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Alternative to Rockets
"Roger Stokes" wrote in message ...
As was pointed out in an earlier post to this web site, well designed and packed "cargo" can withstand hundreds to thousands of gees acceleration. A 1000G electromagnetic launcher would only I'm well aware of the ability for cargo to survive 1000G (and higher) launches. I was specifically addressing passengers in cannon-type launch systems. Mike Miller, Materials Engineer |
#22
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Alternative to Rockets
"George Kinley" wrote in message ...
Are there any way for rockets to fly in space , other then throwing mass out in one direction and moving in other I computed a table relating power to thrust, and was off by a factor of g0 - that's the acceleration of gravity. In metric units this is 9.82 m/s/s. So the table posted parallel to this was WATTS PER NEWTON, not WATTS PER KG as stated in the text. Okay so the revised table for WATTS PER KG OF THRUST is; HOW BIG IS YOUR ENGINE? IN WATTS Auto Airline Supertanker Type Ve W/kg HP/lb 1000 300000 500000000 Chemical5.6 27496 16.76 27.4E+6 8.25E+9 1.3748E+13 Fission 42000 206E+6 125702 2.1E+11 6.2E+13 1.0311E+17 Fusion 134000 657E+6 401050 6.6E+11 2.0E+14 3.2897E+17 Photon 300000 1.47E+9 897875 1.5E+12 4.4E+14 7.365E+17 Other interesting Numbers: Average US Home: 833 200 HP Engine: 143,000 US Utility Grid: 800E+9 Humanity (all forms)4E+12 Solar Output: 3.8E+26 If humanity were space faring they'd have say, four billion fusion rocket fliers the size of autos, along with say 4 million airliner sized vehicles and 40,000 supertanker size freighters. At any one time a quarter of the autosized vehicles and airliner sized vehicles might be operating, three-quarters of the big guys would be operating, so humanity's power consumption if spacefaring would be; AUTO - FUSION - 1E9 * 6.6E11 = 6.6E20 AIRCRAFT - FUSION - 1E6 * 2.0E14 = 2.0E20 SUPERTANK- PHOTON - 3E4 * 7.4E17 = 2.2E22 INTERNAL USE - industrial use 2.0E13 Which all adds up to 2.2E22 watts of usage - about 1/17,000th the sun's total output At a 7% economic growth rate we could double usage every 10 years. This lets us compute that it would take 323 years for humanity to reach this level of consumption. Of course, widespread use of laser beamed energy and nuclear fusion power (once its available) would be a quantum leap that would not be part and parcel of the natural growth of the existing energy infrastructure. In that case, we might expect a doubling every year rather than every ten years. Just as low cost computing caused a doubling of computer use. That would mean we could transition to a space faring species with a spaceship in every garage in a single generation. Sweet. |
#23
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Alternative to Rockets
Mike Miller wrote:
2) Mass drivers/railguns/coilgun launchers. Unfortunately, the big electromagnetic launchers that can fling a spaceship into orbit without turning passengers to goo is really, really long, like 600-700 miles for a 3G launch. Not that it would be a "make or break" factor, but they did centrifuge tests way back where the subjects were immersed in water, then spun up. The water pressure outside the body opposed the internal pressures, and the subjects/victims were able to carry on conversations at 12+ G's. I've thought that if you need to carry water on missions, for shielding and all of the other reasons, might as well put it to work for you. Just did a quick google...the Swiss have a suit called the Libelle that is based on the principle, lets you chit chat at 12 G's sustained. It would be higher laying back in a couch. |
#24
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Alternative to Rockets
2) Mass drivers/railguns/coilgun launchers. Unfortunately, the big
electromagnetic launchers that can fling a spaceship into orbit without turning passengers to goo is really, really long, like 600-700 miles for a 3G launch. Mike Miller, Materials Engineer AFAIK, if a human being is suspended in a fluid (easily deformable medium) which has the same specific gravity as the mean specific gravity of human tissue, then g-loadings on face down prone individuals can be very high for periods of several seconds and even minutes before significant short term ill effects are seen. I cannot recall the source, but believe the Air Force looked at "wet" cockpits to permit pilots to sustain maneuvers of many tens of g's, and determined that while the costs outweighed the benefits, no plane could be built which would overstress the pilot during the duration of the ACM that might be required. Perhaps 100g's for very short times would be tolerable. Certainly blood pooling of short durations is an acceptable risk for many when the destination is considered. Can anyone say how seconds a human being so supported can tolerate being accelerated at 10, 100, and (doubtfully at all) 1000gs. If I remember it ok, 10 seconds is little trouble indefinitely, 100 is barely doable for tens of seconds, and 1000 is out of the question (bones falling through soft tissue, etc.). Thank you, Tom Perkins |
#25
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Alternative to Rockets
A. A light sail.
B. A light sail that is also a "solar cell" and uses the electricity to power an ion rocket. Assume equal mass for A and B (at the start), that everything is 100% efficient and your speed is nowhere near relativistic. At the start, do you get more "go" from B or are they the same? Why? My guess is A: The solar cell is much heavier than a reflective sail. This effect totally dominates the more interesting effects, probably even if a reflective solar sail concentrates light on a much smaller solar cell. My guess is that B has better acceleration: you lose energy in the thrust stream, maybe 95% of it. But you put that energy into a much larger amount of momentum, supposing Ve C. But B will run out of "go" sooner than A, so A has more total impulse. Here's an interesting question of perhaps more relevance in the shorter term: is there a limit to the amount of velocity that can be picked up from gravitational slingshot maneovers, and if so, what sets that limit? I can see one kind of limit, which is that the perigee during a planet pass has a practical minimum, and so objects approaching with more velocity get less directional change. At some speed no alignment of the planets will bend the trajectory back into the solar system and the craft is on its way. |
#26
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Alternative to Rockets
In article , Olli Wilkman writes:
On Mon, 08 Mar 2004 16:30:28 GMT, "George Kinley" wrote: Are there any way for rockets to fly in space , other then throwing mass out in one direction and moving in other This isn't exactly in response to the question, but what is the current opinion on laser rockets? The idea is fairly simple, but I get the impression that currently it is not a very strong candidate. It is excellent grantmanship. Not much else. The latest news I found (and that was from November 2000) is that they've lifted a 51g craft to an altitude of 71 meters using a 10kW laser. "The 51 g, 12 cm diameter Lightcraft is propelled skyward when the laser beam hits a parabolic condensing reflector on its underside. This ablates a thin plastic coating, sending the craft upwards." (http://optics.org/articles/news/6/11/9/1) This thing is developed by a company called Lightcraft Technologies, Inc. (http://www.lightcrafttechnologies.com/news.html) as a method of launching micro-satellites. I wonder how they are currently doing - the "Latest Developements" section of their website is last updated in Dec 2000. The website describes the technology thus: "The back side of the craft is a large, highly polished parabolic mirror that is designed to capture the laser beam projected at it from the ground. The mirror focuses the beam, rapidly heating the air to 5 TIMES the temperature of the sun, creating a blast wave out the back that pushes the vehicle upward. As the beam is rapidly pulsed, the vehicle is continuously propelled forward, on its way to orbit." This seems to imply that no propellant is used as such, but the news article mentions a platic coating. If all you rely on is the air that's being heated up in the mirror's focus, there is precious little of that. If you introduce some solid to be ablated, this serves as propellant. Again, there is pretty little of this in the focal spot. Mati Meron | "When you argue with a fool, | chances are he is doing just the same" |
#27
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Alternative to Rockets
In sci.space.tech Mark Foskey wrote:
George Kinley wrote: Are there any way for rockets to fly in space , other then throwing mass out in one direction and moving in other If they don't work that way, then we don't call them rockets. One other possibility is a solar sail that uses the pressure of sunlight, but such a sail would have very low thrust. Strictly speaking, the solar sail too throws mass (photons) out in one direction and moves in the other direction. Where the mass being thrown out comes from is not too important. -- Sander +++ Out of cheese error +++ |
#28
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Alternative to Rockets
In article ,
wrote: In sci.physics Gordon D. Pusch wrote: 2.) Anything that does _not_ "throw mass out the back" (or more precisely, _momentum_) in order to accelerate would violate Newton's 3rd Law of Motion (AKA, the conservation of Momentum). In 300 years, _NO ONE_ has observed a replicatable violation of Conservation of Momentum. -- Gordon D. Pusch Ummm, how about "catching" momentum, i.e. a sail. Yeah, I know, it is still conserved. Homework problem: Given: A. A light sail. B. A light sail that is also a "solar cell" and uses the electricity to power an ion rocket. Assume equal mass for A and B (at the start), that everything is 100% efficient and your speed is nowhere near relativistic. At the start, do you get more "go" from B or are they the same? Why? For a given amount of energy in your exhaust stream, you'll get more thrust when you're throwing out more mass. If nothing else, B could be made to have more "go" by letting its specific impulse go to crap. But an ion engine, the propellant, and solar cells all add weight. I know there are solar panels either existing or in development that have organic layers on a thin plastic sheet, but designing solar sails involves engineering tradeoffs between the mass of aluminum deposited on the sail and the transparancy! For some reasonable figures on payload weight and sail weight and area (about a square kilometer) you're looking at about 0.5 mm/s^2 (recalling info from a book I'd read on the subject...). Solar sails won't win any sprints. The advantage is over the long haul, with an acceleration that never quits. -- "When the fool walks through the street, in his lack of understanding he calls everything foolish." -- Ecclesiastes 10:3, New American Bible |
#29
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Alternative to Rockets
In article ,
nafod40 wrote: Mike Miller wrote: 2) Mass drivers/railguns/coilgun launchers. Unfortunately, the big electromagnetic launchers that can fling a spaceship into orbit without turning passengers to goo is really, really long, like 600-700 miles for a 3G launch. Not that it would be a "make or break" factor, but they did centrifuge tests way back where the subjects were immersed in water, then spun up. The water pressure outside the body opposed the internal pressures, and the subjects/victims were able to carry on conversations at 12+ G's. I've thought that if you need to carry water on missions, for shielding and all of the other reasons, might as well put it to work for you. Just did a quick google...the Swiss have a suit called the Libelle that is based on the principle, lets you chit chat at 12 G's sustained. It would be higher laying back in a couch. Cool! If they're chit chatting and, well, breathing, I assume the head doesn't need additional protection at 12 G's? I think the standard flight suit applies regular pressure on the legs and torso, but as I recall a pilot can only go to about 8 G's before blacking out in a turn. What's different about that? -- "Things should be made as simple as possible -- but no simpler." -- Albert Einstein |
#30
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Alternative to Rockets
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