You are right of course; in a more theoretical sense aluminum *can* burn in LOX. It's very difficult to get going because it conducts heat away like a mad thing; you need to vapourise or atleast melt metal to sustain a flame- but a big enough spark will get it lit, and the Shuttle tank 'fails the hammer test' with a non zero probability-the Shuttle engineers claimed that hammers were unlikely to strike the vehicle in flight and got a waiver- this was before Columbia:-(.
On the other hand, combustion chambers like Agena were built from aluminum, and flew many, many times without problems. I've also met people who built and ran alloy LOX cooled combustion chambers that developed cracks and leaked LOX straight into the combustion chamber- no problem. They also ran tests where they threw gravel into LOX and ran it through an alloy pipe- again no problem (the firemen present were upset at that.)
Graphite is rather more dodgy. There is a qualitive and quantitive difference between graphite and charcoal, which you are skirting around. Charcoal is much more fluffy stuff, graphite tends to be solid, and highly thermally conductive. That makes a *big* difference.
But I agree that the Apollo stirrer design is rather more risky than it needed to be. I still believe the official version; but I don't discount your theory totally either- but the official explanation seems more likely; given the abuse that the tank had been through.
In order to have a 'level' to measure they had to create an artificial gravity inside the tank by swirling the contents with an internal electric motor and a blade.
They didn't use artificial gravity to seperate the LOX; quite the opposite.
In fact, in zero gravity LOX tends to divide up into regions of gas and liquid. If the gas happens to float past the sensor, then they get an incorrect reading of the density, and hence they don't know how much is in there. This was a big problem on previous flights. Stirring the tank mixes it all up and makes it the same density; allowing a reliable reading to be taken.
you have several pounds of highly combustible aluminum and graphite parts
Aluminum, particularly bulk aluminum is *not* combustible in LOX. It's used on the Space Shuttle main tank fer heavens sake!
Graphite can't really burn either; for it to burn it needs to reach ~3000K, and the LOX is pretty keen on it not reaching that temperature.
LOX only really explodes in contact with greases- it's soluble in them, and they form a contact explosive.
and you have a DC motor with brushes sparking up a storm
Provided the brushes are carefully chosen, this need not be a problem.
That's not actually what caused the explosion anyway.
During testing a relay welded itself shut due to incorrect voltages. In flight, the wiring overheated- and the insulation burnt in the LOX. That caused the LOX tank to overpressure, and it blew away half the side of the vehicle.
Look, you take a fusion reactor, stuff in the fuel, heat it up- it fuses.
Now, the heat energy you put into the reaction; most of that comes out as fast neutrons; plus the fusion reaction energy- again most of that energy is in the fast neutrons.
So you've got a net loss of energy.
One way to recover the energy is to line the inside of the reactor with lithium. The fast neutrons transmute the lithium- you then haul off the lithium and stuff it into a fission reactor, and go through the steam cycle to make electricity.
Clean? No.
Cleaner? Maybe, maybe not. The one advantage you have is that the half life of most of the waste is only a hundred years or so IRC, so you're still better off.
But of course all of this assumes that you can actually get fusion to work- the good news is that it's only 20 years away! That's much better than 30 years ago, when it was 30 years away!
Could a vehicle obtain a thin-atmosphere flight envelope and reduce its speed at a more gradual rate?
That's what the Shuttle does. Doing that reduces the temperature on the skin of the aircraft- but at a big price- the vehicle is reentering for longer- and hence more heat energy leaks into the vehicle. That's why the Shuttle looks like an inside-out kiln.
Perhaps even to the point where no shielding is required?
At the hypersonic lift ratios that are actually achieved, this is not quite possible. However, early designs for the Space Shuttle had far less extensive shielding requirements.
These designs were changed when the military requirements imposed a *longer* reentry to return to the launch site after a launch to a polar orbit.
But they are really setting the price. Let's say n is the number of shares they are selling.
They already have a bunch of bids in; and with the dutch auction it's the n'th lowest bid that counts- that's the price that everyone pays.
Presumably they've looked at the current price, and realised that at the old 'n', the price is in the dirt, so they've reduced 'n' to push up the price- and *increase* the overall money they take.
Of course not all the bids are in yet- that's why there's some variability on the sale price.
I'm a little bit surprised that they can do this at this stage. I wonder what the price there is on the first few bids! What if they had changed the number of sold shares down to 1? Did some lunatic bid $1 million dollars, not expecting to have to pay? Inquiring mind needs to know:-)
Second, people here know quite well that fusion is not having the same issues with redioactive waste as more traditional forms of nuclear power
That's a myth. Most of the energy in a fusion reaction comes out as fast neutrons; these gradually mess up the structure of the reactor vessel and make it radioactive.
Secondly, most or all of the possible ways to catch the fast neutrons create secondary nuclear waste.
The idea that fusion power is 'clean' is not backed up by the facts.
On the other hand; if I build several hundred houses, and on each one the tiles keep falling off every winter, when they shouldn't; and I just keep patching the roof, and not bothering to work out what went wrong.
And then, eventually a tile falls off and hits somebody on the head and kills them.
Who's to blame? The architect that told you that it was a prototype design? Or the house owner that keeps sweeping the problem under the carpet and not investigating?
Or the house builder who keeps using the same design that is known to be flawed for more than 30 years?
"Sorry, you've shown insufficient remourse for illegally downloading Michael Jackson's album; so you're going to have to stay in prison for another 5 years. You're clearly not rehabilitated.":-)
Historically, that's what it really meant; some people never got out of the joint for relatively minor crimes. Is that just?
Yeah, it's boostrapped- he used CLisp to write a Slate interpreter, then using the Slate language he wrote a new compiler/interpreter, and then compiled the interpreter/compiler to machine code; then he restarted Slate running on the new compiler/interpreter; and CLisp is gone now. Any future changes to the compiler will be self compiled.
OK, that was sloppy. Carmack isn't an electrical engineer. He's learnt the hard way that connectivity is important and unreliable.
*no protection against inductive kickback(essential around any combination of electromechanical and electronic devices)
Yup. Sloppy.
*not restricting allowable user inputs (ie joystick)
Borderline. They didn't expect the joystick to fail in that way, and it was the same joystick used on the simulation, which showed no problems.
*underrated power transistors for drive unit (this is very basic stuff)
So, they screwed that one up slightly- IRC the main problem there was a short circuit. In any case, look what happened on Rutans 100km flight- he had a thermal cut-off trigger- basically the same sort of thing. Are you saying Rutan is simply being careless too?
*finally, not setting minimum fuel level for takeoff
They loaded the vehicle up with twice the expected usage; the problem seems have been that they not only burnt more on the ground than they expected, the engine wasn't burning efficiently so they burnt more on the way up too.
Sure, with 20-20 hindsight they could have put more in and/or scrubbed the launch, but they only had the estimated burning rate to go on; and they had expected that to be a lot lower.
Re:I wonder how Newton would do on slashdot...
on
The Unknown Newton
·
· Score: 2, Interesting
I think that if newton did post to slashdot (which would be rare since he was at times a bit of a recluse as well), he would be modded troll and flamebait.
Nah, he'd be modded up to +5 almost every time.
Look what happens when John Carmack posts stuff (and I've absolutely nothing against JC, he's just an example of somebody famous.)
Why? Because Microsoft is afraid the Justice Dept will wag their finger and make *tsk tsk* noises again?:]
LOL.
The difference this time is that Google is already a huge competitor- they can afford the legal armies and lobby the politicians and so forth if Microsoft try that sort of thing again.
Oh, that's nothing; in the UK we have specialised in stupid taxes.
We have even had an air tax; well, we called it a 'poll tax' (aka community charge); but it was clearly an air tax, since you only had to pay it as long as you were breathing:-)
And of course the tea tax we levied on one of our (now ex) colonies... they never completely forgave us for that (p.s. the UK likes what you've done with the place- we want it back now):-)
Yeah, America has certainly shown how to run a foreign policy. This Saddam, was all bottled up, keeping his country under (reasonably lawful albeit despotic) control, and disuading Iran from invading; and with a minimum of weapons.
Now, you've pissed off half of Islam (and Islam is a big, big place; bigger than America). Iraq's economy is all but destroyed, Iran is eyeing up the place and Americans and Iraqis are dying by the hundreds/thousands. The US governments budget is in deficit.
About the only one happy about the situation is Osama Bin Laden; America has managed to fumble the situation in every one of the top holy places of Islam. Nice work.
That UN- what do they know? They know enough not to take a poison chalice...
And you know what? Dumb moves like create the kind of uncertainty that helps put cameras in American cities.
Well, given that the cooling depends to some degree on the processor load, which in turn depends on what you are running, it mainly depends how long you play your FPS for.
Slashdot Mirror
On the other hand, combustion chambers like Agena were built from aluminum, and flew many, many times without problems. I've also met people who built and ran alloy LOX cooled combustion chambers that developed cracks and leaked LOX straight into the combustion chamber- no problem. They also ran tests where they threw gravel into LOX and ran it through an alloy pipe- again no problem (the firemen present were upset at that.)
Graphite is rather more dodgy. There is a qualitive and quantitive difference between graphite and charcoal, which you are skirting around. Charcoal is much more fluffy stuff, graphite tends to be solid, and highly thermally conductive. That makes a *big* difference.
But I agree that the Apollo stirrer design is rather more risky than it needed to be. I still believe the official version; but I don't discount your theory totally either- but the official explanation seems more likely; given the abuse that the tank had been through.
They didn't use artificial gravity to seperate the LOX; quite the opposite.
In fact, in zero gravity LOX tends to divide up into regions of gas and liquid. If the gas happens to float past the sensor, then they get an incorrect reading of the density, and hence they don't know how much is in there. This was a big problem on previous flights. Stirring the tank mixes it all up and makes it the same density; allowing a reliable reading to be taken.
you have several pounds of highly combustible aluminum and graphite parts
Aluminum, particularly bulk aluminum is *not* combustible in LOX. It's used on the Space Shuttle main tank fer heavens sake!
Graphite can't really burn either; for it to burn it needs to reach ~3000K, and the LOX is pretty keen on it not reaching that temperature.
LOX only really explodes in contact with greases- it's soluble in them, and they form a contact explosive.
and you have a DC motor with brushes sparking up a storm
Provided the brushes are carefully chosen, this need not be a problem.
That's not actually what caused the explosion anyway.
During testing a relay welded itself shut due to incorrect voltages. In flight, the wiring overheated- and the insulation burnt in the LOX. That caused the LOX tank to overpressure, and it blew away half the side of the vehicle.
Now, the heat energy you put into the reaction; most of that comes out as fast neutrons; plus the fusion reaction energy- again most of that energy is in the fast neutrons.
So you've got a net loss of energy.
One way to recover the energy is to line the inside of the reactor with lithium. The fast neutrons transmute the lithium- you then haul off the lithium and stuff it into a fission reactor, and go through the steam cycle to make electricity.
Clean? No.
Cleaner? Maybe, maybe not. The one advantage you have is that the half life of most of the waste is only a hundred years or so IRC, so you're still better off.
But of course all of this assumes that you can actually get fusion to work- the good news is that it's only 20 years away! That's much better than 30 years ago, when it was 30 years away!
But it had a bookmark!
This story has a history on Slashdot.
Is available in the archives.
Has ceased to be current. Been previously released. Your eyeballs should have purveyed its existance at this site. Not fresh.
Of a not unreleased nature. Available to the in-site search function.
Not news even if you are a nerd. Stuff that mattered.
It's a dupe. A dupe. Dupe- dupe- dupe!
I'm never sure whether it's because he failed, or because he tried :-)
Still, who cares- it's a party and we get fireworks!
That's what the Shuttle does. Doing that reduces the temperature on the skin of the aircraft- but at a big price- the vehicle is reentering for longer- and hence more heat energy leaks into the vehicle. That's why the Shuttle looks like an inside-out kiln.
Perhaps even to the point where no shielding is required?
At the hypersonic lift ratios that are actually achieved, this is not quite possible. However, early designs for the Space Shuttle had far less extensive shielding requirements.
These designs were changed when the military requirements imposed a *longer* reentry to return to the launch site after a launch to a polar orbit.
So we have the Shuttle you see today.
Have you ever used a toaster? They are not exactly the most reliable things in the world!
I'd say it's a good analogy.
They already have a bunch of bids in; and with the dutch auction it's the n'th lowest bid that counts- that's the price that everyone pays.
Presumably they've looked at the current price, and realised that at the old 'n', the price is in the dirt, so they've reduced 'n' to push up the price- and *increase* the overall money they take.
Of course not all the bids are in yet- that's why there's some variability on the sale price.
I'm a little bit surprised that they can do this at this stage. I wonder what the price there is on the first few bids! What if they had changed the number of sold shares down to 1? Did some lunatic bid $1 million dollars, not expecting to have to pay? Inquiring mind needs to know :-)
That's a myth. Most of the energy in a fusion reaction comes out as fast neutrons; these gradually mess up the structure of the reactor vessel and make it radioactive.
Secondly, most or all of the possible ways to catch the fast neutrons create secondary nuclear waste.
The idea that fusion power is 'clean' is not backed up by the facts.
And then, eventually a tile falls off and hits somebody on the head and kills them.
Who's to blame? The architect that told you that it was a prototype design? Or the house owner that keeps sweeping the problem under the carpet and not investigating?
Or the house builder who keeps using the same design that is known to be flawed for more than 30 years?
No, no. They've proved it; they even included the source code.
Unlikely at the moment, but he'll probably need replacements after Apple's lawyers are through with him.
Purely?
"Sorry, you've shown insufficient remourse for illegally downloading Michael Jackson's album; so you're going to have to stay in prison for another 5 years. You're clearly not rehabilitated." :-)
Historically, that's what it really meant; some people never got out of the joint for relatively minor crimes. Is that just?
Hint: no.
'Job's a good'un'.
OK, that was sloppy. Carmack isn't an electrical engineer. He's learnt the hard way that connectivity is important and unreliable.
*no protection against inductive kickback(essential around any combination of electromechanical and electronic devices)
Yup. Sloppy.
*not restricting allowable user inputs (ie joystick)
Borderline. They didn't expect the joystick to fail in that way, and it was the same joystick used on the simulation, which showed no problems.
*underrated power transistors for drive unit (this is very basic stuff)
So, they screwed that one up slightly- IRC the main problem there was a short circuit. In any case, look what happened on Rutans 100km flight- he had a thermal cut-off trigger- basically the same sort of thing. Are you saying Rutan is simply being careless too?
*finally, not setting minimum fuel level for takeoff
They loaded the vehicle up with twice the expected usage; the problem seems have been that they not only burnt more on the ground than they expected, the engine wasn't burning efficiently so they burnt more on the way up too.
Sure, with 20-20 hindsight they could have put more in and/or scrubbed the launch, but they only had the estimated burning rate to go on; and they had expected that to be a lot lower.
Nah, he'd be modded up to +5 almost every time.
Look what happens when John Carmack posts stuff (and I've absolutely nothing against JC, he's just an example of somebody famous.)
Your average X-ray machine will trivially see it isn't powered and doesn't contain explosives and they'll just ignore it.
"So what does your son do?"
"He's in prison after writing the worlds most successful computer viruses. Ouch! Don't hit me! Ouch! Stoppp!
LOL.
The difference this time is that Google is already a huge competitor- they can afford the legal armies and lobby the politicians and so forth if Microsoft try that sort of thing again.
Um.... No. No way. That's midsized.
Come back when you have atleast 600,000 lines; or 6 million.
I've worked on projects with 500+ people hacking on the same code, or different streams of the same code. That's a big system. And there are bigger.
We have even had an air tax; well, we called it a 'poll tax' (aka community charge); but it was clearly an air tax, since you only had to pay it as long as you were breathing :-)
We also used to have window taxes and clock taxes; with predictably silly results.
And of course the tea tax we levied on one of our (now ex) colonies... they never completely forgave us for that (p.s. the UK likes what you've done with the place- we want it back now) :-)
Now, you've pissed off half of Islam (and Islam is a big, big place; bigger than America). Iraq's economy is all but destroyed, Iran is eyeing up the place and Americans and Iraqis are dying by the hundreds/thousands. The US governments budget is in deficit.
About the only one happy about the situation is Osama Bin Laden; America has managed to fumble the situation in every one of the top holy places of Islam. Nice work.
That UN- what do they know? They know enough not to take a poison chalice...
And you know what? Dumb moves like create the kind of uncertainty that helps put cameras in American cities.
Where: FPS = Fish Poaching Software; natch