That figure is old. The last figure I had from Brad Edwards was above $500/kg. It critically depends on the usage rate; just like rockets. You need to repay the huge loan. $100/kg probably assumes 100% usage, but you can't assume 100% usage of the elevator- where's the market?
Jeez, you're actually supporting what I say, just not realizing the implications of it. That $500/kg does not come from the recurring cost of launching materials. It comes from the cost of the space elevator. There's a huge difference. Take a look at LiftPort's financial plan to see why - there are other ways to pay back a loan, but there are not other ways to buy rocket fuel, or pay for the materials for a rocket.
In other words, the cost goes down over time. Or, it starts off much, much lower if the government doesn't care about getting the money back.
Look, the point is not "how cheap will it be?" but "how cheap can it be?" Rockets can only get cheap if there's a huge market for them. The space elevator starts off cheap, and meets market prices.
You said that "reusable rockets are too expensive to develop." Well, that's not really true, as they're being developed right now (SpaceX's booster). In any case, even if you develop reusable rockets, it doesn't matter. You still have to use propellant., which will always cost money, and the only way you get it down to $50/kg is if the market is there to drive economies of scale (i.e. making 1,000,000 liters of rocket fuel is not much more expensive than 100,000 when all costs are taken into account). So rockets need a market to lower costs. A space elevator does not. It lowers the costs to meet market demand. The operating costs of the elevator itself are virtually zero. The operating costs of the business are not, but neither are the operating costs of a rocketry business.
It's not. The cost of money is not zero. In a fairly real sense both the space elevator and the rocket are currently, in a fairly real sense
You don't understand what I'm saying, then. The space elevator requires power to get things into orbit. Nothing else. All of the things you're talking about (paying back the loan) are fixed costs, not recurring costs. Rocketry has recurring costs. It will always cost money to launch rockets. You have to pay for the rocket, after all! With the space elevator, all you need to do is pay for power, and as I said, the elevator could eventually power itself with panels from orbit.
bridges to nowhere. How much traffic would you expect?
I don't have the figures on me because usually I can just point people to the NASA studies that show demand vs. cost-per-pound goes up dramatically at low levels. It *has* to. Right now there's no reason to even consider mining the asteroids. You can figure their net worth, then figure the cost to get there and return them, and it's a losing proposition. If you reduce the cost to get there, suddenly, it's not crazy, it's a business model. Ditto for energy satellites. Then you start talking about commercialization of space, and demand explodes.
Bridge to nowhere? Then why is Delta offering trips into space with frequent flyer miles? There's demand there. It can't be met currently. It will be met eventually.
So, if I understand you correctly you are arguing that conventional rocketry will never be cheap because the space launch market it is too small. But the space elevator will be cheaper and so will create a larger space launch market... for conventional rocketry too.
Conventional rocketry can only get so cheap, because fundamentally, you're wasting energy. It can never be as cheap as a space elevator. Fundamentally, the efficiency of a space elevator *could* become a significant fraction of "1" - that is, (energy used)/mgh to get it out of the gravity well. Obviously not 1, and probably not even 0.1, but maybe 0.01 or so. A rocket doesn't have a prayer of reaching that, because it's throwing away so much energy in drag.
More importantly, the economies of scale for conventional rocketry are ill-defined. Can rocket fuel become cheap with more demand? Fundamentally you require a minimum amount of rocket fuel to launch, and so there's a minimum amount of money that you have to spend - it doesn't matter how cheap the rocket fuel gets, it will never be free.
The economies of scale for a space elevator are perfectly well defined. You have an initial cost, and then elevator operating costs, then overhead operating costs. The elevator operating costs can be lowered to virtually zero if need be - the climbers could be powered by the counterweight space station, which is powered by sunlight. If the elevator can't recoup its cost at the demand level it has, oh well, borrow more money, toss up another elevator, and lower the costs by a factor of two, because your capacity just doubled, and your costs remained basically fixed.
The economies of scale apply just as much to conventional rocketry as to the space elevator- as I say, I've seen the figures for both space elevators and rocketry and it is much more arguable than you seem to think- the underlying, per launch, costs of both are very small indeed (maybe $50/kg); in both cases they are hidden behind the fact you need to borrow billions of dollars to build them in the first place.
Fundamentally, this cannot be true. Rocketry uses a consumable. The space elevator does not. I've never seen realistic figures that rocketry could ever get down to $50/kg. With the space elevator, $50/kg is a joke. Even if you assume massive overhead due to elevator maintenance, or massive inefficiencies in the power delivery mechanism (not likely, as it's proven technology), $50/kg is still nothing. All the costs that the NIAC proposal gives ($100/kg) are that high because they are repaying the cost of the elevator.
Anyway, there've been plenty of studies showing the potential market for space applications. The critical mass is about a few $100/kg. Once you hit there, the demand goes sky high. The problem is that you need to get to $100/kg in order for it to go sky high. Rocketry can't do that, because the only way it can get to $100/kg is by making its consumables cheap by creating a huge market. Chicken/egg scenario.
The space elevator circumvents this because fundamentally, its cost/weight is virtually zero, so it's approaching the market from "bottom-up", whereas rocketry is "top-down". The elevator can lower costs to make demand explode, whereas rocketry can't, because they need the demand to lower the price.
ALL good engineering is research, by that definition, because they're doing something that hasn't been done before. When engineers design a new fiber-optic network that's faster than any other network in the world, that'd be research? When engineers design *anything* that's better than what's been done before, that's research?
The difference between "evolutionary" progress in science and "revolutionary" progress in science are pretty well understood. You can speed up "evolutionary" progress by throwing money at them. You can't speed up "revolutionary" progress in science the same way.
What you call research is just evolutionary progress, which is what I call engineering. The point is that no new "revolutionary" progress needs to be made. CNTs exist. They can make a space elevator. The problem is now how to do it. This isn't a small problem. But it is tractable, and more importantly, it can be sped up just by throwing money at it.
Nope. That's a theoretical maximum strength; but the theory is probably wrong. Current experimental strength of short fibers is about 120 GPa, and that's only just what you'd need to do this (about 60 GPa is needed, plus a safety factor of say 2).
Early experimental strength is 1/3 to 1/2 of what theory predicts, and the theory is probably wrong? The theory is for pure nanotube fibers, based on carbon-carbon bond strength. Considering early experiments are so close to the theory, it's probably correct.
And 60 GPa, again, is what you'd need for a cable of the design listed in the NIAC proposal. You can steal a bit of strength by tapering the cable more. It just gets a little silly after a while.
Not quite. If you dope a plastic with nanotubes you'd end up with a material whose strength and weight were dominated by the polymer. That would be wayyyy too heavy and weak. The idea is that you have to use an absolute bare minimum of glue to stick the nanotubes fibers together. Trouble is no-one knows how to do this right now with adequate strength; nanotubes are slippery and particularly hard to glue; and as noted, we don't have a great deal of strength to play with- we need a safety factor for practical reasons.
Again - if worst comes to worst, you use pure nanotube fibers. It *must* be possible to fuse them together (it's already been done, on a small scale). Scaling it up to produce almost a hundred thousand kilometers may be prohibitively expensive, but that's virtually the definition of an engineering problem.
Those fibers aren't even as strong as Kevlar.
Because they weren't intended to be. No one is trying to make space elevator cable right now. That would be like trying to run before you walk. What they're trying to do is make a scalable process, then you improve the process.
You think Kevlar was as strong as kevlar when it was first invented? Not likely.
The engineering begins when we have a cable even a few feet long; of the right strength/weight ratio.
No, then the space elevator engineering begins. Right now the nanotube engineering is taking place. But it's an engineering problem. A solution has to exist.
Let me put this another way. If SETI discovered a message from the stars tomorrow, and they were sending us images of their home planet, and they showed a space elevator made out of carbon nanotubes, we would not ask "how is that even possible?", which we would have asked 20 years ago. We would ask "how did you get good interfacial adhesion with the nanotubes?" or "how did you produce nanotubes of such length?", which are engineering questions, not physics questions.
I'm not disagreeing with you - there's still plenty of distance left to go. But some people try to write the space elevator off as if it will never happen. Those people are like the people who claimed we'd never break the sound barrier. It will be possible - it's "evolutionary" science, not "revolutionary" science.
I think that's more than a little bit premature. Sure, it seems like we can make them a little easier now in the lab... but as an earlier poster mentioned, we're going to need some pretty long lengths to streach into orbit. Nowhere have I heard how exactly the little fibres that are grown in the lab will be joined together *at the usual nanotube strength* over and over again to make these long lengths.
Wow, that's surprising, considering that Slashdot has had plenty of explanations as to how you do it.:)
Nanotube strength is more than you need. Much more. Pure carbon nanotube strands are strong enough to make a completely untapered elevator, all by themselves. (300 GPa tensile strength).
For a space elevator, you're not building one continuous nanotube to orbit. That'd be insane. What you do is you build a composite fiber, just like you have fiberglass, or Kevlar fibers - you dope some composite with nanotubes to increase their strength.
Now, you may say "so what? they still have to build them!". They have. Kilometer-long doped CNT fibers have already been produced. No, they're not as strong as you need. Yes, that's being worked on, and yes, it's an engineering problem, not a fundamental flaw. Once you've got kilometer-long length, it's not much more of a step to be thousands of km long (believe it or not). At *absolute worst* you could build a system to join segments of the elevator together. There have already been presentations and ideas on this theory, and it's perfectly sound.
There is nothing fundamental preventing the space elevator from being built. It's just a matter of time, and this is one (very large) step along the way. But it's important to remember that it's just engineering problems - big, but tractable.
Focusing I am 100% sure of. And the fact that x-ray is also depth-contrallable treatment I am even surer (if there is such a thing).
Yes, but it's not depth-controllable in the sense you're thinking of. They maximize the damage to the region of interest, but the surrounding regions do get irradiated, just to a lesser extent. The degree to which they're irradiated depends on either the number of beams (in a multi-beam apparatus) or the rate of rotation (in a rotating apparatus).
The problem is that if you want to increase the dosage to a certain area, you need to increase the rate of rotation or the number of beams to keep the same low level of damage to the surrounding area.
With this method, you can arbitrarily increase the dosage (beam luminosity) without increasing the damage to the surrounding area significantly, with no change in the apparatus. (This is a 'probably': if the depth dependence is exponential, and the luminosity dependence is linear, then doubling the intensity doubles the dosage everywhere. However, depending on what the critical distance is, if it's really short, then it doesn't really matter how much you increase the luminosity, because all of the rest of the body is "far" from the 'impact point', and is way, way down on the exponential decay anyway).
L4 and L5 are stable. That means dust and rocks tend to get stuck there, or orbit around/through there.
Yes. L4 and L5 are dirty, for obvious reasons.
L1, L2, and L3 are unstable. The only stuff there is the stuff you put there and that you choose to keep there with the occasional thruster puff.
Yes. This is what I said before (although someone said Buzz said L2 - this would be dumb, as it'd be in comms blackout with Earth forever, being behind the Moon).
Given the relative velocities of even the slowest stuff, I'd rather be at L1 than L4.
Huh? Orbits about L4/L5 would be slow, not quick, shouldn't they? It would be relatively trivial to "clean out" the L4/L5 points, but you'd have to constantly do it (and you'd constantly be being 'pinged' by small stuff, though it WOULD just be a ping - they'd approach the point very slowly).
It should also be noted that L1 is stable in two directions, but not the third, so that in fact, you'd still have to deal with incoming 'stuff'. I can't remember regarding L2 and L3.
L4/L5 are quite useful for spacecraft that have a limited fuel supply - SOHO, for instance. For spacecraft that have an infinite fuel supply (because they're being refueled), L1 and L3 are quite nice. L3 has the disadvantage of not having line-of-sight to the Moon, though.
Yes. And while all the Lagrange points are stable, the L4 and L5 points are even more stable (more massive objects can sit in them and catch the ride, as it were).
No. While all the Lagrange points are *balanced* - that is, there's no net acceleration towards either of the two objects, only L4 and L5 are stable. If you nudge something at L1,L2, or L3, they fall away.
L1 is between the two objects. This is obvious why it works: because one object pulls one way, and one object pulls the other way. Where the two pulls are equal, there's no net force.
L2 is on the other side of the (smaller) mass. Since it's farther away from the (larger) body, it should orbit slower than the (smaller) mass, but the added gravity makes it orbit at the same speed as the (smaller) mass, making it stationary.
L3 is on the other side of the (larger) mass. Same reasoning, just substitute "faster" for "slower".
All of these three are unstable: if you push something at L1, it goes towards the body you pushed it towards, ditto with L2,L3.
They talk about L1/L2/L3 because of the positional convenience of them. Yes, you have to active stationkeep, but this isn't impossible, and the drift rate would still be slow for reasonable timespans.
Regarding L4 and L5, L5 is more convenient than L4 because of dynamics of the Earth-Sun-Moon system, rather than just the Earth-Moon system.
What you're assuming is that everyone can read - that is, education is now at a level that "reading" is a default. (This isn't really true, especially in some of the lesser educated areas, where you really do want to make sure voting is safe).
I'm not saying that assuming people can read is too much. What I'm saying is that trust needs to start somewhere. How do you know the paper isn't printed with a special ink that disappears after a few hours, and another name reappears?
It's not the record that's important. It's the auditability: an outside source can come in, and read the vote record, somehow. If you have to give them the format that the vote is in, fine. That's not too much to ask. They can then check that the two totals match each other.
Could someone still defraud the election? Of course. But someone could do that with paper ballots, too - you just replace the paper ballots after the voting is done. Obviously, there are safeguards to prevent that. In this case, you prevent defrauding an electronic voting system by publicly testing the same machines before the election starts.
Because a scantron system can screw up, and destroy all of the ballots, so paper is dangerous.
Plus paper is expensive. Plus counting is only fast if you have the people (or the machines, which are dangerous) to do it.
Plus scantrons are ambiguous. There's a recognition issue there, and while they're pretty good, the margin of error is nonzero (as it is with all counting systems, but here it's measurably non-zero). And then you'd get into "pregnant chad" lands again, just with, I dunno, "pregnant bubbles".
Look, the paper trail isn't the important part. The important part is that a hardcoded audit trail is available, and that it can be easily spot checked to ensure that the machines are working as they are supposed to be working.
Electronic voting is the right way to go, in the future. As you scale the number of people, the logistics get insane, and wasting money on elections is not what I want a government to be doing. We're talking about *counting* here, something that's been done since the first person looked at his fingers.
What you need, though, is a foolproof system. A system without friggin' software, a system running on bare metal, just logic gates, writing to a verifiably safe write-once-read-many storage medium.
Unfortunately, in order to develop that, you need to have some technical expertise, which Diebold and co definitely don't have. Come on. Commercial off-the-shelf crap? Jeez. Take out a damned electronics CAD package and design something that doesn't suck.
Well, kindof. They have SOME advantages over NiMH: for one, they're cheaper, and for two, they've got virtually no internal resistance. They can source huge amounts of current - do NOT, repeat, do NOT short a NiCad battery.
Other than those (extraordinarily specific) advantages, though, yah, they pretty much suck.
L4 and L5 are actually good choices for this sort of thing - if you miss, the beam goes nowhere, not towards Earth.
It also should be mentioned that lack of stability isn't that important when you have megawatts of power streaming through you (SOHO, for instance, sits at L1 of the Earth-Sun system). They could active stationkeep rather easily. However, the other Lagrange points would suck for this application (especially L2 and L3, as L3 is behind the Earth, and L2 is behind the Moon. L1 sucks because if you miss, you hit the Earth).
The downside to L4/L5 is that they're heavily dust polluted, but megawatts of microwave would tend to clear that out real quick. You'd have to stationkeep the relay satellite, though, as the downside to L4/L5 is that the relay angle will push the satellite out of the Lagrange points. Probably wouldn't be that difficult, though.
You already know the beam's target position, right? You also would know the maximum speed at which the off-axis beam could move and still cause damage. If it moved really fast (like a few miles a second), it wouldn't spend long enough in any area to actually do real damage.
The only real worry you'd have is off-axis drifting, which is what I'm talking about here. The beam isn't going to jerk and move 50 miles in a quarter second and hit San Diego, or something - that you can avoid just by having sensors on the actual transmitter detect its angular movement (using a guide star) and shutting off the beam if the angular velocity exceeds some constraint. Since this'd be local to the transmitter, it'd be instant - no worries.
With off-axis drifting (that is, the beam slowly moves away from the receiver), you would just clear out the area that the beam could possibly do damage to in the two seconds it takes for light travel time. It probably wouldn't be more than a square mile or so. If the beam is fairly tightly collimated, if it moves that quickly (miles in seconds), it isn't going to be depositing much energy at all.
No no - clear, as in buy it, and leave it unused. Like airports. Don't have to worry about the beam going there, because if it does, there's no one there anyway.
In areas with public transportation, it's the speed of the transport system that matters, not the car, and that's dependent upon energy, not anything else. Replace old rail systems with highspeed links, and the suburbs extend even farther. This is already true in France.
Hell, some people are willing to fly to work: when planes are free, how many more people will?
You said it yourself - they're small. Just design it so it can take the impact of a few small meteors - it's basically equivalent to hail. Plus you can build it Earthside, where there are fewer meteor impacts - hence the reason that the mare still exist on the Moon.
Anyway, you can calculate it, and deal with it. Not a big deal.
See three down from you, in the reply to the same post.
Land value is all about consumer access, and consumer access is tied to energy costs. When plane travel becomes free, does anyone really give a damn about living far from extended family?
People prefer to live in the suburbs, not in the city - so if you extend the suburbs (because energy's free, and you can transport people rapidly free), you increase the supply, with fixed demand, that means the price should go down.
My guess is that the beam could traverse a very wide arc in 1.28 s and kill many people--though it would probably be a quick, painless death.
Go from the Moon, to a satellite in GEO, and aim to miss the entire Earth if you lose tracking.
Plus, if the beam is traversing a "very wide arc", then it's not going to deposit anywhere near as much energy as if it was stationary. Remember your targets are stationary, and the beam is supposed moving. It'd be trivial to figure out what the maximum radius that severe damage would occur at, and clear that area. Anything past that, and if the beam moves out there that quickly, it's moving too fast to deposit enough energy to do damage.
I'm sure this is all answered by Feynman in QED, but hell if I can figure out how.
Probably a little earlier - think Maxwell.:)
What's the delay (speed of light) between moon transmission and earth reception? What is the fastest this beam could change angles, and give that delay/amount of time before it could be shut off (ie, realize via speed of light that it's out of alignment) what is the maximum arc it can traverse.
You wouldn't do it directly from the Moon to the Earth - you'd probably go Moon->LSO (lunar synchronous - I have NO idea what the equivalent of "geo" is for the moon) -> GEO -> Earth. The longest transmit hop would be LSO->GEO, and that'd be a lightspeed delay of a few seconds. You'd build into the system that it couldn't move more than a few hundredths of a degree a second (whatever it needs to track the GEO satellite). You'd also set it up so that it's always aiming at GEO at a glancing angle, so that any loss of tracking means that the beam zips away into empty space.
I think the wider the arc it moved, the less damage it would do (note, i'm thinking of the microwaves as quanta/packets to guesstimate that). I'm curious of others thoughts, if you have a machine gun and you moved it 1 arc/degree (or some measurement) the spread some distances away would have gaps between it. What happens when you do that with a microwave 'beam' (or a laser light for that matter). Does the light skip sections? Does it avg out over the spread pattern? Is it less powerfull then?
When you move a light beam, the amount of damage it will do is just its intensity (power/area) times the cross sectional area hit, times the time spent in that cross sectional area. If you move the beam quickly, less time, less power. This is true for machine guns, light beams, particle beams, and potato guns, so it's pretty universal.:)
Does the light skip sections? We're talking GHz beams here, so wavelengths of ~cm, so you'd have to make it move several cm in a few hundred picoseconds, which, given the lever arm that you have (thousands of km), might be possible.
There are no fusion power generation experiments, using He-3 or otherwise, which produce anything near a sustained output surplus. Typical sustained values are output around 30 times input power for the most advanced tokmahoks. I hope you will please correct me with an authoratative cite if I am wrong.
Wow, that value is VERY wrong. From 1994 (10 years ago!!)
The TFTR machine in the U.S. sets a record by generating 10 megawatts (MW) of fusion power, a key step validating the progress of fusion research.
(for the same 30 MW input power - now only 3 times).
Then, in 1999, JT-60U in Japan reached what would have been breakeven, had they had D-T fusion rather than pure D fusion (since it's not a real reactor, you can just scale D fusion to D-T - you don't actually need to go through the efforts of getting tritium). In the UK, JET produced 16 MW from 25 MW input: that's pretty damned close to breakeven.
Anyway, the point is that all of these reactors are using crap fuel: everyone knows that He-3 is a better fuel, and would produce a higher energy output. It's trivial to scale the energy output of something that uses, say, D-D fusion to see what it would produce using D-T fusion.
Now, none of them have reached ignition, which may be what you're claiming for "sustained" (>couple hundred seconds): but as the directors for ITER have noted, ignition isn't important - all you care about is energy output > energy input for a commercial reactor. A factor of 50 or so is what you need, and ITER (without He-3) will probably get a factor of 10, so it's close. Essentially the fusion reactor would act as a "boost" reactor for a smaller scale reactor - essentially it'd be "weaning" us off of coal, fission, etc.
Helium-3 would make perfect fusion reactors. This is known. We could build them, they'd be economically feasible, and they would generate power. However, there are no plans to travel to the Moon to recover Helium-3, so no one has any plans to build one.
Re:Space elevator makes *everything* easier...
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I'm not a scientist, but from what I understand there currently isn't a space elevator propulsion system fast and efficient enough to make a trip to the moon. If you suggest rockets, then why have the elevator structure in the first place?
Unfortunately, then, you understand wrong. The elevator itself is a propulsion system - once you go out to the "far end" of the elevator (past geosync) you're moving superorbitally (greater than orbital speed for a given height) and so when you "let go" of the elevator, you'll continue travelling at that speed, and leave orbit.
A 91,000 km elevator can reach all the inner planets (but not the Sun) and as far out to Saturn, if memory serves, simply by letting go at the far end at the right time. No propulsion needed.
Re:Space elevator makes *everything* easier...
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However, nobody has demonstrated a macroscopic-size sample of a material that is strong enough to make a space elevator, let alone the ability to churn out thousands of tonnes of the stuff.
No one's thrown enough money at it. They now know they can fuse carbon nanotubes together, so you don't need to actually manufacture them long, just engineer them long. There are also methods for building the elevator out of linked chains of nanotube material, which wouldn't require building thousands of miles of ribbon, just smaller chunks of them.
IMHO, throwing some money at nanotube research is a very good investment, considering the myriad applications. However, designing your entire space program around a technology that may never be possible seems overly risky.
It's not a never. It can't be a never. It's inevitable - it will happen. It must be possible - there's nothing fundamentally preventing an elevator made up of single carbon nanotubes. The problem is that it's not economically feasible right now to build nanotubes that long. If we threw all of our resources at it, we'd make it - guaranteed. It's just an engineering problem, not a fundamental problem.
It's like "why don't we use superconductors for power transmission"? It's not that we can't do it - we can - but there are enough 'nagging' issues (cooling, maximum current load, etc.) that it would cost far too much.
Or, for a more realistic example, it'd be as if we had just discovered steel, and then someone said "we may never be able to build tall skyscrapers". Any engineer at the time would've told that person that he's crazy - the material's been found. Now we just need to dot the i's and cross the t's. It'll take a while, and a lot of money, but it will happen.
This is why Dr. Edwards keeps pushing for the elevator, even though the material "doesn't exist" yet. It's because it does - it's carbon nanotubes, in some application or another. Fundamentally, there must be a way to do it. We just have to find it.
The unfortunate thing is when you see something that appears to you to be total crap, and a bunch of people are saying, "it just went over your head," there's not way of knowing for sure which is the case. Maybe you just didn't "get it".
Half the other problem is the fact that humans apparently have very little middle ground when it comes to movies. It either is "total crap" or "incredibly brilliant". Can't something be a good movie, with flaws?
I mean, Fellowship of the Ring, for me, was a good movie, with some real flaws - the pacing of the movie was terrible. It should've been split into two movies. If you watch the movie on DVD nowadays, you could hit "stop" when Frodo wakes up in Rivendell, and feel happy and complete, and then come back in two weeks, and watch the second half, and the second half would feel like a good movie too.
Similarly, Reloaded, for me, was a good movie with some real flaws (the fight scene with Smith was tacked on - probably because Smith needed to be in the movie more, and they needed to stress the "Smith replicating like mad" bit in this movie so that it could appear in the next one).
I wish there was an option in rottentomatoes.com to remove the glowingly positive and the violently negative reviews from a movie. Of course, that would probably give 1 review per movie, so that wouldn't help much.
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That figure is old. The last figure I had from Brad Edwards was above $500/kg. It critically depends on the usage rate; just like rockets. You need to repay the huge loan. $100/kg probably assumes 100% usage, but you can't assume 100% usage of the elevator- where's the market?
Jeez, you're actually supporting what I say, just not realizing the implications of it. That $500/kg does not come from the recurring cost of launching materials. It comes from the cost of the space elevator. There's a huge difference. Take a look at LiftPort's financial plan to see why - there are other ways to pay back a loan, but there are not other ways to buy rocket fuel, or pay for the materials for a rocket.
In other words, the cost goes down over time. Or, it starts off much, much lower if the government doesn't care about getting the money back.
Look, the point is not "how cheap will it be?" but "how cheap can it be?" Rockets can only get cheap if there's a huge market for them. The space elevator starts off cheap, and meets market prices.
You said that "reusable rockets are too expensive to develop." Well, that's not really true, as they're being developed right now (SpaceX's booster). In any case, even if you develop reusable rockets, it doesn't matter. You still have to use propellant., which will always cost money, and the only way you get it down to $50/kg is if the market is there to drive economies of scale (i.e. making 1,000,000 liters of rocket fuel is not much more expensive than 100,000 when all costs are taken into account). So rockets need a market to lower costs. A space elevator does not. It lowers the costs to meet market demand. The operating costs of the elevator itself are virtually zero. The operating costs of the business are not, but neither are the operating costs of a rocketry business.
It's not. The cost of money is not zero. In a fairly real sense both the space elevator and the rocket are currently, in a fairly real sense
You don't understand what I'm saying, then. The space elevator requires power to get things into orbit. Nothing else. All of the things you're talking about (paying back the loan) are fixed costs, not recurring costs. Rocketry has recurring costs. It will always cost money to launch rockets. You have to pay for the rocket, after all! With the space elevator, all you need to do is pay for power, and as I said, the elevator could eventually power itself with panels from orbit.
bridges to nowhere. How much traffic would you expect?
I don't have the figures on me because usually I can just point people to the NASA studies that show demand vs. cost-per-pound goes up dramatically at low levels. It *has* to. Right now there's no reason to even consider mining the asteroids. You can figure their net worth, then figure the cost to get there and return them, and it's a losing proposition. If you reduce the cost to get there, suddenly, it's not crazy, it's a business model. Ditto for energy satellites. Then you start talking about commercialization of space, and demand explodes.
Bridge to nowhere? Then why is Delta offering trips into space with frequent flyer miles? There's demand there. It can't be met currently. It will be met eventually.
So, if I understand you correctly you are arguing that conventional rocketry will never be cheap because the space launch market it is too small. But the space elevator will be cheaper and so will create a larger space launch market... for conventional rocketry too.
Conventional rocketry can only get so cheap, because fundamentally, you're wasting energy. It can never be as cheap as a space elevator. Fundamentally, the efficiency of a space elevator *could* become a significant fraction of "1" - that is, (energy used)/mgh to get it out of the gravity well. Obviously not 1, and probably not even 0.1, but maybe 0.01 or so. A rocket doesn't have a prayer of reaching that, because it's throwing away so much energy in drag.
More importantly, the economies of scale for conventional rocketry are ill-defined. Can rocket fuel become cheap with more demand? Fundamentally you require a minimum amount of rocket fuel to launch, and so there's a minimum amount of money that you have to spend - it doesn't matter how cheap the rocket fuel gets, it will never be free.
The economies of scale for a space elevator are perfectly well defined. You have an initial cost, and then elevator operating costs, then overhead operating costs. The elevator operating costs can be lowered to virtually zero if need be - the climbers could be powered by the counterweight space station, which is powered by sunlight. If the elevator can't recoup its cost at the demand level it has, oh well, borrow more money, toss up another elevator, and lower the costs by a factor of two, because your capacity just doubled, and your costs remained basically fixed.
The economies of scale apply just as much to conventional rocketry as to the space elevator- as I say, I've seen the figures for both space elevators and rocketry and it is much more arguable than you seem to think- the underlying, per launch, costs of both are very small indeed (maybe $50/kg); in both cases they are hidden behind the fact you need to borrow billions of dollars to build them in the first place.
Fundamentally, this cannot be true. Rocketry uses a consumable. The space elevator does not. I've never seen realistic figures that rocketry could ever get down to $50/kg. With the space elevator, $50/kg is a joke. Even if you assume massive overhead due to elevator maintenance, or massive inefficiencies in the power delivery mechanism (not likely, as it's proven technology), $50/kg is still nothing. All the costs that the NIAC proposal gives ($100/kg) are that high because they are repaying the cost of the elevator.
Anyway, there've been plenty of studies showing the potential market for space applications. The critical mass is about a few $100/kg. Once you hit there, the demand goes sky high. The problem is that you need to get to $100/kg in order for it to go sky high. Rocketry can't do that, because the only way it can get to $100/kg is by making its consumables cheap by creating a huge market. Chicken/egg scenario.
The space elevator circumvents this because fundamentally, its cost/weight is virtually zero, so it's approaching the market from "bottom-up", whereas rocketry is "top-down". The elevator can lower costs to make demand explode, whereas rocketry can't, because they need the demand to lower the price.
ALL good engineering is research, by that definition, because they're doing something that hasn't been done before. When engineers design a new fiber-optic network that's faster than any other network in the world, that'd be research? When engineers design *anything* that's better than what's been done before, that's research?
The difference between "evolutionary" progress in science and "revolutionary" progress in science are pretty well understood. You can speed up "evolutionary" progress by throwing money at them. You can't speed up "revolutionary" progress in science the same way.
What you call research is just evolutionary progress, which is what I call engineering. The point is that no new "revolutionary" progress needs to be made. CNTs exist. They can make a space elevator. The problem is now how to do it. This isn't a small problem. But it is tractable, and more importantly, it can be sped up just by throwing money at it.
Nope. That's a theoretical maximum strength; but the theory is probably wrong. Current experimental strength of short fibers is about 120 GPa, and that's only just what you'd need to do this (about 60 GPa is needed, plus a safety factor of say 2).
Early experimental strength is 1/3 to 1/2 of what theory predicts, and the theory is probably wrong? The theory is for pure nanotube fibers, based on carbon-carbon bond strength. Considering early experiments are so close to the theory, it's probably correct.
And 60 GPa, again, is what you'd need for a cable of the design listed in the NIAC proposal. You can steal a bit of strength by tapering the cable more. It just gets a little silly after a while.
Not quite. If you dope a plastic with nanotubes you'd end up with a material whose strength and weight were dominated by the polymer. That would be wayyyy too heavy and weak. The idea is that you have to use an absolute bare minimum of glue to stick the nanotubes fibers together. Trouble is no-one knows how to do this right now with adequate strength; nanotubes are slippery and particularly hard to glue; and as noted, we don't have a great deal of strength to play with- we need a safety factor for practical reasons.
Again - if worst comes to worst, you use pure nanotube fibers. It *must* be possible to fuse them together (it's already been done, on a small scale). Scaling it up to produce almost a hundred thousand kilometers may be prohibitively expensive, but that's virtually the definition of an engineering problem.
Those fibers aren't even as strong as Kevlar.
Because they weren't intended to be. No one is trying to make space elevator cable right now. That would be like trying to run before you walk. What they're trying to do is make a scalable process, then you improve the process.
You think Kevlar was as strong as kevlar when it was first invented? Not likely.
The engineering begins when we have a cable even a few feet long; of the right strength/weight ratio.
No, then the space elevator engineering begins. Right now the nanotube engineering is taking place. But it's an engineering problem. A solution has to exist.
Let me put this another way. If SETI discovered a message from the stars tomorrow, and they were sending us images of their home planet, and they showed a space elevator made out of carbon nanotubes, we would not ask "how is that even possible?", which we would have asked 20 years ago. We would ask "how did you get good interfacial adhesion with the nanotubes?" or "how did you produce nanotubes of such length?", which are engineering questions, not physics questions.
I'm not disagreeing with you - there's still plenty of distance left to go. But some people try to write the space elevator off as if it will never happen. Those people are like the people who claimed we'd never break the sound barrier. It will be possible - it's "evolutionary" science, not "revolutionary" science.
I think that's more than a little bit premature. Sure, it seems like we can make them a little easier now in the lab... but as an earlier poster mentioned, we're going to need some pretty long lengths to streach into orbit. Nowhere have I heard how exactly the little fibres that are grown in the lab will be joined together *at the usual nanotube strength* over and over again to make these long lengths.
:)
Wow, that's surprising, considering that Slashdot has had plenty of explanations as to how you do it.
Nanotube strength is more than you need. Much more. Pure carbon nanotube strands are strong enough to make a completely untapered elevator, all by themselves. (300 GPa tensile strength).
For a space elevator, you're not building one continuous nanotube to orbit. That'd be insane. What you do is you build a composite fiber, just like you have fiberglass, or Kevlar fibers - you dope some composite with nanotubes to increase their strength.
Now, you may say "so what? they still have to build them!". They have. Kilometer-long doped CNT fibers have already been produced. No, they're not as strong as you need. Yes, that's being worked on, and yes, it's an engineering problem, not a fundamental flaw. Once you've got kilometer-long length, it's not much more of a step to be thousands of km long (believe it or not). At *absolute worst* you could build a system to join segments of the elevator together. There have already been presentations and ideas on this theory, and it's perfectly sound.
There is nothing fundamental preventing the space elevator from being built. It's just a matter of time, and this is one (very large) step along the way. But it's important to remember that it's just engineering problems - big, but tractable.
Focusing I am 100% sure of. And the fact that x-ray is also depth-contrallable treatment I am even surer (if there is such a thing).
Yes, but it's not depth-controllable in the sense you're thinking of. They maximize the damage to the region of interest, but the surrounding regions do get irradiated, just to a lesser extent. The degree to which they're irradiated depends on either the number of beams (in a multi-beam apparatus) or the rate of rotation (in a rotating apparatus).
The problem is that if you want to increase the dosage to a certain area, you need to increase the rate of rotation or the number of beams to keep the same low level of damage to the surrounding area.
With this method, you can arbitrarily increase the dosage (beam luminosity) without increasing the damage to the surrounding area significantly, with no change in the apparatus. (This is a 'probably': if the depth dependence is exponential, and the luminosity dependence is linear, then doubling the intensity doubles the dosage everywhere. However, depending on what the critical distance is, if it's really short, then it doesn't really matter how much you increase the luminosity, because all of the rest of the body is "far" from the 'impact point', and is way, way down on the exponential decay anyway).
L4 and L5 are stable. That means dust and rocks tend to get stuck there, or orbit around/through there.
Yes. L4 and L5 are dirty, for obvious reasons.
L1, L2, and L3 are unstable. The only stuff there is the stuff you put there and that you choose to keep there with the occasional thruster puff.
Yes. This is what I said before (although someone said Buzz said L2 - this would be dumb, as it'd be in comms blackout with Earth forever, being behind the Moon).
Given the relative velocities of even the slowest stuff, I'd rather be at L1 than L4.
Huh? Orbits about L4/L5 would be slow, not quick, shouldn't they? It would be relatively trivial to "clean out" the L4/L5 points, but you'd have to constantly do it (and you'd constantly be being 'pinged' by small stuff, though it WOULD just be a ping - they'd approach the point very slowly).
It should also be noted that L1 is stable in two directions, but not the third, so that in fact, you'd still have to deal with incoming 'stuff'. I can't remember regarding L2 and L3.
L4/L5 are quite useful for spacecraft that have a limited fuel supply - SOHO, for instance. For spacecraft that have an infinite fuel supply (because they're being refueled), L1 and L3 are quite nice. L3 has the disadvantage of not having line-of-sight to the Moon, though.
Yes. And while all the Lagrange points are stable, the L4 and L5 points are even more stable (more massive objects can sit in them and catch the ride, as it were).
No. While all the Lagrange points are *balanced* - that is, there's no net acceleration towards either of the two objects, only L4 and L5 are stable. If you nudge something at L1,L2, or L3, they fall away.
L1 is between the two objects. This is obvious why it works: because one object pulls one way, and one object pulls the other way. Where the two pulls are equal, there's no net force.
L2 is on the other side of the (smaller) mass. Since it's farther away from the (larger) body, it should orbit slower than the (smaller) mass, but the added gravity makes it orbit at the same speed as the (smaller) mass, making it stationary.
L3 is on the other side of the (larger) mass. Same reasoning, just substitute "faster" for "slower".
All of these three are unstable: if you push something at L1, it goes towards the body you pushed it towards, ditto with L2,L3.
They talk about L1/L2/L3 because of the positional convenience of them. Yes, you have to active stationkeep, but this isn't impossible, and the drift rate would still be slow for reasonable timespans.
Regarding L4 and L5, L5 is more convenient than L4 because of dynamics of the Earth-Sun-Moon system, rather than just the Earth-Moon system.
It's an appeal.
The fact that you don't know that you can appeal a decision in most civilized countries reflects badly on your educational system.
Only if he can read.
What you're assuming is that everyone can read - that is, education is now at a level that "reading" is a default. (This isn't really true, especially in some of the lesser educated areas, where you really do want to make sure voting is safe).
I'm not saying that assuming people can read is too much. What I'm saying is that trust needs to start somewhere. How do you know the paper isn't printed with a special ink that disappears after a few hours, and another name reappears?
It's not the record that's important. It's the auditability: an outside source can come in, and read the vote record, somehow. If you have to give them the format that the vote is in, fine. That's not too much to ask. They can then check that the two totals match each other.
Could someone still defraud the election? Of course. But someone could do that with paper ballots, too - you just replace the paper ballots after the voting is done. Obviously, there are safeguards to prevent that. In this case, you prevent defrauding an electronic voting system by publicly testing the same machines before the election starts.
Because a scantron system can screw up, and destroy all of the ballots, so paper is dangerous.
Plus paper is expensive. Plus counting is only fast if you have the people (or the machines, which are dangerous) to do it.
Plus scantrons are ambiguous. There's a recognition issue there, and while they're pretty good, the margin of error is nonzero (as it is with all counting systems, but here it's measurably non-zero). And then you'd get into "pregnant chad" lands again, just with, I dunno, "pregnant bubbles".
Look, the paper trail isn't the important part. The important part is that a hardcoded audit trail is available, and that it can be easily spot checked to ensure that the machines are working as they are supposed to be working.
Electronic voting is the right way to go, in the future. As you scale the number of people, the logistics get insane, and wasting money on elections is not what I want a government to be doing. We're talking about *counting* here, something that's been done since the first person looked at his fingers.
What you need, though, is a foolproof system. A system without friggin' software, a system running on bare metal, just logic gates, writing to a verifiably safe write-once-read-many storage medium.
Unfortunately, in order to develop that, you need to have some technical expertise, which Diebold and co definitely don't have. Come on. Commercial off-the-shelf crap? Jeez. Take out a damned electronics CAD package and design something that doesn't suck.
nicads are just crap.
Well, kindof. They have SOME advantages over NiMH: for one, they're cheaper, and for two, they've got virtually no internal resistance. They can source huge amounts of current - do NOT, repeat, do NOT short a NiCad battery.
Other than those (extraordinarily specific) advantages, though, yah, they pretty much suck.
Ack, good point. Should've thought more.
L4 and L5 are actually good choices for this sort of thing - if you miss, the beam goes nowhere, not towards Earth.
It also should be mentioned that lack of stability isn't that important when you have megawatts of power streaming through you (SOHO, for instance, sits at L1 of the Earth-Sun system). They could active stationkeep rather easily. However, the other Lagrange points would suck for this application (especially L2 and L3, as L3 is behind the Earth, and L2 is behind the Moon. L1 sucks because if you miss, you hit the Earth).
The downside to L4/L5 is that they're heavily dust polluted, but megawatts of microwave would tend to clear that out real quick. You'd have to stationkeep the relay satellite, though, as the downside to L4/L5 is that the relay angle will push the satellite out of the Lagrange points. Probably wouldn't be that difficult, though.
You already know the beam's target position, right? You also would know the maximum speed at which the off-axis beam could move and still cause damage. If it moved really fast (like a few miles a second), it wouldn't spend long enough in any area to actually do real damage.
The only real worry you'd have is off-axis drifting, which is what I'm talking about here. The beam isn't going to jerk and move 50 miles in a quarter second and hit San Diego, or something - that you can avoid just by having sensors on the actual transmitter detect its angular movement (using a guide star) and shutting off the beam if the angular velocity exceeds some constraint. Since this'd be local to the transmitter, it'd be instant - no worries.
With off-axis drifting (that is, the beam slowly moves away from the receiver), you would just clear out the area that the beam could possibly do damage to in the two seconds it takes for light travel time. It probably wouldn't be more than a square mile or so. If the beam is fairly tightly collimated, if it moves that quickly (miles in seconds), it isn't going to be depositing much energy at all.
No no - clear, as in buy it, and leave it unused. Like airports. Don't have to worry about the beam going there, because if it does, there's no one there anyway.
Two words: commuter rail.
In areas with public transportation, it's the speed of the transport system that matters, not the car, and that's dependent upon energy, not anything else.
Replace old rail systems with highspeed links, and the suburbs extend even farther. This is already true in France.
Hell, some people are willing to fly to work: when planes are free, how many more people will?
You said it yourself - they're small. Just design it so it can take the impact of a few small meteors - it's basically equivalent to hail. Plus you can build it Earthside, where there are fewer meteor impacts - hence the reason that the mare still exist on the Moon.
Anyway, you can calculate it, and deal with it. Not a big deal.
See three down from you, in the reply to the same post.
Land value is all about consumer access, and consumer access is tied to energy costs. When plane travel becomes free, does anyone really give a damn about living far from extended family?
People prefer to live in the suburbs, not in the city - so if you extend the suburbs (because energy's free, and you can transport people rapidly free), you increase the supply, with fixed demand, that means the price should go down.
My guess is that the beam could traverse a very wide arc in 1.28 s and kill many people--though it would probably be a quick, painless death.
Go from the Moon, to a satellite in GEO, and aim to miss the entire Earth if you lose tracking.
Plus, if the beam is traversing a "very wide arc", then it's not going to deposit anywhere near as much energy as if it was stationary. Remember your targets are stationary, and the beam is supposed moving. It'd be trivial to figure out what the maximum radius that severe damage would occur at, and clear that area. Anything past that, and if the beam moves out there that quickly, it's moving too fast to deposit enough energy to do damage.
I'm sure this is all answered by Feynman in QED, but hell if I can figure out how.
Probably a little earlier - think Maxwell.
What's the delay (speed of light) between moon transmission and earth reception? What is the fastest this beam could change angles, and give that delay/amount of time before it could be shut off (ie, realize via speed of light that it's out of alignment) what is the maximum arc it can traverse.
You wouldn't do it directly from the Moon to the Earth - you'd probably go Moon->LSO (lunar synchronous - I have NO idea what the equivalent of "geo" is for the moon) -> GEO -> Earth. The longest transmit hop would be LSO->GEO, and that'd be a lightspeed delay of a few seconds. You'd build into the system that it couldn't move more than a few hundredths of a degree a second (whatever it needs to track the GEO satellite). You'd also set it up so that it's always aiming at GEO at a glancing angle, so that any loss of tracking means that the beam zips away into empty space.
I think the wider the arc it moved, the less damage it would do (note, i'm thinking of the microwaves as quanta/packets to guesstimate that). I'm curious of others thoughts, if you have a machine gun and you moved it 1 arc/degree (or some measurement) the spread some distances away would have gaps between it. What happens when you do that with a microwave 'beam' (or a laser light for that matter). Does the light skip sections? Does it avg out over the spread pattern? Is it less powerfull then?
When you move a light beam, the amount of damage it will do is just its intensity (power/area) times the cross sectional area hit, times the time spent in that cross sectional area. If you move the beam quickly, less time, less power. This is true for machine guns, light beams, particle beams, and potato guns, so it's pretty universal.
Does the light skip sections? We're talking GHz beams here, so wavelengths of ~cm, so you'd have to make it move several cm in a few hundred picoseconds, which, given the lever arm that you have (thousands of km), might be possible.
There are no fusion power generation experiments, using He-3 or otherwise, which produce anything near a sustained output surplus. Typical sustained values are output around 30 times input power for the most advanced tokmahoks. I hope you will please correct me with an authoratative cite if I am wrong.
Wow, that value is VERY wrong. From 1994 (10 years ago!!)
http://fusedweb.pppl.gov/FAQ/section6-results.txt
The value of 6 MW should be compared to
the roughly 30 MW of input power used,
Hrm, 5 times input power. Let's move forward in time, one year (1995)
http://www.itercanada.com/introduction/s2/history
The TFTR machine in the U.S. sets a record by generating 10 megawatts (MW) of fusion power, a key step validating the progress of fusion research.
(for the same 30 MW input power - now only 3 times).
Then, in 1999, JT-60U in Japan reached what would have been breakeven, had they had D-T fusion rather than pure D fusion (since it's not a real reactor, you can just scale D fusion to D-T - you don't actually need to go through the efforts of getting tritium). In the UK, JET produced 16 MW from 25 MW input: that's pretty damned close to breakeven.
Anyway, the point is that all of these reactors are using crap fuel: everyone knows that He-3 is a better fuel, and would produce a higher energy output. It's trivial to scale the energy output of something that uses, say, D-D fusion to see what it would produce using D-T fusion.
Now, none of them have reached ignition, which may be what you're claiming for "sustained" (>couple hundred seconds): but as the directors for ITER have noted, ignition isn't important - all you care about is energy output > energy input for a commercial reactor. A factor of 50 or so is what you need, and ITER (without He-3) will probably get a factor of 10, so it's close. Essentially the fusion reactor would act as a "boost" reactor for a smaller scale reactor - essentially it'd be "weaning" us off of coal, fission, etc.
Helium-3 would make perfect fusion reactors. This is known. We could build them, they'd be economically feasible, and they would generate power. However, there are no plans to travel to the Moon to recover Helium-3, so no one has any plans to build one.
I'm not a scientist, but from what I understand there currently isn't a space elevator propulsion system fast and efficient enough to make a trip to the moon. If you suggest rockets, then why have the elevator structure in the first place?
Unfortunately, then, you understand wrong. The elevator itself is a propulsion system - once you go out to the "far end" of the elevator (past geosync) you're moving superorbitally (greater than orbital speed for a given height) and so when you "let go" of the elevator, you'll continue travelling at that speed, and leave orbit.
A 91,000 km elevator can reach all the inner planets (but not the Sun) and as far out to Saturn, if memory serves, simply by letting go at the far end at the right time. No propulsion needed.
However, nobody has demonstrated a macroscopic-size sample of a material that is strong enough to make a space elevator, let alone the ability to churn out thousands of tonnes of the stuff.
No one's thrown enough money at it. They now know they can fuse carbon nanotubes together, so you don't need to actually manufacture them long, just engineer them long. There are also methods for building the elevator out of linked chains of nanotube material, which wouldn't require building thousands of miles of ribbon, just smaller chunks of them.
IMHO, throwing some money at nanotube research is a very good investment, considering the myriad applications. However, designing your entire space program around a technology that may never be possible seems overly risky.
It's not a never. It can't be a never. It's inevitable - it will happen. It must be possible - there's nothing fundamentally preventing an elevator made up of single carbon nanotubes. The problem is that it's not economically feasible right now to build nanotubes that long. If we threw all of our resources at it, we'd make it - guaranteed. It's just an engineering problem, not a fundamental problem.
It's like "why don't we use superconductors for power transmission"? It's not that we can't do it - we can - but there are enough 'nagging' issues (cooling, maximum current load, etc.) that it would cost far too much.
Or, for a more realistic example, it'd be as if we had just discovered steel, and then someone said "we may never be able to build tall skyscrapers". Any engineer at the time would've told that person that he's crazy - the material's been found. Now we just need to dot the i's and cross the t's. It'll take a while, and a lot of money, but it will happen.
This is why Dr. Edwards keeps pushing for the elevator, even though the material "doesn't exist" yet. It's because it does - it's carbon nanotubes, in some application or another. Fundamentally, there must be a way to do it. We just have to find it.
The unfortunate thing is when you see something that appears to you to be total crap, and a bunch of people are saying, "it just went over your head," there's not way of knowing for sure which is the case. Maybe you just didn't "get it".
Half the other problem is the fact that humans apparently have very little middle ground when it comes to movies. It either is "total crap" or "incredibly brilliant". Can't something be a good movie, with flaws?
I mean, Fellowship of the Ring, for me, was a good movie, with some real flaws - the pacing of the movie was terrible. It should've been split into two movies. If you watch the movie on DVD nowadays, you could hit "stop" when Frodo wakes up in Rivendell, and feel happy and complete, and then come back in two weeks, and watch the second half, and the second half would feel like a good movie too.
Similarly, Reloaded, for me, was a good movie with some real flaws (the fight scene with Smith was tacked on - probably because Smith needed to be in the movie more, and they needed to stress the "Smith replicating like mad" bit in this movie so that it could appear in the next one).
I wish there was an option in rottentomatoes.com to remove the glowingly positive and the violently negative reviews from a movie. Of course, that would probably give 1 review per movie, so that wouldn't help much.