At very short distance scales, the two great physical theories of general relativity and quantum mechanics (the Standard Model) are incompatible. Something interesting must occur on the scale of the Planck length = 10^-35 meters.
Kindof. It's definitely not true that quantum field theory and general relativity are incompatible. Quantum field theory spans ridiculous orders of magnitude in what it's been verified over - from several hundred GeV (in position space, a tiny fraction of the width of a proton) to interstellar distances. It's a quantum theory that generalizes easily to a continuum limit. That is, it's ideal for a 'fundamental theory' of nature. The reason we believe something else is there is because it isn't that elegant. Big whoop.
General relativity is not. It also spans pretty ridiculous orders of magnitude in verification, because in the weak-field limit, it's just gravity (though Pioneer acts weird...) and we've verified it pretty dang well in the strong field limit.
But it is NOT a good quantum theory. It does not generalize well in the distance -> 0 limit (equivalently the high energy case). Therefore, everyone knows it can't be a fundamental theory of nature. It's a continuum limit - just like good old electricity & magnetism are the continuum limit of quantum electrodynamics.
People say general relativity breaks down in the singularity of a black hole. That's true - the metric becomes singular at that point, and we don't know how to handle singularities in a continuum limit. We're pretty good at handling them in a quantum sense - they usually arise from a misunderstanding of the object being measured.
The problem that people are having is that quantum field theories seem to be fundamentally limited in the physics that they can possibly describe, and gravity doesn't seem to be within that limit. Hell, the strong interactions seem to be BARELY within that limit. So the -ideas- that quantum field theory is describing are fine. It's just that we don't have the math (or the math may not exist: no one ever said it has to exist!) to describe gravity in such a way. Hence the reason that people are doing wacko weird things.
And go fig. Those wacko weird things aren't as easy as dimensional arguments would seem. Never would've guessed. Most likely the Planck scale is a bit farther off. Couple factors of (1/2pi) maybe.
C'mon, you know about the Apollo 13 mission. It's NASA's only instance where there was an emergency they definitely knew about (a crippled spacecraft), and we came through. You just don't think about failing. You do whatever is necessary to make it work.
Go and talk to the astronauts right now and ask them - if they had been asked, would they be willing to go up on Atlantis to save the Columbia crew?
I'd bet a lot of money you'd get almost all of them to respond. We could've done it. There's no way you can honestly believe that if we had known about the problem, we couldn't've saved them. Or, more importantly, we wouldn't've tried. We would've tried. Human lives are worth far more than any amount of money.
Unfortunately, that's not really correct. It's quantum gravity that's having the problem, not quantum mechanics.
Do we have a good theory of quantum gravity? Well, no. Guess what? It has problems. Good old quantum mechanics - the kind that doesn't try to look at times below the Planck time - still works perfectly fine.
(Incidentally, redshifted light wouldn't cause a problem with the Big Bang - the Big Bang's best evidence is the god-awful huge ball of fire that we're bathed in that's taken the age of the universe minus about 100K years to cool. If light redshifts over large distances, that would mean that the universe is younger than we thought. Still would mean that it blew up.)
What exactly do you mean? All quantum operations can be represented as unitary transformations upon the state - the language encodes those transformations into code.
They address the completeness issue in the paper at least twice - first in the desiderata (i.e. a desire to do so, which means if the proposed language isn't inclusive, then it needs to be refined) and then second in the low-level primitive section - they're building a language one step above 'machine language' for a quantum computer. You don't know which gates will be available, so you write a language which can handle any "complete" set of gates ("complete" means that they can generate any other set of operations through linear combinations - thus, they form a basis for all operations). If the quantum portion doesn't have a complete set of gates, it isn't a quantum computer, it's a quantum machine.
As per the general purpose quantum computer setup, I still don't see your point. The "algorithms" so far can be used in many general purpose computations : Grover's algorithm is a good example, and the quantum prime factoring algorithm as well. It's stupid to think that there aren't an infinite number of useful quantum algorithms.
Did you read the paper? If you had, you'd realize that the people who wrote the paper in fact do understand how quantum computers work, and they in fact do mainly think in terms of gates (well, primitive operations) as well.
The main point that they make is that a final quantum computer will be a hybrid of a classical computer and a quantum "add-on". The classical computer handles all portions of the algorithm that are deterministic, and sets up the quantum portions and controls the measurements.
There are many, many algorithms out there (okay, not 'many, many', but at least 'many') for quantum computers, and they even give code snippets for those portions. The code snippets contain many abstractions (like QFourier, QHadamard, etc.) which right now require a lot of tweaking and careful setting-up by the experimenters, but will hopefully in the future be automatable (I'm probably wrong - it's probably automatable now).
We know certain things about quantum computers - after all, we can build simulators for them trivially - it's just that the computations will take much much longer than they would on corresponding hardware (with sufficiently large N, where N is the number of elements to deal with, assuming a proper quantum computer with a sufficiently large number of qubits).
The paper's not bogus, and this kind of stuff is needed - it'll let people write algorithms in a standard defined way, and eventually when a quantum computer is built, they can construct a "compiler" for it fairly trivially. In this case, a compiler is not what we normally think of as a compiler - it's more like a processor - something that takes instructions and performs the operations on the setup.
This paper is the equivalent of saying "Well, if we're going to build a computer, we need to know what instructions we want to process. What do we need? AND, OR, XOR, LOAD, STORE, ADD, SHIFT." Here it's more complicated, but it's the same idea - just with a quantum computing paradigm.
The current state of quantum computing really doesn't have a 'processor' - the experimenters set things up, and let things run. Eventually that'll change, and this is anticipating it. I think you're being a bit naive to think that a general-purpose quantum computer setup could never be built. Anything that experimenters can do, engineers can automate.
Actually, not quite. The spikes come from overexposure of the CCD pixels - CCDs tend to bleed in two perpendicular directions when the amount of light exceeds their dynamic range (they "bubble over").
You are correct that the "star filter" effect is the unaltered image. Bright stars "bloom" in CCD images. This's typically why you want to try to avoid bright stars in a deep-field image: the bright stars will just overwhelm the whole image. This'd happen on film, too, but CCD produces the weird "crosshair" effect.
When soldering SMT components, it is imperative that a component recieves no more than 2 degrees C (about 3 degrees F) a second ramp-up in temperature. This is to prevent thermal shock and damage to the components. It is OK for a component to be exposed to soldering temperatures, ideally for as little as possible; a few seconds.
No one would argue with you on the first part - that's 100% correct, though it's probably overkill - in general most components can take thermal shock without any problems. In fact, some that fail that way would've failed anyway, because parts fail early and late in their average lifespan, less so in the middle (the bathtub curve).
However, the second part doesn't really make sense - if you read the article, you'd realize that they're pretty careful about the actual profile being used, though the ramp (temp vs. time) seems uncontrolled.
It is, however, EASY to control the ramp. Just put a thermal sink in there - like, I don't know, -water-, or something else that'll slow down the temperature rise (though, water will boil...). Or you could very slowly increase the temperature of the oven.
After all, this -should- work. Many reflow ovens (in the beginning - and still some low grade ones) are just commercial toaster ovens with modifications (like a simple temperature feedback). If they're careful, and you actually map the profile carefully, this is a lot safer and more efficient than any soldering iron technique, unless you're really good.
As mentioned elsewhere, PCBExpress (www.pcbexpress.com, a division of ECD) lists the profiles of several commercial toaster ovens and gives info on essentially exactly what I said above.
It's not that different from the way that boards are professionally made. It's significantly less thermal stress than a soldering iron puts on them - there, they're subjected to several hundred degrees (something like 600-700 F) for a short time. Here, it's much, much less (usually 450 F - around 200 C) though for a longer time. Thermal shock for components is usually exponential - they can take a higher temperature for a short time, and a lower temperature for a very long time.
Especially if you consider that a person who solders badly can a lot of times place WAY too much heat on a part, this is a lot safer.
Also, I'm not sure what you mean by thermal inertia of the oven. The oven's thermal mass doesn't matter too much - it just extends the preheat period and extends the cooldown period, which -could- do bad things to the part, but if you really needed to, I'm sure you could cool it down quicker.
Heck, for a while there were professional reflow ovens that were just modified commercial toaster ovens. It's the same technology, just a little better controlled if you spend money.
Short answer: reflow = less thermal stress = better.
The challenge is in coming up with a design that works, and then trying to actually install everything correctly with equipment that's not good enough for what you're doing.
The amazing thing about SMD is all that you can do with it, and ESPECIALLY if people get good at using common items like a toaster oven. Then it becomes feasible for people to "garage tinker" up an entire computer.
Which is not out of the question.
Especially when you can get simple PC boards for something like $20 - in quantities of 1. No real reason to bother with perfboards if you've got a complex design.
Wouldn't this paste have a higher resistance than the solder we know and love? Couln't a soldering iron be used to heat it with greater efficiency? Does it have any use outside of SMD?
No, it wouldn't have a higher resistance, at least not significantly more (or less). It's still just basically solder.
As for uses outside of SMD - no, not really. Traditional rosin-core, or whatever else floats your boat, is best for through-hole.
However, through hole is a pain in the butt. It's also impossible to use throughhole for more advanced circuits. Through-hole is a dying technology. It's terrible noise-performance wise, space wise, and in solderability. SMD is terrific - you just need to get used to it.
It also takes a fraction of the time to solder this way, and (done properly) reflow has the distinct advantage that an idiot can do it. The parts will simply wick to their proper locations. It's (mostly) foolproof. Plus (if you're careful) you won't damage components because you're not heating them with several-hundred-degree heat like a soldering iron does.
.05% per decade. Three decades is.15%, not 1.25%. Everyone here is somehow seeing.05%/year. 1.25% would be very, very, bad. Over a century,.05%/year would be 5% - we'd all be dead.
While that is true about water, it's also true about ammonia! There's quite strong hydrogen bonding in ammonia, which is why its boiling point and freezing point is so much higher than methane which genuinely doesn't have any hydrogen bonding. Methane has molecular weight of 16, ammonia of 17 and water of 18, so all these hydrides are quite similar in that respect. Their boiling points at atmospheric pressure are -161.6C, -33.4C and 100C respectively.
Definitely true (well, I can't argue with facts!) and it has a large dipole moment as well.
However, it should be obvious from the above that ammonia will only work at temperatures below -33.4C (liquid-ammonia based reactions have to be in liquid ammonia, after all). It's unlikely (if not impossible, but I don't discount life's ingenuity) that ammonia life would form and then regulate an atmosphere to be below its albedo temperature (planets cool, not heat, after all) so we would have to expect the planet's average temperature to be well below -33.4C in order to find ammonia-carbon based life.
It's easy enough to think of what life to look for, then: just glance at the temperature in the area. However, I think ammonia-based life is really seriously unlikely : all reactions would proceed significantly slower due to the fact that they're occuring at a temperature lower than that with water-based life. Considering it already took something like a few billion years for life to evolve here, I don't think ammonia-based life is feasible at all near stars like the Sun. Maybe near red dwarves, but even they don't live forever.
The lack of education is the problem. You can bitch and moan that people should have personal responsibility all you want, but you can't blame them if they don't know. Nor can you blame people for wanting to put the word out on the street.
Well, this sounds good, but then...
I couldn't sleep well, I couldn't eat well, I was jittery and just desperately wanted to get back to the game. I was at E3, probably my favorite geek convention of all time, and I was miserable.
er..? and..
I used to play EQ... a lot, an unhealthy amount.
If education is really the problem, let's have the government place a really big sign (on the Moon!) that says
"If There Is Anything You Do That When You Stop Doing It, You Shake And Can't Sleep, You've Got A Problem"
C'mon. Knowing that spending all of your time on MMORPGs or any sort of MUD or anything like that is unhealthy isn't an "education" issue. It's common sense, for crying out loud. Anything is addictive. Reading books is addictive, but you don't need warning labels on books. You need people to have some self-control (and personal responsibility).
"That definition" was the "held together by its own gravity" rather than chemical forces definition. Ceres is semi-spherical.
If you take this idea one more iteration, you'll may end up with brown dwarfs being considered "planets" in what would otherwise be considered a "binary star system."
Of course, defining "brown dwarf" is tricky as it is...
No it's not. Brown dwarves are objects which fractionally complete the PP chain at their core, but cannot fully complete the PP chain. Thus they generate some fusion, but because they require exotic constituents (deuterium, tritium, lithium, He-3) rather than plain old hydrogen, they don't explode into a star.
I don't see any reason why you wouldn't want to distinguish between "binary star - brown dwarf systems" and "a massive parent star with a brown dwarf planet." If you think about it, the two must be formed by very different processes (one has a high total mass, the other has a low total mass), so you'd want them separated anyway.
It's probably better to define a star as anything which completes the PP chain (or better) at its core. All objects radiate in the visible... just... very very dimly.
Plus brown dwarves (which progress through a portion of the PP chain) most likely radiate in the visible quite noticeably. I think (stress think) that we've seen a brown dwarf via non-reflected light.
A brown dwarf would be any object which can complete a portion of, but not all of, the PP chain at its core.
A better definition would be simply anything that orbits the planet in an elliptic or circular path. Simply put,
In the reference frame of the parent celestial body in question, if it is possible to describe a circle or ellipse which contains as its (or one of its, for an ellipse) foci a location inside the celestial body which describes the orbit of a natural satellite with good precision, that satellite is a moon.
If, instead, one of the foci is the approximate center of mass of the body-satellite system, and outside the body and the satellite, the system is a binary planet.
This makes the Moon a moon (the center-of-mass is way within the Earth), and makes Pluto/Charon a binary planet.
Also, by that definition of planet, Ceres is a planet. I don't have a problem with this - but other people probably would. I think a couple other asteroids are planets by this definition as well.
Let me ask you something: Do you even know what a tide is? I don't think you have the foggiest. A tide is the rising and falling of the ocean due to the effects of gravity from Luna and the Sun. It usually varies by 6 feet or something, depending on the area, from low tide to high tide. How exactly, then would the ocean rise up and swallow everything? It seems to me that it would just stay the same all of the time, if there were no tides. BTW, the moon is slowly getting farther out. It will eventually leave earth orbit anyway.
The moon's getting farther out because tides are slowing it down, just like it's causing the tides, which are slowing us down. Eventually the Earth and the Moon will be tidally locked (1 day = 1 month = something like 2 weeks), but the Moon is most distinctly gravitationally bound to Earth. And then some.
"Wacko websites" do not get $500K from NASA in a NIAC grant.
Where the hell did you get the weight/radius crap? You don't have to make a cable -you can make a ribbon perfectly fine (it doesn't have to be a cylinder). The original idea was to use steel and taper the thing insanely before carbon nanotubes came around. With steel the cost would've been astronomical - with CNTs they're doable. The current idea is to taper it rather significantly. It'll be a ribbon - about a meter wide but a few microns thick.
As for the deformations, it's about 10% stretch. Yes, it's under tension, but it's also got 100 GPa tensile strength. At that tension it would resist (global) deformation rather well. Locally it'd take very little to push it around, but as soon as you let go, it'd spring right back into place (and a happy wave will travel up the cable at the speed of sound, and arrive back in about 14 hours).
Also, they're not using CNTs: they're using CNT composites. That is, you take an epoxy and dope CNTs into them. They've currently made km-length ropes of the stuff with tensile strengths of order 10 GPa, which is an order of magnitude too low, but that's with a small CNT doping, and they're still working on it. It seems eminently feasible.
It seems that wacko science postings who stick words from a first-year engineering course do not make reality either. Check credentials before you start bashing perfectly legitimate science.
No, there're just two sections of the elevator: below GEO and past GEO. There isn't any "disagreement" - for crying out loud, we're talking about physics that you learn in high school.
If the tether were cut near the bottom, the part that's below the cut would fall to Earth (and it would likely be in the first few km, so it wouldn't really be much at all - it'd be like a very long string falling back. No one would be hurt, no environmental impact, no nothing) and the part that's above the cut would shift its position based on the new center-of-mass orbit location. Fixing this is trivial - you spool out more cable, and the elevator is back to normal, just moved a little bit. Moving it back would take some time (that's a fair amount of mass to move) but eminently possible, and still a cheap repair.
Severing higher up would likely be much more catastrophic in terms of repairability of the elevator, but virtually all of the elevator below GEO (the part that would plummet back to Earth) would burn up in the atmosphere. The mass-length-whatever of something doesn't determine how much burns up. For the most part, it's just surface area, and these things would have about a meter-wide surface area. They'd burn up in a rather spectacular show.
This doesn't make sense to me. If there has to be a counterweight 'station' at the other end of the string, and it extends beyond geo-sync orbit, what's keeping it moving faster than the orbital speed for that distance??
Gravity! That's what's so cool - gravity is providing the tension which is what's forcing it to continue moving. That's why when you let go, zip! off you go!
Why should the cable remain taut if the weight at the end of it keeps wanting to slide backwards relative to the spot on the earth where the other end of it is connected? Wouldn't it slide backward, and then the fact that its tied to a single point on the Earth means that it would be pulled closer to the Earth's surface the farther it fell back (ie. wrapping around the earth until it finally plunges into the ocean)?
The center of mass of the object is located at GEO, which means that the entire object will remain fixed at one place relative to the Earth's surface. The counterweight does want to orbit slower than it actually is moving, however, the tension of the remainder of the cable keeps provides the additional centripetal force required to keep it moving at that velocity.
And how are you going to get equal weights moving up and down the cable at the same time? You would basically be accomplishing absolutely nothing if you had to move the same mass up and down every time you travelled. (ie. Where can your satellite/ship go if you need the weight of it to carry up the next load? And how did you get the initial weight up there that you brought back down while moving your satellite up there in the first place? Seems like a chicken/egg thing, unless you plan on slowly moving an initial weight 'car' up the pole as it was being constructed, and no future loads could be heavier than that one.)
You don't need to have equal up/down loads. Doing that eliminates the oscillations caused by moving things up and down the cable. (Moving things up accelerates them laterally due to a normal force from the cable and an incredible tension on the cable preventing it from bowing. This produces a counterclockwise torque until it reaches GEO, and then a clockwise torque after it reaches GEO). This can also be compensated for by active damping, since the torque is really small and the period is long term, so you just need to make sure it damps out over time, rather than holding it still.
It literally just is a "big cable that goes up to space" - you crawl up the cable slowly (it takes ~week or so to reach the top. You don't want to go fast, otherwise you start getting killed by air resistance just like all the other launch vehicles). and once you reach the orbit you want, you let go. You presumedly then fire attitude correction rockets to get out of the way of the elevator, but that's a trivial change.
The best way to think about it is this: a satellite's orbit is determined by the height above the surface of the Earth of its center of mass. That is, you place a satellite in GEO, and it stays there relative to the surface of the earth (it orbits the earth once every earth day, just like we do). If it extended big metal "feelers" both towards and away from Earth, keeping its center of mass where it is, it wouldn't move. A space elevator is just a dramatically excessive version of this, where those "feelers" extend all the way down to Earth's surface.
Unfortunately, this isn't right. I was kindof at a loss to prove it until now, hence the late repost, but for a more detailed description, read Carmack's post at www.beyond3d.com. To quote:
There is no discernable quality difference, because everything is going into an 8 bit per component framebuffer. Few graphics calculations really need 32 bit accuracy.
What you missed from before is that the result from the fragment path program is truncated (because it goes into an 8-bit-per-component framebuffer) and so doing it in 24-bit vs. 32-bit (which is what is really going on: in the ARB2 path it tries to request 24-bit, but the NV30 only has 32 bit, so it has to calculate at a higher precision. I think there's a typo at Beyond3D there...) is completely pointless.
The ONLY place it would matter is in a fringe case where a multiply-rounded 24-bit calculation would fall into a different bin than a multiply-rounded 32-bit calculation, which is basically never.
The proposal is to have an exclusion zone around of the order of 10-100 miles. It would be extremely hard to fly unnoticed into such an area. Attacks from underneath (submarines, etc) and attacks from people actually travelling on the elevator are harder to deal with. In the end it doesn't matter however. Once one elevator is up, you build more, and you keep a few reels of carbon nanotubes "parked" in space to cover this eventuality and natural disasters.
Actually, what I can't figure out is that attacks on anything below a huge fraction of the length of the elevator won't do anything. Nothing at all. Think about it. The way the actual elevator is manufactured, the portion in the atmosphere is the skinniest, and the portion at the edge (91,000 km away!) is the thickest. So the first 10 km of cable represent virtually no mass whatsoever.
The top part slowly drifts off into space. There's even the possibility of repairing a broken cable by lowering more down to earth before it drifts off.
THIS is correct, and moreso than you were implying. It drifts off slowly - VERY slowly. Do the math: assume the cable is linear in density (which it isn't, so this is even a worst-case scenario) If you remove even 10 km (which is about the maximum height than any plane could get to, or any missile could get to) you've only removed 10/91,000 ~ 10/100,000 ~ 1/10,000 of the mass: that's 0.01%! That will move the center of mass upwards 0.01%, and decrease the orbital speed by (since v = sqrt(GM/R), v/v0 = sqrt(R0/R)) 0.005%. That's NOTHING. To put it in real terms, it'd move 2 kilometers a day. That is, it'd take something like 2 weeks before it even moves out of that exclusion zone, and if memory serves, the idea was to have the base platform mobile, so that spooling it down slowly would be a trivial exercise. When you've already spooled out 91,000 km, spooling out an additional 10 is nothing.
I really hope these guys do okay. I do know that I've been strongly considering trying to give a hand, because to be honest, if it does happen, when it does happen, everything changes. Everything. Suddenly we have a future again.
I'm not so sure those numbers would work out -- if you have a reference, I'd be interested to see it. For now, let me go through a few mental steps:
Check out the NIAC proposal at www.highliftsystems.com. You can trivially figure out accessible orbits vs. cable length via a first year undergrad equation.
Incidentally, the base station is at sea level. On the sea, in fact.
The cable extends rather far past GEO. It doesn't take too long to get to escape vel: you just have to be traveling at 1.4 * your orbital velocity, and poof, you're out of Earth orbit, and traveling rather fast w.r.t. the rest of the solar system, depending on when in the day and year you let go.
The "standard plan" for the cable length (91,000 km) gets you to Mars, Jupiter, etc. Actually to Mars doesn't require very much at all - I think it's like 60,000 km or so. This sounds insane (it's a third the distance to the moon!) but it's really not that big a deal, as all you're doing is spooling out cable, and considering how thin the cable is, it's easy to bundle it up tightly.
I did a calculation (on Slashdot, actually) of the release velocity and transit time for a 91,000 km cable a while ago, but I can't find it. The moon was definitely of order 10s of minutes, and Mars was of order 2 months (days was a bit off, but 2 months vs. years is still incredibly better!). I didn't take into consideration out--of-plane velocities, so your launch time would be once or twice every couple of years at this speed, but otherwise you just need a plane-correction rocket and a bit more time (few more days at most).
At 91000 km, you're moving 7 km/s with respect to the surface or so. 7 km/s! You'd get to the Moon in about half a day. So, I was a little optimistic, but keep in mind this is without ANY fuel. None. And you're already in orbit when this happens, so speeding up your trip is as easy as flinging mass out the back, and getting a delta-v in front.
I think this is your mistake -- you're assuming that the elevator's base station up at 60k miles is somehow permanently fixed relative to the earth. It is not. It is in orbit, and if you apply a lateral acceleration to it, it will speed up or slow down just like any other satellite.
You don't apply a lateral acceleration to it. In order to do that, you need to apply an acceleration at its center of mass at GEO (it's an extended object) and that's not what you're doing. You're torquing it at a certain radius, which will induce oscillations if there is a fixed point, and rotation if there isn't. In this case, there is a fixed point - the Earth. Anyway, you already posted the correct info on this, but the real ideal fix is to simply damp the oscillations, since they're such an incredibly long period.
I should have described this in my original post: this rail gun/maglev launching device would have to terminate a a very high altitude -- one high enough to be above at least the majority of the atmosphere. But I think this would be no more difficult than building the base station for the elevator -- which, according to at least one proposal I've heard, would have to be something like 10km high. Build that on top of a mountain, you'll get another few kilometers. That may well be high enough to make atmo resistance a relatively minor concern (remember, atmo density decreases exponentially as you go up). Though of course, I don't know the precise numbers.
Exponentially, yes, but not that fast!
At the top of Mt. Everest, you've still got about 1/3 of the atmospheric pressure to deal with, which coupled with the temperature decrease means slightly more than 1/3 the density at the surface. Decreasing the air resistance by 1/3 isn't that helpful, when air resistance goes as v^2. Tacking on an additional 10 km is at best going to get you down to about 5% of the original atmospheric pressure, which is still not that good. It means that you can shoot about 4 times faster than you could on the ground before running into the same air resistance, but somehow I doubt that the amount of "net velocity once out of the atmosphere" from the railgun on the surface is that good.
Plus, where would you rather transport your materials: the top of Mt. Everest, or a sunny tropical place at the equator?:) It should be noted you're again defeating your initial reason for building a rail gun by restricting its location.
Rail guns would be ideal on, for instance, the Moon (two stage launch process! space elevator to the Moon, then rail gun off again) or maybe Olympus Mons, where you have no air resistance, but ANY air resistance anywhere comparable to the surface air resistance kills you.
Whoops, typo. Should say "angular velocity of 360 degrees/day" instead of "1 earth circumference". Rest of the argument still stays the same, though. The lateral acceleration is provided simply by the requirement that the elevator has to be taut (it can't "drift", and while it will have a natural period of oscillation, that can be damped rather easily).
It's in orbit. It just happens to be so ridiculously elongated that a portion of it touches the ground. Think in the smaller sense - if someone walks back and forth along the length of the space station, does it drift in one direction? No. It'll start oscillating, yes, but since you can fix one point of the space elevator, you can damp the thing.
I think you're the one who needs to brush up on his physics. Or maybe geometry.
But it doesn't matter -- see the other response to my post, regarding how it's not a problem due to descending elevators cancelling it out -- as long as you have equivalent mass going up/down.
What the heck are you talking about? What you're doing is taking an object that's spinning at 1 earth circumference/day, and moving it out to a point where it is STILL moving at 1 earth circumference/day. It doesn't speed up or slow down at all.
What you have done is increased its angular momentum, since you increased its radius. That increase came from the Earth, since the elevator remained taut during the entire time (again, gravity is doing this) and applied a torque against the Earth.
You don't need equal mass going up and down. It's functionally identical to a skater spinning around, and extending a string with a counterweight on it. She'll slow down slightly, but not much, because the string has so little mass. The angular momentum of the counterweight is now quite high, and the skater's angular momentum is a little less, but the angular momentum of the system is still the same.
The skater could then slide more counterweights down the string - imagine her spinning fast enough to keep the string taut. The string won't "bow" or move laterally as counterweights along the string - it'll stay taut, because that's what the forces on it are forcing it to do. This is the exact same situation that you have with the space elevator, except gravity is providing the tension rather than a skater.
The skater could slide as many counterweights down the string as she wanted to. None need to come back. All that happens is she slows down a little more each time.
Also, space elevators vs. rail guns are pretty silly - rail guns would be FAR more inefficient than a space elevator for the same reason that the Shuttle is inefficient. Air resistance. A rail gun has one shot at applying escape velocity to an object, and it then has to propagate through the atmosphere, dissipating tons of energy, so the rail gun needs to impart even MORE energy to begin with.
This isn't the case for a space elevator. Air resistance goes as velocity^2, so going slowly, you burn less energy. If the elevator climbers simply move slowly, they will be so insanely more efficient than a rail gun that it wouldn't even be worth talking about.
It's also trivial to transmit power to the climbers - just use a laser, in a frequency where the atmosphere doesn't absorb. This is already what they're planning on, and then the "track distance" doesn't matter. The efficiencies would still be incredibly above a rail gun, simply because they don't have to fight air resistance - all you need to do is just beat gravity.
A space elevator is by far the ideal method for launching satellites. One thing that people forget is that not only do you get the object into orbit (just walk it up, and poof! off it goes) since the cable needs to extend PAST GEO, you can continue past GEO, at which point you're moving at superorbital velocity for that point. If you continue far enough, and then just let go, you will actually continue on with a ridiculously high velocity, without ANY use of boosters, rockets, anything like that. Obviously this is true for any launch vehicle, but most of them do this in a second stage while in orbit, because they barely make orbit.
Yes. That's right. You get to Mars in a matter of a few days by climbing a very large cable, and then letting go. No engines. Just maneouvering rockets. You get to the Moon in hours, if not less.
If you read the NIAC proposal to NASA regarding the Space Elevator, you'll realize that the proposed elevator they're talking about is flat cheap - $10 billion, and that's including something like a 2X contingency for overrun, and it could get to Mars, Venus, Jupiter or the asteroids with NO ENGINES. No fuel. No nothing. The efficiency of the system becomes so ridiculously far above other launch mechanisms that it becomes silly. No fuel. Just math, and timing.
Rail guns can't do that (remember, air resistance goes as v^2, so it gets harder and harder to launch something into higher and higher orbits). Nothing can do that save a space elevator. Space elevators are the logical ideal launch mechanism. The only thing that had been holding us back was the lack of a material, and now carbon nanotubes look like they were handed to us on a silver platter.
All launch vehicles have to fight air resistance. A space elevator is the only one that fights it the best way possible - with a low "v", and a long "t".
Slashdot Mirror
At very short distance scales, the two great physical theories of general relativity and quantum mechanics (the Standard Model) are incompatible. Something interesting must occur on the scale of the Planck length = 10^-35 meters.
Kindof. It's definitely not true that quantum field theory and general relativity are incompatible. Quantum field theory spans ridiculous orders of magnitude in what it's been verified over - from several hundred GeV (in position space, a tiny fraction of the width of a proton) to interstellar distances. It's a quantum theory that generalizes easily to a continuum limit. That is, it's ideal for a 'fundamental theory' of nature. The reason we believe something else is there is because it isn't that elegant. Big whoop.
General relativity is not. It also spans pretty ridiculous orders of magnitude in verification, because in the weak-field limit, it's just gravity (though Pioneer acts weird...) and we've verified it pretty dang well in the strong field limit.
But it is NOT a good quantum theory. It does not generalize well in the distance -> 0 limit (equivalently the high energy case). Therefore, everyone knows it can't be a fundamental theory of nature. It's a continuum limit - just like good old electricity & magnetism are the continuum limit of quantum electrodynamics.
People say general relativity breaks down in the singularity of a black hole. That's true - the metric becomes singular at that point, and we don't know how to handle singularities in a continuum limit. We're pretty good at handling them in a quantum sense - they usually arise from a misunderstanding of the object being measured.
The problem that people are having is that quantum field theories seem to be fundamentally limited in the physics that they can possibly describe, and gravity doesn't seem to be within that limit. Hell, the strong interactions seem to be BARELY within that limit. So the -ideas- that quantum field theory is describing are fine. It's just that we don't have the math (or the math may not exist: no one ever said it has to exist!) to describe gravity in such a way. Hence the reason that people are doing wacko weird things.
And go fig. Those wacko weird things aren't as easy as dimensional arguments would seem. Never would've guessed. Most likely the Planck scale is a bit farther off. Couple factors of (1/2pi) maybe.
C'mon, you know about the Apollo 13 mission. It's NASA's only instance where there was an emergency they definitely knew about (a crippled spacecraft), and we came through. You just don't think about failing. You do whatever is necessary to make it work.
Go and talk to the astronauts right now and ask them - if they had been asked, would they be willing to go up on Atlantis to save the Columbia crew?
I'd bet a lot of money you'd get almost all of them to respond. We could've done it. There's no way you can honestly believe that if we had known about the problem, we couldn't've saved them. Or, more importantly, we wouldn't've tried. We would've tried. Human lives are worth far more than any amount of money.
Unfortunately, that's not really correct. It's quantum gravity that's having the problem, not quantum mechanics.
Do we have a good theory of quantum gravity? Well, no. Guess what? It has problems. Good old quantum mechanics - the kind that doesn't try to look at times below the Planck time - still works perfectly fine.
(Incidentally, redshifted light wouldn't cause a problem with the Big Bang - the Big Bang's best evidence is the god-awful huge ball of fire that we're bathed in that's taken the age of the universe minus about 100K years to cool. If light redshifts over large distances, that would mean that the universe is younger than we thought. Still would mean that it blew up.)
What exactly do you mean? All quantum operations can be represented as unitary transformations upon the state - the language encodes those transformations into code.
They address the completeness issue in the paper at least twice - first in the desiderata (i.e. a desire to do so, which means if the proposed language isn't inclusive, then it needs to be refined) and then second in the low-level primitive section - they're building a language one step above 'machine language' for a quantum computer. You don't know which gates will be available, so you write a language which can handle any "complete" set of gates ("complete" means that they can generate any other set of operations through linear combinations - thus, they form a basis for all operations). If the quantum portion doesn't have a complete set of gates, it isn't a quantum computer, it's a quantum machine.
As per the general purpose quantum computer setup, I still don't see your point. The "algorithms" so far can be used in many general purpose computations : Grover's algorithm is a good example, and the quantum prime factoring algorithm as well. It's stupid to think that there aren't an infinite number of useful quantum algorithms.
Did you read the paper? If you had, you'd realize that the people who wrote the paper in fact do understand how quantum computers work, and they in fact do mainly think in terms of gates (well, primitive operations) as well.
The main point that they make is that a final quantum computer will be a hybrid of a classical computer and a quantum "add-on". The classical computer handles all portions of the algorithm that are deterministic, and sets up the quantum portions and controls the measurements.
There are many, many algorithms out there (okay, not 'many, many', but at least 'many') for quantum computers, and they even give code snippets for those portions. The code snippets contain many abstractions (like QFourier, QHadamard, etc.) which right now require a lot of tweaking and careful setting-up by the experimenters, but will hopefully in the future be automatable (I'm probably wrong - it's probably automatable now).
We know certain things about quantum computers - after all, we can build simulators for them trivially - it's just that the computations will take much much longer than they would on corresponding hardware (with sufficiently large N, where N is the number of elements to deal with, assuming a proper quantum computer with a sufficiently large number of qubits).
The paper's not bogus, and this kind of stuff is needed - it'll let people write algorithms in a standard defined way, and eventually when a quantum computer is built, they can construct a "compiler" for it fairly trivially. In this case, a compiler is not what we normally think of as a compiler - it's more like a processor - something that takes instructions and performs the operations on the setup.
This paper is the equivalent of saying "Well, if we're going to build a computer, we need to know what instructions we want to process. What do we need? AND, OR, XOR, LOAD, STORE, ADD, SHIFT." Here it's more complicated, but it's the same idea - just with a quantum computing paradigm.
The current state of quantum computing really doesn't have a 'processor' - the experimenters set things up, and let things run. Eventually that'll change, and this is anticipating it. I think you're being a bit naive to think that a general-purpose quantum computer setup could never be built. Anything that experimenters can do, engineers can automate.
Actually, not quite. The spikes come from overexposure of the CCD pixels - CCDs tend to bleed in two perpendicular directions when the amount of light exceeds their dynamic range (they "bubble over").
You are correct that the "star filter" effect is the unaltered image. Bright stars "bloom" in CCD images. This's typically why you want to try to avoid bright stars in a deep-field image: the bright stars will just overwhelm the whole image. This'd happen on film, too, but CCD produces the weird "crosshair" effect.
When soldering SMT components, it is imperative that a component recieves no more than 2 degrees C (about 3 degrees F) a second ramp-up in temperature. This is to prevent thermal shock and damage to the components. It is OK for a component to be exposed to soldering temperatures, ideally for as little as possible; a few seconds.
No one would argue with you on the first part - that's 100% correct, though it's probably overkill - in general most components can take thermal shock without any problems. In fact, some that fail that way would've failed anyway, because parts fail early and late in their average lifespan, less so in the middle (the bathtub curve).
However, the second part doesn't really make sense - if you read the article, you'd realize that they're pretty careful about the actual profile being used, though the ramp (temp vs. time) seems uncontrolled.
It is, however, EASY to control the ramp. Just put a thermal sink in there - like, I don't know, -water-, or something else that'll slow down the temperature rise (though, water will boil...). Or you could very slowly increase the temperature of the oven.
After all, this -should- work. Many reflow ovens (in the beginning - and still some low grade ones) are just commercial toaster ovens with modifications (like a simple temperature feedback). If they're careful, and you actually map the profile carefully, this is a lot safer and more efficient than any soldering iron technique, unless you're really good.
As mentioned elsewhere, PCBExpress (www.pcbexpress.com, a division of ECD) lists the profiles of several commercial toaster ovens and gives info on essentially exactly what I said above.
It's not that different from the way that boards are professionally made. It's significantly less thermal stress than a soldering iron puts on them - there, they're subjected to several hundred degrees (something like 600-700 F) for a short time. Here, it's much, much less (usually 450 F - around 200 C) though for a longer time. Thermal shock for components is usually exponential - they can take a higher temperature for a short time, and a lower temperature for a very long time.
Especially if you consider that a person who solders badly can a lot of times place WAY too much heat on a part, this is a lot safer.
Also, I'm not sure what you mean by thermal inertia of the oven. The oven's thermal mass doesn't matter too much - it just extends the preheat period and extends the cooldown period, which -could- do bad things to the part, but if you really needed to, I'm sure you could cool it down quicker.
Heck, for a while there were professional reflow ovens that were just modified commercial toaster ovens. It's the same technology, just a little better controlled if you spend money.
Short answer: reflow = less thermal stress = better.
The challenge is in coming up with a design that works, and then trying to actually install everything correctly with equipment that's not good enough for what you're doing.
The amazing thing about SMD is all that you can do with it, and ESPECIALLY if people get good at using common items like a toaster oven. Then it becomes feasible for people to "garage tinker" up an entire computer.
Which is not out of the question.
Especially when you can get simple PC boards for something like $20 - in quantities of 1. No real reason to bother with perfboards if you've got a complex design.
Wouldn't this paste have a higher resistance than the solder we know and love? Couln't a soldering iron be used to heat it with greater efficiency? Does it have any use outside of SMD?
No, it wouldn't have a higher resistance, at least not significantly more (or less). It's still just basically solder.
As for uses outside of SMD - no, not really. Traditional rosin-core, or whatever else floats your boat, is best for through-hole.
However, through hole is a pain in the butt. It's also impossible to use throughhole for more advanced circuits. Through-hole is a dying technology. It's terrible noise-performance wise, space wise, and in solderability. SMD is terrific - you just need to get used to it.
It also takes a fraction of the time to solder this way, and (done properly) reflow has the distinct advantage that an idiot can do it. The parts will simply wick to their proper locations. It's (mostly) foolproof. Plus (if you're careful) you won't damage components because you're not heating them with several-hundred-degree heat like a soldering iron does.
.05% per decade. Three decades is .15%, not 1.25%. Everyone here is somehow seeing .05%/year. 1.25% would be very, very, bad. Over a century, .05%/year would be 5% - we'd all be dead.
While that is true about water, it's also true about ammonia! There's quite strong hydrogen bonding in ammonia, which is why its boiling point and freezing point is so much higher than methane which genuinely doesn't have any hydrogen bonding. Methane has molecular weight of 16, ammonia of 17 and water of 18, so all these hydrides are quite similar in that respect. Their boiling points at atmospheric pressure are -161.6C, -33.4C and 100C respectively.
Definitely true (well, I can't argue with facts!) and it has a large dipole moment as well.
However, it should be obvious from the above that ammonia will only work at temperatures below -33.4C (liquid-ammonia based reactions have to be in liquid ammonia, after all). It's unlikely (if not impossible, but I don't discount life's ingenuity) that ammonia life would form and then regulate an atmosphere to be below its albedo temperature (planets cool, not heat, after all) so we would have to expect the planet's average temperature to be well below -33.4C in order to find ammonia-carbon based life.
It's easy enough to think of what life to look for, then: just glance at the temperature in the area. However, I think ammonia-based life is really seriously unlikely : all reactions would proceed significantly slower due to the fact that they're occuring at a temperature lower than that with water-based life. Considering it already took something like a few billion years for life to evolve here, I don't think ammonia-based life is feasible at all near stars like the Sun. Maybe near red dwarves, but even they don't live forever.
The lack of education is the problem. You can bitch and moan that people should have personal responsibility all you want, but you can't blame them if they don't know. Nor can you blame people for wanting to put the word out on the street.
Well, this sounds good, but then...
I couldn't sleep well, I couldn't eat well, I was jittery and just desperately wanted to get back to the game. I was at E3, probably my favorite geek convention of all time, and I was miserable.
er..? and..
I used to play EQ... a lot, an unhealthy amount.
If education is really the problem, let's have the government place a really big sign (on the Moon!) that says
"If There Is Anything You Do That When You Stop Doing It, You Shake And Can't Sleep, You've Got A Problem"
C'mon. Knowing that spending all of your time on MMORPGs or any sort of MUD or anything like that is unhealthy isn't an "education" issue. It's common sense, for crying out loud. Anything is addictive. Reading books is addictive, but you don't need warning labels on books. You need people to have some self-control (and personal responsibility).
"That definition" was the "held together by its own gravity" rather than chemical forces definition. Ceres is semi-spherical.
If you take this idea one more iteration, you'll may end up with brown dwarfs being considered "planets" in what would otherwise be considered a "binary star system."
Of course, defining "brown dwarf" is tricky as it is...
No it's not. Brown dwarves are objects which fractionally complete the PP chain at their core, but cannot fully complete the PP chain. Thus they generate some fusion, but because they require exotic constituents (deuterium, tritium, lithium, He-3) rather than plain old hydrogen, they don't explode into a star.
I don't see any reason why you wouldn't want to distinguish between "binary star - brown dwarf systems" and "a massive parent star with a brown dwarf planet." If you think about it, the two must be formed by very different processes (one has a high total mass, the other has a low total mass), so you'd want them separated anyway.
It's probably better to define a star as anything which completes the PP chain (or better) at its core. All objects radiate in the visible... just... very very dimly.
Plus brown dwarves (which progress through a portion of the PP chain) most likely radiate in the visible quite noticeably. I think (stress think) that we've seen a brown dwarf via non-reflected light.
A brown dwarf would be any object which can complete a portion of, but not all of, the PP chain at its core.
A better definition would be simply anything that orbits the planet in an elliptic or circular path. Simply put,
In the reference frame of the parent celestial body in question, if it is possible to describe a circle or ellipse which contains as its (or one of its, for an ellipse) foci a location inside the celestial body which describes the orbit of a natural satellite with good precision, that satellite is a moon.
If, instead, one of the foci is the approximate center of mass of the body-satellite system, and outside the body and the satellite, the system is a binary planet.
This makes the Moon a moon (the center-of-mass is way within the Earth), and makes Pluto/Charon a binary planet.
Also, by that definition of planet, Ceres is a planet. I don't have a problem with this - but other people probably would. I think a couple other asteroids are planets by this definition as well.
Let me ask you something: Do you even know what a tide is? I don't think you have the foggiest. A tide is the rising and falling of the ocean due to the effects of gravity from Luna and the Sun. It usually varies by 6 feet or something, depending on the area, from low tide to high tide. How exactly, then would the ocean rise up and swallow everything? It seems to me that it would just stay the same all of the time, if there were no tides. BTW, the moon is slowly getting farther out. It will eventually leave earth orbit anyway.
The moon's getting farther out because tides are slowing it down, just like it's causing the tides, which are slowing us down. Eventually the Earth and the Moon will be tidally locked (1 day = 1 month = something like 2 weeks), but the Moon is most distinctly gravitationally bound to Earth. And then some.
"Wacko websites" do not get $500K from NASA in a NIAC grant.
Where the hell did you get the weight/radius crap? You don't have to make a cable -you can make a ribbon perfectly fine (it doesn't have to be a cylinder). The original idea was to use steel and taper the thing insanely before carbon nanotubes came around. With steel the cost would've been astronomical - with CNTs they're doable. The current idea is to taper it rather significantly. It'll be a ribbon - about a meter wide but a few microns thick.
As for the deformations, it's about 10% stretch. Yes, it's under tension, but it's also got 100 GPa tensile strength. At that tension it would resist (global) deformation rather well. Locally it'd take very little to push it around, but as soon as you let go, it'd spring right back into place (and a happy wave will travel up the cable at the speed of sound, and arrive back in about 14 hours).
Also, they're not using CNTs: they're using CNT composites. That is, you take an epoxy and dope CNTs into them. They've currently made km-length ropes of the stuff with tensile strengths of order 10 GPa, which is an order of magnitude too low, but that's with a small CNT doping, and they're still working on it. It seems eminently feasible.
It seems that wacko science postings who stick words from a first-year engineering course do not make reality either. Check credentials before you start bashing perfectly legitimate science.
No, there're just two sections of the elevator: below GEO and past GEO. There isn't any "disagreement" - for crying out loud, we're talking about physics that you learn in high school.
If the tether were cut near the bottom, the part that's below the cut would fall to Earth (and it would likely be in the first few km, so it wouldn't really be much at all - it'd be like a very long string falling back. No one would be hurt, no environmental impact, no nothing) and the part that's above the cut would shift its position based on the new center-of-mass orbit location. Fixing this is trivial - you spool out more cable, and the elevator is back to normal, just moved a little bit. Moving it back would take some time (that's a fair amount of mass to move) but eminently possible, and still a cheap repair.
Severing higher up would likely be much more catastrophic in terms of repairability of the elevator, but virtually all of the elevator below GEO (the part that would plummet back to Earth) would burn up in the atmosphere. The mass-length-whatever of something doesn't determine how much burns up. For the most part, it's just surface area, and these things would have about a meter-wide surface area. They'd burn up in a rather spectacular show.
This doesn't make sense to me. If there has to be a counterweight 'station' at the other end of the string, and it extends beyond geo-sync orbit, what's keeping it moving faster than the orbital speed for that distance??
Gravity! That's what's so cool - gravity is providing the tension which is what's forcing it to continue moving. That's why when you let go, zip! off you go!
Why should the cable remain taut if the weight at the end of it keeps wanting to slide backwards relative to the spot on the earth where the other end of it is connected? Wouldn't it slide backward, and then the fact that its tied to a single point on the Earth means that it would be pulled closer to the Earth's surface the farther it fell back (ie. wrapping around the earth until it finally plunges into the ocean)?
The center of mass of the object is located at GEO, which means that the entire object will remain fixed at one place relative to the Earth's surface. The counterweight does want to orbit slower than it actually is moving, however, the tension of the remainder of the cable keeps provides the additional centripetal force required to keep it moving at that velocity.
And how are you going to get equal weights moving up and down the cable at the same time? You would basically be accomplishing absolutely nothing if you had to move the same mass up and down every time you travelled. (ie. Where can your satellite/ship go if you need the weight of it to carry up the next load? And how did you get the initial weight up there that you brought back down while moving your satellite up there in the first place? Seems like a chicken/egg thing, unless you plan on slowly moving an initial weight 'car' up the pole as it was being constructed, and no future loads could be heavier than that one.)
You don't need to have equal up/down loads. Doing that eliminates the oscillations caused by moving things up and down the cable. (Moving things up accelerates them laterally due to a normal force from the cable and an incredible tension on the cable preventing it from bowing. This produces a counterclockwise torque until it reaches GEO, and then a clockwise torque after it reaches GEO). This can also be compensated for by active damping, since the torque is really small and the period is long term, so you just need to make sure it damps out over time, rather than holding it still.
It literally just is a "big cable that goes up to space" - you crawl up the cable slowly (it takes ~week or so to reach the top. You don't want to go fast, otherwise you start getting killed by air resistance just like all the other launch vehicles). and once you reach the orbit you want, you let go. You presumedly then fire attitude correction rockets to get out of the way of the elevator, but that's a trivial change.
The best way to think about it is this: a satellite's orbit is determined by the height above the surface of the Earth of its center of mass. That is, you place a satellite in GEO, and it stays there relative to the surface of the earth (it orbits the earth once every earth day, just like we do). If it extended big metal "feelers" both towards and away from Earth, keeping its center of mass where it is, it wouldn't move. A space elevator is just a dramatically excessive version of this, where those "feelers" extend all the way down to Earth's surface.
What you missed from before is that the result from the fragment path program is truncated (because it goes into an 8-bit-per-component framebuffer) and so doing it in 24-bit vs. 32-bit (which is what is really going on: in the ARB2 path it tries to request 24-bit, but the NV30 only has 32 bit, so it has to calculate at a higher precision. I think there's a typo at Beyond3D there...) is completely pointless.
The ONLY place it would matter is in a fringe case where a multiply-rounded 24-bit calculation would fall into a different bin than a multiply-rounded 32-bit calculation, which is basically never.
The proposal is to have an exclusion zone around of the order of 10-100 miles. It would be extremely hard to fly unnoticed into such an area. Attacks from underneath (submarines, etc) and attacks from people actually travelling on the elevator are harder to deal with. In the end it doesn't matter however. Once one elevator is up, you build more, and you keep a few reels of carbon nanotubes "parked" in space to cover this eventuality and natural disasters.
Actually, what I can't figure out is that attacks on anything below a huge fraction of the length of the elevator won't do anything. Nothing at all. Think about it. The way the actual elevator is manufactured, the portion in the atmosphere is the skinniest, and the portion at the edge (91,000 km away!) is the thickest. So the first 10 km of cable represent virtually no mass whatsoever.
The top part slowly drifts off into space. There's even the possibility of repairing a broken cable by lowering more down to earth before it drifts off.
THIS is correct, and moreso than you were implying. It drifts off slowly - VERY slowly. Do the math: assume the cable is linear in density (which it isn't, so this is even a worst-case scenario) If you remove even 10 km (which is about the maximum height than any plane could get to, or any missile could get to) you've only removed 10/91,000 ~ 10/100,000 ~ 1/10,000 of the mass: that's 0.01%! That will move the center of mass upwards 0.01%, and decrease the orbital speed by (since v = sqrt(GM/R), v/v0 = sqrt(R0/R)) 0.005%. That's NOTHING. To put it in real terms, it'd move 2 kilometers a day. That is, it'd take something like 2 weeks before it even moves out of that exclusion zone, and if memory serves, the idea was to have the base platform mobile, so that spooling it down slowly would be a trivial exercise. When you've already spooled out 91,000 km, spooling out an additional 10 is nothing.
I really hope these guys do okay. I do know that I've been strongly considering trying to give a hand, because to be honest, if it does happen, when it does happen, everything changes. Everything. Suddenly we have a future again.
I'm not so sure those numbers would work out -- if you have a reference, I'd be interested to see it. For now, let me go through a few mental steps:
:) It should be noted you're again defeating your initial reason for building a rail gun by restricting its location.
Check out the NIAC proposal at www.highliftsystems.com. You can trivially figure out accessible orbits vs. cable length via a first year undergrad equation.
Incidentally, the base station is at sea level. On the sea, in fact.
The cable extends rather far past GEO. It doesn't take too long to get to escape vel: you just have to be traveling at 1.4 * your orbital velocity, and poof, you're out of Earth orbit, and traveling rather fast w.r.t. the rest of the solar system, depending on when in the day and year you let go.
The "standard plan" for the cable length (91,000 km) gets you to Mars, Jupiter, etc. Actually to Mars doesn't require very much at all - I think it's like 60,000 km or so. This sounds insane (it's a third the distance to the moon!) but it's really not that big a deal, as all you're doing is spooling out cable, and considering how thin the cable is, it's easy to bundle it up tightly.
I did a calculation (on Slashdot, actually) of the release velocity and transit time for a 91,000 km cable a while ago, but I can't find it. The moon was definitely of order 10s of minutes, and Mars was of order 2 months (days was a bit off, but 2 months vs. years is still incredibly better!). I didn't take into consideration out--of-plane velocities, so your launch time would be once or twice every couple of years at this speed, but otherwise you just need a plane-correction rocket and a bit more time (few more days at most).
At 91000 km, you're moving 7 km/s with respect to the surface or so. 7 km/s! You'd get to the Moon in about half a day. So, I was a little optimistic, but keep in mind this is without ANY fuel. None. And you're already in orbit when this happens, so speeding up your trip is as easy as flinging mass out the back, and getting a delta-v in front.
I think this is your mistake -- you're assuming that the elevator's base station up at 60k miles is somehow permanently fixed relative to the earth. It is not. It is in orbit, and if you apply a lateral acceleration to it, it will speed up or slow down just like any other satellite.
You don't apply a lateral acceleration to it. In order to do that, you need to apply an acceleration at its center of mass at GEO (it's an extended object) and that's not what you're doing. You're torquing it at a certain radius, which will induce oscillations if there is a fixed point, and rotation if there isn't. In this case, there is a fixed point - the Earth. Anyway, you already posted the correct info on this, but the real ideal fix is to simply damp the oscillations, since they're such an incredibly long period.
I should have described this in my original post: this rail gun/maglev launching device would have to terminate a a very high altitude -- one high enough to be above at least the majority of the atmosphere. But I think this would be no more difficult than building the base station for the elevator -- which, according to at least one proposal I've heard, would have to be something like 10km high. Build that on top of a mountain, you'll get another few kilometers. That may well be high enough to make atmo resistance a relatively minor concern (remember, atmo density decreases exponentially as you go up). Though of course, I don't know the precise numbers.
Exponentially, yes, but not that fast!
At the top of Mt. Everest, you've still got about 1/3 of the atmospheric pressure to deal with, which coupled with the temperature decrease means slightly more than 1/3 the density at the surface. Decreasing the air resistance by 1/3 isn't that helpful, when air resistance goes as v^2. Tacking on an additional 10 km is at best going to get you down to about 5% of the original atmospheric pressure, which is still not that good. It means that you can shoot about 4 times faster than you could on the ground before running into the same air resistance, but somehow I doubt that the amount of "net velocity once out of the atmosphere" from the railgun on the surface is that good.
Plus, where would you rather transport your materials: the top of Mt. Everest, or a sunny tropical place at the equator?
Rail guns would be ideal on, for instance, the Moon (two stage launch process! space elevator to the Moon, then rail gun off again) or maybe Olympus Mons, where you have no air resistance, but ANY air resistance anywhere comparable to the surface air resistance kills you.
Whoops, typo. Should say "angular velocity of 360 degrees/day" instead of "1 earth circumference". Rest of the argument still stays the same, though. The lateral acceleration is provided simply by the requirement that the elevator has to be taut (it can't "drift", and while it will have a natural period of oscillation, that can be damped rather easily).
It's in orbit. It just happens to be so ridiculously elongated that a portion of it touches the ground. Think in the smaller sense - if someone walks back and forth along the length of the space station, does it drift in one direction? No. It'll start oscillating, yes, but since you can fix one point of the space elevator, you can damp the thing.
I think you're the one who needs to brush up on his physics. Or maybe geometry.
But it doesn't matter -- see the other response to my post, regarding how it's not a problem due to descending elevators cancelling it out -- as long as you have equivalent mass going up/down.
What the heck are you talking about? What you're doing is taking an object that's spinning at 1 earth circumference/day, and moving it out to a point where it is STILL moving at 1 earth circumference/day. It doesn't speed up or slow down at all.
What you have done is increased its angular momentum, since you increased its radius. That increase came from the Earth, since the elevator remained taut during the entire time (again, gravity is doing this) and applied a torque against the Earth.
You don't need equal mass going up and down. It's functionally identical to a skater spinning around, and extending a string with a counterweight on it. She'll slow down slightly, but not much, because the string has so little mass. The angular momentum of the counterweight is now quite high, and the skater's angular momentum is a little less, but the angular momentum of the system is still the same.
The skater could then slide more counterweights down the string - imagine her spinning fast enough to keep the string taut. The string won't "bow" or move laterally as counterweights along the string - it'll stay taut, because that's what the forces on it are forcing it to do. This is the exact same situation that you have with the space elevator, except gravity is providing the tension rather than a skater.
The skater could slide as many counterweights down the string as she wanted to. None need to come back. All that happens is she slows down a little more each time.
Also, space elevators vs. rail guns are pretty silly - rail guns would be FAR more inefficient than a space elevator for the same reason that the Shuttle is inefficient. Air resistance. A rail gun has one shot at applying escape velocity to an object, and it then has to propagate through the atmosphere, dissipating tons of energy, so the rail gun needs to impart even MORE energy to begin with.
This isn't the case for a space elevator. Air resistance goes as velocity^2, so going slowly, you burn less energy. If the elevator climbers simply move slowly, they will be so insanely more efficient than a rail gun that it wouldn't even be worth talking about.
It's also trivial to transmit power to the climbers - just use a laser, in a frequency where the atmosphere doesn't absorb. This is already what they're planning on, and then the "track distance" doesn't matter. The efficiencies would still be incredibly above a rail gun, simply because they don't have to fight air resistance - all you need to do is just beat gravity.
A space elevator is by far the ideal method for launching satellites. One thing that people forget is that not only do you get the object into orbit (just walk it up, and poof! off it goes) since the cable needs to extend PAST GEO, you can continue past GEO, at which point you're moving at superorbital velocity for that point. If you continue far enough, and then just let go, you will actually continue on with a ridiculously high velocity, without ANY use of boosters, rockets, anything like that. Obviously this is true for any launch vehicle, but most of them do this in a second stage while in orbit, because they barely make orbit.
Yes. That's right. You get to Mars in a matter of a few days by climbing a very large cable, and then letting go. No engines. Just maneouvering rockets. You get to the Moon in hours, if not less.
If you read the NIAC proposal to NASA regarding the Space Elevator, you'll realize that the proposed elevator they're talking about is flat cheap - $10 billion, and that's including something like a 2X contingency for overrun, and it could get to Mars, Venus, Jupiter or the asteroids with NO ENGINES. No fuel. No nothing. The efficiency of the system becomes so ridiculously far above other launch mechanisms that it becomes silly. No fuel. Just math, and timing.
Rail guns can't do that (remember, air resistance goes as v^2, so it gets harder and harder to launch something into higher and higher orbits). Nothing can do that save a space elevator. Space elevators are the logical ideal launch mechanism. The only thing that had been holding us back was the lack of a material, and now carbon nanotubes look like they were handed to us on a silver platter.
All launch vehicles have to fight air resistance. A space elevator is the only one that fights it the best way possible - with a low "v", and a long "t".