the length. The tube can be closed up, except for some vents, and steam pumped into it. Once the steam has displaced the air in the tube the vents can be closed and condensers, at the distal end of the steam vents, enabled. The condensers
would start condensing the steam to the vapor pressure of water near liquid nitrogen temperatures. This is very close to a vacuum. As the walls of the tube would have been heated by the steam above this temperature, any condensation on the walls would evaporate and be removed by the condensers.
This gives a near vacuum but it also has other advantages. Unlike air, which is far above its critical temperature, the water vapor in the tube will be far below its critical temperature. As the vapor is compressed in front of the accelerating mass, unlike air, it will condense. As long as the accelerating mass can remove the heat of condensation quickly enough there will be no shock wave created. While the condensation will have to be accelerated as it impinges the mass, it will not drain energy or create turbulence like a shock wave. The front of the moving body could be funnel shaped to collect the condensate and handle it safely.
To accelerate the mass, the steam generators behind the mass would be turned on again. The mass, being carried in a sled that closely fits the tube, would be accelerated like a steam locomotive on steroids. The accelerating force on the mass and sled would be equivalent to the steam pressure times the area of the tube. The sled can be several times larger in cross section than the mass, and unlike a sled for a magnetic system, can be made of low density composites.
By angling the steam vents in a forward direction, creating a curve on the back end of the sled like a very curvy curly brace "{" and timing the impulse of steam coming from the vents, the steam can be caused to accelerate around the curve and end up directed in the opposite direction. This would transfer approximately 2sin(è)ñ momentum where ñ is the momentum of the steam and è is the incident angle. For some actions there can be a double and opposite reaction. See the design of piton wheels for dams.
Toward the end of its run, the space vehicle could fire its engines for an instant. The pressure between the space vehicle and the sled would eject the space vehicle from the sled, transfer the sleds momentum to the space vehicle and decelerate the sled for recovery. The space vehicle would pop out of the sled like a mortar from its launch tube and the ejected gases push past the space vehicle to equalize the pressure in the tube allowing the upper end of the tube to be opened, similar to launching a Poseidon missile from a sub, though at an angle of about 0.646. Steam would follow behind to push out the noncondensable gasses.
All the space vehicles needs to do is maintain its speed against the air resistance once launched. Orbital maneuvering devices may be sufficient. If not, a very small solid fuel device.
Note that by closing doors along the tube as the sled passes, the vacuum creation portion of the cycle can begin before a launch cycle is fully finished. 10 tons could be launched from a 3 meter by 25 km tube to a 1000 mile orbit with just 300 psi about once every 30 seconds. Vents, cold salt water spray and liquid N2 in heat exchangers successively for vacuum creation, secondary pressure tubes and nuclear steam generators for propulsion. At that rate you could build a massive space station and supply it with all the resources it needs in less than a year.
That ought to be easer to build than the superconducting supercollider. The tunneling at least.
Orbital Velocity Calculator
http://liftoff.msfc...bmech/vel_calc.html
[BunsenHoneydew, Dec 06 2006]
Shuttle
http://harv.rcat.ut...tle/HTML/index.html
Maximum Velocity: 28,158 km/h = 7822m/s [BunsenHoneydew, Dec 06 2006]
ESA Phoenix/Hopper program
http://science.box....ead.php?newsid=5328
".. would launch on a sled running on a four-kilometre-long track ... accelerated by either magnetic fields or steam. ..." [BunsenHoneydew, Dec 06 2006]
Vertical Slinghsot Launch Hangliders
Vertical_20Slinghso...Launch_20Hangliders
source of the 9G figure and [baconbrain]'s quote [BunsenHoneydew, Dec 06 2006]
G-Suit
http://en.wikipedia.org/wiki/G-Suit
How a G-Suit Works [emjay, Dec 07 2006]
Old stuff
http://www.astronau...om/lvs/valongun.htm
Valier-Oberth Moon Gun, from 1926 [ldischler, Dec 10 2006]
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Such a long explanation for such a simple idea. |
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A space launch facility will never be simple since safety and the high energies involved will not allow you to wish away the nonlinearities and such. Eject the Devil, Success is in the details.
Still you can read as much or as little as you wish, just the synopsis for instance. This post was an extraction of a much larger concept description and rough analysis. |
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I read the first paragraph. Did I miss much? |
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All sounds very Jules Verne, launching people into space from a big gun. |
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Would the steam be able to propel the projectile at faster than the speed of sound? |
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The question you might want to ask Ling is “the speed of sound in what” the gas streaming away from the sun is traveling at millions of miles per hour. The gas coming out the back of rockets and jets is a mix of super heated steam and CO2. These gases must travel faster that the device they are pushing against. By increasing the pressure in the combustion chamber the gas comes out faster than the speed of sound (at environmental t and p)
Imagine a series of steam vents not unlike a series of rocket engines pushing against the sled. Time their blow correctly and they, due to reaction for every action, push against the sled as if they were mounted on the sled. Except that by shaping the back of the sled you can get nearly twice the specific impulse than you can by mounting them on the sled. |
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// gases must travel faster that the device they are pushing against. // Not necessarily true. It is the usual case for jets, true; for a rocket operating in vacuum, "faster" basically loses meaning. The only relevant measurement is the mass of gas ejected from the engine and its velocity relative to the rocket.
Since your steam source is not mounted on the vehicle, the highest speed the vehicle could acheive would be less than the speed of the released steam; the relative velocity at impingement would determine the force exerted on the vehicle. |
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// All the space vehicles needs to do is maintain its speed against the air resistance once launched. // A ten-ton 3 meter diameter vehicle, encountering atmosphere at 1 atm pressure and orbital velocity, would encounter far higher thermodynamic loading than a similar vehicle reentering from space, and would likely fully ablate before reaching 10000 meters altitude. |
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//The question you might want to ask Ling is “the speed of sound in what” // |
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Cocky answer: In a vacuum? |
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According to goddard, the prime combustion chamber pressure is about 1,000 psi. This is still the formula used in modern rockets. The trick is to maintain that amount of pressure and vary the size of the combustion chamber and the diameter of the nozzel. This is where thrust comes from (without going into the complex math). So...any 'impigement" device is just an inside-out rocket and the speed of the exhaust gasses will be very critical to such a device. I can not seem to come up with a speed much faster than 5,000 mph at best for this device. A speed of (+-)17,000 mph is necessary for "escape velocity". The electro magnet rail gun has no limitations on speed. I think the rail gun will exceed this device in performance. I do believe rail gun or "relay thrust" devices will be the answer for low cost orbital insertions. But, with some strict limitations. I doubt humans will ever be launced into orbit this way. Even with a mile long gun, the average time to maximum velocity will be around .44 seconds (That's 4.4 tenths of a second). Such accelleration would kill any living creature...microbes might be the exception. |
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I am giving this idea a bun because I am so pleased to see an idea describing a fantastic mechanical marvel, not something silly. I learn a lot from these sorts of posts, since they attract comments by people who know something. More like this, [cjacks]. |
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As I understand it, this is essentially a pneumatic cannon, with details. You could condense the steam onto the walls by cooling them - first by flooding them (they are hollow) with cold water then with cryogenic gas. This is akin to the party trick where you put a pop can on the burner, fill it with steam, then upend it into ice water - condensing the steam (and crushing the can). |
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The tunnel will need to be long - longer than a missile silo. It will need to be able to withstand expansion from the superheated steam. The closing segments along the tunnel will also obviate the need to keep old steam in the proximal tunnel very hot. Assuming no friction between rocket and tunnel and an infinitely long tunnel, I do not think there is any limit on the speeds this sort of acceleration could attain. |
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I like the use of steam. Nice and retro, but practical, easy to work with, and reclaimable. In space, you would only need to replace the steam that escaped out with the rocket from the last segment of tunnel. |
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The last segment of tunnel could use aerosolized fuel and oxygen instead of water. As the rocket left this would be ignited behind it, for extra oomph. |
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/Since your steam source is not mounted on the vehicle, the highest speed the vehicle could acheive would be less than the speed of the released steam/[lurch] |
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This is true if the vehicle is spurting steam from behind. If thes team serves only to pressurize, and the vehicle is the interface between high pressure and low pressure, as long as there is a pressure differential the vehicle will continue to accelerate. If there is no frictional loss, constant acceleration has an upper speed limit of the speed of light. |
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// vehicle is the interface between high pressure and low pressure // notice that the high pressure isn't a logical abstraction - there's compressed *stuff* there, i.e., steam; and the vehicle is moving away from it. If it doesn't follow, you have *no* pressure. If you want pressure, the steam has got to be in motion. |
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As you accept that a jet pushes gasses out at very high speeds, what is the ratio of orbital velocity at a 1000 mile orbit to the upper limit of NASA’s scram jet technology? While at lower velocities the pressure differential will likely represent the major energy transfer, at higher velocities momentum transfer will likely predominate. I don’t have the equations and I don’t think this audience would want them. Much will depend on the pressure in the reservoirs and the nozzle shape. |
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Due to the creation of a vacuum, the vehicle won’t have to deal with air resistance till it hits the upper end and pops out. Herein lies why all these space launch gun ideas are likely to remain half baked for a long time. They have to be very long and if they are angled upwards, about 37 degrees for this concept, the upper end is very high. Tunneling through a mountain won’t get it to the end. Either the largest solid core building ever built is needed or a series of buildings connected by the highest flying buttress ever conceptualized is needed. But as the question goes, why would you want to live in a tin cup in space when you haven’t figured out how to keep from fouling your own environment on the wide earth. I’ll reserve the answer to that question for another post. |
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The cycling of pressure would fatigue the tubes relatively quickly and the expansion and contraction would create “fit” problems. So you create a thick tube of fiber reinforced concrete and wrap it alternately radially and longitudinally with something like Kevlar fiber. The precompression of the concrete should be such that the pressure cycling represents less than 5% of the stress on the concrete. This should reduce the expansion and contraction significantly and thereby reduce the formation of microfractures, it will also have been made with a relatively dry mix to reduce its porosity. The fiber can be coated with a tar like substance while it is being applied. Once a vacuum can be drawn on the section, a layer of nickel, copper allow is vacuum deposited on the inner wall and polished to interferometer smoothness. This will seal the inner wall and the residual vacuum in the body of the concrete will draw the tar like substance into the outer pores.
The inner layer of the alloy is then coated by known methods with a layer of diamond. This layer can be augmented from time to time to as wear indicates. If the diamond layer creation method is too slow one could use silicon carbide or some other super hard compound but the thermal conductivity and coefficient of friction of diamond is hard to beat. |
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I think that inside this rather rambling and confused post there is quite a good idea trying to get out. |
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What is clear though, is that this idea truly sucks... on a galactic scale. |
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It's interesting though... pity the math doesn't work. |
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The electromag railgun is a brilliant idea, but you have to have your projectile moving at transsonic or slightly supersonic speeds at insertion, or the plasma arc absolutely destroys the projectile. This steam rig would be an excellent way to get the capsule up to speed. |
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Stepping slightly away from Jules Verne (but with a respectful tip of the hat to his prescience), we build the gun in a nice long tube up the side of Mt. Kilimanjaro, which is convenienty next to the equator, very tall at 19,000+ feet, and not difficult to get around on. At those heady heights, the explosive emergence of the capsule will have no nearby lifeforms to disturb. |
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[bungston] //The last segment of tunnel could use aerosolized fuel and oxygen instead of water.// |
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Why not every stage? Creates a multi-stage cannon, with surviveable Gs at every point, and a much shorter tube. Still using the steam-created vacuum ahead of the craft, perhaps. |
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I'll do some maths, based on a suviveable acceleration of 9G, quoted in another idea as the point at which fighter pilots black out, and the Shuttle's orbital height of 300km, and orbital velocity of 7.73 km/sec [link] |
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Okay, someone tell me if I have this right: |
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v1, v2, v(av): initial, end and average velocity in tube
a: acceleration
t: time in tube
l: length of tube
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v1 = 0 m/s
v2 = 7730 m/s
a = 9 G
~ ~90 m/s2
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v2 = v1 + at : solve for t |
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v2 = at
t = v2/a
= 7730/90
~ 86 seconds
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v(av) = (v1+v2)/2
= 3865 m/s
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l = v(av)t
= 3865 m/s x 86 s
= 332890 m
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So you end up with a 300km long cannon to reach low earth orbit, no matter how the cannon/railgun/etc is powered. |
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Even worse because I doubt a sustained 9G is human-surviveable for around a minute and a half, and I've left out the speed lost to gravity betweeb leaving the barrel and reaching orbit. The shuttle by comparison accelerates at a leisurely 2 to 3G. |
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Maybe unmanned hardware could survive higher Gs and allow a shorter tube. Maybe. |
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This also assumes that the cannon/etc is the only launch power, rather than a first stage. |
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I remember seeing a Russian private enterprise proposal to use a vertical tube in the ocean - pump out all the water, put your capsule in, and let the water back in from the bottom. This was a first-stage booster only - rockets engines engaged once it left the tube. |
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Bunsenhonedew.....it appears you are talking to yourself. |
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Well gag me with a fishbone - check out [link] number three. |
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Even *worse* worse: as quoted from [baconbrain] at [link] 4: |
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//One G of vertical acceleration for any distance will throw you precisely that same height above the end of your launcher, 2 Gs will throw you twice as high, et c. ... So, an 9-G launch will throw you less than 9 times as high as your tower// |
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The orbital velocity is all horizontal, so it can be applied horizontally without adding height to your track. But you have to get to 300km up to reach that orbit: at 9G vertical you need a ~30km high track end. |
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Of course 9G vertical + 9G horizontal = a lot more than 9Gs, so you either need a root-2 times high and long track, or much more robust hardware and/or astronauts. Or conventional rocket upper stages. |
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It's always good when you come
around, [Bunsen]. Especially with the
maths. |
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I am pondering why high G forces are
bad for folks. I suspect it has to do
with perfusing the brain. This is why
those MAST trousers help pilots - they
keep blood from pooling in the legs. |
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I wonder if you spun the astronaut in a
plane parallel to the acceleration, you
could induce blood to flow to and then
away from the head, and preserve
consciousness? |
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....Or, what if you encased them in a capsule of that oxygen-bearing liquid we all remember from the movie Abyss? The stuff's real, but a tad risky to use. |
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I wonder if you made a perfectly upporting mould of someone's back (possibly that specifically supported bone structures, and retained body shape), and encased them and the mould in a capsule of "liquid air". Now, you could somewhat pressurise the liquid, and remove all of the airgap, making a constant volume enclosure. I think this would make a "perfect" G-suit, and I reckon someone could withstand much higher g-forces inside a capsule like this. You could monitor and modify the pressure in the enclosure quite easily to maximise external suport for the person. |
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I do not think it would make a lick of difference whether the person experiencing 9g was in air, water or custard. The amount of oxygen in the environment makes no difference if blood cannot reach your head to bring the oxygen to your thinker. |
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bungston, I don't agree. That is exactly how those suits work for fighter pilots. |
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Actually, fighter pilot G-Suits use air to inflate sections of the suit and restrict bloodflow to certain areas of the body, thus preventing all the blood from pooling in your head (and causing a "red out" as your brain is flooded with blood) or feet (and causing a "black out" as your brain runs out of oxygen) |
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See [link] for more information. |
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Thanks [emjay]. I look forward to seeing what [Ling] produces after reading about MAST trousers. The rotating pilot scheme alternates between blackout and redout. |
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Ok, maybe I had better explain a little:
Of course, G-Suits work by preventing blood from pooling in the lower body when the pilot is experiencing high positive G force. Why does the blood pool? It is because the pressure of the air surrounding his legs is almost the same as before, but the pressure of the blood is changed as follows: |
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At 1 G, the differential pressure of blood (head to toe)is about 1m height of water. The differential pressure of the air is also 1m height of air. |
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At 9G, the differential pressure of blood is about 9m height of water. The differential pressure of the air is also 9m height of air. |
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9m of water pressure is almost 1 bar: nearly 15psi.
9m of air column pressure is very little. |
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The point is that the G-suit tries to compensate for the 15 psi increase in blood pressure. |
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Now, without a G-suit, why would it make a difference if our pilot was standing in air or water?
It is because in air, he experiences a big difference in pressure between the blood in his legs and the surrounding air, but in water, the pressure of the blood in his legs is the same as the pressure of the water. |
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By the way, I don't think the system of pressurising the lower extremes prevents red out. How can squeezing the blood out of the lower body be responsible for reducing the blood in the head? Unless G-suits can make a vacuum. |
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What effect does differential pressure of things outside the body have on the differential pressure of things inside the body? |
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MAST trousers work by effectively decreasing the size of the circulatory system. When they are on you do not perfuse your legs. I am sure your legs do not like that, but they put up will all kinds of abuse. |
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I should have posted that rotary pilot thing as a seperate idea, since this discussion has little to do with the steam launcher. |
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Basically, the pressure outside the body equalises the pressure inside the body. When the pressure outside and inside is the same, then there is no reason for the blood to gather in that area. |
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/then there is no reason for the blood to gather in that area./ |
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Many folks have experienced greyout or blackout on standing up quickly when dehydrated. The heart must force blood uphill to the head, and if blood pressures are low it can be difficult to do. It is work to push blood uphill. At 9G it is a very steep hill. The AS in MAST means antishock, and they were developed to help folks who had lost blood and had low blood pressure. They artificially decrease vascular space and increase effective blood volume. |
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But if you experienced 9G acceleration while standing in water (which is also experiencing the same acceleration), then the water acts just like the trousers. |
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[Ling], you are a smart [Ling], and I know that if you prove me wrong I will have learned something. If what you say is true, then pilots could avoid blacking out simply by having a suit containing an inch of gelatin adjacent to their skin at all points. This instead of MAST which effectively puts tourniquets on their legs. I think that if the outside and the inside are not in continuity, the only effect pressure difference have is to strain the sides of the vessel. |
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Here is a thought experiment. You have a closed loop of pipe one meter high, containing water. In the pipe is a pump. You must pump a liter of water from the bottom of the pipe up and over the top. Let us neglect the upward tension draw of the water descending. |
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Your apparatus is at earth gravity. You perform your first run at sea level on the beach at Hanalei (where I often find myself during thought experiments). You run it again at the bottom of the Marianas trench. You run it a third time back on the beach,but this time in a glass bell containing a hard vacuum (tourists press their noses up to the glass, watching you). |
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Does your engine use differing amounts of energy each time? /Why does the blood pool? It is because the pressure of the air surrounding his legs is almost the same as before, but the pressure of the blood is changed as follows:/ If this is true, then the energy requirement foryour pump should be different each time. But how does the water in the pipe know what is outside? |
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bungston, I think you are missing a key concept. I will try to answer you points one by one, then I will try to explain in another way. |
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//pilots could avoid blacking out simply by having a suit containing an inch of gelatin adjacent to their skin at all points//.
Yes and No. Just simply covering yourself with gelatin might be fun, but it wouldn't work. The gelatin must be inside a rigid container, then it would work. |
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//Here is a thought experiment//.
Yes, you are right, there is no difference for a closed loop inside a rigid container. |
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I guess my answers didn't help much, so I will try with a balloon:
The balloon is inflated with water. Under normal Earth gravity, the balloon tends to sag a bit and bulge out at the bottom. The balloon probably resembles some of the Earth's inhabitants. The pressure at the bottom of the balloon is higher than the pressure at the top of the balloon, because of the height of the water above it.
Now if we put the balloon in a swimming pool, what happens to the shape of the balloon? It is supported rather well, and I would expect that it would most likely take on a rounder shape, with no bulging at the bottom. This is because the pressure of the water in the swimming pool also varies according to the height in exactly the same way, and perfectly compensates the variation of pressure in the balloon.
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If we were to take the swimming pool and balloon, and accelerate it upwards at high G force, the balloon would not change shape because the water pressure in the pool compensates exactly for the water pressure in the balloon. |
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Now replace balloon with person, and swimming pool with a smaller tank of water, and we will have a G-Force compensation system. |
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//The mass, being carried in a sled that closely fits the tube, would be accelerated like a steam locomotive on steroids. //
Bad science. You can't get your vehicle to go faster than the speed of sound of steam at the temperature you're using, and that is ten times less than orbital velocity.
The V(rms) of a steam molecule at 1000F is .86 km/s, while orbital velocity is 8 km/s for a low orbit. The vehicle can't go faster than the molecules of gas pushing it, so you never make orbit.
If you heat hydrogen to the same temperature, the max speed is then 2.6 km/s, which is still short of orbital velocity. |
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[Ling], what you say is true for balloons, but people generally adhere to their shapes. Vessels do not stretch that much. People with hypertension do not bulge grotesquely, distended by the high pressures within. I do not think the ankle of a pilot experiencing 9G is 9 times the diameter that it was at 1G. |
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//what you say is true for balloons//, OK, to spare everyone, let's agree that we could send a balloon at high G into space by putting it in a tank of water, and forget about people. Balloons are so much prettier. |
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//It's always good when you come around, [Bunsen]. Especially with the maths.// |
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Why thankyou [bungston]. This is the only place I really get to exercise my year 10 algebra and physics. |
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Meanwhile, this would work just fine on the moon, where gravity is lower. |
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Isn't this less an issue of pressure and more an issue of pumping head(which is similar to pressure but quite different to) The heart like any pump is capable of producing a certain amount of flow at a certain head or back pressure. This is based on the Horsepower rating of the pump. In the above sited example of a closed loop pipe you could operate said pump at any given outside pressure(or internal pressure) if entire system is operated at that pressure. The difference comes in when you consider head or back pressure. This is caused by either an elevated discharge or a restriction in the flow. All pumps have a maximum head that they can pump against before they deadhead or stop pumping all together. |
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For this question(human G Tolerance) we have 2 points of concern, internal backpresure caused by tissue compression(ie in a G suit or swimming pool) and vertical head pressure. As the G force increases all other things being equal the blood will pool because the heart can only overcome a certain vertical head(distance above the discharge point of the pumping chamber in this case the beginning of the aorta) as G forces increase you reach a point at which this head height falls below the top of the brain thus leaving parts of the brain without flow(and blacking out the pilot) By increasing the static back pressure of the circulatory system(a g suit)by compressing the tissue and causing a flow restriction the pump can then achieve a higher maximum head(height) thus continuing to flow blood to the brain. I think it is important to note that this can only be achieved by SQUEEZING the body(or the muscles as part of the HIC Maneuver which is part of the G suit system) this restricts the flow of blood. This is a double edge sword however as by restricting flow you are reducing oxygen delivery to the tissues of the body. The effective increase in head height is the key factor here. If a pilot is laying on his back then the effective head required is dropped from say 1.5 feet to less than 6 inches thus allowing a greated acceleration to be tolerated. |
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There is however a secondary concern and that is the compression of the body and the differential pressure to the atmosphere. As blood pressure increases the risk of rupture increases as well. Simply squeezing harder and increasing G force with the environment around the body at 1 Atm will result in an internal hemorrhage, burst blood vessles or lungs. I would guess that increases in atmospheric pressure would allow for the body to tolerate a much greater G force, but that the same issues that apply to deep sea diving would apply here. The need for decompression to avoid the bends. Use of a fluid based breathing medium could reduce potential for these sorts of injuries but does not address injuries to tissue due to pressure. Bone, muscle and cellular structure will eventually collapse under excess pressure but it has been shown that shock loads of 50Gs can be survived. This will also not address the issue of the bends if an increased atmospheric pressure is experienced by the pilot. |
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I hope this makes some sense. |
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