> Laser systems could vaporize metal fragments, but this vapor will simply congeal into > globlets and cool into the space equivalent of bird shot
Are you sure ?
I am not a physicist, but I think that the speed of light (app. 300m/s) should give an ballpark estimate on the average speed of a molecule at room temperature.
If I evaporate matter in space with a laser, I would expect the speed of the resulting molecules and atoms to be at least that high, and ions would even repel each other.
All these particles would fly away from each other in random directions at these speeds.
Now I see two possibilities:
1) The atmosphere is thick enough (low earth orbit) so they hit with air molecules so their statistical tendency to fly away from the original location is reduced before they get far away.
In this case, there may be lot of them around that have low enough speed deltas so they might form goblets, but while they are still small, they have a very high ratio of cross-section to mass, so they will be quickly be decelerated by the atmosphere and eventually fall to earth.
2) If there are only a few air molecules around in higher orbits, then after a few days, they would be evenly spaced around the earth.
I do not see how they could form goblets of a critical size so they would pose a hazard to spacecrafts.
Marvin wrote: > It's simply Intel moving to a new instruction set (ARM V5) > and building a (slow) emulation of the old one (ARM V4), > and Microsoft says it would be horribly difficult to > support two different instruction sets, so the choice was to either > live with the new CPU performing slower than the old one or > cut off support for the old hardware.
This is not correct.
All ARMV4 instructions are implemented natively in the XSCALE core.
The XSCALE core, just as the SA1110, executes almost all ARMV4 instructions in one clock, and, as far as I remember, uses more clocks only for very few instructions:
- shift register by register (2 instead of 1) - mul / mul-acc (extra latency cycle in some cases) - branch miss in the added BPU - maybe some coprocessor accesses
Except for an assembly rewrite of some inner loops in the kernel, there is not much MS can do about the Memory interface that hasn't scaled with the CPU clock.
I do not think that compiler tweaking will gain much more than 10% in performance.
There are no new ARMv5 instructions that affect performance in any noticable way for general purpose computing (i.e using an optimized C-Compiler with your old code).
The main new instructions are:
- a "find first one bit in word" instruction, which helps software division and huffman encoding
- some DSP-instructions like 16x16 bit multiplication/40Bit add for filters (audio-encoding, etc)
Both these enhancencents more or less require assembly coding
The other major architectural enhancements are branch-prediction (offset by higher penalties on branch misses) and larger caches (32K dcache versus 8K and 32K icache vs 16K, if i remember correctly)
However, the cache latency has increased from 1 to 3 cycles.
It means that when you load a value from memory and hit the cache, the compiler needs to find 3 unrelated instructions you can execute before you can use the result in the fourth instruction after the load.
This is a severe blow if your compiler does not figure it in, and even if it tries, or if you use assembly, you often cannot find three such instructions (table walks, or under register pressure)
In the worst case (table-walk, LUT's), this effectively halves your processor speed.
As far as i know, the bus interface has not improved from the SA1110, and this was not too efficient to start with (does not exploit accessing preloaded bank, cache-line has to be.clompletely filled before execution, etc)
Apart from that, there are some issues in the PXA silicon, which I think force some timeconsuming workarounds (extra cache flushes, Writeback-cache does not work, slow bus cycles). I would guess that these affect performance even more than the 100MHz SDRAM clock - after all that's about what you find in your 1GHz+ P-III-design.
However, this is only what i gathered from the datasheets, I have not yet used a PXA system as it does not yet seem to be an improvement over the SA1110 that justifies a new design.
I do not believe that there is some sort of a moral right for you to be able to buy a particular book at a particular price, any more than you have a right to any other good.
However, you should have reasonably convenient access to the information in this book, because free speech in my opinion also mandates free listening, or, in this case, free (as in speech) reading.
I think that in the US, as in many other countries, a publisher has to give a copy of any book he publishes to the library of congress.
Why not expand this duty to a copy in electronic form, such as a PDF?
Then, after a book goes out of print for more than a very short time (e.g. two months), anybody should have a right to have a copy of that book "printed on demand" in a library or bookshoop for something like 120% of the initial price of the book.
Of this 120%, 30% should go to the author, 20% to the publisher and 20% to the Library of congress for providing the service and the PDF, and 50% for the place that does the "print-on-demand".
I think this would be fair to everybody (author and publisher probably make more out of this than by selling new books), and would resolve the problem of books that have not enough readers to warrant a reprint.
And, of course, there should be an international treaty on cross-providing this service, so nobody could reprieve people of their right to a free flow of information by not publishing books in some countries for economic and other reasons.
But I think it is perfectly legal to sell used CD's in garage sales or on ebay, as long as you do not retain any form of copy (digital or analog, e.g. cassete tape)
Then how about this scenario:
Someone sets up a big warehouse containing thousands of CD-drives, with a rack for something like a hundred CD's next to each CD-drive.
You can rent or buy a CD-drive and a rack in this warehouse and send in your CD-collection to be stored in your rack.
If you want to listen to one of your CD's, you dial up the warehouse's server over the internet and instruct something like a tape robot to insert your CD into your drive and then have the music streamed to your home. You do not make a copy of this stream, except for a few seconds buffer while listening.
If you do not like a CD any longer, you put it up for sale on something like ebay. If the buyer has a rack in that same warehouse, you just instruct the "CD-robot" to move the CD you sold from your rack to the buyers rack.
Transaction costs would be low, and chances are somebody would open up an onlines CD-store with big discounts and free delivery to the warehouse next door.
So, you could buy a new CD for the full price, and sell it a few days or even hours later for almost the initial price.
Then, if you want to listen to it again later, chances are you can purchase a copy of this CD again from the "used" market.
I think this would be a perfectly legal scheme, while taking the burden of the high cost for the making and distribution of CD off the record companies shoulders.
Well, I think there are limits - they are defined by your input channels.
You cannot view the whole earth at one cm resolution at once, so there is no need to store it locally.
As soon as the data transfer rate and latency for accesses to "main" memory is no longer a bottleneck, the need for local cache suddenly goes away.
For "audio" input, this limit is almost reached for the home user.
Unless you have golden ears (which might be inconvenient if you plan to spend the winter in Minnesota, anyways), 256Kbit will do. If that Bandwith comes at no extra cost, once the copyright issues are sorted out, one way or another, there is no reason to distribute a few hundred thousend songs several thousand copies each.
Along comes internet radio and the virtual jukebox!
For video input, if the display was shaped to the limitations of your eyes, something like a 1000x1000 pixels at 500 dpi resolution in the center of your vision (2 inches square), plus another 1000x1000 pixels in the periphery, will do (Think of a monitor that watches where your eyes look, and renders that part of the screen with extra resolution)
At 50Hz with some temporal interpolation, this is something like a 3 gigabits raw or a 100Mbits compressed, even now within the reach of your LAN, if compression and Display hardware were advanced enough.
I would guess that more than 95% of what is on harddisks these days is duplicated elsewhere, and therefore see tough times coming up for HD vendors once the networking guys catch up.
To my (laymans) understanding, this is the "thermal efficiency"
n= (T1-T2)/T2,
an upper limit for the effeciency of all cyclic thermal to mechanical converters (piston engines, turbines).
It says about this:
You have a cylinder with a freely movable piston that is set up via a mechanism to do mechanical work. External and internal pressure are equal.
1) You heat the gas inside the cylinder (for simplicity, although this does not make sense, say electrically)
2) The gas expands, the piston moves, you exert mechanical work
3) You short circuit the internal and external gas using a thermal resistor (eg. the walls of your cylinder), until the thermal difference has been canceled (this will take indefinetely long, but you can stop at 0.01%, or whenever, this will just degrade n slightly)
4) Doing this, the gas contracts, retracts the piston and exerts more mechanical work.
5) You repeat this indefinetly
Then, if you do not have any mechanical friction and no thermal conduction and capacitance while heating up the gas and before the mechanical movement is finished, your efficiency is n =(T1-T2)/T2.
Now, if instead of a simple thermal resistor, you use a peltier element to short circuit the two gases, you can generate some electricity, lead it with a pair of wire to australia, and light a light bulb there.
However, the amount of mechanical work done does not change !
Is this a perpetuum mobile ?
No, because
- the electric energy generated is taken from the fraction (1-n) of the electric energy that was put in in the first place
- Your cylinder *and* its surroundings will be slightly cooler if you use a peltier rather than a resistor, until finally the heat generated by the light bulb in australia makes its way back.
So I think it should be possible to increase the efficiency of a thermal to mechanical to electrical converter by adding a nonmechanical stage, though I doubt that will be economically viable.
The better idea, obviously, is to put this thing in your cellar and use it to heat your house, or distribute the waste heat from the power station to heat houses in the neighbourhood.
It is actually a collection of sci-fi short stories, but for everybody who is going to do any real-time programming, this is a must read !
The best story, which was written, if I remember correctly, in the early fifties, describes how a program for a complex guidance computer for a manned spaceship is overdesigned by a paranoid programmer and eventually chokes on complexity in a critical situation.
Don't ever board a plane unless you are sure the designers of the software read this book !
> A penny from a tall building can leave a pretty big crater.
No it cannot - at least not in earth's athmosphere.
Without a detailed calculation, I would guess it would not gain a speed much in excess of 20 m/s, app. 45mph.
However, you can check that for yourself:
Suspend a penny from a thin string and dangle it out of the window of your car (driven by a friend, of course).
While you pick up speed, the air-drag will increase the angle of the suspending string to the normal (vertical). When this angle reaches 45 degrees, the air-drag is just as big as the gravitational force exerted on the penny. The speed you then read on your odometer is the maximum speed a free-falling penny could attain.
If this speed were 20m/s, then it would be attained after the penny fell from a height of app 20m (65 feet), disregarding air-resistance during this first 2 seconds of acceleration.
In practice, it will not make a noticable difference to the speed of the penny if it was released from 100 feet or 1000 feet.
If released from space, from any height or at any initial speed, it would either burn up completely, or be checked to just that 45mpH before reaching the surface of the earth.
If you throw out a penny at 45mph from the window of your car, or release it from the 6th floor of a building, it will not create an impression I would care to call a crater.
Otherwise, people would be killed when hit by bird-droppings any day !
Do you really not see the obvious, or are you just sticking your head in the sand ?
As effiency goes, you can compare the military to largish corporations. When you look at their websites, you will always find that they get their competitiveness not just from advanced technology, but from the superior motivation and *training* of their workforce.
Now, until now, the chinese military had to use pretty dated kit, such as lowly Z80-powered gameboys, to train their soldiers. This effectively restricted them to 2D-warfare. They could amass millions of soldiers in lines, circles and rectangles, and threaten to send them over to taiwan in surface crafts, or chase CIA-agents through labyrinths.
But they had no way to cope with US Submarines, planes or satellites.
As soon as they get access to advanced 3D-consoles for training, be prepared that the dam holding back the red flood will be undermined or overflown in no time.
Didn't you notice that as soon as the PS2 was available in even limited quantity outside countries with strict export laws, such as the US and Japan, a military spy-plane was downed ?
According to the article, this not a mainly nuclear powered rocket, but a chemically fueled ramjet which uses fission rods to preheat its fuel (hydrogen) to increase efficiency.
The idea of a rocket is to throw out any mass you can lay your hand on at the highest possible speed in the opposite direction of your your flight. Your own speed increase then is proportional to the speed decrease of your fuel (and the ratio of masses, of course).
In a chemical rocket, the mass of the propellant is limited at start, so you try use propellant that will give a maximum of expansion when burned.
To achieve this, you try to get the exhausts as hot as possible, because the pressure in your combustion chamber rises with temperature.
A Ramjet uses air scooped up in the athmosphere as one part of the propellant, so it does not have to
carry it along from the start. The oxygene (app. 20%) is burned with the fuel, while the nitrogene making up most of the rest is heated up along with it. A hydrogene-powered ramjet has the additional advantage that the fuel is very light (2 parts per molecule) as compared to the oxidizer (oxygene, 16 parts per molecule) or the nitrogene (14 parts per molecule).
You burn two hydrogene molecules together with one oxygene molecule and heat up four nitrogene molecules.
The idea of this "nuclear booster scheme" seems to be to use the fact that one hydrogene molecule has almost twice the specific heat capacitance as a nitrogene or oxygene atom.
Thus, the hydrogene molecules, weighing in at only 5% of the mass of the exhaust gases, contribute over 40% to the thermal mass that needs to be heated up the exhaust temperature.
If you pre-heat them to half the final temperature, you would probably gain a maximum of a 25% increase in exhaust temperature.
But is this really worth carrying a nuclear reactor into orbit ?
After all, once the air gets too thin, you have to rely on real rockets for the last few km/sec into orbit, and then you carry your reactor and its shield as dead weight. You also need fuel for maneuvering in orbit and reentry.
Finally, how do you heat hydrogene to 2000 degrees Centigrade with nuclear fisson rods if uranium melts at 1100 degrees and plutonium at 650 degrees ? I think in reactors they use zirkonium tubes, but even that melts at 1800 degrees.
Ever tried to cool one of these newfangled processors ? How much area does your heat exchanger need to heat up helium at a rate of something like a ton per minute ?
What do you do, once you are in space and have cut the engine, and the fission-by products keep on generating heat even though the main nuclear reaction stopped. (remember, you were using a ton of Hydrogene per minute just keep it to somewhere above 2000 degrees a few seconds ago !)
And as for the potential cost savings, I really do think this is utter nonsense !
You can easily generate hydrogene at home by throwing the hairdryer in your bathtub (please do this only when your mother-in-law is not in!).
Your utility will burn somthing like ten tons of oil for each ton of hydrogene you generate, so a 100 tons of hydrogene for your rocket will set you back some 200,000 dollars (after some hard bargaining, and only outside california)
You would probably have to send the entire population of Houston up on a weekend trip to eventually recoup your engineering costs.
I think a nuclear drive only has its merits once you are in orbit and have all the time in the world to use generated electricity to speed single ions to several orders of magnitude faster speeds than chemical reactions could, using a small and lightweight reactor.
But then, near the sun, photocells could probly do that better.
I seems as if the main reasons for the sluggish acceptance micropayment has gotten so far are privacy concerns, the lack of a "killer-Application" and standard.
Much of the popularity of the use of computers by others than hobbyists and businesses stems from the internet and E-mail.
Both are reasonably standardized and attractive enough tomake people bother with computers, inspite of the price, difficulties of learning how to use them and the drawbacks associated with them, such as spam and privacy concerns.
I think a clever way to make these factors work for the acceptance of micropaymants would be a scheme of paying for sending E-Mails.
It works like this :
- You set up an account with an Email-Provider.
- You get an E-Mail address, such as John-Smith.50cents@payed-email.com
- Whenever somebody wants to send you an Email, he has to attach 50 cents worth of micropayments with it, otherwise it will not be forward to you by payed-email.com
- When you receive the Email, you decide whether the sender of the E-mail had a legitimate cause, and if you think so, return the 50 cents to the senders account at payed-email.com. Otherwise you keep it, or you could set up an account such as John-Smith.50cents-for-red-cross@payed-email.com, where all the money from bounced E-mails is donated to your favourite charity.
- payed email retains a small fee, such as 2%, on each such mail to cover its expenses
-Depending on how you high value your privacy, you could decide how high your fee is, and even have different accounts with varying fees for private or high priority business mail.
- Artists could then just open an account like JoeMusician.50cents-thank-you.@payed-email.com , which would never be expected to be returned.
I think this scheme would put an end to all spam worries.
The only snag, as with all micropayment issues, is security, to prevent others from spoofing your account data and password and draining the money you payed up front into your account by sending emails to themselves.
Slashdot Mirror
> Laser systems could vaporize metal fragments, but this vapor will simply congeal into
> globlets and cool into the space equivalent of bird shot
Are you sure ?
I am not a physicist, but I think that the speed of light (app. 300m/s) should give an ballpark estimate on the average speed of a molecule at room temperature.
If I evaporate matter in space with a laser, I would expect the speed of the resulting molecules and atoms to be at least that high, and ions would even repel each other.
All these particles would fly away from each other in random directions at these speeds.
Now I see two possibilities:
1) The atmosphere is thick enough (low earth orbit) so they hit with air molecules so their statistical tendency to fly away from the original location is reduced before they get far away.
In this case, there may be lot of them around that have low enough speed deltas so they might form goblets, but while they are still small, they have a very high ratio of cross-section to mass, so they will be quickly be decelerated by the atmosphere and eventually fall to earth.
2) If there are only a few air molecules around in higher orbits, then after a few days, they would be evenly spaced around the earth.
I do not see how they could form goblets of a critical size so they would pose a hazard to spacecrafts.
Marvin wrote:
> It's simply Intel moving to a new instruction set (ARM V5)
> and building a (slow) emulation of the old one (ARM V4),
> and Microsoft says it would be horribly difficult to
> support two different instruction sets, so the choice was to either
> live with the new CPU performing slower than the old one or
> cut off support for the old hardware.
This is not correct.
All ARMV4 instructions are implemented natively in the XSCALE core.
The XSCALE core, just as the SA1110, executes almost all ARMV4 instructions in one clock, and, as far as I remember, uses more clocks only for very few instructions:
- shift register by register (2 instead of 1)
- mul / mul-acc (extra latency cycle in some cases)
- branch miss in the added BPU
- maybe some coprocessor accesses
Except for an assembly rewrite of some inner loops in the kernel, there is not much MS can do about the Memory interface that hasn't scaled with the CPU clock.
I do not think that compiler tweaking will gain much more than 10% in performance.
There are no new ARMv5 instructions that affect performance in any noticable way for general purpose computing (i.e using an optimized C-Compiler with your old code).
.clompletely filled before execution, etc)
The main new instructions are:
- a "find first one bit in word" instruction, which helps software division and huffman encoding
- some DSP-instructions like 16x16 bit multiplication/40Bit add for filters (audio-encoding, etc)
Both these enhancencents more or less require assembly coding
The other major architectural enhancements are branch-prediction (offset by higher penalties on branch misses) and larger caches (32K dcache versus 8K and 32K icache vs 16K, if i remember correctly)
However, the cache latency has increased from 1 to 3 cycles.
It means that when you load a value from memory and hit the cache, the compiler needs to find 3 unrelated instructions you can execute before you can use the result in the fourth instruction after the load.
This is a severe blow if your compiler does not figure it in, and even if it tries, or if you use assembly, you often cannot find three such instructions (table walks, or under register pressure)
In the worst case (table-walk, LUT's), this effectively halves your processor speed.
As far as i know, the bus interface has not improved from the SA1110, and this was not too efficient to start with (does not exploit accessing preloaded bank, cache-line has to be
Apart from that, there are some issues in the PXA silicon, which I think force some timeconsuming workarounds (extra cache flushes, Writeback-cache does not work, slow bus cycles). I would guess that these affect performance even more than the 100MHz SDRAM clock - after all that's about what you find in your 1GHz+ P-III-design.
However, this is only what i gathered from the datasheets, I have not yet used a PXA system as it does not yet seem to be an improvement over the SA1110 that justifies a new design.
Here's an easy alternate way of type enforcement:
/usr/bin/X11R6
rm -rf
All the type enforcment you'll ever want !
But then, how about prior art ?
I do not believe that there is some sort of a moral right for you to be able to buy a particular book at a particular price, any more than you have a right to any other good.
However, you should have reasonably convenient access to the information in this book, because free speech in my opinion also mandates free listening, or, in this case, free (as in speech) reading.
I think that in the US, as in many other countries, a publisher has to give a copy of any book he publishes to the library of congress.
Why not expand this duty to a copy in electronic form, such as a PDF?
Then, after a book goes out of print for more than a very short time (e.g. two months), anybody should have a right to have a copy of that book "printed on demand" in a library or bookshoop for something like 120% of the initial price of the book.
Of this 120%, 30% should go to the author, 20% to the publisher and 20% to the Library of congress for providing the service and the PDF, and 50% for the place that does the "print-on-demand".
I think this would be fair to everybody (author and publisher probably make more out of this than by selling new books), and would resolve the problem of books that have not enough readers to warrant a reprint.
And, of course, there should be an international treaty on cross-providing this service, so nobody could reprieve people of their right to a free flow of information by not publishing books in some countries for economic and other reasons.
But I think it is perfectly legal to sell used CD's in garage sales or on ebay, as long as you do not retain any form of copy (digital or analog, e.g. cassete tape)
Then how about this scenario:
Someone sets up a big warehouse containing thousands of CD-drives, with a rack for something like a hundred CD's next to each CD-drive.
You can rent or buy a CD-drive and a rack in this warehouse and send in your CD-collection to be stored in your rack.
If you want to listen to one of your CD's, you dial up the warehouse's server over the internet and instruct something like a tape robot to insert your CD into your drive and then have the music streamed to your home. You do not make a copy of this stream, except for a few seconds buffer while listening.
If you do not like a CD any longer, you put it up for sale on something like ebay. If the buyer has a rack in that same warehouse, you just instruct the "CD-robot" to move the CD you sold from your rack to the buyers rack.
Transaction costs would be low, and chances are somebody would open up an onlines CD-store with big discounts and free delivery to the warehouse next door.
So, you could buy a new CD for the full price, and sell it a few days or even hours later for almost the initial price.
Then, if you want to listen to it again later, chances are you can purchase a copy of this CD again from the "used" market.
I think this would be a perfectly legal scheme, while taking the burden of the high cost for the making and distribution of CD off the record companies shoulders.
Does anybody know of such a venture ?
Well, I think there are limits - they are defined by your input channels.
You cannot view the whole earth at one cm resolution at once, so there is no need to store it locally.
As soon as the data transfer rate and latency for accesses to "main" memory is no longer a bottleneck, the need for local cache suddenly goes away.
For "audio" input, this limit is almost reached for the home user.
Unless you have golden ears (which might be inconvenient if you plan to spend the winter in Minnesota, anyways), 256Kbit will do. If that Bandwith comes at no extra cost, once the copyright issues are sorted out, one way or another, there is no reason to distribute a few hundred thousend songs several thousand copies each.
Along comes internet radio and the virtual jukebox!
For video input, if the display was shaped to the limitations of your eyes, something like a 1000x1000 pixels at 500 dpi resolution in the center of your vision (2 inches square), plus another 1000x1000 pixels in the periphery, will do (Think of a monitor that watches where your eyes look, and renders that part of the screen with extra resolution)
At 50Hz with some temporal interpolation, this is something like a 3 gigabits raw or a 100Mbits compressed, even now within the reach of your LAN, if compression and Display hardware were advanced enough.
I would guess that more than 95% of what is on harddisks these days is duplicated elsewhere, and therefore see tough times coming up for HD vendors once the networking guys catch up.
I think this is misleading.
,
To my (laymans) understanding, this is the "thermal efficiency"
n= (T1-T2)/T2
an upper limit for the effeciency of all cyclic thermal to mechanical converters (piston engines, turbines).
It says about this:
You have a cylinder with a freely movable piston that is set up via a mechanism to do mechanical work. External and internal pressure are equal.
1) You heat the gas inside the cylinder (for simplicity, although this does not make sense, say electrically)
2) The gas expands, the piston moves, you exert mechanical work
3) You short circuit the internal and external gas using a thermal resistor (eg. the walls of your cylinder), until the thermal difference has been canceled (this will take indefinetely long, but you can stop at 0.01%, or whenever, this will just degrade n slightly)
4) Doing this, the gas contracts, retracts the piston and exerts more mechanical work.
5) You repeat this indefinetly
Then, if you do not have any mechanical friction and no thermal conduction and capacitance while heating up the gas and before the mechanical movement is finished, your efficiency is n =(T1-T2)/T2.
Now, if instead of a simple thermal resistor, you use a peltier element to short circuit the two gases, you can generate some electricity, lead it with a pair of wire to australia, and light a light bulb there.
However, the amount of mechanical work done does not change !
Is this a perpetuum mobile ?
No, because
- the electric energy generated is taken from the fraction (1-n) of the electric energy that was put in in the first place
- Your cylinder *and* its surroundings will be slightly cooler if you use a peltier rather than a resistor, until finally the heat generated by the light bulb in australia makes its way back.
So I think it should be possible to increase the efficiency of a thermal to mechanical to electrical converter by adding a nonmechanical stage, though I doubt that will be economically viable.
The better idea, obviously, is to put this thing in your cellar and use it to heat your house, or distribute the waste heat from the power station to heat houses in the neighbourhood.
Regards, Klaus
It is actually a collection of sci-fi short stories, but for everybody who is going to do any real-time programming, this is a must read !
The best story, which was written, if I remember correctly, in the early fifties, describes how a program for a complex guidance computer for a manned spaceship is overdesigned by a paranoid programmer and eventually chokes on complexity in a critical situation.
Don't ever board a plane unless you are sure the designers of the software read this book !
> A penny from a tall building can leave a pretty big crater.
No it cannot - at least not in earth's athmosphere.
Without a detailed calculation, I would guess it would not gain a speed much in excess of 20 m/s, app. 45mph.
However, you can check that for yourself: Suspend a penny from a thin string and dangle it out of the window of your car (driven by a friend, of course).
While you pick up speed, the air-drag will increase the angle of the suspending string to the normal (vertical). When this angle reaches 45 degrees, the air-drag is just as big as the gravitational force exerted on the penny. The speed you then read on your odometer is the maximum speed a free-falling penny could attain.
If this speed were 20m/s, then it would be attained after the penny fell from a height of app 20m (65 feet), disregarding air-resistance during this first 2 seconds of acceleration.
In practice, it will not make a noticable difference to the speed of the penny if it was released from 100 feet or 1000 feet. If released from space, from any height or at any initial speed, it would either burn up completely, or be checked to just that 45mpH before reaching the surface of the earth.
If you throw out a penny at 45mph from the window of your car, or release it from the 6th floor of a building, it will not create an impression I would care to call a crater.
Otherwise, people would be killed when hit by bird-droppings any day !
Do you really not see the obvious, or are you just sticking your head in the sand ?
As effiency goes, you can compare the military to largish corporations. When you look at their websites, you will always find that they get their competitiveness not just from advanced technology, but from the superior motivation and *training* of their workforce.
Now, until now, the chinese military had to use pretty dated kit, such as lowly Z80-powered gameboys, to train their soldiers. This effectively restricted them to 2D-warfare. They could amass millions of soldiers in lines, circles and rectangles, and threaten to send them over to taiwan in surface crafts, or chase CIA-agents through labyrinths.
But they had no way to cope with US Submarines, planes or satellites.
As soon as they get access to advanced 3D-consoles for training, be prepared that the dam holding back the red flood will be undermined or overflown in no time.
Didn't you notice that as soon as the PS2 was available in even limited quantity outside countries with strict export laws, such as the US and Japan, a military spy-plane was downed ?
According to the article, this not a mainly nuclear powered rocket, but a chemically fueled ramjet which uses fission rods to preheat its fuel (hydrogen) to increase efficiency.
The idea of a rocket is to throw out any mass you can lay your hand on at the highest possible speed in the opposite direction of your your flight. Your own speed increase then is proportional to the speed decrease of your fuel (and the ratio of masses, of course).
In a chemical rocket, the mass of the propellant is limited at start, so you try use propellant that will give a maximum of expansion when burned.
To achieve this, you try to get the exhausts as hot as possible, because the pressure in your combustion chamber rises with temperature.
A Ramjet uses air scooped up in the athmosphere as one part of the propellant, so it does not have to carry it along from the start. The oxygene (app. 20%) is burned with the fuel, while the nitrogene making up most of the rest is heated up along with it. A hydrogene-powered ramjet has the additional advantage that the fuel is very light (2 parts per molecule) as compared to the oxidizer (oxygene, 16 parts per molecule) or the nitrogene (14 parts per molecule).
You burn two hydrogene molecules together with one oxygene molecule and heat up four nitrogene molecules.
The idea of this "nuclear booster scheme" seems to be to use the fact that one hydrogene molecule has almost twice the specific heat capacitance as a nitrogene or oxygene atom.
Thus, the hydrogene molecules, weighing in at only 5% of the mass of the exhaust gases, contribute over 40% to the thermal mass that needs to be heated up the exhaust temperature.
If you pre-heat them to half the final temperature, you would probably gain a maximum of a 25% increase in exhaust temperature.
But is this really worth carrying a nuclear reactor into orbit ?
After all, once the air gets too thin, you have to rely on real rockets for the last few km/sec into orbit, and then you carry your reactor and its shield as dead weight. You also need fuel for maneuvering in orbit and reentry.
Finally, how do you heat hydrogene to 2000 degrees Centigrade with nuclear fisson rods if uranium melts at 1100 degrees and plutonium at 650 degrees ? I think in reactors they use zirkonium tubes, but even that melts at 1800 degrees.
Ever tried to cool one of these newfangled processors ? How much area does your heat exchanger need to heat up helium at a rate of something like a ton per minute ? What do you do, once you are in space and have cut the engine, and the fission-by products keep on generating heat even though the main nuclear reaction stopped. (remember, you were using a ton of Hydrogene per minute just keep it to somewhere above 2000 degrees a few seconds ago !)
And as for the potential cost savings, I really do think this is utter nonsense !
You can easily generate hydrogene at home by throwing the hairdryer in your bathtub (please do this only when your mother-in-law is not in!).
Your utility will burn somthing like ten tons of oil for each ton of hydrogene you generate, so a 100 tons of hydrogene for your rocket will set you back some 200,000 dollars (after some hard bargaining, and only outside california)
You would probably have to send the entire population of Houston up on a weekend trip to eventually recoup your engineering costs.
I think a nuclear drive only has its merits once you are in orbit and have all the time in the world to use generated electricity to speed single ions to several orders of magnitude faster speeds than chemical reactions could, using a small and lightweight reactor.
But then, near the sun, photocells could probly do that better.
I seems as if the main reasons for the sluggish acceptance micropayment has gotten so far are privacy concerns, the lack of a "killer-Application" and standard. Much of the popularity of the use of computers by others than hobbyists and businesses stems from the internet and E-mail. Both are reasonably standardized and attractive enough tomake people bother with computers, inspite of the price, difficulties of learning how to use them and the drawbacks associated with them, such as spam and privacy concerns. I think a clever way to make these factors work for the acceptance of micropaymants would be a scheme of paying for sending E-Mails.
It works like this :
- You set up an account with an Email-Provider.
- You get an E-Mail address, such as John-Smith.50cents@payed-email.com
- Whenever somebody wants to send you an Email, he has to attach 50 cents worth of micropayments with it, otherwise it will not be forward to you by payed-email.com
- When you receive the Email, you decide whether the sender of the E-mail had a legitimate cause, and if you think so, return the 50 cents to the senders account at payed-email.com. Otherwise you keep it, or you could set up an account such as John-Smith.50cents-for-red-cross@payed-email.com, where all the money from bounced E-mails is donated to your favourite charity.
- payed email retains a small fee, such as 2%, on each such mail to cover its expenses
-Depending on how you high value your privacy, you could decide how high your fee is, and even have different accounts with varying fees for private or high priority business mail.
- Artists could then just open an account like JoeMusician.50cents-thank-you.@payed-email.com , which would never be expected to be returned.
I think this scheme would put an end to all spam worries.
The only snag, as with all micropayment issues, is security, to prevent others from spoofing your account data and password and draining the money you payed up front into your account by sending emails to themselves.