Given that of the 16 landers that have been dispatched to Mars, only 6 of them actually ended up on the surface in working order, I think it's more accurate to say that it hasn't been done.
Certainly, but given that there's no magic way of turning ordinary matter into antimatter, the only way of getting that 18 tonnes of antimatter is to make the stuff --- which is where the 4e21 joules of energy comes in.
And frankly, if I wanted to devastate a planet and had 18 tonnes of antimatter around, it would be far more convenient just to take the lid off the bottle than to do all that fiddly messing around with space travel.
(Right now state of the art is just about at the stage of producing one fundamental particle of antimatter at a time. I recall a few years ago that someone had actually managed to assemble a single anti-hydrogen atom that was stable for a while, until they dropped it.)
Wouldn't a tungsten telephone pole going.99c punch right through the Earth and keep going?
Surprisingly, no. IIRC --- I can't find a reference --- high speed impacts tend to turn the matter on both sides into plasma. This is great if you're a spaceship, because a thin layer of foil will vaporise any small impacts and by the time the expanding ball hits your main hull it's diffuse enough not to do too much damage. It's less good if you're a planet, because there's nowhere for it to expand.
So you'll get an cone of plasma burrowing its way into the planet. IIRC again, about half the energy will get soaked up by the rock and mantle and the other half gets radiated out into space. Half of 4e21 joules is still a hell of a lot --- at these scales the planet will act like it's made of liquid, and will splash. I would say that the shockwave would scour the surface clean, but the surface here is irrelevant. The entire mantle will basically get churned up and it may even end up disrupting the core (and we still don't know what that's made of --- there are serious theory that it contains exotic matter).
However, it's not enough to actually destroy the Earth. You need about 1e33 joules to lift Earth's mass out of its own gravity well. So, while enough debris will get splashed out to render the inner solar system a very bad place to live for the next million years or so, once everything dies down Earth will be a relatively normal white hot ball of boiling rock.
Just wait a few billion years for the next intelligent species to evolve and they can do it all over again.
(It's possible I'm overstating things; this is all a best guess written on a Friday night. Perhaps all that would happen is that the surface would be scoured down to the mantle by a supersonic shockwave of vaporised rock...)
You'd probably want to use it in spaceship to spaceship combat as I imagine a solid tungsten telegraph pole traveling at the speed of light would be mildly unfortunate for an entire planet...
One megatonne is about 4e15 joules. Therefore, given that the telegraph pole impacting a planet is going to liberate its entire kinetic energy very very rapidly, the 4e21 joule impact would be about equivalent to about a million megatonnes.
That would be cool to watch, from a safe distance --- such as the far side of the moon. Plus, I wouldn't want it to happen to anywhere within about a light minute of anywhere I was wanting to live.
Video cards run nothing like an OS on the hardware, and you won't be getting one running yourself. Most GPUs don't have branch instructions (newer ones kind of do, but only in the "skip forward" sense). It's kinda hard to run an OS without those.
No, no, my reverse quantum widget doesn't resist motion. It resists acceleration. In other words, when it's switched on (if indeed it can be switched off!) it will make your vehicle act like it has a greater mass than it really does.
What this would be useful for is, for example, a satellite in low orbit: residual air drag will tend to decelerate it and cause it to deorbit. But with the quantum brake, at least some of the momentum change would be safely radiated off as heat (or whatever) and so the satellite would be affected much less. You would end up having to spend much less fuel in station keeping.
A telegraph pole is ~10m long and about ~0.2m wide. Cross section: 0.03m^2. Volume: 0.3m^3.
The density of tungsten is 19300 kg m^-3, so your tungsten telegraph pole masses about 6000kg.
The relativistic momentum of an object is (m v) / (1 - v^2 / c^2)^-2: 13e13 Ns.
The relativistic kinetic energy of a mass is (p^2 c^2 + m^2 c^4)^-2, where p is the momentum: 4e21 joules.
Assuming I've got my maths right, which given that it's late on Friday afternoon is highly questionable, that is a very big number. It's equal to about ten years worth of total planetary energy use. And every single joule of that you have had to generate and feed to your drive.
So I don't think we're going to see relativistic kill vehicles any time soon.
I've often wondered why more reverse engineering isn't done to create Linux drivers rather than just complaining about the manufacturer of the hardware.
Because these days it's really, really hard.
A modern graphics card, for example, is actually a complete computer. It's got RAM, a processor, a bunch of peripherals, a complete miniature operating system... and you don't even know what type of processor it is. A lot of peripherals work like this; a wireless card is typically an ARM processor with some RAM attached on one end to the radio and on the other to an I/O controller that talks to the computer.
So in order to reverse engineer a graphics card you both need to decompile your way through multiple megabytes of binary blob driver that runs on the PC, but also decompile your way through multiple megabytes of binary blob operating system image that runs on the card... and you don't even know what the CPU architecture is!
It's actually more productive to hassle the manufacturers into releasing documentation. Which in some ways is a pity; it would be really cool to be able to run your own bare-metal OS on the GPU.
Assuming this works, could the process be made reversible?
This would result in a device that resists momentum change, instead absorbing kinetic energy and using it to rotate the nanoparticles (and I assume dumping the energy out as heat).
This would be really useful for a lot of purposes. Spaceflight, naturally (anything that lets you play with momentum is useful in spaceflight); it gives you a brake that would cause your spacecraft to resist acceleration, which would be very useful for satellite stationkeeping. Around planets the devices would fall slowly; you might be able to use one as a parachute. You could install one on the tops of tall buildings to make them resist swaying in the wind. An aircraft with one installed would behave really oddly (possibly usefully). The possibilities are endless...
If you can accelerate a ship to near-c with little difficulty, there's not much stopping you from extorting the Earth by threatening to drop the ship (or for that matter, a bunch of tungsten telephone poles traveling at.99c) on them.
Well, you could.
Alternatively, since all that kinetic energy doesn't come out of nowhere, you'd still need to supply a really huge battery. And if you've got one of those, there's probably more convenient ways to use it to kill people than all that inconvenient fiddling about with spaceflight.
I did read the article (well, the non-mathematical bits). I quote:
Quantum fluctuations of the
position or of the magneto-electric constant of particles
do not affect the average value of their momentum, as a
consequence of the conservation of momentum law.
A propulsion engine may be designed by using for instance an addressable array of small magneto-electric
particles or wires. Rotating (see Fig. 1) or aggregating
(see Fig. 2) these particles will result in velocity:
He brings up attitude control of satellites as an example because, I think, it's a situation where very small amounts of momentum do useful work (you only need to rotate the satellite by a degree or so a day, he says). He's definitely talks about propulsion in the body, not just orientation.
As reactionless drives are very much Weird Science, not mentioning propulsion in the abstract could well be entirely deliberate to make the article more publishable --- you may not that it's incredibly well referenced.
I hope someone tests this soon; it sounds easy to do, and if it's true, it'll be an incredible breakthrough. Apart from producing awesome space drives it would also provide a way of coupling energy to momentum. As energy has dimensionality MASS.DISTANCE^2.TIME^-2 and momentum has dimensionality MASS.DISTANCE.TIME^-1, that would open up whole new areas of science to pick apart.
I feel that those who represent us in this country have long ago forgotten the best interests of those they serve, the People, or more correctly, have just decided that it's more profitable serving Corporations and sacrificing essential freedoms for temporary security and monetary reward.
The government is not some strange alien entity living in Washington. The government is made of people.
Corporations are not faceless office blocks full of hive drones. Corporations are made of people.
There is no them vs. us. There's just us. If you believe otherwise, then you have missed what democracy is all about.
You have a problem with the way the government behaves? Well, you elected them, which makes it your fault. You participated in the democratic process, which means that 1/500e6th of the government's behaviour is your responsibility. You don't like the country largely being run by corporations? Well, you chose for the economy to work in such a way that 1000 people working together have more than 1000 times the influence of one person working alone. It's easy to whine about the Man keeping you down. It's less easy to realise that you are the Man.
You live in a democracy. You chose your government. In about three years you'll have a chance to choose again.
Hypervisors are already widely used in mobile phones --- L4 is very popular. I think that this is largely because it allows the vendors to easily reconfigure the user mode address space to abstract over any platform-specific issues involved with a particular phone model. I've also seen some very neat tricks using L4 such as doing on-demand page fetching from a compressed NAND flash device. (In essence, that gives you the equivalent of executable ROM from a smaller, non-mappable flash part.)
So it wouldn't be much of a bigger step to use L4's other hypervisor features to support two different user space modes, each running a complete operating system. This has a lot of advantages to the phone manufacturer. Right now, most smartphones such as the G1 have a big chunky processor running the application OS and a smaller processor running the hard realtime radio stack OS. Using a hypervisor would allow them to run both operating systems on the same processor, with the hypervisor's own scheduler ensuring that the radio stack remains real-time no matter what the user OS is doing. That reduces the hardware complexity, and therefore the build price, while still maintaining the regulator-mandated isolation between the application processor and the radio processor.
As for the actual printer, I've learned to buy LASER printers. They have a high initial cost but low-priced ink (~$50 for 5000 pages). The laser printer ends-up being cheaper after you pass 800 pages.
Absolutely.
Couple of years ago I bought myself a Konica Minolta PagePro 1400W for 50 UKP (about 70 of your dollars). It's a basic black-and-white printer. It Just Worked with Ubuntu. It'll do a page every five seconds or so, it's got a fast startup time, the page quality is excellent, it's got a sheet feeder that actually works...
Toner cartridges are expensive, costing approximately the same amount as the whole printer, but refill kits are available for about 20 to 30 dollars. I haven't yet had to use one.
So, engineers and physicists, when you see statements like that, how do you cope:
Easily, because I know that a heat pump is a machine that allows me to move 5X amount of heat from one location to another while only using X amount of energy to do it.
(BTW, if you heat your house using electrical resistive heating, and you have a garden... go look up 'ground source heat pumps' from that article and save yourself lots of money.)
Yes, definitely worth watching. Good effects, good science, a good script and even good acting --- and given that this is a fake documentary that's saying something (documentary acting normally rivals training-video acting for awfulness). It's got a few rough edges but you have to look closely to spot them.
Do go get the uncut 4-hour BBC version, not the edited US version, though.
I know, it burns up. But I would kinda like to see that process. It seems that they have imagery from the ground of the thing in space even after it has separated. How long does it take to come down and what does that look like? That is what I found myself wondering at the end of the video.
What probably happens is that it goes over the horizon and is out of range for both telescopes and the rocketcam receivers. At that point the shuttle's done most of the boost into orbit and all that is left to do is circularisation (the shuttle's tiny internal tanks don't store much delta-vee). So the tank is going to go a long way before reentering.
But you're right --- I'd love to see its final moments. Surely, given how much money they're spending, they could station some observation stations downrange?
There does seem to be a bit of a phobia in the space industry about showing things going wrong, though. Remember the SpaceX Falcon 1 test flights that didn't make it? They would shut off the rocketcam footage at the first sign of trouble. I'm sure they've got footage of the vehicle tumbling/disintegrating, but they're not going to make it public. Perhaps NASA have decided that rocketcam footage of the external tank burning up is not something sufficiently reassuring to be shown.
Space shuttle factoid: the pipe which pumps propellant from the external tank to the shuttle is 43cm wide.
Does ZFS on FreeBSD still suffer from random kernel panics when it gets low on memory?
I'm particularly referring to this bit of documentation:
To use ZFS, at least 1GB of memory is recommended (for all architectures) but more is helpful as ZFS needs *lots* of memory. Depending on your workload, it may be possible to use ZFS on systems with less memory, but it requires careful tuning to avoid panics from memory exhaustion in the kernel.
Yeah, kernel infrastructure that can't cope with running out of memory. That fills me with confidence. Particularly I've run ZFS on OpenSolaris on a 48MB Pentium laptop and it coped fine.
Unfortunately the FreeBSD ZFS pages are a wiki, which means they're badly organised and out of date. I have no idea when the above was written or whether it's still valid. Does anyone know?
The cause of the Chernobyl disaster, however, was the poor design of Russian nuclear power plants.
Yeah, cooling your reactor by pumping oxygen-laden air through a red-hot carbon lattice is a really good idea. Excuse me, I need to go slap someone.
France generates pretty much all of its electricity from nuclear, with reprocessing, using pressurised water reactors. Not only do they have a number of handy engineering benefits such as isolating the water loop through the reactor from the water loop through the turbines, but they also have a particularly useful safety feature in that they're self-regulating --- temperature goes up, power output goes down. France has an excellent safety record; I can find only one major incident, which was a coolant spill in 2008.
They even do their own waste reprocessing into plutonium, which is then reused to generate more power. Unaccountably, terrorists don't seem to have stolen any of it.
If you've got a compatible GSM phone, bring it. You can buy PAYG sims in most supermarkets --- Tesco's starts at 5 UKP (with 10 UKP of calling time). You don't need ID. Just plug it in and you have a proper working phone with a UK number and no roaming charges. Prices are usually around 10-20 pence per minute, although calls to other mobile networks are sometimes much more expensive (30 to 40 pence per minute). And because Britain is a civilised country, you don't pay for incoming calls and your minutes don't expire, which means that having such a phone is a really cheap way of being contactable.
(Virgin Mobile also do GPRS data connections via PAYG at 30p a day, only on the days you use it, although you're heavily penalised if you go above 25MB a day. Not easy on GPRS.)
If you don't have a compatible GSM phone you can normally buy one for stupidly small amounts of money. Again, at Tesco's they start at about 10 UKP for a LG GB102 with T-Mobile PAYG SIM. It's crap, but it'll let you do voice calls and text messages. (Yes, it's precisely the kind of simple phone that Anonymous Coward keeps complaining about not being able to get.)
Remember, this is Europe; everyone has a phone, everyone uses text messaging, and if you're meeting friends here they'll be expecting you to have one.
Well maybe what we could use instead in C byte code, or some other form of byte code, and then have on the JIT low-level compilations.
You may be interested to look at TenDRA. It's a BSD-licensed C and C++ compiler that compiles into portable bytecode which gets translated into native machine code at install time --- so you install a generic package that will then run on anything (that has a TenDRA package installer on it).
It never really took off, for reasons that are a bit obscure to me. I certainly found the source code for the compiler totally incomprehensible when I looked at it, even more so than gcc; and that's saying a lot. I've certainly never seen it used anywhere, even in a world that's so desperate for a BSD C compiler that they've even resurrected pcc.
There are revival projects at tendra.org and ten15.org but they're both borked right now.
Slashdot Mirror
I don't think the US has an exclusive monopoly on stupidity.
I'm sure that's true, but it is one of your major exports.
And yet it has been done.
Given that of the 16 landers that have been dispatched to Mars, only 6 of them actually ended up on the surface in working order, I think it's more accurate to say that it hasn't been done.
Certainly, but given that there's no magic way of turning ordinary matter into antimatter, the only way of getting that 18 tonnes of antimatter is to make the stuff --- which is where the 4e21 joules of energy comes in.
And frankly, if I wanted to devastate a planet and had 18 tonnes of antimatter around, it would be far more convenient just to take the lid off the bottle than to do all that fiddly messing around with space travel.
(Right now state of the art is just about at the stage of producing one fundamental particle of antimatter at a time. I recall a few years ago that someone had actually managed to assemble a single anti-hydrogen atom that was stable for a while, until they dropped it.)
Wouldn't a tungsten telephone pole going .99c punch right through the Earth and keep going?
Surprisingly, no. IIRC --- I can't find a reference --- high speed impacts tend to turn the matter on both sides into plasma. This is great if you're a spaceship, because a thin layer of foil will vaporise any small impacts and by the time the expanding ball hits your main hull it's diffuse enough not to do too much damage. It's less good if you're a planet, because there's nowhere for it to expand.
So you'll get an cone of plasma burrowing its way into the planet. IIRC again, about half the energy will get soaked up by the rock and mantle and the other half gets radiated out into space. Half of 4e21 joules is still a hell of a lot --- at these scales the planet will act like it's made of liquid, and will splash. I would say that the shockwave would scour the surface clean, but the surface here is irrelevant. The entire mantle will basically get churned up and it may even end up disrupting the core (and we still don't know what that's made of --- there are serious theory that it contains exotic matter).
However, it's not enough to actually destroy the Earth. You need about 1e33 joules to lift Earth's mass out of its own gravity well. So, while enough debris will get splashed out to render the inner solar system a very bad place to live for the next million years or so, once everything dies down Earth will be a relatively normal white hot ball of boiling rock.
Just wait a few billion years for the next intelligent species to evolve and they can do it all over again.
(It's possible I'm overstating things; this is all a best guess written on a Friday night. Perhaps all that would happen is that the surface would be scoured down to the mantle by a supersonic shockwave of vaporised rock...)
You'd probably want to use it in spaceship to spaceship combat as I imagine a solid tungsten telegraph pole traveling at the speed of light would be mildly unfortunate for an entire planet...
One megatonne is about 4e15 joules. Therefore, given that the telegraph pole impacting a planet is going to liberate its entire kinetic energy very very rapidly, the 4e21 joule impact would be about equivalent to about a million megatonnes.
That would be cool to watch, from a safe distance --- such as the far side of the moon. Plus, I wouldn't want it to happen to anywhere within about a light minute of anywhere I was wanting to live.
Video cards run nothing like an OS on the hardware, and you won't be getting one running yourself. Most GPUs don't have branch instructions (newer ones kind of do, but only in the "skip forward" sense). It's kinda hard to run an OS without those.
How are Cg subroutines and jumps compiled, then?
No, no, my reverse quantum widget doesn't resist motion. It resists acceleration. In other words, when it's switched on (if indeed it can be switched off!) it will make your vehicle act like it has a greater mass than it really does.
What this would be useful for is, for example, a satellite in low orbit: residual air drag will tend to decelerate it and cause it to deorbit. But with the quantum brake, at least some of the momentum change would be safely radiated off as heat (or whatever) and so the satellite would be affected much less. You would end up having to spend much less fuel in station keeping.
Just out of interest:
A telegraph pole is ~10m long and about ~0.2m wide. Cross section: 0.03m^2. Volume: 0.3m^3.
The density of tungsten is 19300 kg m^-3, so your tungsten telegraph pole masses about 6000kg.
The relativistic momentum of an object is (m v) / (1 - v^2 / c^2)^-2: 13e13 Ns.
The relativistic kinetic energy of a mass is (p^2 c^2 + m^2 c^4)^-2, where p is the momentum: 4e21 joules.
Assuming I've got my maths right, which given that it's late on Friday afternoon is highly questionable, that is a very big number. It's equal to about ten years worth of total planetary energy use. And every single joule of that you have had to generate and feed to your drive.
So I don't think we're going to see relativistic kill vehicles any time soon.
I've often wondered why more reverse engineering isn't done to create Linux drivers rather than just complaining about the manufacturer of the hardware.
Because these days it's really, really hard.
A modern graphics card, for example, is actually a complete computer. It's got RAM, a processor, a bunch of peripherals, a complete miniature operating system... and you don't even know what type of processor it is. A lot of peripherals work like this; a wireless card is typically an ARM processor with some RAM attached on one end to the radio and on the other to an I/O controller that talks to the computer.
So in order to reverse engineer a graphics card you both need to decompile your way through multiple megabytes of binary blob driver that runs on the PC, but also decompile your way through multiple megabytes of binary blob operating system image that runs on the card... and you don't even know what the CPU architecture is!
It's actually more productive to hassle the manufacturers into releasing documentation. Which in some ways is a pity; it would be really cool to be able to run your own bare-metal OS on the GPU.
Here's an interesting question:
Assuming this works, could the process be made reversible?
This would result in a device that resists momentum change, instead absorbing kinetic energy and using it to rotate the nanoparticles (and I assume dumping the energy out as heat).
This would be really useful for a lot of purposes. Spaceflight, naturally (anything that lets you play with momentum is useful in spaceflight); it gives you a brake that would cause your spacecraft to resist acceleration, which would be very useful for satellite stationkeeping. Around planets the devices would fall slowly; you might be able to use one as a parachute. You could install one on the tops of tall buildings to make them resist swaying in the wind. An aircraft with one installed would behave really oddly (possibly usefully). The possibilities are endless...
If you can accelerate a ship to near-c with little difficulty, there's not much stopping you from extorting the Earth by threatening to drop the ship (or for that matter, a bunch of tungsten telephone poles traveling at .99c) on them.
Well, you could.
Alternatively, since all that kinetic energy doesn't come out of nowhere, you'd still need to supply a really huge battery. And if you've got one of those, there's probably more convenient ways to use it to kill people than all that inconvenient fiddling about with spaceflight.
To EdZ: also, your parent just popped up and I realised you were actually replying to someone else. Er, oops! Sorry.
Quantum fluctuations of the position or of the magneto-electric constant of particles do not affect the average value of their momentum, as a consequence of the conservation of momentum law. A propulsion engine may be designed by using for instance an addressable array of small magneto-electric particles or wires. Rotating (see Fig. 1) or aggregating (see Fig. 2) these particles will result in velocity:
He brings up attitude control of satellites as an example because, I think, it's a situation where very small amounts of momentum do useful work (you only need to rotate the satellite by a degree or so a day, he says). He's definitely talks about propulsion in the body, not just orientation.
As reactionless drives are very much Weird Science, not mentioning propulsion in the abstract could well be entirely deliberate to make the article more publishable --- you may not that it's incredibly well referenced.
I hope someone tests this soon; it sounds easy to do, and if it's true, it'll be an incredible breakthrough. Apart from producing awesome space drives it would also provide a way of coupling energy to momentum. As energy has dimensionality MASS.DISTANCE^2.TIME^-2 and momentum has dimensionality MASS.DISTANCE.TIME^-1, that would open up whole new areas of science to pick apart.
I feel that those who represent us in this country have long ago forgotten the best interests of those they serve, the People, or more correctly, have just decided that it's more profitable serving Corporations and sacrificing essential freedoms for temporary security and monetary reward.
The government is not some strange alien entity living in Washington. The government is made of people.
Corporations are not faceless office blocks full of hive drones. Corporations are made of people.
There is no them vs. us. There's just us. If you believe otherwise, then you have missed what democracy is all about.
You have a problem with the way the government behaves? Well, you elected them, which makes it your fault. You participated in the democratic process, which means that 1/500e6th of the government's behaviour is your responsibility. You don't like the country largely being run by corporations? Well, you chose for the economy to work in such a way that 1000 people working together have more than 1000 times the influence of one person working alone. It's easy to whine about the Man keeping you down. It's less easy to realise that you are the Man.
You live in a democracy. You chose your government. In about three years you'll have a chance to choose again.
Choose differently.
Hypervisors are already widely used in mobile phones --- L4 is very popular. I think that this is largely because it allows the vendors to easily reconfigure the user mode address space to abstract over any platform-specific issues involved with a particular phone model. I've also seen some very neat tricks using L4 such as doing on-demand page fetching from a compressed NAND flash device. (In essence, that gives you the equivalent of executable ROM from a smaller, non-mappable flash part.)
So it wouldn't be much of a bigger step to use L4's other hypervisor features to support two different user space modes, each running a complete operating system. This has a lot of advantages to the phone manufacturer. Right now, most smartphones such as the G1 have a big chunky processor running the application OS and a smaller processor running the hard realtime radio stack OS. Using a hypervisor would allow them to run both operating systems on the same processor, with the hypervisor's own scheduler ensuring that the radio stack remains real-time no matter what the user OS is doing. That reduces the hardware complexity, and therefore the build price, while still maintaining the regulator-mandated isolation between the application processor and the radio processor.
Are these 70 of our "Earth" dollars?
I thought it, but you said it...
As for the actual printer, I've learned to buy LASER printers. They have a high initial cost but low-priced ink (~$50 for 5000 pages). The laser printer ends-up being cheaper after you pass 800 pages.
Absolutely.
Couple of years ago I bought myself a Konica Minolta PagePro 1400W for 50 UKP (about 70 of your dollars). It's a basic black-and-white printer. It Just Worked with Ubuntu. It'll do a page every five seconds or so, it's got a fast startup time, the page quality is excellent, it's got a sheet feeder that actually works...
Toner cartridges are expensive, costing approximately the same amount as the whole printer, but refill kits are available for about 20 to 30 dollars. I haven't yet had to use one.
So, engineers and physicists, when you see statements like that, how do you cope:
Easily, because I know that a heat pump is a machine that allows me to move 5X amount of heat from one location to another while only using X amount of energy to do it.
(BTW, if you heat your house using electrical resistive heating, and you have a garden... go look up 'ground source heat pumps' from that article and save yourself lots of money.)
Woo! Someone else who's seen this!
Yes, definitely worth watching. Good effects, good science, a good script and even good acting --- and given that this is a fake documentary that's saying something (documentary acting normally rivals training-video acting for awfulness). It's got a few rough edges but you have to look closely to spot them.
Do go get the uncut 4-hour BBC version, not the edited US version, though.
I know, it burns up. But I would kinda like to see that process. It seems that they have imagery from the ground of the thing in space even after it has separated. How long does it take to come down and what does that look like? That is what I found myself wondering at the end of the video.
What probably happens is that it goes over the horizon and is out of range for both telescopes and the rocketcam receivers. At that point the shuttle's done most of the boost into orbit and all that is left to do is circularisation (the shuttle's tiny internal tanks don't store much delta-vee). So the tank is going to go a long way before reentering.
But you're right --- I'd love to see its final moments. Surely, given how much money they're spending, they could station some observation stations downrange?
There does seem to be a bit of a phobia in the space industry about showing things going wrong, though. Remember the SpaceX Falcon 1 test flights that didn't make it? They would shut off the rocketcam footage at the first sign of trouble. I'm sure they've got footage of the vehicle tumbling/disintegrating, but they're not going to make it public. Perhaps NASA have decided that rocketcam footage of the external tank burning up is not something sufficiently reassuring to be shown.
Space shuttle factoid: the pipe which pumps propellant from the external tank to the shuttle is 43cm wide.
Does ZFS on FreeBSD still suffer from random kernel panics when it gets low on memory?
I'm particularly referring to this bit of documentation:
To use ZFS, at least 1GB of memory is recommended (for all architectures) but more is helpful as ZFS needs *lots* of memory. Depending on your workload, it may be possible to use ZFS on systems with less memory, but it requires careful tuning to avoid panics from memory exhaustion in the kernel.
Yeah, kernel infrastructure that can't cope with running out of memory. That fills me with confidence. Particularly I've run ZFS on OpenSolaris on a 48MB Pentium laptop and it coped fine.
Unfortunately the FreeBSD ZFS pages are a wiki, which means they're badly organised and out of date. I have no idea when the above was written or whether it's still valid. Does anyone know?
The cause of the Chernobyl disaster, however, was the poor design of Russian nuclear power plants.
Yeah, cooling your reactor by pumping oxygen-laden air through a red-hot carbon lattice is a really good idea. Excuse me, I need to go slap someone.
France generates pretty much all of its electricity from nuclear, with reprocessing, using pressurised water reactors. Not only do they have a number of handy engineering benefits such as isolating the water loop through the reactor from the water loop through the turbines, but they also have a particularly useful safety feature in that they're self-regulating --- temperature goes up, power output goes down. France has an excellent safety record; I can find only one major incident, which was a coolant spill in 2008.
They even do their own waste reprocessing into plutonium, which is then reused to generate more power. Unaccountably, terrorists don't seem to have stolen any of it.
But... neither of the Obamas are black. Barack is a very pale brown, more of a beige really. Michelle is a much warmer colour verging on amber.
If you want black, go see an Australian bushman. They're really impressive. So dark they're almost blue.
If you've got a compatible GSM phone, bring it. You can buy PAYG sims in most supermarkets --- Tesco's starts at 5 UKP (with 10 UKP of calling time). You don't need ID. Just plug it in and you have a proper working phone with a UK number and no roaming charges. Prices are usually around 10-20 pence per minute, although calls to other mobile networks are sometimes much more expensive (30 to 40 pence per minute). And because Britain is a civilised country, you don't pay for incoming calls and your minutes don't expire, which means that having such a phone is a really cheap way of being contactable.
(Virgin Mobile also do GPRS data connections via PAYG at 30p a day, only on the days you use it, although you're heavily penalised if you go above 25MB a day. Not easy on GPRS.)
If you don't have a compatible GSM phone you can normally buy one for stupidly small amounts of money. Again, at Tesco's they start at about 10 UKP for a LG GB102 with T-Mobile PAYG SIM. It's crap, but it'll let you do voice calls and text messages. (Yes, it's precisely the kind of simple phone that Anonymous Coward keeps complaining about not being able to get.)
Remember, this is Europe; everyone has a phone, everyone uses text messaging, and if you're meeting friends here they'll be expecting you to have one.
Well maybe what we could use instead in C byte code, or some other form of byte code, and then have on the JIT low-level compilations.
You may be interested to look at TenDRA. It's a BSD-licensed C and C++ compiler that compiles into portable bytecode which gets translated into native machine code at install time --- so you install a generic package that will then run on anything (that has a TenDRA package installer on it).
It never really took off, for reasons that are a bit obscure to me. I certainly found the source code for the compiler totally incomprehensible when I looked at it, even more so than gcc; and that's saying a lot. I've certainly never seen it used anywhere, even in a world that's so desperate for a BSD C compiler that they've even resurrected pcc.
There are revival projects at tendra.org and ten15.org but they're both borked right now.