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| [Rant] Why I dislike Space Enthusiasts; Even though I arguably am one? | |
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| Topic Started: Jan 15 2012, 11:14 AM (3,280 Views) | |
| Ànraich | Jan 17 2012, 03:06 AM Post #46 |
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L'évolution Spéculative est moi
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I was being serious. I'll be damned if we let the Chinese or, god forbid, the French put people on other worlds before America. |
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We should all aspire to die surrounded by our dearest friends. Just like Julius Caesar. "The Lord Universe said: 'The same fate I have given to all things from stones to stars, that one day they shall become naught but memories aloft upon the winds of time. From dust all was born, and to dust all shall return.' He then looked upon His greatest creation, life, and pitied them, for unlike stars and stones they would soon learn of this fate and despair in the futility of their own existence. And so the Lord Universe decided to give life two gifts to save them from this despair. The first of these gifts was the soul, that life might more readily accept their fate, and the second was fear, that they might in time learn to avoid it altogether." - Excerpt from a Chanagwan creation myth, Legends and Folklore of the Planet Ghar, collected and published by Yieju Bai'an, explorer from the Celestial Commonwealth of Qonming Tree That Owns Itself
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| lamna | Jan 17 2012, 08:15 AM Post #47 |
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Unless we're going along with the French as part of a European effort. |
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Living Fossils Fósseis Vibos: Reserva Natural 34 MYH, 4 tonne dinosaur. [flash=500,450] Video Magic! [/flash] | |
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| Kamidio | Jan 17 2012, 03:33 PM Post #48 |
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The Game Master of the SSU:NC
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I was serious as well. Preston Afleck for whenever he decides to run for office. He'll have my vote. |
SSU:NC - Finding a new home. Quotes WAA
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| Zerraspace | Jan 17 2012, 05:04 PM Post #49 |
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When presenting your argument, you could have the courtesy to read the attached articles, which mention all of these issues and accompanying solutions all possible with available or readily foreseeable technologies, hence I will not repeat them here. If NASA does not believe these problems are insurmountable, I'll presume they've done their research better than I and go with it. You are also contradicting yourself or missing the point. Yes, we cannot mass produce carbon nanotubes, that is why we require an advancement in manufacturing technology to make this feat possible, and if we can create them to any extent currently then greater extents should be possible (please do not argue that these extents will always remain minute, you have no proof of that but that we cannot do it currently). You also say if such extent were possible, we could not produce bulk material with their tensile strength. I think it is assumed the desired technology is to mass produce tubes with said strength. The satellite figure was from Aerospace America, and it wasn't the only source to list it. What I was trying to prove that there was an available market capable of paying for a worthy space travel scheme (like my orbital elevator), without any advances, increased demand or radical changes in the economy. My asteroid mining scheme involves fusion thrusters (or drives if you prefer) simply because they provides far higher thrust than chemical rockets while consuming much less fuel, allowing a Brachistochrone orbit that we needn't wait for a flight window, and if it were possible to create a proton-proton I chain fusion reactor (however harder that may be than deuterium-tritium fusion), the fuel would be extremely abundant and dirt cheap (whereas tritium certainly is not)! Current hydrogen costs range from $0.7 to $12 dollars per kilo, and I assumed the latter amount for this exercise. With the orbital elevator, every kilogram could be transported for values ranging between a few to nearly $220 dollars; again I assumed the "worst-case" scenario. Thus far I have only finished calculations for a mineral collection vehicle, but the results look promising. Picture a mineral collection vehicle (MCV), massing roughly 1000 tons before fueling (less than the space shuttle with tanks and booster fully loaded) and capable of holding several multiples of that in cargo and propellant. The MCV is held in high earth orbit by a space elevator, and released and left to drift before starting so as to avoid harming the station. Once activated, it begins accelerating at a steady 0.1 G (I would have rather it could do 1 G, but the fuel weight rapidly got out of hand) towards a chosen target in the asteroid belt. Continuing to assume the worst numbers possible, our example is an asteroid at the outer borders of the asteroid belt (roughly 3.28 AU) that will, upon arrival, be directly opposite the Earth’ current position from the sun, and we will be following a circular rather than straight path towards it. Delta-V is nearly 2x10^6 m/s, and proton-proton fusion allows for maximum effective exhaust velocity of 11.7% lightspeed, hence the current mass ratio is 1.06 (this only includes the fuel required to get us here – more will be consumed delivering the cargo on the return journey), and the time till arrival is 23 days. A base has been set by earlier craft and was manned largely by smart automatons and perhaps one or two human overseers, meaning that a supply of freshly mined ores is already available. The ship’s canisters can carry a full weight of 8000 tons (probably higher, but without exact knowledge of the ore’s composition and ship volume I must resort to guesswork), and once readied the ship turns tail and heads back for the Earth. Again delta-V is 2x10^6 m/s, the mass ratio is 1.06 (this time most fuel will in fact be burned), and the journey will take nearly 23 days (somewhat less, since the Earth moves in its orbit faster than the asteroid and has therefore closed in, but I am not taking that into account). Depending on the type of asteroid chosen, the returned ores may be 50% iron; many M-types are near pure iron-nickel. Refined iron currently sells for $72/kg, and if the organization in charge of the craft owns suitably equipped refineries, this single load may yield in excess of $288 million dollars worth of metals, without taking into account that iron is considerably cheap – chrome sells for $320/kg and neodymium for $4200/kg (it would be even more rewarding if the refineries were on the asteroid itself, but I decided not to press the point). The main calculable expense is fuel; for the values displayed here, 632.4 tons of fuel would be required – 92.4 to send the fully fueled ship to the asteroid, and 540 for the return journey with cargo (again I wish fuel stores could be replenished at the asteroid, but I doubt the infrastructure would be present) – topping more practically at 700 tons for powering the ship, orbiting and emergency maneuvers. All this comes with a purchasing cost of $8.4 million and another $154 million to ship up the elevator, for a grand total of $162.4 million – just over 55% the worth of the returned metals. Other expenses have not yet been factored, but thus far, potential for profit is available. What the calculations don’t tell you is that the fusion drive is assumed to be running at maximum possible power. In reality only a fraction of the products provide directly usable energy, and while there are planned means to utilize the remainder inefficiency will always be a boon to performance. This time, let us assume 20% efficiency. At this power fuel costs quickly outstrip earnings, but by halving acceleration we can maintain roughly the same mass ratio and hence fuel weight, such that the only noticeably increased cost is time – 33 days to move either direction rather than 23. Again, this is all assuming the longest desirable journey and the highest costs possible, and a better specialized cargo transport would probably have greater containment area relative to structure and crew quarters (the space shuttle itself is a good example – the external tank can carry almost 30 times its own weight in fuel, or 10 times the weight of the orbiter). Thus ends my contribution, and I am open to your input (although I have a suspicious feeling I know what it will be). You would receive less opposition, T. Neo, if you respected your opponents. Please remember that you are attending the Speculative Evolution forum in the company of several intelligent and inspirational individuals, and you cannot expect to gain any support from them regardless of the validity of your arguments if you continue to treat them condescendingly. Edited by Zerraspace, Jan 17 2012, 05:07 PM.
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| Spugpow | Jan 17 2012, 07:42 PM Post #50 |
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Prime Specimen
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T.Neo, have you read The High Frontier, by Gerard K. O'Neill? I think he presents a fairly compelling case for space colonization in that book. I'm still holding out hope that wormholes are a: real, and b: possible to create. An interplanetary (interstellar?) network of wormholes would solve all distance problems nicely I think. |
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| Ànraich | Jan 17 2012, 09:42 PM Post #51 |
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L'évolution Spéculative est moi
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Wormholes are real, we know that. I don't think it's possible to make them, but with the right amount of power and technology you should theoretically be able to expand an existing one to a usable size. Not that it matters, you don't get to choose where it goes. It could go to another solar system, or another time, or another solar system in another time. Or an entirely different universe. Even if you could make it go where you want, where would it go to? The nearest habitable planet? How do you get it to go there when you don't know where that is? Of course this is all theoretical, there is no physical proof wormholes exist. Math says they do, but then again math also says that bumblebees shouldn't be able to fly. |
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We should all aspire to die surrounded by our dearest friends. Just like Julius Caesar. "The Lord Universe said: 'The same fate I have given to all things from stones to stars, that one day they shall become naught but memories aloft upon the winds of time. From dust all was born, and to dust all shall return.' He then looked upon His greatest creation, life, and pitied them, for unlike stars and stones they would soon learn of this fate and despair in the futility of their own existence. And so the Lord Universe decided to give life two gifts to save them from this despair. The first of these gifts was the soul, that life might more readily accept their fate, and the second was fear, that they might in time learn to avoid it altogether." - Excerpt from a Chanagwan creation myth, Legends and Folklore of the Planet Ghar, collected and published by Yieju Bai'an, explorer from the Celestial Commonwealth of Qonming Tree That Owns Itself
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| T.Neo | Jan 17 2012, 10:19 PM Post #52 |
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Translunar injection: TLI
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Sorry, I didn't notice the links. Firstly, just because (some people at) NASA think it is true, doesn't mean it is true- that is a pretty bad argument. NASA is extremely fallible, and history proves this. And NASA comes up with a lot of farfetched concepts that do not necessarily meet up with reality (sadly, they also come up with a whole lot of of not-so-farfetched concepts that don't meet up with reality either). Secondly, my points about space elevator feasibility were written with the counter-points to the points in mind. I know about the suggested solutions.
Desiring something doesn't make it magically fall into one's lap. Sure, materials that enable the construction of a space elevator could some day exist... but by that logic I could also say that someday fusion powered, aircraft carrier sized SSTO RLVs will exist. (Also, it is an important note that the required advances in material science to create a space elevator would also greatly revolutionise launch vehicle technology. This is not so much an argument against cheap space access, but just against space elevators.)
My point was that after several decades, this market has done nothing to pay for a 'worthy space cause'- in fact, some could say that in some aspects it has prevented it. Space tourism would be a better market. Assuming that you can get the price down to a point where a viable market exists, you suddenly have a high volume payload that can be easily integrated into the vehicle (humans!).
I may be misunderstanding here, do you mean that fusion drives are higher thrust than chemical rockets? If so you'd be wrong- they have a much lower T/W, and are capable of only much lower accelerations (i.e. on the order of milligees). If you mean that for a set amount of thrust they require less propellant, (that their ISP is much higher), you're right.
How much acceleration are you envisioning for such a trajectory? On the order of a G, or even a sizable fraction of a G, the power output of the drive would be on the order of terawatts or tens of terawatts, and waste heat would be enormous- enough to destroy the engine, and the ship. In addition, the T/W of even the more advanced fusion propulsion concepts (such as the Daedalus interstellar probe study) is too low to allow for such acceleration. A brachistochrone with an acceleration on the order of milligees would be much easier, and would still allow for pretty nicely reduced travel times... but the benefits and drawbacks of such a trajectory must be weighed up; - Launch windows can be a problem, but they're probably not that much of a problem than one might think. If waiting for a launch window means that the vehicle and its operations can be less expensive, then it will obviously be the desirable option. There is nothing wrong with being required to launch at a specific time- spaceflight operations are planned years in advance, and the ability to launch spontaneously is not really required, especially for a mining operation. - Reduced travel time is a huge bonus for passenger travel, but 'dumb' cargo doesn't care if it takes 9 months, or two years, to reach the destination. Neither does the spacecraft- spacecraft have historically withstood decades of operation, often greatly exceeding their design life. A brachistochrone compared to say, a hohmann transfer, would mean larger, more expensive engines, probably more propellant, etc. Slow and steady wins the day. My personal favourite in this case would be solar-electric propulsion (using VASIMR or a similar concept and hydrogen propellant).
Much harder. So hard I could say that it is nigh impossible without uncertainty. You have to fuse four protons together, at once. If you want to avoid tritium, there are other fuel combinations that you can use. Such as D-D, or D-He3, or He3-He3, or even proton-Boron 11 fusion, which while it is much more difficult than D-T fusion, it is still far easier to do than proton-proton fusion. Plus, the materials for it are relatively common. See this list
Better to compare dry masses with dry masses, rather than wet masses when talking about hardware. For a comparison to an orbital vehicle, the ISS is something like 450 tons. A Mars mission would be 500-700 tons payload to LEO, depending on who you ask- most of this is propellant, of course, but it has to be lifted to orbit all the same. In this case, being able to carry many multiples of its own mass in propellant is no boon, but a hindrance (though a necessary one, physics demands it- though it depends on your trajectory). If you need something like 10 000 tons of propellant, that's a huge amount of mass- and a huge amount of money to truck it to orbit (even at your rates of $220/kg).
- You never actually touch on the cost of the ship. The development cost, the unit cost, and the recurring costs. These are a highly important part of the whole operation- they make or break it. - This ship is really fancy- it gives me an overwhelming "Star Trek" feeling. Even if you had the technology to make a ship like that work, you wouldn't build a ship like that- at least not for a task like this. - Why not choose a more realistic target asteroid and trajectory? I know you're consistently trying for a worst case scenario, but I think a more realistic scenario would be a useful comparison. - Likewise you don't describe the cost of the facility on the asteroid itself, just a basic explanation of what it might be like. - This page might be a helpful reference in terms of asteroid mineral compositions. - I would much rather refine metals on the asteroid itself, due to the nature of the rocket equaiton, spaceflight, etc, you obviously want to ship around as little mass as possible. You don't need to refine the metals into their pure form- for example, creating a "mongrel alloy" of rare-Earths would be a far more efficient way of taking them home than trucking back raw asteroidal material.
Other things aside, the other expenses are the issue. In space launch, only a tiny fraction of the total cost is propellant. Most has to do with the manufacture of the vehicle and the operation of the facility that launches it. Development cost is divided over the number of flights in a program, and unit cost divided over the number of flights of a unit. Recurring costs- the costs that come with each flight, will also need to be factored in. Even if your vehicle is reusable, the reuse process itself will incur extra costs- this is what makes a reusable launch vehicle so difficult (even airliners have these recurring costs though, so they don't spell doom). You also have to include the cost of the mining operation. You say your ship carries 8000 tons of cargo, ore. Based on the link I posted, and the concentration of elements in "CM" class asteroids, the breakdown is as follows: Aluminium: 1.13% Titanium: 0.055 % Vanadium: 0.0075 % Chromium: 0.265 % Manganese: 0.165% Iron: 21.3% Cobalt: 0.056% Nickel: 1.23% Copper: 0.013% Molybdenum: 0.00014 % Lead: 0.00016 % Ruthenium: 0.000087 % Rhenium: 0.000016 % Palladium: 0.000063 % Silver: 0.000016 % Osmium: 0.000067 % Iridium: 0.000058 Platinum: 0.00011 % Gold: 0.000015 % Using Wolfram Alpha and my crappy math skills, I calculated $4 974 000 for all these minerals (minus iridium, for some reason that didn't want to calculate). Verify it yourself if you wish. Also, I left out magnesium. I thought it wouldn't be important, but apparently it adds another $4 563 000, so that brings the total for metals up to $9 537 000. That bearly covers the purchasing cost of your propellant. Let alone the vehicle itself, for example... which I could say has a pricetag of anything... even a quadrillion dollars, since it's impossible. There are probably better ways to mine asteroids though.
The costs haven't really been described though, and I'd say the ones that have been described are far from the highest possible.
Volume is pretty much secondary here. Mass is king in the rocket equation. You don't even have to really enclose your payload in this case.
Er? What exactly are you trying to get at with this paragraph? I almost always respect my opponents (sadly there are some people I don't respect). But I don't always respect the arguments they use. If I treat people condescendingly, it is generally unintentional; sorry. If I intend to, I can be really, really mean. Also, I have practically pulled an all-nighter finishing this post, so...
No, I have not. I've read up a fair amount about a lot of those colony concepts (the Stanford Torus, the O'Neill Cylinders, etc). The idea as I understand it is that the habitats would be homes to people who would build and maintain solar power satellites. I don't know, it doesn't really check out. The cost would probably be way too high, it'd be much cheaper to do it with machines and minimal human oversight if it is economically viable at all. In the world of the Von Braun Collier's articles- the 1950s, when automation was pretty much nonexistant, it would be more plausible though. Not sure what case O'Neill puts forth in The High Frontier though.
Wormholes exist in theoretical physics. We don't know if a traversable, stable one is possible and we don't know how it would be made. Another possibility is that the wormhole mouthes form close together and you have to ship one end to the destination at a subluminal velocity. Ignoring all the other constraints that wormholes would presumably posess (assuming traversable ones are actually possible), it might improve the transit problem, but it really doesn't make exploration any easier. Edited by T.Neo, Jan 17 2012, 10:26 PM.
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| A hard mathematical figure provides a sort of enlightenment to one's understanding of an idea that is never matched by mere guesswork. | |
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| lamna | Jan 18 2012, 03:10 AM Post #53 |
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Engineering and physics, can't say much about that. But I do know that the calculations that predict bumblebees can't fly are based on aircraft, not insects. As far as I know it was done at a 30's dinner party as a joke. Maths might be an evil and arcane thing, but it's usually right. |
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Living Fossils Fósseis Vibos: Reserva Natural 34 MYH, 4 tonne dinosaur. [flash=500,450] Video Magic! [/flash] | |
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| Zerraspace | Jan 18 2012, 06:23 AM Post #54 |
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Mostly what insults me is your feeling that things must "magically" happen to make this all possible. I'm trying to suggest techniques that are foreseeable, or at the very least have basis in our current understanding, rather than what is simply theoretical with no current basis whatsoever. There is no way of knowing if it will happen; my scheme requires that it does happen. If it does not, then my method will never be available for us (at least the way it is), but this does not bar different schemes with different requirements that again may or may not happen. If you simply said that you doubt the technology will ever be available or that we cannot count on its appearance without treating the opinion as some simple fool's gambit, then I would be inclined to disagree with you, but treat you more civilly. Perhaps you feel that because the technology does not exist today for any of these schemes then it will not happen, but then you're simply arguing certainty when in fact it is probability, which is as big a mistake as arguing that it will happen. Perhaps it would be best if I assumed middle ground - I feel that eventual expansion into space is the most likely fate for mankind (to which I've already given my reasons). You feel that any form of expansion is unlikely simply because circumstances (current and unexpectedly stretching into the future) do not support it. That being said, I'm touched that you spent an all-nighter researching this, which makes me wonder if I had enough points (or enough mistakes) to warrant that much research, or that you secretly want all this to happen but simply don't see it coming to fruition. Could you please forward some relevant material regarding fusion drive operation and the issues mentioned (and not a Wikipedia page), along with similar information for the other propulsion systems mentioned? I swear our sources are at odds here (by the way, I did access Atomic Rockets website; it's how I calculated the effective exhaust velocity of my ship, but I wish I could find a means to estimate thrust). They certainly disagree as far as metal prices go (I'm still trying to figure out how I can sell a kilo of iron for more than you can sell a ton). I did realize the enormous difficulty of proton-proton fusion - I went as far as saying such - but chose to use it anyway because of how relatively inexpensive the fuel was and the enormous effective exhaust velocity (and yes, when referring to thrust I did mean the second). I had read that muon catalysis would make the process much more likely, but then I suppose there is the issue of procuring the muons. Perhaps a multiple stage deuterium-deuterium/deuterium-tritium/deuterium-helium-3 fusion drive could be utilized instead, with a maximum exhaust velocity of 8.679% lightspeed while making up for the issue of tritium acquisition, but then we'll need more fuel and it will be quite a bit more expensive than overabundant hydrogen (deuterium costs range from several hundred to thousands of dollars per kilogram). I only calculated fuel costs because I had no idea how to go about calculating the rest. Current mining equipment would likely be unsuitable for the task, given the differences in gravity, ambient radiation levels and manpower required (most likely the equipment would be almost fully automated with the occasional remote intervention despite lethargic response times, but then it's a matter of artificial intelligence). Manufacture of the space shuttle Endeavor cost $1.7 billion dollars, but that doesn't give us a clue of what it would take to create the MCV because production means, design and manufacture would of necessity be vastly different. As a cargo transport I assumed the MCV's cargo capacity should greatly exceed the dry mass of its main body, while its great mass would likely complicate landing and takeoff so it would probably have to be assembled in orbit, with other craft delivering its cargo down to Earth (say something like Skylon or the orbital elevator, which would incur costs of their own). Seeing as it wouldn't need to enter Earth's atmosphere, the outer surface would no longer have to be built to survive the heat of re-entry, which again throws any comparisons off balance. Then there are the salaries of the pilots, mining and mission overseers, the price of food and drink... The intended acceleration is 0.1-0.05 G, the former for an optimal engine, the latter for 20% efficiency. True, the cargo and spaceship might not really care how long it takes to reach their destination, but the people on the other end do, and you have the issue of how long the pilots can be sustained (unless you can also fully automate the spaceship, but that doesn't resolve the first issue). Certain rates will be expected to support a profitable business (to be honest I thought 2 months back and forth for a single delivery was a bit of stretch), so producing a fleet of MCV's notwithstanding (when you doubt that we could build even one), acceleration rates of single milligees are not acceptable. I hadn't mentioned this in my original argument but I was presuming the asteroid in question to be an M-type asteroid (not CM). To quote your own source - "M-type asteroids are 5%-62% nickel and often more than 90% iron, but on average and are 88% iron, 10% nickel, 0.5% cobalt". Following your prices, an 8000 ton chunk should yield $208384 of iron, $29.76 million dollars of nickel, and $1.89 million dollars of cobalt - sadly still far short of our fuel prices, but much of the potential earnings is wasted on all that iron. If the metals had been sorted beforehand and we filled the spaceship with nickel or cobalt instead (I'm hoping here that the numbers are obvious), we could still break even. I would like to know how you attach them from the outside, however. Nevertheless, I digress; simply fueling the ship is getting out of hand, even when using the cheap fuel, and Hohmann transfer would probably take too long to be practical for a single courier. You seem to have an alternative, T. Neo, and if you're willing to divulge the details I'd be happy to hear it (I don't care if you don't think it will happen, just that it could happen). |
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| T.Neo | Jan 18 2012, 04:22 PM Post #55 |
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Translunar injection: TLI
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That's one of the problems I have with this sort of nonexistant technological capacity (and one of the reasons I keep using the word "magic"). It's difficult to put limits on what it can do. If for example your scheme uses a specific hypothetical technology, and there's a potential problem with that hypothetical technology, you just assume that it's fixed for the purpose of the thought experiment- and it magically is. Unfortunately in reality things don't work just because it is assumed that they do. And because it is difficult to define the limitations, it can also get very out of hand. For example, you say that we can have the ability to mine the asteroids... but then I can come along and say we could have the ability to create valuable elements out of dirt... or that we could have the ability to mine the mantle, etc.
What is unexpected about Earth remaining the richest environment for human habitation for at least several light-years?
How is this a secret? I thought I made this pretty obvious. I may play devil's advocate, and I may get annoyed when people take the attitude "whatever is needed to make my fantasy come true will happen!!!", but it isn't like I actually dislike the idea. If I did, I wouldn't spend the time I do trying to understand things like space lift technology...
Unfortunately I would suggest the Wikipedia page first, but mostly as something that can point to better resources, NASA papers, etc. Atomic Rockets describes the issues with fusion drives and high accelerations, though perhaps not clearly enough. Unfortunately the sort of drive you're describing sounds like something out of fictionland rather than any realistic concept. Also, I've grappled with the jaws of physics myself on this issue, and I ended up getting burnt. By several terawatts of energy. There's a thread somewhere here on this forum where I beat myself up about it...
I don't think it really makes sense to choose the nigh impossible fuel because it's cheaper. Fuel costs aren't the only concern, and if a design is far more difficult to execute then that'll increase costs as well. Since proton-proton fusion is nigh impossible, one might as well say that the drive costs quadrillions of dollars. There's no reference point here. You might want to consider proton-boron fusion. It is much harder than D-T or D-He3 fusion, but not to the massive extent of proton-proton fusion. Boron is $0.94/kg (according to Wolfram Alpha), and Boron 11 apparently makes up 80% of natural boron.
The problem is that calculating the cost of all the other stuff is vitally important, so with only propellant costs you definitely don't get the full picture. Endeavour was also built from structural spares. If you built a shuttle totally from scratch, it'd cost more than that. Of course, it is a pretty bad example, since a shuttle orbiter and a large interplanetary vehicle are two totally different things. The total program cost of the ISS is apparently something around $100 billion, but this includes launch costs, crew costs, other hardware costs, resupply costs, etc. But it's not difficult to imagine a single ISS module costing over a billion dollars. Of course this isn't an 11 ton ISS module or a 5 ton satellite. Larger vessels/objects/things are cheaper by the kilogram, so that helps somewhat... but not much.
Ok... well, in that case, you've got a ship, effective exhaust velocity is 35 000 000 m/s, maximum mass is something like 9700 tons, or 9 700 000 kilograms. To accelerate at 0.1 g, you will need 9 500 000 newtons, or 9.5 meganewtons, of thrust. Based on the thrust power equation, P = F*v/2, where P is thrust power, F is thrust in newtons, and v is exhaust velocity in m/s, the thrust power is thus roughly 166 terawatts. If it is 20% efficient, the total power produced os 830 terawatts- nearly an entire petawatt (by comparison, the Earth recieves under 200 petawatts from the Sun). 664 of these terawatts are waste heat. In other words, your 1000 ton space vehicle has to contend with over 40 times the power consumption of humanity in waste heat. It is really a huge magnitude of power. Now, let's assume that: - Your engine is a hemispherical shell. Exhaust is directed by magnetic fields, not physically. - All waste heat is produced in a point source at the center of the hemispherical dome as nonionising radiation. - The inward surface of the dome reflects 99.5% of light (emissivity of 0.005). - The operating temperature of the inward surface of the dome is 2500 Celsius, or 2773 Kelvin- roughly 100 degrees below the melting point of Molybdenum. Using this equation: Sqrt[P * e / (4*Pi*K*T^4)] Where: P = power e = emissivity of the surface of the engine K = Stefan's constant (5.67e-8) T= temperature of the facing material in Kelvin The hemisphere is thus 280 meters in radius, or 560 meters in diameter. This is purely for thermal reasons, the limitation of how many watts per square meter the material can be exposed too without being raised to too high a temperature. Furthermore (if my math is correct) a molybdenum hemisphere, 560 meters across and a tenth of a millimeter thick would mass over 500 tons, and this is not including its support structure, the magnetic coils to redirect the exhaust, all the hardware to actually make the fusion happen (assuming this is an IC fusion drive, the pellet injector, the particle guns/lasers), all the other supporting hardware, coolant, etc... And some of the waste heat- nearly 1.7 terawatts- (assuming half the total waste heat emitted is intercepted by the hemisphere) will not be reflected, and will heat the facing material. This heat then needs to be removed. Passive radiation through the hemisphere won't do the trick- you need coolant, and you need radiators. Formidable radiators, radiators that will run at thousands of degrees Kelvin. Radiators kilometers in size. Radiators that could mass hundreds or even thousands of tons... Every time I revisit the idea, it has a bad ending. It reminds me of a quote, which I believe was from von Braun; "Mother nature is a harsh mistress, but heed her rules and she will reward you kindly." (paraphrasing, I don't remember the exact quote.) Also, I see no reason why it is not possible to run things with much lower trip rates, and any people on the other end (or on the ship, personally I find either unlikely) should be able to handle such durations. It is an inexorably better solution than acceleration rates that simply are not feasible and would add a huge amount of extra cost anyway.
M-type asteroids would be a better bet, they just had a more detailed breakdown of CM and CI asteroids. I agree- removing the less valuable metals and concentrating the more valuable ones would be highly preferable. This is obviously far easier when the mixture is heterogenous, but a homogenous mixture of metals seems more likely. Rare Earth elements would probably be the best bet for something you'd want to retrieve from an asteroid.
I'd be happy to explain the methods I believe would be more suitable, but not in this post- perhaps later. Edited by T.Neo, Jan 18 2012, 04:24 PM.
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| A hard mathematical figure provides a sort of enlightenment to one's understanding of an idea that is never matched by mere guesswork. | |
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| Kamidio | Jan 18 2012, 05:28 PM Post #56 |
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The Game Master of the SSU:NC
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Like I ███████ said. T. Neo would get provoked into taking up literally half the ████ page with one post. Zerraspace just had to do it. |
SSU:NC - Finding a new home. Quotes WAA
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| Ànraich | Jan 18 2012, 11:46 PM Post #57 |
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L'évolution Spéculative est moi
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T. Neo, have you ever considered the possibility of space colonization simply for the sake of expanding human civilizations to the very frontier of its realm of existence? Why shouldn't humans go live on other planets if they can and want to? Science fiction is all about discovering new civilizations, but placing humans on other worlds provides us with the ability to form new human civilizations. |
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We should all aspire to die surrounded by our dearest friends. Just like Julius Caesar. "The Lord Universe said: 'The same fate I have given to all things from stones to stars, that one day they shall become naught but memories aloft upon the winds of time. From dust all was born, and to dust all shall return.' He then looked upon His greatest creation, life, and pitied them, for unlike stars and stones they would soon learn of this fate and despair in the futility of their own existence. And so the Lord Universe decided to give life two gifts to save them from this despair. The first of these gifts was the soul, that life might more readily accept their fate, and the second was fear, that they might in time learn to avoid it altogether." - Excerpt from a Chanagwan creation myth, Legends and Folklore of the Planet Ghar, collected and published by Yieju Bai'an, explorer from the Celestial Commonwealth of Qonming Tree That Owns Itself
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| lamna | Jan 19 2012, 02:25 AM Post #58 |
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Probably because living in space isn't enough for most people to give up sunshine, ducks and air that isn't constantly being filtered. If there were good economic reasons to do so, people would live in space, people will live just about anywhere for money. But not many people are going to go simply because it's in space. Other than science, there is no good reason for anyone to want to live on the moon, especially for your whole life. It's just like Antarctica, no economy, no permanent residents. And space don't even have sheathbills. |
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Living Fossils Fósseis Vibos: Reserva Natural 34 MYH, 4 tonne dinosaur. [flash=500,450] Video Magic! [/flash] | |
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| T.Neo | Jan 19 2012, 08:46 AM Post #59 |
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Translunar injection: TLI
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What lamna said. People don't colonise (poor) environments for such nebulous 'benefits' as "expanding human civilisations to the very frontier of existence" or "form new civilisations". It's a far more elegant way of putting things, but it's pretty much the same as "we should do it for the sake of it". Of course the whole dynamic could change if there was a habitable planet in our system, but unfortunately such a planet does not exist and would not exist without an astronomical economic expenditure and considerable advancement in logistical abilities. Edited by T.Neo, Jan 19 2012, 08:56 AM.
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| A hard mathematical figure provides a sort of enlightenment to one's understanding of an idea that is never matched by mere guesswork. | |
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| Zerraspace | Jan 19 2012, 09:34 AM Post #60 |
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UD Needs You!
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At least I’ve solved the world’ energy crisis (I hope)… ![]() Your point’s certainly come across. While personally I feel that the spacecraft of the future would be much more reliably powered by deuterium chains (they have lower much lower Lawson Criterion and deliver more energy per weight), due to cost concerns I’ll consider your suggestion of proton-Boron fusion, allowing maximum exhaust velocity of 4.482% lightspeed. The mass required for every reaction is 91.62% boron and 8.38% percent hydrogen, leading to the average fuel price of $1.85/kg. Given the power issues facing our vessel it may be desirable to lower the mass of the MCV (say to one-tenth, something more resembling the space shuttle), but for the moment let’s assume the same ship – dry mass of 1000 tons with cargo capacity of 8000 tons. Accelerating at 1 milligee with 20% efficiency, the mass ratio is 1.08 (much of the fusion energy is lost as X-rays, and while this may be reclaimed through use of a gas laser, I’ll assume the MCV has no such capability). 720 tons of fuel will be required for the return journey and about 84.6 tons for the approach, ending with a total of 824.6 tons (let’s say the ship can hold 850 tons in case of emergencies). The combined fuel costs $1.571 million dollars, and another $187 million to lift. The time to reach the asteroid is now 232.4 days (I really wanted it under six months, but as is I can hardly pay for the propellant), and the power required for operation is roughly 3.29 tW, with 2.632 tW lost as heat. Following your example values, the spherical engine must have a radius 17.68 meters, and if 0.1 mm thick, would weigh about 4 tons, with 6.7 gW remaining that must still be dealt with. Would the required radiators then be small enough to fit within the 1000 ton mass (and where is David Brin’s refrigeration laser when you need one)? I do not think lower accelerations are tolerable, even with huge fleets of MCV’s, but perhaps with smaller models and higher engine efficiencies it could be worked out (for %50 efficiency, the mass ratio is 1.03, which translates into only 311.5 total tons of fuel), and if we use a material with a higher melting point (say graphite or diamond, which reach 4000 Kelvin), we could shrink the hemisphere even further. There’s also the possibility of accelerating only in short bursts, saving us some fuel and giving time for components to cool down. Alternate propulsion schemes result in mass ratios too high for my liking (I’m tempted to choose solar sails, but there is the matter of sail size and how to move towards the sun) – including VASIMIR. That being said, it does interest me for a different reason. As far as I can see it simply involves ionizing, heating and directing propellant with a magnetic field, steps reminiscent of the fusion drive. Could the two systems be coupled (say, having the propellant fused within a magnetic field only to be ionized by its own radiation, or the heat transmitted with the ejected material)? By the way, calculating the costs of an official space program is apparently a lot more complex than simply factoring in expenses, as this article points out. If we really want to establish a presence of Earth, it seems it’s going to have to be private. I don't see large populations living elsewhere in the solar system - not before advanced terraforming, or a very advanced asteroid base anyway - but there's still potential for space-based industry, particularly if it's close to Earth or automated. With cheaper means of lifting off passengers and cargo, I don't see too many who would mind being up there, knowing that they're only hours away from home (the sight of the Earth from their workplace may be comfort enough). |
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