The article cites the danger level as 1 U T where the u is a fancy symbolic one - probably your micro telsa.
Move off planet, then. 1 uT is 1E-6 tesla which is 0.01 gauss.
The Earth's magnetic field is 0.5 gauss. That's 50 uT. A bar magnet is a couple of gauss.
For crying out loud, I'd bet that a human's brain generates a few uT!
For some people this is a health problem.
If this were true, cancer patients would be wearing mu-metal clothing. It isn't. It's a crock. If they're claiming 1 uT is a problem, they're out of their minds.
There is no way that a magnetic field of 1 uT could possibly do anything. Look. Ordinary magnetic fields are weak. Really weak. Really really weak. They're down by a factor of 1/c from electric fields. Now, if you lived in a static electric field for a few years, I'd believe there might be a concern. Especially as you'd be sparking everywhere you go. But a 1 uT field probably couldn't move a microscopic amount of iron lying on a table. There's no way it could do anything to you.
Yah, it'd be great if he meant 2.5 gauss rather than 2.5 T. Here's a hint - if 2.5 gauss is dangerous to you, you've got a problem. You better be wearing mu-metal clothing your entire life, as Earth is about 0.5 gauss, and can be much more near magnetite deposits.
It's the voltage that creates ionisation and thus ozone, current is irrelevant:
No. What you're talking about here is basic Ohm's law. You can of course say that the current is a "consequence", but it's not, really. The only thing that will generate ozone is a coronal discharge, which is caused by current flowing and creating a low-resistance ionization path.
I can put 10 kV across air and not get a whit of ozone production. Just rub a balloon. Poof, 10 kV, and until you touch something grounded, that's 10 kV across air. Yah. 10 kV - that's pretty normal for static electricity.
That's what makes this study so completely stupid. Coronal discharges cause ozone. Really! No joke! But simple voltage sure as hell doesn't cause ozone. If they wanted to check that, they could rub a balloon with an ozone meter nearby.
(Truth be told, the best explanation is that it's the voltage gradient that matters - dV/dx - because coronal discharge happens when the trickle current is enough to create an ionization path and lower the resistance by orders of magnitude.)
Based upon an electric company measurement, a electric meter box will general a 1 telsa field thru a stone wall (on the other side of the wall of a cinder block wall).
A 1T field will cause a hammer to stick to it almost a meter away, and walking near it with metal-toed boots will make you feel lighter. It will also erase credit cards, etc. 2.5T is an absolutely massive magnetic field. You can generally only get it with superconducting magnets, because you need a completely throbbing amount of current in a toroid.
I highly think your numbers are really really wrong. By that argument, a compass would still point towards an electric meter box from well more than 10 feet away! (If it's just the static field from a net current, it'd be an absolutely huge distance away : 2 miles! The static field from a net current drops as 1/D, not 1/D^3).
It should also be noted that magnetic induction is vector, not scalar: it doesn't add simply. Likely if you had several in a room, you could get any combination of all of the fields, including zero.
I would believe 2.5 mT, not 2.5 T. Even that's still a huge field. 1 A, at 1 meter, will give you about 1 milligauss. At 1 foot, then, it'd be *3* milligauss, or so. Maybe 9 if it's a bunch of conductors. Say 10 milligauss.
You'd then have to have 1 million amperes of current to generate 1 T.
On the other hand, some physicists claim "Geometry Equals Force", so augmenting geometry is creating new forces, and we are back to dark energy again.
This is not a claim. It is a definition. The best example of it is the Coriolis and centrifugal "forces".
This comes about because we define motion under no forces as motion in a Cartesian reference frame. Therefore any deviation from that motion is a force.
I guess you could make the statement that "well, maybe that definition is wrong", but physicists would invoke one of the Fundamental Rights of Physicists and say that if motion under no forces is "very very close to but not quite" motion in a Cartesian reference frame, then it is, and the deviation is caused by another effect, which we will term a "force".
Well, the lack of newlines didn't help, so here's a simpler version.
Dark matter is implied by several things:
Galactic rotation curves
The velocities of galaxies in clusters
Anisotropy of the Cosmic Microwave Background
I'm leaving out Type Ia supernovae because I don't think they really imply dark matter *by themselves*.
Galactic rotation curves: If you have an object that rotates, and you know the velocity as a function of radius, you should be able to get the density as a function of radius. This is obvious, because the velocity is coming from gravity.
The problem: you can also get the density by assuming that light-emitting material carries the majority of the matter (stars - pretty good approximation) and then looking at the luminosity as a function of radius (how bright it is). So, in a perfect world, these two profiles would match.
They don't. Therefore either
Not all of the matter is light emitting
Gravity doesn't work.
Option 1 there breaks the least physics, so it's preferred.:) There are also other concerns - namely, there are some galaxies that do rotate correctly, and some that don't. So either gravity sometimes works and sometimes doesn't work, or option 1.
Velocity dispersion in clusters: See above - just with galactic clusters, rather than galaxies. Note that fixing one of these problems would probably fix the other!
Anisotropy of the CMB: This one's tougher to explain easily. 100,000 years after the Big Bang, the Universe was an extraordinarily uniform big fireball. Extremely uniform - because electrons hadn't cooled enough to form hydrogen yet, so it was one big hot plasma.
When hydrogen cooled, the photons in the Universe suddenly found themselves free to move, because hydrogen can only absorb certain wavelengths, and free electrons absorb continuously. Those photons are the Cosmic Microwave Background. Their uniformity is a very good indicator that the Big Bang theory is real - at least, from 100,000 years after the Big Bang to now.
However, matter that was in that fireball DID distort the radiation slightly - through gravity. And so we see anisotropy (nonuniformity) in the microwave background, and it looks very much like standing waves in the sky. The ratios of the strengths of certain frequencies tell us the ratio of dark energy ("lambda", the cosmological constant) to matter, AND also tell us how "flat" - i.e., how much total energy - the Universe has. It's flat. Exactly. Really really flat. It has exactly as much energy as would be needed to reverse the initial Big Bang (if it were all in matter, which it isn't). And it also tells us that dark energy is 70% of the energy content of the universe, and matter is 30%.
Big bang nucleosynthesis. BBN basically says "you can only get this much normal matter from a big bang explosion cooling to form atoms". It's amazingly accurate so far - it gives great answers for the ratio of certain elements, for instance. But it also puts a stringent limit on the amount of normal matter, of about 5%. The CMB *also* gives this same measurement - and, amazingly! - they agree! There are in fact even OTHER measurements which give values consistent with this number - 5% - so it's hard to imagine how measurements coming from completely different areas of physics (one is standing waves in the early Universe, one is nuclear physics) could give the same answers, and both be wrong. (But Nature can be perverse...)
So, Omega_m has to be about 30%, and Omega_b is about 5%. Plus there has to be something making stars and galaxies rotate too fast. Physicists, wanting elegance, say "two problems, one solution is a great theory."
Basically: If dark matter doesn't exist, we've got a lot of work to do to come up with other models, and a huge amount of it would affect gravity, which we thought we were beginning to understand!
It's very hard to imagine a form of gravity which could answer all of these problems, AND still be consistent with what we observe today.
Although I generally agree with the spirit of your message, this specific statement is not accurate:
Yes it is. While you were mentioning practical concerns, I was mentioning theoretical. There is a theoretical speed limit. There is no theoretical "travel time" limit.
First, there's a biophysical upper bound on acceleration: the body cannot concievably withstand much more than several g's for long. This limits your Lorentz factor.
This definitely doesn't bound velocities. It bounds accelerations. While this would matter for short distances, for extremely long distances, the acceleration period really wouldn't matter all that much.
Second, once v/c ~.93-4 interstellar dust, and eventually gas, starts being a major concern. At these velocities a shield is essentual, which limits you cargo and fuel mass. The closer a ship is to C, the larger a shield. (Plus, gas and dust collisions also reduce ship momentum: over long voyage this is effectively a very non-linear viscosity...). The trade-off and viscosity limits spaceship velocities so that time-dilations much more than 10 are not feasible.
Problems start kicking in much lower than that. You probably can't get much past 0.3c with conventional techniques - the mass/impulse ratio is too high, and so Newton's third law limits you quite dramatically.
However, I find it odd that we have a standard modle full of particles, but yet have not found any of their sparticles.
So do I, but then I realize that supersymmetry is a "well-conceived theory" - that is, it has enough parameter space to just about completely avoid ever being disproved.:)
I can't remember who it was, but at a seminar here a while ago, one of the presenters said "Supersymmetry predicts a huge number of particles... half of which have been discovered."
at some very very high speed that still takes you tens of thousands of years to get anywhere.
You apparently haven't taken enough physics lessons in reality, either. There is a universal speed limit - c - but there is no lower bound on the amount of proper time it takes to get from one place to another.
If you could accelerate to, say, a decent fraction of light speed, it could take you an arbitrarily short time due to time dilation.
This is, of course, ignoring things like wormholes or Alcubierre warp drives - both of which are perfectly valid science, mind you.
Of course, a reasonable maximum is probably 0.3c, which would take you years to get anywhere outside of this system. But then again...
The ocean analogy has been brought up before and it continues to demosntrate how ignorant most people are of basic science.
You know, those whole "ocean travelers" took months - and even years - to get anywhere too. If you're talking about intrastellar distances, months/years are perfectly reasonable. With a space elevator, a trip to Mars would be a few months. With a high powered nuclear engine, even less.
And I think you're being incredibly naive when you believe that space is harsh to humans. There's no evidence for that. We have precisely one data point so far: zero g and between zero g and 1g there's a hell of a lot of data.
In fact, naively, you'd immediately believe that humans would live longer in a lower gravity environment. It's far less stress on their heart and lungs. The only problem is bone mass, but that's only significant if the gravity is near-zero. There's probably some minimum gravity to activate the piezoelectric effect in bones, but I doubt it's that much. Lunar gravity - 1/6 g - would actually probably be plenty. Remember, you don't care about bone loss - you care about unbounded bone loss. Your body only needs strong bones if it plans on coming back to Earth, but it, of course, needs some framework and structure.
Will humans ever be zipping across the galaxy freely? Not in my lifetime, no way. But in the next few hundred years, I could easily see expensive expeditions to nearby (does sound remarkably like ocean travel from the 1600s, now doesn't it?
I would have thought that the memory would be swapped out
Swapped out? To where? You're being a bit recursive here. The operation failing is the initialization and reading of the flash. You can't swap to flash while you're initializing it.
However, I doubt they implemented virtual memory on the thing. It's far too much overhead in the OS to actually implement paging, etc. They were probably just very, very careful about the amount of memory in use at any one time, as with most embedded systems. Someone, however, didn't check that in a massively fragmented flash filesystem, the directory read wouldn't take up the entire RAM. Oops.
I don't think ID ignores this possibility, it just claims that it is equally provable/disprovable as the notion that there are many independent universes out there which we can't detect or measure but we happen to live in a lucky one. The anthropic principle is philosophy, not science. (Although I'd agree with you also that ID is philosophy, not science.)
If ID would claim that it is equally provable/disprovable as chance development, it's crap still. They're not "equally" provable or disprovable. Chance development and ID are both unprovable - moreover, they're the same bloody thing! (Take the example of a painter who splats paint on a thousand canvases, and creates a masterpiece on one of them. Who created the art - the painter, or chance?) It's a perfect example of a journalistic error - assuming that the answer to one direction of a question can answer another.
See, this is the problem that I have: philosophy isn't exempt from science. Science is founded on logic, and so is philosophy, and anyone can trivially show using logic that the strong anthropic principle is unprovable, so it's complete crap to talk about the strong anthropic principle at all, and likewise intelligent design. It's also crap to talk about "chance creation of the Universe", which is why I hate scientists who talk about it. You can't - absolutely can't talk about "why" the Universe was created, or "who" created the Universe, because such a question involves information outside this Universe.
Intelligent design versus chance design isn't even a question of philosophy. Metaphysics, maybe, or properly theology (if theology would ever become a real damned science like it should be). Philosophy is the study of human thought, and it's meaningless to talk about things in that context outside of human thought. Whether or not you can build a consistent framework outside of human thought is another question.
So it is not correct to say we are running out of Helium, just that we are running out of known reserves
Not exactly. Helium is only generated after astronomically long amounts of time, which is why there's even an appreciable amount here. The other problem is that helium is lighter than air, of course, and it escapes the atmosphere. So unless you're actively looking for helium, you tend to just let it float away.
The main problem is that helium happens to be found near something extremely valuable: fossil fuels. Almost all of the helium deposits are sitting on top of fossil fuel pockets. So most people just punch in, extract the fossil fuels, and vent the helium off into never never land.
We will run out of helium eventually. Reasonable estimates basically show that we have enough helium to last till the end of this century, but not much more. If you google for helium reserve, you'll find a number of papers which have estimates on the amount of helium remaining.
100 years is not a lot of time, especially when you consider that helium is irreplacable, unlike fossil fuels.
The He3 reactions are interesting because a reactor based on them would produce much less radioactive waste than a D-T reactor.
It's more than that, though. Every neutron that escapes your plasma is energy that can't keep your plasma going, and there are a lot of neutrons generated via D-T, D-D fusion, and a huge number of them escape. D-He3 is aneutronic, and the single-particle output that it does have are protons - which *are* containable.
So, I'm a little confused - I had always heard that while D-T is the (obviously) lowest energy threshold fusion reaction among practical sources, D-He3 was best for both the radioactive and practical plasma heating reasons. D-He3 should be ignitable in cases where D-T is only barely in ignition.
Blue of course! The night sky is the same color as the day.
Um, no. The only reason the sky is blue is because we're looking at it in blue-green light - the Sun. The Sun's spectrum peaks in the blue-green - not the orange that we see, because the blue is scattered in the atmosphere. Rayleigh scattering actually peaks in the violet, not the blue, so depending on how you define color, the color of the sky should probably be purple. If you put the sky underneath a uniform spectral source (something with a flat color dependence), it'd probably look much more purple than it does now.
The Moon shines in reflected sunlight, but of course, the reflected spectrum of the Sun, off the Moon, is not the same as the initial spectrum of the Sun, because the Moon absorbs in some wavelengths and not in others. (*obviously*: if the Moon looked like our Earth, it would be blue, now wouldn't it? and if it was Mars, it'd be red).
If the sky is blue during the night - and I haven't done a spectrophotometer measurement of the night sky - it's not an "of course" : it would just turn out to be dumb luck that the Moon reflected a spectrum from the Sun that was mostly identical to the incident solar spectrum.
You bet. The eye can resolve tremendous amounts of contrast. It has to: it works in day *and* night with (ignoring pupil dilation) virtually the same aperture/focal length/shutter speed!), and virtually everything else is linear (which is what *science* wants it to be).
This is why stellar magnitudes are listed in a logarithmic scale, as well, so that "twice as bright" stars are (somewhat) twice the magnitude (There's linear scaling that I can't quite remember: I want to say a factor of 5 in magnitude is a factor of 100 in intensity, but I could be wrong).
Everyone involved in astronomical imaging (and probably a lot of professional photography) knows this: while humans can *see* both the Sun and the trees around them clearly, even though the two have intensities millions of times away from each other, try to take a picture of it, and you don't have a prayer. Same thing with the Moon - try to get a picture of the moon, and if you try to not overexpose the Moon, there are *no* stars around it, while your eye can clearly see stars nearby.
I say "somewhat" logarithmic because a logarithmic response (i.e., something "twice as bright" is 10 times brighter) is an approximation for the eye's response to intensity, which is very complicated. But it is pretty good.
As the article states - instead of throwing away wavelengths above the visible spectrum (as the human eye would do), they are instead clamped. Anything bright infra-red becomes bright visible-red. Net result - way too much red in the pictures.
Wow, you read the article, but apparently missed the entire point! I'm impressed.
CCDs are color blind. They take intensity maps only. Generally, they use R, G, and B filters with wavelengths as listed in the article. Many of the pictures were taken with an "R" filter that has a much longer wavelength than the usual R.
You can't "throw away" wavelength information because you don't have any. All you have are intensity maps at 3 wavelengths. You simply do not intensity maps at the middle.
If you want NASA to put out only near-true-color images, enjoy. I'll take all the other pictures and not worry so much, along with the rest of the normal humans. Of course, you'll also still have to deal with the fact that CCDs respond linearly to intensity and your eye is (somewhat) logarithmic, so any time you look at a bright source, everything will be completely wrong. Of course, everyone already knows this - pictures never look exactly the same as reality, unless they've been very very carefully taken with someone comparing the result to what they see with their own eyes, or in very controlled circumstances.
Want to know what Mars really looks like to the human eye? Go there (*). Currently, there's no other "real" practical way, without building some very expensive (and very useless) piece of equipment.
(*: You could also calculate it because you know the atmosphere and you know the input spectrum. NASA has - it's something like a yellowish-brownish-red ("butterscotch", they call it).
I have my own theory that also accounts for the observed quantization of the red shift of light
There are science trolls on Slashdot now? That's new!
Well, I like to feed trolls to make sure that someone perusing/. doesn't think that things are real...
The quantization of red shift was an artifact. There's a paper in MNRAS from quite some time ago which shows no periodicity in redshifts as was thought before.
The rest of your post is pretty much pure troll, as photons can't interact with photons without a virtual electron/positron set. Y'know, the whole "fundamental vertex of QED" bit. This is the little bit that few people know about -photons need stray charges around to interact with each other.
It's possible that each point on the equator will sweep over every point covered by the equator, but it's not by any means certain. The moon's orbit is NOT static; even given all the time in the world it won't repeat itself.
I think you're missing something: the Earth rotates much faster than the Moon orbits, and the moon has physical width. When the elevator is "rising" on the moon, it points radially aligned with the axis of the moon. Then, it hits one spot on the moon. As the Earth rotates, the place where the payload would impact would trace across the moon's surface, forming a projection of the equator on the Moon's surface.
That projection will then rotate up and down as the relative inclinations of the Moon and the Earth continue, ignoring the times when the two do not align at all.
If someone's going to perform this attack, they have to prepare for it and execute it in a TINY window.
Engineering problem. If I calculate the path of all trajectories from a space elevator at its maximum extension, and let that run over time, and look at those trajectories which impact the moon, it will cover a large surface of the moon. That's what I'm saying. I didn't say it was practical to hit some tiny location with major precision.
The moon may be easy to hit; but your target isn't any easier to hit than it would have been in open space.
Imagine you've got a ball, in empty space, and a target, in empty space, and you're trying to hit the target. Now, if you throw the ball, there's only one path that can hit the target, if you throw at a velocity fast enough that the gravitational potential energy of the target is negligible.
Now put that target on a planet. If I throw radially at the target, from directly above it, that's the exact same path I would take in empty space. The resultant vector that the ball has on impact is radially towards the target - obviously, nothing changed it. If I throw say, five degrees to the left, gravity, being an acceleration, will change the path of the ball. If I'm radially above the target, it of course could still hit the target. If I had let the ball go with no velocity, it would hit the target. But even if I'm not, there exists a path, based on the angle that I throw it at, that will hit the target still. I've got 1 degree of freedom - angle - that of course translates into position of impact on the planetary body.
Just take this to the extreme. With careful timing, the elevator could put something directly into lunar orbit - granted a highly parabolic orbit, but lunar orbit nonetheless. Clearly then the path of all possible elevator releases must cover a significant region of the lunar surface, because by altering that path slightly (releasing slightly later or earlier), what was an orbit could be an impact with a highly tangential velocity.
The moon wouldn't be parallel, but neither would it be perpendicular to launch.
The moon's velocity is perpendicular to the Earth-Moon radial line (at least, mostly - the Moon's orbit isn't spherical, but like all orbits, it's very close). Basic circular motion. If the elevator releases the payload when the elevator is perpendicular to the Earth-Moon radial line, the two velocities will be perpendicular, because the payload's velocity will be parallel.
Time-shifted, of course: the velocity of the Moon at launch wouldn't be perpendicular to the payload velocity, but if you project the location of the Moon to time of arrival of the payload, that projection would have a velocity that's perpendicular to the Moon's velocity. This is obvious.
Of course, it doesn't have to be. You can take any path you want - launch the payload when the Moon is directly overhead of the elevator, and the payload will take a roughly parallel path to the Moon. This would take longer, of course.
And yes, I'm assuming the limit of infinite elevators. The lunar cycle is in fact a harmonic of the Earth's r
My application isn't a real-time system, so I can't comment on whether Linux is applicable as a real-time OS, but on the other hand I need to be able to resolve time on the nanosecond scale, and Linux/GCC does that just fine. So despite the article I think I'll stick with what works for me.
Realtime performance means fast interrupt servicing, and this is the part I don't understand: uClinux gives interrupt latencies of about 10-40 microseconds to the top half of the interrupt handler, about 50-100 microseconds to the bottom half of the interrupt handler, and about 300 microseconds from interrupt -> data read if the bottom half is putting data through the I/O and another process is reading it. That's on a 66MHz system - so it's about a thousand clock cycles or so to the top half. That's not bad. Granted, other RTOSs are better - I've also used Microware's OS-9000, and that's got an interrupt service latency in the tens of microseconds, and that's even after using system events to signal another process. So that's really quite good. But depending on what you need, I can't see how uClinux could really hurt you that much. If you desparately need speed, try to put as much as you can in the top half, and you should get quite good performance. (Plus I think there are other ways to get the latency down, but I've never bothered, as it's never been important)
Plus having the source is incredibly helpful. You can actually figure out what the heck is going on in certain cases without wasting days upon days trying to talk to crappy customer support for commercial RTOSes. Ugh. Maybe if the project I work with had infinite money, sure, but...
This thing (will) must have quite impressive normal modes... my guess is there will be non-negligible shear forces in the cable.
Thankfully, the normal modes are not near any natural frequency - 7 hours or so. The shear forces are quite manageable, and could easily be actively damped as well.
The elevator isn't everywhere on the Earth's equator -- it's only at one point.
No, it's everywhere - the Earth rotates. Therefore the (corrected for the 90 degree phase difference, since the elevator shoots perpendicular to its radial axis) projection of the equator on the Moon is the target that the Moon can hit.
The point is that there's only ONE trajectory you can follow to hit your desired target;
Yah. That's not the point. Ignoring the launch window problem (which is an engineering problem - a big one, granted - but not a theoretical) the point is that the envelope of all trajectories launched perpendicular to the elevator's axis (and we'll ignore the possibility that you can alter your velocity by moving up and down the ribbon) sweeps over a rather large area on the lunar surface as a function of time, though it does miss a lot of it if there's only one space elevator and so the phase of the elevator's rotation and the lunar conjunction might not align. With several, you can hit more, and with the limit of infinite, you sweep over a rather large area.
I wish this actually worked -- my target shooting would be a lot better if it did! But it doesn't. Gravity doesn't magically pull bullets toward their targets; it merely accelerates masses toward each other. The problem is that the mass of the moon FAR outweighs the mass of your actual target; your sabot isn't going to be drawn toward the target, but rather the moon as a whole.
Actually, this *does* work. Go look it up in any basic high-energy physics book: any force with a 1/r^2 dependence has an effective cross section at low velocities (energies) of twice the hard-sphere model. This is obvious. If you try to hit the moon, gravity pulls you towards the moon, so you'll hit it. Yes, you're trying to hit a specific spot, but thankfully, vectors add, not replace each other, so you can compute the trajectory such that the impact point is your target. Then you just have to wait for the elevator to line up.
The problem is that as the energy increases, the hard-sphere cross section stays fixed, and the interaction cross section goes down. Obviously, the effective cross section will always be larger than the hard-sphere model, but after a certain point it will be insignificantly more (generally when the KE is bigger than the potential energy is when it's a negligible effect).
You actually said this - "gravity doesn't magically pull bullets toward their target", but it "accelerates objects towards each other." Well, pull means force, and acceleration is force, so you just said that gravity doesn't do something it does.:) The problem in shooting something, like a bullet, is that the gravitational attraction is virtually zero and the kinetic energy greatly exceeds the potential energy.
So, it depends on how fast it's going.
But you're not trying to shoot the moon. That's already been done -- see those craters? You're actually trying to hit a tiny spot on the moon.
Uhm. Yes. And? The question is not "can you hit any spot at any given time?" No, of course not. You only have one free parameter - time - and restricting that of course restricts your options.
Think about it, though -- the counterweight will be moving about 2km/s relative to the moon (geosync is 3km/s, moon is 1km/s)
Moon's velocity would be perpendicular to the projectile velocity. They wouldn't add or subtract. Relative velocity would be 3 km/s (for a counterweight at virtually infinite distance, less for one closer to geosync, obviously).
Plus gravity cuts down on transit time, though I don't know how much in this case.
How are you going to have microsecond accuracy on cutting the cable
Engineering problem, not a fundamental one. Anyway, this isn't a completely stupid thing to think about, because while you're not g
It's covered in the book and in the NIAC proposal. Basically, the base of the elevator can be put far from any common air routes (it has to be anyway) and so protecting it would be fairly easy. Besides, airlines don't pay for all of their security, do they?
Keep in mind that the only real way you can do damage to a space elevator is by hitting it a significant fraction of the way to GEO. And that's a LONG distance. The day that a single person or small group can fire a ground-to-space missile, we've got other problems than protecting the space elevator.:)
eOnce a critical flaw is made, it will zoom through the ribbon at fantastic speed concentrating stress.
Make the ribbon extremely wide in areas of high-impact, thus minimizing the affect that a loss of a small portion of the ribbon will have.
But it doesn't matter because no one involved with the space elevator concepts is even looking at toughness, which means they haven't considered reliability.
It's in the space elevator book, I believe. I don't have it here, but I'm pretty sure I remember reading it.
And given the make money fast reading list of the guy who runs the spacelift sham company out of Banbringe Washington,
What about the guy who actually proposed it to NASA? ISR certainly isn't a sham company!
it's a pipe dream at best
You might want to tell that to NASA and all the other engineers/scientists who are convinced that it'll work. Who knows, you might actually be on to something that they missed, but they've done stress simulations and impact analysis, so I don't think it's a real problem.
I admit I was being brief (I know the alignments aren't perfect); but this complication doesn't change things at all. There are still huge tracts of land on the moon which don't line up with any trajectory of an elevator break (in fact, that's an understatement made strictly because I wanted to use the phrase "huge tracts of land on the moon"), and because the lineup isn't exact, it's much worse for any potential attacker -- any given target will present itself once, and essentially never again.
Once every few years, that is. The moon-Earth cycle repeats on a few-year basis. Heck, if you're trying for surprise mass destruction, what's a few years to wait?
Besides, I don't understand why you don't see what I mean: the area of land that the elevator can impact is (kindof) the projection of the Earth's axis on the Moon. Since the relative orientation of those two things change over the year and over the month, the elevator can hit the entire area that it sweeps over, which is pretty large. Plus the lunar "wiggles" will help you here too, since the Moon doesn't present "exactly" the same face to us all the time (lunar librations are the term, I think).
What do you mean? This is basic ballistics;
I don't get it: suppose the Moon and the Earth are lined up, and everything's aligned. Then basic ballistics says you can only fire when the straightline projection of the path impacts the moon.
However, gravity increases the effective cross-section of any object by a factor of two - something fired with a straightline projection "near" an object will hit the object. In the case of high-speed impacts this isn't true, but it does affect it by a large amount. Therefore, if the straightline projection misses the moon by a bit, the gravitationally affected path will not.
In the aligned case, this doesn't do anything except allow you to hit around the back of the moon a bit more. In the unaligned case, since the velocity vector and the lunar radial vector aren't aligned, it will allow you to hit spots that a straightline projection would not (though it may remove points as well, but it, overall, will increase the spread in impact positions).
I can't see that being easy, though. It depends on an impressive list of things, foremost amongst them is there being a lunar base in any sort of position to be hit by the counterweight. It's not like you can aim; all you can do is time the break.
The axis of the Moon's orbit and the Earth's rotation aren't aligned. You'd actually have a large portion of the surface of the Moon that you could aim at. Perhaps all of it. You'd just have to wait until the proper alignment of the elevator and the Moon.
Plus gravity is very helpful with these sort of things. Makes the cross-section of the moon twice as big, after all (if memory serves).:)
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The article cites the danger level as 1 U T where the u is a fancy symbolic one - probably your micro telsa.
Move off planet, then . 1 uT is 1E-6 tesla which is 0.01 gauss.
The Earth's magnetic field is 0.5 gauss. That's 50 uT. A bar magnet is a couple of gauss.
For crying out loud, I'd bet that a human's brain generates a few uT!
For some people this is a health problem.
If this were true, cancer patients would be wearing mu-metal clothing. It isn't. It's a crock. If they're claiming 1 uT is a problem, they're out of their minds.
There is no way that a magnetic field of 1 uT could possibly do anything. Look. Ordinary magnetic fields are weak. Really weak. Really really weak. They're down by a factor of 1/c from electric fields. Now, if you lived in a static electric field for a few years, I'd believe there might be a concern. Especially as you'd be sparking everywhere you go. But a 1 uT field probably couldn't move a microscopic amount of iron lying on a table. There's no way it could do anything to you.
Yah, it'd be great if he meant 2.5 gauss rather than 2.5 T. Here's a hint - if 2.5 gauss is dangerous to you, you've got a problem. You better be wearing mu-metal clothing your entire life, as Earth is about 0.5 gauss, and can be much more near magnetite deposits.
It's the voltage that creates ionisation and thus ozone, current is irrelevant:
No. What you're talking about here is basic Ohm's law. You can of course say that the current is a "consequence", but it's not, really. The only thing that will generate ozone is a coronal discharge, which is caused by current flowing and creating a low-resistance ionization path.
I can put 10 kV across air and not get a whit of ozone production. Just rub a balloon. Poof, 10 kV, and until you touch something grounded, that's 10 kV across air. Yah. 10 kV - that's pretty normal for static electricity.
That's what makes this study so completely stupid. Coronal discharges cause ozone. Really! No joke! But simple voltage sure as hell doesn't cause ozone. If they wanted to check that, they could rub a balloon with an ozone meter nearby.
(Truth be told, the best explanation is that it's the voltage gradient that matters - dV/dx - because coronal discharge happens when the trickle current is enough to create an ionization path and lower the resistance by orders of magnitude.)
Based upon an electric company measurement, a electric meter box will general a 1 telsa field thru a stone wall (on the other side of the wall of a cinder block wall).
A 1T field will cause a hammer to stick to it almost a meter away, and walking near it with metal-toed boots will make you feel lighter. It will also erase credit cards, etc. 2.5T is an absolutely massive magnetic field. You can generally only get it with superconducting magnets, because you need a completely throbbing amount of current in a toroid.
I highly think your numbers are really really wrong. By that argument, a compass would still point towards an electric meter box from well more than 10 feet away! (If it's just the static field from a net current, it'd be an absolutely huge distance away : 2 miles! The static field from a net current drops as 1/D, not 1/D^3).
It should also be noted that magnetic induction is vector, not scalar: it doesn't add simply. Likely if you had several in a room, you could get any combination of all of the fields, including zero.
I would believe 2.5 mT, not 2.5 T. Even that's still a huge field. 1 A, at 1 meter, will give you about 1 milligauss. At 1 foot, then, it'd be *3* milligauss, or so. Maybe 9 if it's a bunch of conductors. Say 10 milligauss.
You'd then have to have 1 million amperes of current to generate 1 T.
Check those numbers again.
On the other hand, some physicists claim "Geometry Equals Force", so augmenting geometry is creating new forces, and we are back to dark energy again.
This is not a claim. It is a definition. The best example of it is the Coriolis and centrifugal "forces".
This comes about because we define motion under no forces as motion in a Cartesian reference frame. Therefore any deviation from that motion is a force.
I guess you could make the statement that "well, maybe that definition is wrong", but physicists would invoke one of the Fundamental Rights of Physicists and say that if motion under no forces is "very very close to but not quite" motion in a Cartesian reference frame, then it is, and the deviation is caused by another effect, which we will term a "force".
So, yup, back to dark energy.
Dark matter is implied by several things:
- Galactic rotation curves
- The velocities of galaxies in clusters
- Anisotropy of the Cosmic Microwave Background
I'm leaving out Type Ia supernovae because I don't think they really imply dark matter *by themselves*.Galactic rotation curves: If you have an object that rotates, and you know the velocity as a function of radius, you should be able to get the density as a function of radius. This is obvious, because the velocity is coming from gravity.
The problem: you can also get the density by assuming that light-emitting material carries the majority of the matter (stars - pretty good approximation) and then looking at the luminosity as a function of radius (how bright it is). So, in a perfect world, these two profiles would match.
They don't. Therefore either
- Not all of the matter is light emitting
- Gravity doesn't work.
Option 1 there breaks the least physics, so it's preferred.Velocity dispersion in clusters : See above - just with galactic clusters, rather than galaxies. Note that fixing one of these problems would probably fix the other!
Anisotropy of the CMB : This one's tougher to explain easily. 100,000 years after the Big Bang, the Universe was an extraordinarily uniform big fireball. Extremely uniform - because electrons hadn't cooled enough to form hydrogen yet, so it was one big hot plasma.
When hydrogen cooled, the photons in the Universe suddenly found themselves free to move, because hydrogen can only absorb certain wavelengths, and free electrons absorb continuously. Those photons are the Cosmic Microwave Background. Their uniformity is a very good indicator that the Big Bang theory is real - at least, from 100,000 years after the Big Bang to now.
However, matter that was in that fireball DID distort the radiation slightly - through gravity. And so we see anisotropy (nonuniformity) in the microwave background, and it looks very much like standing waves in the sky. The ratios of the strengths of certain frequencies tell us the ratio of dark energy ("lambda", the cosmological constant) to matter, AND also tell us how "flat" - i.e., how much total energy - the Universe has. It's flat. Exactly. Really really flat. It has exactly as much energy as would be needed to reverse the initial Big Bang (if it were all in matter, which it isn't). And it also tells us that dark energy is 70% of the energy content of the universe, and matter is 30%.
Big bang nucleosynthesis . BBN basically says "you can only get this much normal matter from a big bang explosion cooling to form atoms". It's amazingly accurate so far - it gives great answers for the ratio of certain elements, for instance. But it also puts a stringent limit on the amount of normal matter, of about 5%. The CMB *also* gives this same measurement - and, amazingly! - they agree! There are in fact even OTHER measurements which give values consistent with this number - 5% - so it's hard to imagine how measurements coming from completely different areas of physics (one is standing waves in the early Universe, one is nuclear physics) could give the same answers, and both be wrong. (But Nature can be perverse...)
So, Omega_m has to be about 30%, and Omega_b is about 5%. Plus there has to be something making stars and galaxies rotate too fast. Physicists, wanting elegance, say "two problems, one solution is a great theory."
Basically: If dark matter doesn't exist, we've got a lot of work to do to come up with other models, and a huge amount of it would affect gravity, which we thought we were beginning to understand!
It's very hard to imagine a form of gravity which could answer all of these problems, AND still be consistent with what we observe today.
Although I generally agree with the spirit of your message, this specific statement is not accurate:
.93-4 interstellar dust, and eventually gas, starts being a major concern. At these velocities a shield is essentual, which limits you cargo and fuel mass. The closer a ship is to C, the larger a shield. (Plus, gas and dust collisions also reduce ship momentum: over long voyage this is effectively a very non-linear viscosity ...). The trade-off and viscosity limits spaceship velocities so that time-dilations much more than 10 are not feasible.
Yes it is. While you were mentioning practical concerns, I was mentioning theoretical. There is a theoretical speed limit. There is no theoretical "travel time" limit.
First, there's a biophysical upper bound on acceleration: the body cannot concievably withstand much more than several g's for long. This limits your Lorentz factor.
This definitely doesn't bound velocities. It bounds accelerations. While this would matter for short distances, for extremely long distances, the acceleration period really wouldn't matter all that much.
Second, once v/c ~
Problems start kicking in much lower than that. You probably can't get much past 0.3c with conventional techniques - the mass/impulse ratio is too high, and so Newton's third law limits you quite dramatically.
However, I find it odd that we have a standard modle full of particles, but yet have not found any of their sparticles.
:)
So do I, but then I realize that supersymmetry is a "well-conceived theory" - that is, it has enough parameter space to just about completely avoid ever being disproved.
I can't remember who it was, but at a seminar here a while ago, one of the presenters said "Supersymmetry predicts a huge number of particles... half of which have been discovered."
I was amused.
at some very very high speed that still takes you tens of thousands of years to get anywhere.
You apparently haven't taken enough physics lessons in reality, either. There is a universal speed limit - c - but there is no lower bound on the amount of proper time it takes to get from one place to another.
If you could accelerate to, say, a decent fraction of light speed, it could take you an arbitrarily short time due to time dilation.
This is, of course, ignoring things like wormholes or Alcubierre warp drives - both of which are perfectly valid science, mind you.
Of course, a reasonable maximum is probably 0.3c, which would take you years to get anywhere outside of this system. But then again...
The ocean analogy has been brought up before and it continues to demosntrate how ignorant most people are of basic science.
You know, those whole "ocean travelers" took months - and even years - to get anywhere too. If you're talking about intrastellar distances, months/years are perfectly reasonable. With a space elevator, a trip to Mars would be a few months. With a high powered nuclear engine, even less.
And I think you're being incredibly naive when you believe that space is harsh to humans. There's no evidence for that. We have precisely one data point so far: zero g and between zero g and 1g there's a hell of a lot of data.
In fact, naively, you'd immediately believe that humans would live longer in a lower gravity environment. It's far less stress on their heart and lungs. The only problem is bone mass, but that's only significant if the gravity is near-zero. There's probably some minimum gravity to activate the piezoelectric effect in bones, but I doubt it's that much. Lunar gravity - 1/6 g - would actually probably be plenty. Remember, you don't care about bone loss - you care about unbounded bone loss. Your body only needs strong bones if it plans on coming back to Earth, but it, of course, needs some framework and structure.
Will humans ever be zipping across the galaxy freely? Not in my lifetime, no way. But in the next few hundred years, I could easily see expensive expeditions to nearby (does sound remarkably like ocean travel from the 1600s, now doesn't it?
I would have thought that the memory would be swapped out
Swapped out? To where? You're being a bit recursive here. The operation failing is the initialization and reading of the flash. You can't swap to flash while you're initializing it.
However, I doubt they implemented virtual memory on the thing. It's far too much overhead in the OS to actually implement paging, etc. They were probably just very, very careful about the amount of memory in use at any one time, as with most embedded systems. Someone, however, didn't check that in a massively fragmented flash filesystem, the directory read wouldn't take up the entire RAM. Oops.
I don't think ID ignores this possibility, it just claims that it is equally provable/disprovable as the notion that there are many independent universes out there which we can't detect or measure but we happen to live in a lucky one. The anthropic principle is philosophy, not science. (Although I'd agree with you also that ID is philosophy, not science.)
If ID would claim that it is equally provable/disprovable as chance development, it's crap still. They're not "equally" provable or disprovable. Chance development and ID are both unprovable - moreover, they're the same bloody thing! (Take the example of a painter who splats paint on a thousand canvases, and creates a masterpiece on one of them. Who created the art - the painter, or chance?) It's a perfect example of a journalistic error - assuming that the answer to one direction of a question can answer another.
See, this is the problem that I have: philosophy isn't exempt from science. Science is founded on logic, and so is philosophy, and anyone can trivially show using logic that the strong anthropic principle is unprovable, so it's complete crap to talk about the strong anthropic principle at all, and likewise intelligent design. It's also crap to talk about "chance creation of the Universe", which is why I hate scientists who talk about it. You can't - absolutely can't talk about "why" the Universe was created, or "who" created the Universe, because such a question involves information outside this Universe.
Intelligent design versus chance design isn't even a question of philosophy. Metaphysics, maybe, or properly theology (if theology would ever become a real damned science like it should be). Philosophy is the study of human thought, and it's meaningless to talk about things in that context outside of human thought. Whether or not you can build a consistent framework outside of human thought is another question.
So it is not correct to say we are running out of Helium, just that we are running out of known reserves
Not exactly. Helium is only generated after astronomically long amounts of time, which is why there's even an appreciable amount here. The other problem is that helium is lighter than air, of course, and it escapes the atmosphere. So unless you're actively looking for helium, you tend to just let it float away.
The main problem is that helium happens to be found near something extremely valuable: fossil fuels. Almost all of the helium deposits are sitting on top of fossil fuel pockets. So most people just punch in, extract the fossil fuels, and vent the helium off into never never land.
We will run out of helium eventually. Reasonable estimates basically show that we have enough helium to last till the end of this century, but not much more. If you google for helium reserve, you'll find a number of papers which have estimates on the amount of helium remaining.
100 years is not a lot of time, especially when you consider that helium is irreplacable, unlike fossil fuels.
The He3 reactions are interesting because a reactor based on them would produce much less radioactive waste than a D-T reactor.
It's more than that, though. Every neutron that escapes your plasma is energy that can't keep your plasma going, and there are a lot of neutrons generated via D-T, D-D fusion, and a huge number of them escape. D-He3 is aneutronic, and the single-particle output that it does have are protons - which *are* containable.
So, I'm a little confused - I had always heard that while D-T is the (obviously) lowest energy threshold fusion reaction among practical sources, D-He3 was best for both the radioactive and practical plasma heating reasons. D-He3 should be ignitable in cases where D-T is only barely in ignition.
Blue of course! The night sky is the same color as the day.
Um, no. The only reason the sky is blue is because we're looking at it in blue-green light - the Sun. The Sun's spectrum peaks in the blue-green - not the orange that we see, because the blue is scattered in the atmosphere. Rayleigh scattering actually peaks in the violet, not the blue, so depending on how you define color, the color of the sky should probably be purple. If you put the sky underneath a uniform spectral source (something with a flat color dependence), it'd probably look much more purple than it does now.
The Moon shines in reflected sunlight, but of course, the reflected spectrum of the Sun, off the Moon, is not the same as the initial spectrum of the Sun, because the Moon absorbs in some wavelengths and not in others. (*obviously*: if the Moon looked like our Earth, it would be blue, now wouldn't it? and if it was Mars, it'd be red).
If the sky is blue during the night - and I haven't done a spectrophotometer measurement of the night sky - it's not an "of course" : it would just turn out to be dumb luck that the Moon reflected a spectrum from the Sun that was mostly identical to the incident solar spectrum.
You bet. The eye can resolve tremendous amounts of contrast. It has to: it works in day *and* night with (ignoring pupil dilation) virtually the same aperture/focal length/shutter speed!), and virtually everything else is linear (which is what *science* wants it to be).
This is why stellar magnitudes are listed in a logarithmic scale, as well, so that "twice as bright" stars are (somewhat) twice the magnitude (There's linear scaling that I can't quite remember: I want to say a factor of 5 in magnitude is a factor of 100 in intensity, but I could be wrong).
Everyone involved in astronomical imaging (and probably a lot of professional photography) knows this: while humans can *see* both the Sun and the trees around them clearly, even though the two have intensities millions of times away from each other, try to take a picture of it, and you don't have a prayer. Same thing with the Moon - try to get a picture of the moon, and if you try to not overexpose the Moon, there are *no* stars around it, while your eye can clearly see stars nearby.
I say "somewhat" logarithmic because a logarithmic response (i.e., something "twice as bright" is 10 times brighter) is an approximation for the eye's response to intensity, which is very complicated. But it is pretty good.
As the article states - instead of throwing away wavelengths above the visible spectrum (as the human eye would do), they are instead clamped. Anything bright infra-red becomes bright visible-red. Net result - way too much red in the pictures.
Wow, you read the article, but apparently missed the entire point! I'm impressed.
CCDs are color blind. They take intensity maps only. Generally, they use R, G, and B filters with wavelengths as listed in the article. Many of the pictures were taken with an "R" filter that has a much longer wavelength than the usual R.
You can't "throw away" wavelength information because you don't have any. All you have are intensity maps at 3 wavelengths. You simply do not intensity maps at the middle.
If you want NASA to put out only near-true-color images, enjoy. I'll take all the other pictures and not worry so much, along with the rest of the normal humans. Of course, you'll also still have to deal with the fact that CCDs respond linearly to intensity and your eye is (somewhat) logarithmic, so any time you look at a bright source, everything will be completely wrong. Of course, everyone already knows this - pictures never look exactly the same as reality, unless they've been very very carefully taken with someone comparing the result to what they see with their own eyes, or in very controlled circumstances.
Want to know what Mars really looks like to the human eye? Go there (*). Currently, there's no other "real" practical way, without building some very expensive (and very useless) piece of equipment.
(*: You could also calculate it because you know the atmosphere and you know the input spectrum. NASA has - it's something like a yellowish-brownish-red ("butterscotch", they call it).
I have my own theory that also accounts for the observed quantization of the red shift of light
/. doesn't think that things are real...
There are science trolls on Slashdot now? That's new!
Well, I like to feed trolls to make sure that someone perusing
The quantization of red shift was an artifact. There's a paper in MNRAS from quite some time ago which shows no periodicity in redshifts as was thought before.
The rest of your post is pretty much pure troll, as photons can't interact with photons without a virtual electron/positron set. Y'know, the whole "fundamental vertex of QED" bit. This is the little bit that few people know about -photons need stray charges around to interact with each other.
It's possible that each point on the equator will sweep over every point covered by the equator, but it's not by any means certain. The moon's orbit is NOT static; even given all the time in the world it won't repeat itself.
I think you're missing something: the Earth rotates much faster than the Moon orbits, and the moon has physical width. When the elevator is "rising" on the moon, it points radially aligned with the axis of the moon. Then, it hits one spot on the moon. As the Earth rotates, the place where the payload would impact would trace across the moon's surface, forming a projection of the equator on the Moon's surface.
That projection will then rotate up and down as the relative inclinations of the Moon and the Earth continue, ignoring the times when the two do not align at all.
If someone's going to perform this attack, they have to prepare for it and execute it in a TINY window.
Engineering problem. If I calculate the path of all trajectories from a space elevator at its maximum extension, and let that run over time, and look at those trajectories which impact the moon, it will cover a large surface of the moon. That's what I'm saying. I didn't say it was practical to hit some tiny location with major precision.
The moon may be easy to hit; but your target isn't any easier to hit than it would have been in open space.
Imagine you've got a ball, in empty space, and a target, in empty space, and you're trying to hit the target. Now, if you throw the ball, there's only one path that can hit the target, if you throw at a velocity fast enough that the gravitational potential energy of the target is negligible.
Now put that target on a planet. If I throw radially at the target, from directly above it, that's the exact same path I would take in empty space. The resultant vector that the ball has on impact is radially towards the target - obviously, nothing changed it. If I throw say, five degrees to the left, gravity, being an acceleration, will change the path of the ball. If I'm radially above the target, it of course could still hit the target. If I had let the ball go with no velocity, it would hit the target. But even if I'm not, there exists a path, based on the angle that I throw it at, that will hit the target still. I've got 1 degree of freedom - angle - that of course translates into position of impact on the planetary body.
Just take this to the extreme. With careful timing, the elevator could put something directly into lunar orbit - granted a highly parabolic orbit, but lunar orbit nonetheless. Clearly then the path of all possible elevator releases must cover a significant region of the lunar surface, because by altering that path slightly (releasing slightly later or earlier), what was an orbit could be an impact with a highly tangential velocity.
The moon wouldn't be parallel, but neither would it be perpendicular to launch.
The moon's velocity is perpendicular to the Earth-Moon radial line (at least, mostly - the Moon's orbit isn't spherical, but like all orbits, it's very close). Basic circular motion. If the elevator releases the payload when the elevator is perpendicular to the Earth-Moon radial line, the two velocities will be perpendicular, because the payload's velocity will be parallel.
Time-shifted, of course: the velocity of the Moon at launch wouldn't be perpendicular to the payload velocity, but if you project the location of the Moon to time of arrival of the payload, that projection would have a velocity that's perpendicular to the Moon's velocity. This is obvious.
Of course, it doesn't have to be. You can take any path you want - launch the payload when the Moon is directly overhead of the elevator, and the payload will take a roughly parallel path to the Moon. This would take longer, of course.
And yes, I'm assuming the limit of infinite elevators. The lunar cycle is in fact a harmonic of the Earth's r
My application isn't a real-time system, so I can't comment on whether Linux is applicable as a real-time OS, but on the other hand I need to be able to resolve time on the nanosecond scale, and Linux/GCC does that just fine. So despite the article I think I'll stick with what works for me.
Realtime performance means fast interrupt servicing, and this is the part I don't understand: uClinux gives interrupt latencies of about 10-40 microseconds to the top half of the interrupt handler, about 50-100 microseconds to the bottom half of the interrupt handler, and about 300 microseconds from interrupt -> data read if the bottom half is putting data through the I/O and another process is reading it. That's on a 66MHz system - so it's about a thousand clock cycles or so to the top half. That's not bad. Granted, other RTOSs are better - I've also used Microware's OS-9000, and that's got an interrupt service latency in the tens of microseconds, and that's even after using system events to signal another process. So that's really quite good. But depending on what you need, I can't see how uClinux could really hurt you that much. If you desparately need speed, try to put as much as you can in the top half, and you should get quite good performance. (Plus I think there are other ways to get the latency down, but I've never bothered, as it's never been important)
Plus having the source is incredibly helpful. You can actually figure out what the heck is going on in certain cases without wasting days upon days trying to talk to crappy customer support for commercial RTOSes. Ugh. Maybe if the project I work with had infinite money, sure, but...
This thing (will) must have quite impressive normal modes
Thankfully, the normal modes are not near any natural frequency - 7 hours or so. The shear forces are quite manageable, and could easily be actively damped as well.
You mean equator, of course.
Yup. That was an oops.
The elevator isn't everywhere on the Earth's equator -- it's only at one point.
No, it's everywhere - the Earth rotates. Therefore the (corrected for the 90 degree phase difference, since the elevator shoots perpendicular to its radial axis) projection of the equator on the Moon is the target that the Moon can hit.
The point is that there's only ONE trajectory you can follow to hit your desired target;
Yah. That's not the point. Ignoring the launch window problem (which is an engineering problem - a big one, granted - but not a theoretical) the point is that the envelope of all trajectories launched perpendicular to the elevator's axis (and we'll ignore the possibility that you can alter your velocity by moving up and down the ribbon) sweeps over a rather large area on the lunar surface as a function of time, though it does miss a lot of it if there's only one space elevator and so the phase of the elevator's rotation and the lunar conjunction might not align. With several, you can hit more, and with the limit of infinite, you sweep over a rather large area.
I wish this actually worked -- my target shooting would be a lot better if it did! But it doesn't. Gravity doesn't magically pull bullets toward their targets; it merely accelerates masses toward each other. The problem is that the mass of the moon FAR outweighs the mass of your actual target; your sabot isn't going to be drawn toward the target, but rather the moon as a whole.
Actually, this *does* work. Go look it up in any basic high-energy physics book: any force with a 1/r^2 dependence has an effective cross section at low velocities (energies) of twice the hard-sphere model. This is obvious. If you try to hit the moon, gravity pulls you towards the moon, so you'll hit it. Yes, you're trying to hit a specific spot, but thankfully, vectors add, not replace each other, so you can compute the trajectory such that the impact point is your target. Then you just have to wait for the elevator to line up.
The problem is that as the energy increases, the hard-sphere cross section stays fixed, and the interaction cross section goes down. Obviously, the effective cross section will always be larger than the hard-sphere model, but after a certain point it will be insignificantly more (generally when the KE is bigger than the potential energy is when it's a negligible effect).
You actually said this - "gravity doesn't magically pull bullets toward their target", but it "accelerates objects towards each other." Well, pull means force, and acceleration is force, so you just said that gravity doesn't do something it does.
So, it depends on how fast it's going.
But you're not trying to shoot the moon. That's already been done -- see those craters? You're actually trying to hit a tiny spot on the moon.
Uhm. Yes. And? The question is not "can you hit any spot at any given time?" No, of course not. You only have one free parameter - time - and restricting that of course restricts your options.
Think about it, though -- the counterweight will be moving about 2km/s relative to the moon (geosync is 3km/s, moon is 1km/s)
Moon's velocity would be perpendicular to the projectile velocity. They wouldn't add or subtract. Relative velocity would be 3 km/s (for a counterweight at virtually infinite distance, less for one closer to geosync, obviously).
Plus gravity cuts down on transit time, though I don't know how much in this case.
How are you going to have microsecond accuracy on cutting the cable
Engineering problem, not a fundamental one. Anyway, this isn't a completely stupid thing to think about, because while you're not g
It's covered in the book and in the NIAC proposal. Basically, the base of the elevator can be put far from any common air routes (it has to be anyway) and so protecting it would be fairly easy. Besides, airlines don't pay for all of their security, do they?
:)
Keep in mind that the only real way you can do damage to a space elevator is by hitting it a significant fraction of the way to GEO. And that's a LONG distance. The day that a single person or small group can fire a ground-to-space missile, we've got other problems than protecting the space elevator.
eOnce a critical flaw is made, it will zoom through the ribbon at fantastic speed concentrating stress.
Make the ribbon extremely wide in areas of high-impact, thus minimizing the affect that a loss of a small portion of the ribbon will have.
But it doesn't matter because no one involved with the space elevator concepts is even looking at toughness, which means they haven't considered reliability.
It's in the space elevator book, I believe. I don't have it here, but I'm pretty sure I remember reading it.
And given the make money fast reading list of the guy who runs the spacelift sham company out of Banbringe Washington,
What about the guy who actually proposed it to NASA? ISR certainly isn't a sham company!
it's a pipe dream at best
You might want to tell that to NASA and all the other engineers/scientists who are convinced that it'll work. Who knows, you might actually be on to something that they missed, but they've done stress simulations and impact analysis, so I don't think it's a real problem.
I admit I was being brief (I know the alignments aren't perfect); but this complication doesn't change things at all. There are still huge tracts of land on the moon which don't line up with any trajectory of an elevator break (in fact, that's an understatement made strictly because I wanted to use the phrase "huge tracts of land on the moon"), and because the lineup isn't exact, it's much worse for any potential attacker -- any given target will present itself once, and essentially never again.
Once every few years, that is. The moon-Earth cycle repeats on a few-year basis. Heck, if you're trying for surprise mass destruction, what's a few years to wait?
Besides, I don't understand why you don't see what I mean: the area of land that the elevator can impact is (kindof) the projection of the Earth's axis on the Moon. Since the relative orientation of those two things change over the year and over the month, the elevator can hit the entire area that it sweeps over, which is pretty large. Plus the lunar "wiggles" will help you here too, since the Moon doesn't present "exactly" the same face to us all the time (lunar librations are the term, I think).
What do you mean? This is basic ballistics;
I don't get it: suppose the Moon and the Earth are lined up, and everything's aligned. Then basic ballistics says you can only fire when the straightline projection of the path impacts the moon.
However, gravity increases the effective cross-section of any object by a factor of two - something fired with a straightline projection "near" an object will hit the object. In the case of high-speed impacts this isn't true, but it does affect it by a large amount. Therefore, if the straightline projection misses the moon by a bit, the gravitationally affected path will not.
In the aligned case, this doesn't do anything except allow you to hit around the back of the moon a bit more. In the unaligned case, since the velocity vector and the lunar radial vector aren't aligned, it will allow you to hit spots that a straightline projection would not (though it may remove points as well, but it, overall, will increase the spread in impact positions).
I can't see that being easy, though. It depends on an impressive list of things, foremost amongst them is there being a lunar base in any sort of position to be hit by the counterweight. It's not like you can aim; all you can do is time the break.
The axis of the Moon's orbit and the Earth's rotation aren't aligned. You'd actually have a large portion of the surface of the Moon that you could aim at. Perhaps all of it. You'd just have to wait until the proper alignment of the elevator and the Moon.
Plus gravity is very helpful with these sort of things. Makes the cross-section of the moon twice as big, after all (if memory serves).