Fidelio: I'd say it depends on where you live, but here in Tennessee, if you have a vehicle used on your farm, and only on your farm, you needn't go through the formalities of registration, safety & emissions testing, etc. to use it.
That does indeed depend on where you live; at least in CA, any motor vehicle must be registered, although if you do not intend to operate it on public roads you can get a (relatively cheap) "certificate of non-operation" instead of a regular registration.
Of course, many of those ancient vehicles operating on TN farms are probably producing orders of magnitude more air pollution per mile driven than would be allowed in CA, so their potential for harm is not entirely confined to their owners, or perhaps even to the state of TN. I doubt that the magnitude of the public harm is such that it's worth regulating such vehicles, but someone with asthma might disagree with me. On the other hand, there is quite a lot of harm done by guns that are intended to be kept entirely on private property (or, equivalently, in their owners' control) but are discharged by accident, or stolen and later used in crimes. Comparing private sale of guns to private sale of vehicles not used on public roads thus seems inappropriate.
I'm with Xopher. A fnord is a long, narrow inlet in the coast of Jorway. And blemish is the official language of Felgium.
It's a good thing we invaded Iraq; if we hadn't, the proof of Saddam's weapons of mass destruction-related program activities might have come in the form of a reference to a drawing of a mushroom cloud over an American city!
Patrick: I do note that I'm not seeing any details in the media about the alleged forthcoming better space telescopes, which makes me wonder.
The only "forthcoming better space telescope" that's much beyond the viewgraph stage is the James Webb Space Telescope, formerly the Next Generation Space Telescope (NGST), due to launch in 2010. No bets taken on when it actually launches.
JWST was never a replacement for the Hubble, because it was designed specifically as an infrared telescope, covering 2 - 27 micron wavelengths. It has no visible light or ultraviolet capability; losing Hubble means we'll have no ultraviolet astronomy capability at all, since UV astronomy can't be done from the ground.
JWST was also cut from its original 8 meter diameter to 6 meters diameter (nearly a factor of 2 loss in light-gathering ability) due to budget constraints. It has only three instruments, and will not be serviceable (no instrument upgrades or repairs).
There are lots of plans and proposals for telescopes beyond the JWST, but any new general-purpose astronomy instrument is well over a decade away, even if the "new" NASA doesn't kill its support for astronomical research.
(The only saving grace is that, except for UV astronomy, many of the capabilities of Hubble are becoming available from ground-based telescopes through the use of adaptive optics to eliminate the blurring caused by the atmosphere. It's hard to make adaptive optics work over wide fields of view, so one doesn't get as many beautiful panoramic shots of galaxies, but visible-light astronomy won't be dumped back to its pre-Hubble limits)
Goodness, Erik, such vehemence! I was just pointing out that rolling roads aren't an engineering impossibility, not trying to claim they'd be better than trains. But to address your points briefly:
...unlike a train derailment, a break will effect everyone on the length of the belt. Plus, once the belt parts, you're going to lose braking ability as the belt detensions...
At least in my understanding of the rolling roads, the belts are not under tension, and the loading of the belts on the rollers is due to simple gravity, not belt tension. IIRC, all of the rollers (or at least one in every few rollers) are drive/braking rollers, So no one ahead of the break (by more than a few roller spacings) would be affected; behind the break, they'd only be affected as they approached the break location -- which is why one would stop the belt as quickly as possible. From a physics, and to some extent an engineering, standpoint, there wouldn't be much difference between a continuous belt and a series of separate cars (or even just separate trays, like giant cafeteria trays) moving down the rollers. (In passing, I have seen drawings of a monorail concept in which the "rail" is a series of bicycle-like wheels. Some of the wheels are powered, and push a car as it passes over them; the cars have no on-board propulsion. Sort of midway between a conventional train and the rolling roads.)
-- worse, if the trailing edge of the belt lifts, any part of the belt that isn't on a braking drum is mass that the first brake that is in contact is going to need to stop. Get enough of the belt flying, and you will have a catastrophic cascade of brake failures.
You're right that there could be extra stress on the last few brakes ahead of a break, but it seems like an obvious design point (or it would after the first few belt break accidents) to make sure the belt doesn't lift severely under braking loads. I deliberately picked a 10-second stop time as producing <<1 gee of deceleration; the weight of the belt would still tend to keep it solidly on the rollers. Again, I think your intuition is based on thin belts kept in place by tension and driven by only the end rollers.
How long to slow that belt? Because, now, until you stop it, you're piling the trailing end of the belt into the wreck. If it took an hour, you'd have, oh, 40-60km of belt rammed into the zone at a goodly speed.
I specified 10 seconds to stop a ~100 mph (40 m/s) belt; that's a 0.4 gee braking force, which is comparable to a landing airplane or a panic stop in a car. Might be a little too quick, if most people aren't in seats with seatbelts, but certainly 20-30 sec. would be OK. That's a huge power dump, which is why it has to be dumped into brake rotor heat capacity; there isn't time to convectively cool the brakes.
the other belts need to slow in sync with the main belt.
I'd assume a break in any belt would result in the whole road shutting down (or at least dropping to a low speed), to avoid the problems Heinlein described. But they wouldn't need to do so exactly in synch -- especially if people were warned (a la airplane seat belt warnings) to get away from belt crossings if the emergency alarm goes off. ("Mind the gap!") People passing next to a break would be in danger for a few seconds until everything came to a stop, just like people in adjacent traffic lanes are in danger when a semi blows a tire.
200km x 2 m gives us 400km^2 of belt, positing a density of one person per 10 m^2 gives us 40,000 on the belt. One belt part would injure/kill a significant part of that belt.
I assume you mean 400k (m^2), not 400 (km)^2; and I was assuming easily 1 person/m^2 on a "passenger" belt, quite possibly more at peak times, so 40,000 people on a belt is conservative. But I also picked the slowdown time to limit the "lethal area" where the belt would actually be likely to buckle or otherwise do fatal things to a few hundred meters (200 meters of actual "run into a wall" stopping, although there might be buckling or other problems farther than that) so I was estimating 1000 - 2000 casualties, including a few hundred fatalities, in such a major accident. I don't see any reason why most of a belt should be affected.
Add in the energy to spin up/brake the rollers, which, as written, are very large. Thus, you need to soak that energy as well. Given, there's a near infinite amount of energy available, but I don't see infinite energy sinks. On every belt system I've seen, the rollers *far* outmass the belt, and you have to stop the rollers with the belt.
Note that that's on every belt system you've seen -- some things don't scale. I agree there might be something like the same mass in the rollers in Heinlein's roads as in the belts, but not more. I assumed a 4 inch thick (10 cm) "belt" with no significant flexibility out of plane (remember, it doesn't have to go _around_ any rollers -- the "belt" could perfectly well be made out of 20- foot railroad rails bolted together with occasional expansion joints). IIRC, the drive rollers were a couple of meters high, with, say, 2-cm-thick steel rims, spaced perhaps 10 meters apart, plus smaller support rollers every couple of meters. Equivalent to maybe 1" of moving steel underlying the entire area of the 4" thick belt.
And there are many belts. The KE flying between DC and NYC and Boston would be enormous.
So? It's not much energy *density* because the roads cover so much area.
When you get into the economic premises, I have no argument; it's pretty hard to see how a rolling road is better than a combination of roads and rail. (As described, it's better than rail alone because you can get on and off at any point and at any time -- for a society where linear cities have grown up along transportation routes, that would be a big advantage.) But the engineering isn't obviously bogus to me.
Incidentally, I'm now reminded of _Code Three_ by Rick Raphael, which took surface transport to a different extreme -- 200 mph, 10-lane superhighways populated by personal vehicles the size of railroad cars. Equally unlikely, but also a good read.
Erik, rolling roads may not be a very good solution to long haul transit, but they're not so outrageous as all that. Just to take your example, a 200 km x 2 m x 0.1 m x 2 (out and back) belt is 8 x 10^4 cubic meters of belt, or somewhere around 200,000 tons of belt. Several meters of air moving with the belt adds very little mass; carrying one person per square meter (average) would add maybe 30%. We don't think anything's odd about moving 200,000 tons of supertanker around.
At 40 m/s (about 90 mph) the kinetic energy of the belt is 800 J/kg; call it 200 gigajoules, or about 50 megawatt-hours, for the entire belt. Keeping a road running would presumably take megawatts to 10's of megawatts; starting the belt after a (rare) maintenance shutdown would take perhaps 100 MW for an hour. (I could work out the air drag effects, too, but I'd have to start charging my consulting rates :-) The energy efficiency would be less than that of a train (unless the belt ran more or less continuously loaded) but as someone else pointed out, Heinlein postulated nearly-free distributed solar power.
An emergency stop would dump all the energy into the brakes: you can easily dump 200 kJ into 1 kg of brake drum, so you'd need 1000 tons of dry emergency brake hardware -- or less than 200 tons of water, if you're willing to water-cool the emergency brakes. There would be very few accidents or failures that would actually break a belt -- I'd guess it would be an accident at least as rare as a train derailment at speed or an airplane crash -- and in that case one could easily stop a belt in 10 seconds, which would pile up about 200 meters of belt at the accident site and probably damage 1 km or so of belt-and-supports. Not so different from a train wreck or airplane crash.
I don't recall the details of the rolling-road descriptions, but I see no reason the high-speed belts couldn't have seats for long-distance passengers. (I always assumed, BTW, that the rolling roads never "turned under" the way airport peoplemover belts do, but rather turned around on the surface, with a suitably large radius of curvature, so if you just stayed on one road long enough you'd hit a turnaround and come back to your starting point.)
So there's plenty of room to argue that rolling roads suck as a national transportation system, but I don't see any reason they'd be especially difficult to build from a physics or engineering standpoint.
Patrick,
RE: Pogo Sticks for the state of Minnesota,
Mary Kay says you are a very silly man.
Robert: "Drunken taxicab"? What has it been drinking, premium leaded?
Stefan: Naah. A subsidiary of Lockheed-Martin.
Hey! Mars has a long history of launching both open and clandestine attacks on the United States, including the use of long-range ballistic missiles and chemical weapons -- supported by evidence at least as strong as that the Bushies used to justify invading Iraq. Perhaps we can persuade this administration to forego attacking Iran in favor of invading Mars.
Hmm, there must be *some* Mars probe data could be massaged to provide evidence of large deposits of oil...
Sylvia: There have been many studies of how we perceive risk; dunno if your hypothesis about the origin of our perceptions is valid, but your conclusion agrees with the studies. Risks are weighed more heavily if they're catastrophic, unfamiliar, involuntary, and "dread" (frightening to contemplate, like cancer or sitting in a falling airplane). A quick google shows a more extensive tabulation of factors here
Nuclear power plant accidents and nuclear weapons score high on almost all factors.
Oddly, radioactivity *by itself* (and even nuclear waste disposal) shouldn't rate all that high -- everyone with a tritium-dial (or, once, radium-dial) watch is at least a little familiar with radioactivity, its effects are not likely to be catastrophic, the mechanisms of damage are pretty well understood and known to science, and so on. (OK, its most likely effect -- cancer -- is widely dreaded) So I tend to regard "fear of radioactivity" as a peculiar and artificially-generated artifact of our culture, whereas, say, "fear of nuclear power plants" is unsurprising, and "fear of nuclear weapons" is downright rational. (If you want to be really scared, look into how disassembly of obsolete nuclear warheads is done in this country. How it's being done in the former Soviet Union, I shudder to contemplate.)
I look at a chart like this, and I keep thinking that for a fraction of $78 billion, we could build a half-dozen advanced space launch systems. For $225 billion, or whatever today's total cost figure is, we could have orbiting hotels, lunar colonies, satellite solar power stations, and probably monthly shuttle flights to Mars.
Sylvia: Thanks for a reasoned response. I'm a physicist and I've worked at nuclear labs (Berkeley and Livermore) but I think you have me beat on the age at which I started using the word "cyclotron."
With rant mode off, I'd certainly agree there's likely to be a nonzero amount of DU that makes it into houses, and even into lungs; my point is that the actual damage that will do is probably small -- not zero, but tiny compared to other things,including the casualties of the battles in which the DU was fired. As usual, there's a huge gray area between "It's perfectly harmless" and "It'll render vast tracts of land uninhabitable forever" Alas, most spokespeople seem to insist on one extreme or the other, and my apologies for interpreting your remarks as advocating one extreme.
As far as dust on the ground, yes, size does matter, but my understanding is that it's hard to get uranium (actually UO2, since it oxidizes easily) into a particle size range that's likely to stay airborne and be inhaled. Pu is a somewhat different problem, since it does tend to turn into fine-particle "smoke" when it combusts, and it's significantly more radioactive (though it's still not nearly "the most toxic substance known to Man" as news reports seem to insist on describing it).
I definitely agree that DU is a heavy-metal toxin and that it should be treated with care. Battlefield cleanup is just one of the things the U.S. is falling down on in its military adventures (and anyone who lets US troops do cleanup without good filter masks should be court-martialed). I'm all in favor of more research on its long-term effects. It's the use of radioactivity as a bogeyman that I object to.
Patrick: You make a good point -- the nuclear industry did a really thorough job of destroying its own credibilty, and I'm repeatedly amazed at the sheer stupidity of the nuclear power industry in particular.
I have to say, though, that in my experience, and in what research I've seen, many peoples' fears of nuclear power and radiation are not rational. I started to say that they were as irrational as belief in astrology or fear of witchcraft, but that's not true; there are real risks. But peoples' ability to weigh risks (and to judge credibility of spokespeople) seems to go out the window when the word "nuclear" is mentioned.
>being a heavy metal, aerosolized DU would hardly stay in circulation for very long?
Er, and... so then what happens to the fine powder? It magically dematerializes? ...Or does it fall to the ground, to get on shoes and hands and faces, to be blown about by sandstorms and breathed in, to be tracked into houses, to get into food...
By and large, it falls to the ground and just stays there. It's too heavy to be blown around very much (and just how many people go wandering around in a sandstorm anyway?), it's insoluble, and it's not picked up by plants.
DU is a very weak emitter of radiation, but it effectively stays radioactive forever, in terms of human lifetimes. Once you've distributed copious quantities of finely pulverized DU into an environment, good luck living in that place without getting some of it lodged inside your body in direct contact with living tissue.
"Very weak" is an understatement; it has a half life of 4.5 billion years. Less than a hundred-millionth of it will decay in a human lifetime. Unless you sniff piles of DU powder like snuff, its lifetime dose to you is going to be tiny compared to your dose from cosmic rays, potassium-40, and (depending on where you live) naturally-occuring radon. (Incidentally, radon comes from the decay of the uranium and other isotopes distributed throughout the Earth's crust, whose total quantity is many, many orders of magnitude more than the amount of DU humanity has ever produced. Even if you don't live in a house with a high radon concentration, you probably get more dose from radon than you would from a few micrograms of inhaled DU dust.)
Asbestos isn't radioactive at all, it's only a fibrous rock, but there's a reason they don't use it for house insulation any more.
Yes, asbestos is directly carcinogenic, and far more viciously so than DU, as well as being much easier to get and keep airborne. (And probably overblown as a hazard to non-industry workers as well, although that's another story entirely).
When you say "isn't radioactive at all" you show clearly that you've bought into the utterly baseless belief that radioactivity, in and of itself, is somehow more horrible than chemical toxicity or any other insult to the body. And many kinds of toxic chemicals are toxic forever and ever -- they don't even *have* half lives. Instead of getting worked up about depleted uranium, why don't you get worked up about beryllium, cadmium, and selenium, all of which are highly toxic, and all of which are manufactured in large quantities and disposed of casually all the time. Or have you never tossed a NiCad battery or an old TV set into the trash??
Sorry about the rant, but I get very, very tired of people demonizing radioactivity.
Jordin Kare
Kip: We don't want none o' them damn atoms around here!
I'd be more than slightly skeptical. I find it hard to imagine uranium oxide, especially enriched UO2, being labelled with a skull and crossbones rather than with a radiation hazard logo. "Pure uranium oxide" also sounds like something a scammer would add; I'd expect either just "uranium oxide" or an assay percentage.
Hmm, I wonder if someone working on the Total - er - Turtle - er - Terrier Information Awareness project could be persuaded to use their sophisticated database search technology to cross-correlate actual degrees issued with those claimed by senior Administration personnel....
>Of course, nobody wants to fight near Hectografistani troops, because you get all covered with purple.
Besides, ever since the ABDickation of King Stencil, the Hectografistanis have been busy protecting their capital, Corflu, from the insurgent Dittoheads and their leader, Rush Printjob.
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