Yes, thanks for the website -- I got that in the end. And yes I noticed the first time I saw Terminator that his little computer code screen had 6502 assembly code going by.
They changed it to something else for T2.
I don't know if this is the right place to post this kind of stuff, but I had some trouble doing a Red Hat 9 install that involved not having the drivers for the hard drive on the install discs. The new drive was IDE-SATA, and my install discs couldn't see it. Any thoughts? Where should I post about this to get expert advice?
I was trying to install RedHat 9.0 onto a PC that had a SATA drive (the latest kind of IDE?) and there was no driver on the install disc, so it couldn't find a drive. We tried downloading SATA drivers for Linux and for RedHat and putting them on a CD (burning from Windoze XP). We unpacked the driver files and everything, but the installer (Anaconda) didn't seem to be able to find the stuff on the CD.
We tried the linux dd startup to the install, and it asked for us to insert a CD with the drivers on it, but it never seemed to read it. Either the disc didn't have what it was looking for, or the disc was the wrong format (Windoze XP) or the installer was busted, or something.
Has anybody else had this kind of trouble? Has anybody ever had to install some drivers during the install of RedHat 9? Does it work or not? What does Anaconda need to see on the disc in order to know that there are driver files there? What is it supposed to say when it finds them (or doesn't)?
We just ended up stuck in a "press OK when you put in the disk" or "go back" loop, i.e., we'd press "OK" and nothing would happen, and "going back" didn't go anywhere.
Please help because I may be upgrading some PCs and getting new motherboards that have these new SATA drive buses on them, and I'll be screwed if I can't get my RedHad distribution to load the driver right from the start.
It is true that deficit spending definitely has its place -- it's a macroeconomic truism.
However, when was the last time the Federal Government ran a surplus before Clinton? Not since FDR?
It makes sense to run deficits during economic downturns in order to stimulate the economy, and to keep things on a even keel. However, it also makes sense to run surpluses during boom times for the same reasons, which the government never seems to do, so the national debt keeps growing.
I seem to remember that under Carter (and before) they always mentioned the national debt along with the deficit. Ever since Reagan, and after the debt passed the one trillion mark, the news seemed to stop mentioning the national debt, and only mentioned the deficit.
Robot is slavic for "job" or "to work" and the term was originally coined as a reference to humanoid or android machine workers in the novel Rossum's Universal Robots, by Karel Capek, who I believe was Czech.
In the book, the "robots" were humanoid in shape, and able to perform tasks that humans perform.
I suppose that in the future, if somebody in Russia were to say something like oo menya iest robot, it could be taken to mean either "I have a job" or "I own a humanoid mechanical servant."
My understanding was also that android refers to a subclass of robots that are specifically made to outwardly resemble a real human, e.g., having skin and hair and so forth, human-like behaviour, human-sounding voice, etc. I don't know where the term might have originally been used, however.
The human body is the only infinitiely variable machine that may be built by unskilled labour.
It seems to me that a big issue is having banks in space for space colonists to save up all of their mining money (tax-free, hard currency based on gold and other commodities). With this comes the concept of exchange rates with earth-based currencies, the ability to guage lifestyle in space against lifestyle on earth, being able to buy earth-based commodities and finished goods and have them sent up, etc.
The fact of the Earth gravity well dictates that there will not be all that much exchange between earth and any eventual colonies (at least not for a long time), since moving people and stuff between will remain prohibitively costly. In other words, the colonies will be independent in some important sense. Or rather, they would have to be, in order to be viable long-term ventures, hence the need for banks and such based (legally, at least) in space, and international agreements (or just between the USA and other space-faring nations) about the sovereignty issues of space colonies.
The prospect of total economic and political freedom, if laid out in detail beforehand, could provide a big incentive for people to want to move to space. The whole gravity well issue makes space wars over sovereignty kind of unlikely (it would be hard for earth to send up troops to enforce claims, etc.), but if it is not clarified, then it could still be a problem for individuals, if not for the space society as a whole. Especially individuals who continued to travel between earth and space semi-regularly, who, while they would ultimately be a minority, would still be a vital factor in the growth of space colonization.
If the conditions are monotonous and potentially dangerous, and probably no chance of ever returning to earth, it might be worthwhile considering a prisoners-to-space program. It costs no small amount of money to keep people locked up for life down here anyway, and who else are you going to find to go?
The actual problem is the vertical part of the boost phase, as acceleration spent to counter gravitational acceleration is wasted (doesn't contribute to orbital velocity). Because of this, it's helpful to boost as strongly as possible during the vertical phase of launch. This is only about 1.5-2 km/sec of the launch delta-v, though, and at 4 gravities, you're only getting about a 30% penalty (thrust at 4 gravities, accelerate upwards at 3).
I see. This would be the main reason that an upper atmospheric launch would be of some benefit, is that right?
If you're already in the upper atmosphere, it's even less of a problem, as you can afford to thrust laterally (air resistance won't slow you down much). Boosting at a shallow angle from the horizontal still gives most of your thrust laterally, meaning the one gravity vertical acceleration costs you less than it otherwise would (draw a vector diagram and use the pythagorean theorem to get vector magnitudes to see how this works).
So, if you had a big enough aircraft that could lift enough to haul all of the fuel needed to add on the last Mach 20-25 of delta-v and the spacecraft into the upper atmosphere, you could launch from there with a nearly-horizontal trajectory and save the lost acceleration during the lift phase of a ground launch. I would imagine that a problem with this is that there are no such aircraft available at this time.
You also mentioned balloon launches. I keep imagining lenticular vehicles, perhaps with jettisonable SRBs attached, that would be lifted to altitude by balloons or by other really large lenticular aircraft, and then started up once in the upper atmosphere to make the trip to orbit.
...part of why NERVA-style nuclear rockets are so attractive [high Isp/exhaust velocity]. Passing hydrogen through a fission core gives you pretty much the best exhaust velocity you can get with an engine where engine components have to be at the exhaust temperature.
What does NERVA stand for, by the way? Why is hydrogen the best, here? Would another liquified gas, such as nitrogen, also be good? I would think it would be easier to deal with -- as you alluded to in one of your comments about hydrogen tank mass, etc., that make hydrogen problematic.
What's the deal with engine components having to be at the exhaust temperature? Wouldn't this almost always be true, since the fuel is going through and combusting inside the engine, or is there more to this?
Yes, I have certainly found this thread to be useful and informative! Hopefully I will be able to avoid making any stupid gaffes in any future postings, short stories or books I may try to write in the domain.
Hydrogen still takes enough fuel tank mass overhead that it's questionable whether it's worth it as a fuel, though (hydrocarbons are stored at much higher density, meaning a smaller tank and less craft weight).
So, are there any good hydrocarbon fuels that have comparable Isp to hydrogen? What makes a good hydrocarbon rocket fuel? What are the downsides of using hydrocarbon fuels? Why does liquid hydrogen seem to win in the end?
The NASA Space Shuttle uses solid rocket boosters, and I had gathered that these use some kind of hydrocarbon fuel or other. What's in them and what's good/bad about them?
In practice, Isp times 10 is about equal to your exhaust velocity, and every multiple of your exhaust velocity adds a ratio of 1/e to your dry:wet weight ratio. So, a rocket with a fuel with an Isp of 250 that wanted to go at 8 km/sec would need a delta-v of 3.2x its exhaust velocity (8000 / 2500), for a mass fraction of about 4% (e^-3.2) - i.e., 96% fuel, 4% structure plus cargo plus crew.
I'm not sure I perfectly follow this, so let me try to clarify a bit. For any rocket wanting to get into orbit, a delta-v of 8 km/sec is required, is that right? And in practice the exhaust velocity of the fuel is ten times the specific impulse, which, when divided into the required delta-v (for orbit) yields the multiple (or power?) of 1/e which gives the dry:wet ratio, is that right?
In other words, the delta-v is a fixed quantity for a given orbit, and the exhaust velocity of the fuel is also fixed (in practice 10 times the Isp), and that becomes the exponent on 1/e to yield the dry:wet ratio for the spaceship, right?
I take it that given some "wonder fuel" that provided an Isp of 800 (an exhaust velocity of 8000 km/sec), the launch weight of the fuel would only need to be 63% of the total mass of the craft, is that right?
This 1/e business sounds like it comes from a solution to some sort of definite integral with respect to time and mass of the rocket equation. Does that mean that this 1/e to the power of the delta-v over exhaust velocity only applies directly to single-stage rockets, and that the situation would be improved for multi-stage rockets?
The effect of a higher exhaust velocity is not only a higher impulse, but also the fact that you're ejecting your fuel at a higher rate, thereby lightening your launch vehicle as it flies at a faster rate, which basically translates into a higher overall effeciency. Is that a fair statement?
Just to ramble on a bit further...
The impulse provided by a given fuel depends upon how much fuel mass is ejected, and at what velocity, and for how long (F = mv, times time). This is all tied up in the chemical properties of the fuel and the engine that burns it, e.g., how massive are the ejected burned fuel molecules, how fast does it burn, and how fast does it get blasted out of the engine as it does, etc.
So, hydrogen is a light molecule, but it burns pretty well. What about something like a liquid sodium and flourine or chrlorine engine? Ignoring storage, melting-the-engine, possible pollution problems for the moment, would these fuels be better because the ejected fuel molecules are more massive, or is the reverse true? It seems to me that if such a fuel could provide the same exhaust velocity as hydrogen-oxygen, they would be better since there would be fewer total chemical reactions for the same mass of fuel, so you'd go through the fuel quicker for more initial thrust. Or is that barking up the wrong tree for some reason? I would be interested to hear if NaCl or NaF fuels had ever been considered by anyone.
One final thought: I assume that there is a limit to how great of a "wonder fuel" you could use for launches of human cargoes, since the ideal seems to be getting a lot of acceleration right at the start right away, and that brings you back to the problem of launching humans with rail guns, i.e., the acceleration would be fatal, and so you're stuck to a certain extent hauling a large part of the fuel for a large part of the flight just to provide a reasonably gradual acceleration as opposed to a big jerk at the beginning.
Thanks for the explanation -- that line in the film always bothered me for the same reason, i.e., parsec is a measure of distance, not time (but it sounds like it might be about time, just like a "light-year"...;-)
Thanks again. It sounds like the delta-v issue puts the kybosh on using airplanes to get into space. It all comes back to rockets, again...
Let me just make sure I'm clear on some terms and concepts. Isp means specific impulse or something? Is "delta-v" the same as acceleration, or just that you have to get from sitting still on the earth to 8km/sec in a short period of time to get to orbit? Is 8km/sec escape velocity, by the way? If so, then am I right in saying that 8km/sec is about 28,800 km/hr, and that's about 25 or so times the speed of sound, or Mach 25, which means you need to be going Mach 25 to get into and stay in orbit?
And this is way faster than airplanes go, hence the problem that an airplane fails to solve.
So, in the end, lifting a lot of mass into space from the earth is a big problem, so at some point, infrastructure in space in the form of mining and manufacturing of the heavy stuff has to be put in place, as well as finding the water, carbon, and probably the air for the colonies. We only want to have to shoot up the actual (initial) humans, animals, and plant seeds and such, and somehow find or make the rest of the stuff out there.
How to get that process somehow started seems to be crucial to the question of getting viable off-earth colonies going. Is that a fair statement?
Moving difficult-to-produce finished goods (like complicated machinery and semiconductor products and so forth) from Earth to the building site could be done with a space elevator or with mature chemical launchers. Most of the cost of current space launches is the cost of manufacture and infrastructure for spacecraft, not the cost of fuel. Once materials and techniques advance to the point where launch craft are mature commodity items, and fuel dominates launch cost, it becomes practical to lift machinery, people, and construction craft up.
At this point, colonization of space will begin.
This is a very good point, i.e., that we will start to colonize space once the way to get into space becomes "a commodity," which it arguably is not at the moment.
Why rockets? Are space elevators the only alternative?
Good point about launchers not being to the point that fuel is the critical cost element. I would be interested in more details on the engineering and economics of space elevators, too, by the way.
It seems to me that there is not much attention being given to the idea of large, flying disk/wing aircraft that could fly up to high altitudes and then switch to rocket propulsion as a means for lifting large payloads on a reliable, safe, and regular schedule. The commercial aerospace industry is pretty close to the "fuel as the primary cost" situation which you mention.
Is this notion fundamentally flawed in some way; is there something I'm not seeing?
Popular Mechanics did a
cover story about lenticular aircraft, and there are lots of
other articles there, too. Apparently the Nazis did a lot of work on this, and after WWII the Air Force got all the technology and has been secretly working on it ever since. The point being that these things can be very big, and the whole fuselage is a lift-providing surface, so they could potentially carry a lot of material and still be able to stay aloft in the upper atmosphere.
I wrote a
little blurb about the space shuttle, winged vs. lenticular aircraft, etc., which might elicit some comment, by the way.
I assume that getting out of the atmosphere is not a problem as far as frictional heating of the outer skin of the craft goes, but getting back in would be an issue since it would be slowing down from orbital velocities to upper-atmospheric cruising speeds, so part or all of the skin of the craft would have to be covered with some kind of heat-management material (like the tiles on the space shuttle) or some kind of "active" heat evacuation system.
"In the future, it will take two hours to get anywhere on the planet -- one hour to get there, and one hour to get to the airport." -- Robert McNamarra
In this vein, can we imagine trans-atmospheric aircraft taking off from airports on Earth, flying out of the atmosphere into orbit, and then returning to Earth at another airport? Or, even better, in some cases rendez-vousing with an orbiting airport-spacestation, disembarking and picking up transit passengers, and then returning to Earth? It currently takes 18 hours just to fly from LAX to New Zealand, and many people take much longer flights -- that's plenty of time to get into orbit, dock with an orbiting spaceport/hotel, maybe sta
I think this is all very exciting! I, too, very much like the idea of inflatable space stations orbiting the earth, with people living in them.
How long do you think it will be until we start to see:
Inflatable space stations that are rotating so as to provide artificial gravity
Space stations that are environmentally self-contained, i.e., with plants and animals and goodly amounts of open water and topsoil-like material on board, using the sun's energy to maintain a self-supporting ecosystem
Microcosms of endangered plant and animal ecosystems on earth transplanted or reproduced into large biospheres in space
Biosphere "prisons in space". Lifers and three-time-losers shipped off-planet as the first space colonists (rather like the British did to first colonize Australia). Large part of the prison budget diverted to space colonization.
Universities (and cities) in space
Water and topsoil-like materials mined or collected from near-earth comet-like objects (or the moon) rather than schlepped up there on rockets or trans-atmospheric aerospacecraft
I hope that Zeppelins make a comeback, too. Given that heavier-than-air travel is becoming so over-regulated and a pain-in-the-butt, perhaps for that reason alone we'll see Zeppelin stops all over the place.
Could be a good point that zeppelins could be better than puddle-jumpers for local travel. Plus, if I don't have to be strip-searched to board one, great!
A buddy of mine and I are working on a board game to help teach machine coding concepts. My friend is not a programmer, but he says just the little bit we've done on the game so far has greatly improved his understanding of how computers really work internally.
My motivation is that the next generation of computer programmers (people growing up now and eventually my 6-year-old son and his contemporaries) should have only had exposure to OOPsy languages, GUI-screwy windowing environments and so forth, and won't have a clue about the many, many layers of abstraction that lie between those and the hardware.
I see this as a potential major crisis in the making for the programming community in general.
This is a good point. How does a company like Sony (or Apple, for that matter) make money inventing hardware and then making it "open architecture"?
Patents exist so that inventors may exploit their inventions with an advantageous time-lead or the right to license to others. Is there another model for how to do this so that inventors are actually motivated to come up with new stuff?
I suppose that charging exorbitant licensing fees so that nobody else can afford to compete is "bad," but that's a grey area...
This sounds(?) about right, from what little I know of Dutch pronounciation.
This being the 21st Century already and all, one would think that we'd be to the point where somebody who knows how to pronounce Cassini-Heygens would be able to easily upload a sound clip somehow into a posting so that everybody else could just listen to it. Alas, not quite yet, it seems, but perhaps some of us will live to see it.
Just a thought...it would probably be a good idea to put a right-click menu option, "strangle," or suchlike on little widgets like "clippy" (and that helpful dolphin character...!).
A kind of psychological release similar to the "TV Brick".
P.S.: yes, I've heard that Joe Camel was deliberately designed to look "phalic" (and it is fairly readily seen). I gather that this is a fairly standard hacking-of-the-lower-brain-stem approach that advertizers take (in countries where you cannot just put a nekkid woman next to the product, for instance).
I have misgivings about our being able to get a real foothold in space using rockets (from the earth's surface) but is anybody working on any other approaches? Here's an
article about the space shuttle, etc., that might elicit comment.
Good article about the "uncanny valley" (the last 1% on the road to realism where the results drop off sharply and the characters suddenly start looking freaky, rather than more lifelike).
I'm more and more impressed by the CGI films coming out from Pixar and DreamWorks (Shrek, Antz, Toy Story, Finding Nemo, etc.). There's an evolution from toys (machines), to insects, to animals, and now more and more humanoid characters. I'm have always assume that this trend toward better and better realism would continue, maybe even to the point that actors would become obsolete/optional within the foreseeable future.
In film, I think they use a lot of "biological models" (mechanical models of bones, muscles, skin, etc.) to produce the expressions and the positions of the characters, and the results seem pretty good. I assume that this is not done in games, but I could be wrong (does anybody know?).
Do any games use biological models to produce the characters in real-time, or do they use a simpler, less CPU-intensive approach?
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Yes, thanks for the website -- I got that in the end. And yes I noticed the first time I saw Terminator that his little computer code screen had 6502 assembly code going by. They changed it to something else for T2.
I don't know if this is the right place to post this kind of stuff, but I had some trouble doing a Red Hat 9 install that involved not having the drivers for the hard drive on the install discs. The new drive was IDE-SATA, and my install discs couldn't see it. Any thoughts? Where should I post about this to get expert advice?
I was trying to install RedHat 9.0 onto a PC that had a SATA drive (the latest kind of IDE?) and there was no driver on the install disc, so it couldn't find a drive. We tried downloading SATA drivers for Linux and for RedHat and putting them on a CD (burning from Windoze XP). We unpacked the driver files and everything, but the installer (Anaconda) didn't seem to be able to find the stuff on the CD.
We tried the linux dd startup to the install, and it asked for us to insert a CD with the drivers on it, but it never seemed to read it. Either the disc didn't have what it was looking for, or the disc was the wrong format (Windoze XP) or the installer was busted, or something.
Has anybody else had this kind of trouble? Has anybody ever had to install some drivers during the install of RedHat 9? Does it work or not? What does Anaconda need to see on the disc in order to know that there are driver files there? What is it supposed to say when it finds them (or doesn't)?
We just ended up stuck in a "press OK when you put in the disk" or "go back" loop, i.e., we'd press "OK" and nothing would happen, and "going back" didn't go anywhere.
Please help because I may be upgrading some PCs and getting new motherboards that have these new SATA drive buses on them, and I'll be screwed if I can't get my RedHad distribution to load the driver right from the start.
It is true that deficit spending definitely has its place -- it's a macroeconomic truism.
However, when was the last time the Federal Government ran a surplus before Clinton? Not since FDR?
It makes sense to run deficits during economic downturns in order to stimulate the economy, and to keep things on a even keel. However, it also makes sense to run surpluses during boom times for the same reasons, which the government never seems to do, so the national debt keeps growing.
I seem to remember that under Carter (and before) they always mentioned the national debt along with the deficit. Ever since Reagan, and after the debt passed the one trillion mark, the news seemed to stop mentioning the national debt, and only mentioned the deficit.
Robot is slavic for "job" or "to work" and the term was originally coined as a reference to humanoid or android machine workers in the novel Rossum's Universal Robots, by Karel Capek, who I believe was Czech.
In the book, the "robots" were humanoid in shape, and able to perform tasks that humans perform.
I suppose that in the future, if somebody in Russia were to say something like oo menya iest robot, it could be taken to mean either "I have a job" or "I own a humanoid mechanical servant."
My understanding was also that android refers to a subclass of robots that are specifically made to outwardly resemble a real human, e.g., having skin and hair and so forth, human-like behaviour, human-sounding voice, etc. I don't know where the term might have originally been used, however.
Thanks! I found that NERVA is also an acronym for Nuclear Engine for Rocket Vehicle Application , as well as being a Roman Emperor.
Living in Japan, I guess I sometimes feel a little disempowered when it comes to looking things up for some reason. Must work on that... ;-)
Here's another good link about nuclear engines for space, by the way.
It seems to me that a big issue is having banks in space for space colonists to save up all of their mining money (tax-free, hard currency based on gold and other commodities). With this comes the concept of exchange rates with earth-based currencies, the ability to guage lifestyle in space against lifestyle on earth, being able to buy earth-based commodities and finished goods and have them sent up, etc.
The fact of the Earth gravity well dictates that there will not be all that much exchange between earth and any eventual colonies (at least not for a long time), since moving people and stuff between will remain prohibitively costly. In other words, the colonies will be independent in some important sense. Or rather, they would have to be, in order to be viable long-term ventures, hence the need for banks and such based (legally, at least) in space, and international agreements (or just between the USA and other space-faring nations) about the sovereignty issues of space colonies.
The prospect of total economic and political freedom, if laid out in detail beforehand, could provide a big incentive for people to want to move to space. The whole gravity well issue makes space wars over sovereignty kind of unlikely (it would be hard for earth to send up troops to enforce claims, etc.), but if it is not clarified, then it could still be a problem for individuals, if not for the space society as a whole. Especially individuals who continued to travel between earth and space semi-regularly, who, while they would ultimately be a minority, would still be a vital factor in the growth of space colonization.
If the conditions are monotonous and potentially dangerous, and probably no chance of ever returning to earth, it might be worthwhile considering a prisoners-to-space program. It costs no small amount of money to keep people locked up for life down here anyway, and who else are you going to find to go?
The actual problem is the vertical part of the boost phase, as acceleration spent to counter gravitational acceleration is wasted (doesn't contribute to orbital velocity). Because of this, it's helpful to boost as strongly as possible during the vertical phase of launch. This is only about 1.5-2 km/sec of the launch delta-v, though, and at 4 gravities, you're only getting about a 30% penalty (thrust at 4 gravities, accelerate upwards at 3).
I see. This would be the main reason that an upper atmospheric launch would be of some benefit, is that right?
If you're already in the upper atmosphere, it's even less of a problem, as you can afford to thrust laterally (air resistance won't slow you down much). Boosting at a shallow angle from the horizontal still gives most of your thrust laterally, meaning the one gravity vertical acceleration costs you less than it otherwise would (draw a vector diagram and use the pythagorean theorem to get vector magnitudes to see how this works).
So, if you had a big enough aircraft that could lift enough to haul all of the fuel needed to add on the last Mach 20-25 of delta-v and the spacecraft into the upper atmosphere, you could launch from there with a nearly-horizontal trajectory and save the lost acceleration during the lift phase of a ground launch. I would imagine that a problem with this is that there are no such aircraft available at this time.
You also mentioned balloon launches. I keep imagining lenticular vehicles, perhaps with jettisonable SRBs attached, that would be lifted to altitude by balloons or by other really large lenticular aircraft, and then started up once in the upper atmosphere to make the trip to orbit.
Thanks again for all your great postings!
What does NERVA stand for, by the way? Why is hydrogen the best, here? Would another liquified gas, such as nitrogen, also be good? I would think it would be easier to deal with -- as you alluded to in one of your comments about hydrogen tank mass, etc., that make hydrogen problematic.
What's the deal with engine components having to be at the exhaust temperature? Wouldn't this almost always be true, since the fuel is going through and combusting inside the engine, or is there more to this?
Yes, I have certainly found this thread to be useful and informative! Hopefully I will be able to avoid making any stupid gaffes in any future postings, short stories or books I may try to write in the domain.
Hydrogen still takes enough fuel tank mass overhead that it's questionable whether it's worth it as a fuel, though (hydrocarbons are stored at much higher density, meaning a smaller tank and less craft weight).
So, are there any good hydrocarbon fuels that have comparable Isp to hydrogen? What makes a good hydrocarbon rocket fuel? What are the downsides of using hydrocarbon fuels? Why does liquid hydrogen seem to win in the end?
The NASA Space Shuttle uses solid rocket boosters, and I had gathered that these use some kind of hydrocarbon fuel or other. What's in them and what's good/bad about them?
In practice, Isp times 10 is about equal to your exhaust velocity, and every multiple of your exhaust velocity adds a ratio of 1/e to your dry:wet weight ratio. So, a rocket with a fuel with an Isp of 250 that wanted to go at 8 km/sec would need a delta-v of 3.2x its exhaust velocity (8000 / 2500), for a mass fraction of about 4% (e^-3.2) - i.e., 96% fuel, 4% structure plus cargo plus crew.
I'm not sure I perfectly follow this, so let me try to clarify a bit. For any rocket wanting to get into orbit, a delta-v of 8 km/sec is required, is that right? And in practice the exhaust velocity of the fuel is ten times the specific impulse, which, when divided into the required delta-v (for orbit) yields the multiple (or power?) of 1/e which gives the dry:wet ratio, is that right?
In other words, the delta-v is a fixed quantity for a given orbit, and the exhaust velocity of the fuel is also fixed (in practice 10 times the Isp), and that becomes the exponent on 1/e to yield the dry:wet ratio for the spaceship, right?
I take it that given some "wonder fuel" that provided an Isp of 800 (an exhaust velocity of 8000 km/sec), the launch weight of the fuel would only need to be 63% of the total mass of the craft, is that right?
This 1/e business sounds like it comes from a solution to some sort of definite integral with respect to time and mass of the rocket equation. Does that mean that this 1/e to the power of the delta-v over exhaust velocity only applies directly to single-stage rockets, and that the situation would be improved for multi-stage rockets?
The effect of a higher exhaust velocity is not only a higher impulse, but also the fact that you're ejecting your fuel at a higher rate, thereby lightening your launch vehicle as it flies at a faster rate, which basically translates into a higher overall effeciency. Is that a fair statement?
Just to ramble on a bit further...
The impulse provided by a given fuel depends upon how much fuel mass is ejected, and at what velocity, and for how long (F = mv, times time). This is all tied up in the chemical properties of the fuel and the engine that burns it, e.g., how massive are the ejected burned fuel molecules, how fast does it burn, and how fast does it get blasted out of the engine as it does, etc.
So, hydrogen is a light molecule, but it burns pretty well. What about something like a liquid sodium and flourine or chrlorine engine? Ignoring storage, melting-the-engine, possible pollution problems for the moment, would these fuels be better because the ejected fuel molecules are more massive, or is the reverse true? It seems to me that if such a fuel could provide the same exhaust velocity as hydrogen-oxygen, they would be better since there would be fewer total chemical reactions for the same mass of fuel, so you'd go through the fuel quicker for more initial thrust. Or is that barking up the wrong tree for some reason? I would be interested to hear if NaCl or NaF fuels had ever been considered by anyone.
One final thought: I assume that there is a limit to how great of a "wonder fuel" you could use for launches of human cargoes, since the ideal seems to be getting a lot of acceleration right at the start right away, and that brings you back to the problem of launching humans with rail guns, i.e., the acceleration would be fatal, and so you're stuck to a certain extent hauling a large part of the fuel for a large part of the flight just to provide a reasonably gradual acceleration as opposed to a big jerk at the beginning.
Thanks for the explanation -- that line in the film always bothered me for the same reason, i.e., parsec is a measure of distance, not time (but it sounds like it might be about time, just like a "light-year"... ;-)
Thanks again. It sounds like the delta-v issue puts the kybosh on using airplanes to get into space. It all comes back to rockets, again...
Let me just make sure I'm clear on some terms and concepts. Isp means specific impulse or something? Is "delta-v" the same as acceleration, or just that you have to get from sitting still on the earth to 8km/sec in a short period of time to get to orbit? Is 8km/sec escape velocity, by the way? If so, then am I right in saying that 8km/sec is about 28,800 km/hr, and that's about 25 or so times the speed of sound, or Mach 25, which means you need to be going Mach 25 to get into and stay in orbit?
And this is way faster than airplanes go, hence the problem that an airplane fails to solve.
So, in the end, lifting a lot of mass into space from the earth is a big problem, so at some point, infrastructure in space in the form of mining and manufacturing of the heavy stuff has to be put in place, as well as finding the water, carbon, and probably the air for the colonies. We only want to have to shoot up the actual (initial) humans, animals, and plant seeds and such, and somehow find or make the rest of the stuff out there.
How to get that process somehow started seems to be crucial to the question of getting viable off-earth colonies going. Is that a fair statement?
Wow! Thanks for the reply!
Moving difficult-to-produce finished goods (like complicated machinery and semiconductor products and so forth) from Earth to the building site could be done with a space elevator or with mature chemical launchers. Most of the cost of current space launches is the cost of manufacture and infrastructure for spacecraft, not the cost of fuel. Once materials and techniques advance to the point where launch craft are mature commodity items, and fuel dominates launch cost, it becomes practical to lift machinery, people, and construction craft up.
At this point, colonization of space will begin.
This is a very good point, i.e., that we will start to colonize space once the way to get into space becomes "a commodity," which it arguably is not at the moment.
Why rockets? Are space elevators the only alternative?
Good point about launchers not being to the point that fuel is the critical cost element. I would be interested in more details on the engineering and economics of space elevators, too, by the way.
It seems to me that there is not much attention being given to the idea of large, flying disk/wing aircraft that could fly up to high altitudes and then switch to rocket propulsion as a means for lifting large payloads on a reliable, safe, and regular schedule. The commercial aerospace industry is pretty close to the "fuel as the primary cost" situation which you mention.
Is this notion fundamentally flawed in some way; is there something I'm not seeing?
Popular Mechanics did a cover story about lenticular aircraft, and there are lots of other articles there, too. Apparently the Nazis did a lot of work on this, and after WWII the Air Force got all the technology and has been secretly working on it ever since. The point being that these things can be very big, and the whole fuselage is a lift-providing surface, so they could potentially carry a lot of material and still be able to stay aloft in the upper atmosphere. I wrote a little blurb about the space shuttle, winged vs. lenticular aircraft, etc., which might elicit some comment, by the way.
I assume that getting out of the atmosphere is not a problem as far as frictional heating of the outer skin of the craft goes, but getting back in would be an issue since it would be slowing down from orbital velocities to upper-atmospheric cruising speeds, so part or all of the skin of the craft would have to be covered with some kind of heat-management material (like the tiles on the space shuttle) or some kind of "active" heat evacuation system.
"In the future, it will take two hours to get anywhere on the planet -- one hour to get there, and one hour to get to the airport." -- Robert McNamarra
In this vein, can we imagine trans-atmospheric aircraft taking off from airports on Earth, flying out of the atmosphere into orbit, and then returning to Earth at another airport? Or, even better, in some cases rendez-vousing with an orbiting airport-spacestation, disembarking and picking up transit passengers, and then returning to Earth? It currently takes 18 hours just to fly from LAX to New Zealand, and many people take much longer flights -- that's plenty of time to get into orbit, dock with an orbiting spaceport/hotel, maybe sta
I think this is all very exciting! I, too, very much like the idea of inflatable space stations orbiting the earth, with people living in them.
How long do you think it will be until we start to see:
I hope that Zeppelins make a comeback, too. Given that heavier-than-air travel is becoming so over-regulated and a pain-in-the-butt, perhaps for that reason alone we'll see Zeppelin stops all over the place.
Could be a good point that zeppelins could be better than puddle-jumpers for local travel. Plus, if I don't have to be strip-searched to board one, great!
A buddy of mine and I are working on a board game to help teach machine coding concepts. My friend is not a programmer, but he says just the little bit we've done on the game so far has greatly improved his understanding of how computers really work internally.
My motivation is that the next generation of computer programmers (people growing up now and eventually my 6-year-old son and his contemporaries) should have only had exposure to OOPsy languages, GUI-screwy windowing environments and so forth, and won't have a clue about the many, many layers of abstraction that lie between those and the hardware.
I see this as a potential major crisis in the making for the programming community in general.
This is a good point. How does a company like Sony (or Apple, for that matter) make money inventing hardware and then making it "open architecture"?
Patents exist so that inventors may exploit their inventions with an advantageous time-lead or the right to license to others. Is there another model for how to do this so that inventors are actually motivated to come up with new stuff?
I suppose that charging exorbitant licensing fees so that nobody else can afford to compete is "bad," but that's a grey area...
This sounds(?) about right, from what little I know of Dutch pronounciation.
This being the 21st Century already and all, one would think that we'd be to the point where somebody who knows how to pronounce Cassini-Heygens would be able to easily upload a sound clip somehow into a posting so that everybody else could just listen to it. Alas, not quite yet, it seems, but perhaps some of us will live to see it.
Just a thought...it would probably be a good idea to put a right-click menu option, "strangle," or suchlike on little widgets like "clippy" (and that helpful dolphin character...!).
A kind of psychological release similar to the "TV Brick".
P.S.: yes, I've heard that Joe Camel was deliberately designed to look "phalic" (and it is fairly readily seen). I gather that this is a fairly standard hacking-of-the-lower-brain-stem approach that advertizers take (in countries where you cannot just put a nekkid woman next to the product, for instance).
I have misgivings about our being able to get a real foothold in space using rockets (from the earth's surface) but is anybody working on any other approaches? Here's an article about the space shuttle, etc., that might elicit comment.
Good article about the "uncanny valley" (the last 1% on the road to realism where the results drop off sharply and the characters suddenly start looking freaky, rather than more lifelike).
I'm more and more impressed by the CGI films coming out from Pixar and DreamWorks (Shrek, Antz, Toy Story, Finding Nemo, etc.). There's an evolution from toys (machines), to insects, to animals, and now more and more humanoid characters. I'm have always assume that this trend toward better and better realism would continue, maybe even to the point that actors would become obsolete/optional within the foreseeable future.
In film, I think they use a lot of "biological models" (mechanical models of bones, muscles, skin, etc.) to produce the expressions and the positions of the characters, and the results seem pretty good. I assume that this is not done in games, but I could be wrong (does anybody know?).
Do any games use biological models to produce the characters in real-time, or do they use a simpler, less CPU-intensive approach?