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Rockets not carrying fuel.
Posted to sci.astro:
================================================== ============================= From: Robert Clark ) Subject: Rockets not carrying fuel. Newsgroups: sci.astro, sci.space.policy, sci.physics Date: 2003-07-28 20:59:39 PST From this web page, the weight of the shuttle external tank with the liquid oxygen and hydrogen is 1.6 million pounds: EXTERNAL TANK http://science.ksc.nasa.gov/shuttle/...ewsref/et.html But the amount of liquid oxygen that is burned is only 2,787 pounds per second and the amount of hydrogen 465 pounds per second. Nanotube productions methods are advancing quickly. Suppose it is possible to make a fuel line of carbon nanotube material hundreds of kilometers long. Could fuel be pumped up to a rocket accelerating to orbital velocity? What would be the fuel requirements for a rocket that did not carry its own fuel? Say a rocket with the payload capacity of the shuttle and with engines of the efficiency of the shuttle main engines? Bob Clark ================================================== ============================= From: Robert Clark ) Subject: Rockets not carrying fuel. Newsgroups: sci.astro, sci.space.policy, sci.physics, sci.mech.fluids, sci.engr.mech Date: 2003-07-30 22:03:44 PST The total weight of the fuel and pipe would only have to be carried near the end of the trip. For the lowest part of the trip where typically according to the rocket equation most of the fuel gets burned, little mass for the fuel and pipe would have to be carried. What I wanted to see was how the rocket equation would be changed when for the great majority of the trip there is little fuel "cost" for the fuel weight itself. As for the pipe, I'm estimating according to the strength vs. lightness characteristics of carbon nanotubes that a thin walled pipe composed of nanotube material even a hundred kilometers long whould only weigh in the range of a few thousand kilos. The question then would be the mass of the fuel that needed to be carried or supported by the rocket. The first thing to notice is that when you don't have that huge 1.6 million pound mass attached that needs to be accelerated you might not need the high efficiency that a liquid hydrogen/liquid oxygen engine offers. Then in that case you might be able to do with just gaseous hydrogen and without an additional liquid oxygen oxidizer. This page suggests hydrogen is used in liquid form to save weight and bulk: Spaceflight :Principles of Rocketry "Hydrogen and oxygen are gases at ordinary temperatures. But it is not possible to store them as gases for use in a rocket. They would have to be compressed to carry them in quantity, and these compressed gases would have to be held in thick-walled tanks to withstand their pressure. These tanks would add weight, which is a rocket designer's enemy, for rocket builders always seek the lightest possible weight. When these gases are liquefied at low temperatures, the rocket can carry the largest possible quantities, and the tanks are light in weight." http://www.centennialofflight.gov/es...ockets/SP6.htm Hydrogen gas is quite light at 1 atm pressure, about .08 kg/m^3. So even if the pipe were 100km long and .1m wide giving it a volume on the order of 1000 m^3, the mass of the hydrogen in the pipe would be only 80 kg. But even liquid hydrogen is not very massive at about 71 kg/m^3 so it's mass within this 100km pipe would be only 71,000 kg, still quite a difference from 1.6 million pounds. But what if the rocket never even had to support the mass of the fuel? This page gives an example of a type of pump known as a ram pump that works from gravity alone and can raise liquids many times higher than the distance of the fall of a gravity driven stream: Contents for the pulser pump section of Gaiatech. http://members.tripod.com/~nxtwave/g...lser/index.htm This page gives a more general discussion of ram pumps: Designing a Hydraulic Ram Pump. http://www.lifewater.org/wfw/rws4/rws4d5.htm This method may also be adaptable to work for pumping gases. For a quite large fluid reservoir on the ground the force for raising the fuel to the rocket would be provided by the pump on the ground not the rocket. So the rocket would only be supporting the mass of the fuel pipe itself. In this case you might even be able to use both liquid hydrogen and liquid oxygen if the rocket did not have to support the weight of these liquids. Another possibility for pumping the fuel to the rocket might be to use the principle of a hydraulic lift. As shown on this page a large diameter piston moving a short distance can move a thin diameter piston a long distance via an incompressible fluid: How Hydraulic Machines Work http://science.howstuffworks.com/hydraulic1.htm (though in this case in order to drive the liquid 100km, the weight you might need to apply to the large piston might be that of a battleship.) As for the speed of the fuel and whether it would have to be accelerated to supersonic speeds. Note that what matters is its speed with respect to the *pipe*. So you could have the pipe being accelerated to high speed by the rocket while the fuel is moving at a rather slow speed *with respect to the pipe*, this speed being determined by the rocket's fuel requirements. As for cryogenic requirements, if it turns out you wanted to use a cryogenic fuel you might be able to insulate the fuel line with a vacuum jacket and move the fuel fast enough to limit the loss due to evaporation. Bob Clark Uncle Al wrote in message ... Dan Tilque wrote: Robert Clark wrote: But the amount of liquid oxygen that is burned is only 2,787 pounds per second and the amount of hydrogen 465 pounds per second. Those numbers don't look right. Shouldn't the LOX be about 8 A boundary layer of raw fuel is pumped down the inner walls of each combustion chamber to cool the walls. If you look at an apolitical rocket system launching - the Saturn moon rockets - you note closeup of the running engines at launch shows a black collar around each exhaust that flashes white hot a bit later on down. The black is a sheath of pyrolyzing kerosene that finally combusts. Nanotube productions methods are advancing quickly. Suppose it is possible to make a fuel line of carbon nanotube material hundreds of kilometers long. Could fuel be pumped up to a rocket accelerating to orbital velocity? Got to give you credit for thinking outside the box. This certainly is a unique idea. But I can't imagine there exists a pump that could do this. Or even come close. Especially since it has to operate at liquid oxygen temps. Turbopumping is no big deal, the Germans had it down pat for the V-2. Pumping anything at sonic velocities through a long thin pipe is really stooopid. You plug in the appropriate dimensionless number for flow, you see where the turbulent flow regime begins, then you carefully plan the project so you retire before the first shakedown demo. What insulates the cryogen from ambient temp? Nothing. Stooopid idea. ================================================== ============================= |
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Rockets not carrying fuel.
"Robert Clark" wrote in message
om... Nanotube productions methods are advancing quickly. Suppose it is possible to make a fuel line of carbon nanotube material hundreds of kilometers long. Could fuel be pumped up to a rocket accelerating to orbital velocity? [snipped stuff] An interesting idea. Assuming that a Space Tether is technically feasible it should be possible to do it with enormous compressors, but as you point out, there will be a lot of fuel lost on the way up. Given that it wouldn't be a good idea to run high voltage electrical equipment (like maintenance cars) anywhere near this pipeline, I'm not sure how you would maintain it and if it failed (due to lightning strike or collision) the resulting explosion could be seen for miles! How about going the other way and putting a liquefaction station in LEO?? AFAIK, there is enough atmosphere up there for this to work (just!).. Cameron:-) |
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Rockets not carrying fuel.
Cameron Dorrough wrote:
"Robert Clark" wrote in message om... Nanotube productions methods are advancing quickly. Suppose it is possible to make a fuel line of carbon nanotube material hundreds of kilometers long. Could fuel be pumped up to a rocket accelerating to orbital velocity? [snipped stuff] An interesting idea. Assuming that a Space Tether is technically feasible it should be possible to do it with enormous compressors, but as you point out, there will be a lot of fuel lost on the way up. I doubt you can actually pump fuel that fast without having the pipe end up more massive than the tank due to the pressure it needs to contain at the lower end. -- http://inquisitor.i.am/ | | Ian Stirling. ---------------------------+-------------------------+-------------------------- If God hadn't intended us to eat animals, He wouldn't have made them out of MEAT! - John Cleese |
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Rockets not carrying fuel.
Cameron Dorrough schrieb: How about going the other way and putting a liquefaction station in LEO?? AFAIK, there is enough atmosphere up there for this to work (just!).. Hallo (I'm new here) When I read this, I remember about planes, based on the "Zeppelin" technique. There the idea is to have a plattform in the higher atmosphere, hovering by heliumtanks in equatorial passat-winds around the earth. Such a plattform can be used as a fuel store (and other goods), refilled with ballistic drones from earth, and out of the space the fuel can be carried by a kind of lifter, like an elevator, or something else. There can be more than one plattform like this. They can operate remote controlled like the Helios ultralight aircraft. As I remember, there where planes in USA, with a ring structure in 1950 or so, but never realized. (At this time the solar panel did not work like today.) And this year someone in London brings up the idea to do a sat based internet with balloons over the city (this balloons can also carry traffic control systems or measure air pollution). The point is, that there should be installed a long time equipment for multiple use. The times where a one-way solution is used, seemed to be passed. So it is necessary to think about the cheapest possibility to do the transport, that problem will raise in the near future, and there is not only the way up. Sorry for my english. lin |
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