The death toll in Bam (Iran) was due to the mud-brick structures which had no tensile strength to resist a tremblor and dropped tons of weight onto people as they slept. This is what happened to the classic Citadel of that city; notice that anything beneath the collapse would have to survive something close to a rockslide.
I just replaced a tube over the weekend (2-3 years on that tube) and checked the new GE 3-ways at the hardware store. They claim 10,000 hours on a tube for about $25 (not a big-box store, prices are higher). The 150-watt 3-way incandescents across the aisle were $2.29 and claimed 2000 hours. Figuring 33 watts for the GE going flat-out, over 10,000 hours it will use 330 KWH at a cost of $26.40 for a total cost of $51.40 sans taxes. The 5 incandescents would cost $11.50 in toto and use 1500 KWH at a cost of $120 for a total of $131.50.
It looks like the CF saves about $80 on the first tube and, at a replacement cost of $9.00 per tube, $96 on each subsequent tube. Not bad, eh? Oh, these are 3-way ballasts, a simple one-way on/off would be about $10 cheaper these days.
In casual conversation it's impractical to be so rigorous, but anyone posting to/. has the web available and has zero excuse for not providing pointers to distinguish facts from bullshit. There's too much bullshit running around and it's up to us "nerds" (that includes you) to relegate it to the dungheap where it belongs. Do your part.
One example: scientists discovered that forest fires that burn hotter now due to fire prevention efforts over the last 100 years are able to burn permafrost and release HUGE amounts of carbon dioxide and water vapor (greenhouse gasses).
I thought this sounded fishy, so I Googled "wildfire permafrost" and got this abstract:
Heat transfer by conduction to the permafrost was not significant during fire. Immediately following fire, ground thermal conductivity may increase 10-fold and the surface albedo can decrease by 50% depending on the extent of burning of the surficial organic soil. The thickness of the remaining organic layer strongly affects permafrost degradation and aggradation. If the organic layer thickness was not reduced during the burn, then the active layer (the layer of soil above permafrost that annually freezes and thaws) did not change after the burn in spite of the surface albedo decrease.
In other words, the permafrost is not burned in the slightest, there is no reference to the temperature of the fire (how much fire-fighting effort has there been in permafrost zones?) and it is completely irrelevant outside areas where there is no permafrost.
Now, I'd like you to tell me why it fell to me to take a look and correct what appear to be your misconceptions? Are you happy being ignorant and repeating inaccurate and misleading things?
Get a case with a thermostatically-controlled main fan (not CPU fan, main fan). Put this in a 5-sided wooden box (hardened against critters, screened on the bottom) and insulate it with construction foam (inside) on four sides and the top. Half-inch foam will probably do. Vent the system fan out the bottom.
What this will do is create a "bubble" of warm air inside the box that is vented when the fan is running and stable when it is off. This will keep your box temperature roughly even. If you are concerned about cold-starting hard disks after a period of off-time, make sure you have a power supply which remains off after a power loss and add a 100 W light bulb inside the box. When you want to power the system back on, switch the bulb on and leave it for an hour or two before you hit the power button, then turn the bulb off again. Do not bring cold hardware into a warm, humid house to warm up - you will get condensation.
As long as you have the bottom of the box screened against critters and otherwise isolated, you probably won't have to worry about static or other environmental nastiness.
The X2 rated capacitor I am looking at now is rated to 275 volts AC and is self healing with an epoxy case. It has a value of 0.22mfd, somewhat bigger than your 5000mfd example.
I use a bunch of circle-tube CF's installed in table lamps. They are rated at roughly the same light output as a 150 W incandescent but they use only 34 watts on full (they're 3-way). They will run at least a year between tube replacements and these units cost about $20 new. Figuring 2000 hours of operation @ 34 watts and 8 cents/KWH and $20 up-front, the total cost for those 2000 hours is $25.44. That's assuming that you have to throw away the whole lamp after 2000 hours instead of just replacing the circle tube; if you replace the tube every 2000 hours at $5 each the cost for each incremental 2000 hours goes down to $10.44.
Lifespan of a 150-watt incandescent is what, 200 hours or less? Figuring 10 bulbs at $1 each plus 300 KWH of electricity @ 8 cents, the same 2000 hours of light would cost $34. Looks like your approach is penny-wise, pound-foolish.
If you are going to mess with line current, chokes or anything of the sort, you should know enough to know what component types and values to use, how to connect them safely and how to package them so that they will not exceed their temperature, voltage or other limits in operation.
An educated layman can do this, but if you aren't up to passing the electronics portion of a ham test you should probably defer to people who know more than you do. This may mean as little as finding good designs on the web... but if you have little expertise you're going to have a lot of trouble telling the good from the bad. Especially don't go off based on vague suggestions like this:
3) It's possible to obtain capacitors that are rated for 110/220 volt operation. Have a look inside a PC power supply and you may see one, they are normally encased in yellow transparent epoxy. Wire one of these across the fitting.
If you wire a 5000 microfarad cap across the AC line, your life may get more interesting than you want - it will pull current (perhaps enough to overheat and blow the capacitor) and the high inductance of such a large capacitor will make it a poor bypass for RF emissions. You will want what are known as disc ceramic capacitors rated for several hundred volts (they have to endure line spikes) and with values chosen for the RF frequencies you are trying to get rid of.
Last, the light itself may be radiating enough to bother you. There are probably ways to bypass radiated emissions from a circle tube, but I have not heard about them nor have I investigated the issue.
On the issue of your degree. Arguing to authority. (and almost certianly outside of your field of expertise, since I didn't hear you calaiming to have built (been involved in building) a 20,000-independent-unit sync-alt generation station.)
Does that mean you're taking the bet? Either you really think I'm wrong and you're ready to profit from it, or you're just jawboning without having any confidence in what you're saying. As the saying goes, the latter walks.
Talk about irony. I read it, and I know what it says. I also know what it does not say that I would demand to know before making technical decisions about this scheme, and it's a lot.
See that "Engineer" in my moniker? It's not just for show.
Plus the "electronics" arn't going to effectively be able to put power onto the grid until the station has got a little head.
Don't be silly. You can put power on the grid with a couple of solar panels and a synchronous inverter, back-feeding through a plug in your wall. Power goes right back through the pole-pig transformer at the end of the block, through the distribution lines and back to the substation transformer. There is nothing in the wiring that prefers one direction; that's all in the arrangement of generation and loads.
Besides, there is no way in hell you want to have 20,000 sync-alt generators directly connected to the grid in one place.
Where's your reference or personal expertise that allows you to make this claim?
But they are going to need a big ass bank of capacitors in there somewhere to get themsleves up to operating voltages and menaingful power levels.
You're fixated on capacitors as if they're magical devices. To me, they are reactive impedances at 1 / ( j omega c ).
Among other things, they probably *wont* use sync-alts bare to the grid because of the reactive power that would soak up.
"Reactive power". There's another buzzword you learned without knowing its meaning. Let me tell you something else that you can use to impress rubes without really understanding it: synchronous alternators can either consume or make VARs depending how they are excited; it's induction generators which always consume VARs.
Were I to bet I'd bet on a farm of single independent generators or small clusters of same, near-term rectifiers "just before" a mighty bank of capacitors, and then the step-up electronics to drive the power from the capacitors onto the grid.
I'll take that bet. (I love a sucker.) What do you want to make, a grand at even odds? A system like this is going to parallel the alternators on buses and run the power through transformers (probably a couple of stages, because 480 volts is mighty unweildy at at high power levels) and straight to the grid. No inverters, no fancy switching electronics, no capacitors except for power-factor correction. You want to take me up on it, get my e-mail from my blog.
Large scale hydroelectric installations with dams are easy to throttle as well...
How do you manage this outside of the west, where there are few hydro installations? Even there, how do you manage this while also allowing the river to have its normal seasonal cycles instead of weekday surges as our demand produces?
These heliostat type stirling engines use a at least one stage of heat exchange fluid.
Two things to make you doubt that conclusion:
The engine in these systems is mounted directly to the receiver at the focus point. There isn't room for much.
The Stirling Energy Systems pages are very scarce on technical details such as drawings, but I did find a reference to "heat-pipe receivers". The amount of thermal mass in such a receiver is very small.
Rather than complicating the system with extra elements, it makes much more sense to manage it with the pieces that you already have for other purposes. It's going to be easier to point dishes off-sun to reduce excess production than it would be to store heat, and you can't beat the marginal cost: zero.
Since they have to get up to the (230,000-volt was it?) levels to get menaingfully onto the grid in the first place I suspect that a giant bank of capacitors and a fast switching doodad are pretty much mandatory.
Nope. As implied by the article, the engines are tied to synchronous alternators. These will generate at a few hundred volts (such small units do not have the physical size for the insulation needed for high voltages). Conversion to high-tension is done with transformers; there is no storage.
Even if the production of AC was done with electronics, there would not be much storage in the system. Three-phase inverters have a flat power flow and require essentially none, and even single-phase sine wave inverters need but half a cycle or so. This is tiny compared to the time-scales we're talking about, and can be dismissed.
How not to "waste" the power generated when you aren't cut in is a "what to do with the gravy" kind of issue for the most part.
No, it's more of a "how much extra equipment do you need to manage it properly" issue. I suspect it won't be a huge amount, because the array will need dump loads to deal with the eventuality of transmission breaker trips (loss of load without removing motive power = overspeed and possible damage). You can use the same dump load to soak up the power while you are syncing to the grid. Given that you've got to have a dump load, it's not going to pay to have anything fancier - you are not going to use it enough for it to pay off.
The "steadly increasing" 20MW/second isn't that problematical if you don't put it on the grid right then but instead wait till it was needed...
There are places like California where they can use every watt they can get many days. This is only going to increase if we get grid-chargeable hybrid vehicles. Fortunately, such vehicles are essentially rolling battery banks; if their chargers were synced to the generation coming on-line or going off, they could easily provide the balancing required by the grid. If only 1 million vehicles in California could provide such services, they could soak up a 200 MW change in generation by altering their flow by a mere 200 watts each.
You could do the same with ice-storage air conditioners, varying the cycling of ordinary refrigerators on a second-by-second basis, etc. Appliances like that have enormous potential; how many refrigerators do you think there are among California's 30 million people? If it's as few as 10 million, they consume 250 watts each and half of them are controllable, that's 1.25 GIGAWATTS of potential demand-side balancing from refrigerators alone. If you added air conditioners the available DSM would be a large fraction of the total peak. With battery storage costing more than the power going into it, DSM is where the real potential is.
The Feds determine what is a car, a light truck or heavier vehicle for emissions and CAFE purposes. Yes, this means something can be classed as a truck by the Feds when determining its pollution limits and possible guzzler penalty, and as a car by your state government. Crazy, isn't it?
The fuel-burning generators often have limited rates of change, unless you want to perform an emergency shutdown (not recommended). The grid operators already have command and control systems to regulate generators, but cutting the power output of a boiler putting out a GW-thermal is not something that happens in a few seconds.
According to what I've read about grid regulation, it's not uncommon to have the slower-reacting plants ramping in one direction to follow the general trend while the fast-reacting plants go the opposite way to cover the short-term variations. Really rapid changes aren't managed at all, they are just allowed to change demand by altering the grid frequency slightly (lower frequency = less power demand from anything with a motor). Throwing large transients at this system is a certain way to break it; you want to design around this if you can, or even make the solar generator able to regulate faster than anything else (which gives it another revenue stream).
Even if you managed the system such that one dish started off the grid and further dishes started off the ones already running (exponential progression), you'd still have an issue with the grid balance. Typical grid demand fluctuates by a few megawatts on the time-scale of seconds; if you fired up a 100 MW dish farm over 5 seconds you'd have generation increasing by 20 MW/second for some time. Unless you also had demand, reactive power, transformer taps etc. scheduled in synchrony with this, it would make a lot more sense to leave dishes pointed off-sun until you could guarantee demand and had down-regulation capacity ready to handle any excess. It might make more sense to fire up big farms over 15 minutes or more (unless you can start generating with the weak morning sunlight and eliminate transient issues by following the curve of incoming sunlight).
Lithium-ion, zinc-air... anything that has a lot of WH/kg and can take the automotive environment will do. (Electrolytic hydrogen has an end-to-end efficiency of about 50%, and is so bulky that current vehicles have ranges on the order of 50 miles. Even lead-acid batteries can do better than that; hydrogen is a boondoggle.)
Hummers are legally trucks, and don't pay guzzler taxes.
The "think of the poor!" plea has been around since the 1970's. It has been an excuse for failing to give people any incentive to cut their fuel use, and it's gotten us exactly where we are today. Isn't it time to go back to what works? If your withholding taxes go down won't you be able to afford another quarter for that delivered pizza?
Actually, the H2 is a problem
on
Killer Ozone?
·
· Score: 2, Informative
The H2 is a "heavy light-duty" truck, and is allowed to emit much more of most pollutants than a passenger car. See this document.
Ironically, many California cities restrict trucks over 6500 lbs GVW to truck routes; they wouldn't have to raise mileage standards to get those Hummers and Durangoes off the roads, all they'd have to do is enforce the truck restrictions they already have.
There are hot areas with smog, hot areas with little smog, and cool areas with lots of smog precursors; you can use epidemiological methods to tease out the contribution of each.
Too many newspapers use scientific illiterates to write their science coverage. The Times of London appears to be one of them, if we consider the quality (or lack thereof) of TFA.
a Star Trek-style thruster
Star Trek postulates warp drives (which we have no idea how to build) and "impulse engines". Ion drives are impulse engines, but all rocket motors are impulse engines too.
Had the ion drive fallen just 5 per cent short of maximum thrust, Smart-1 could have collided with the Moon.
It's completely opaque to me how this could be the case. If you don't have enough thrust for one trajectory, you use another.
They work by using electricity from solar panels to charge atoms of the noble gas xenon, which are then fired into space at 1,000mph to power the probe.
The author is obviously innumerate. Impulse of the DS-1 engine peaked at 3100 seconds, for an exhaust velocity of ~30 km/sec. That is not 1000 MPH, it is about 68000 MPH.
This stream of ions accelerates Smart-1 at just 0.2millimetres per second.
Per second squared.
In space, this builds up over time to generate speeds of up to 10miles per second, or 36,000mph.
Except that a mission to the Moon never gets to such speeds; the spacecraft slows down as it spirals outward. Orbital velocity of the Moon around Earth is only about 2200 MPH.
Why newspapers publish drivel like this, I'll never know. If it was hard to get right you wouldn't have amateurs fisking this stuff on Slashdot!
Mars has all the elements required for life, including (if we can trust the evidence) water. It's difficult to get off Mars but you can do it with single-stage rockets. I don't know if you're going to be able to find an asteroid which yields everything you need for building materials, atmosphere, and the rest. Having to do a lot of scooting around to get those things from different rocks may increase your trouble and risk more than putting down on a little planet like Mars.
Even pure Pu-240 or Pu-242 could be built into a bomb. A really, really difficult to engineer bomb, but a bomb nonetheless.
You can engineer rock into a weapon. Launch some sort of spacecraft capable of deploying a solar sail and cruising to a small asteroid. Hook on with a piton and a few km of line, then use the photon thrust to aim the rock at the desired target.
Too much effort, you say? Too hard to make sure it will all work? Takes too long? Other things pay off much more easily? Sure, no argument. Same thing with bombs from spent PWR fuel.
And any reactor output of plutonium can be processed with the types of equipment used to enrich Uranium to get modern weapons grade Pu, if you want. With hundreds of times less separation effort.
But orders of magnitude more threat of detection at any of these stages:
Diversion of spent or reprocessed fuel.
Chemical or radiological accident during purification.
Accident during isotope separation, especially a criticality accident.
Chemical, radiological or criticality accident during conversion to solid.
Fire while in the metal phase.
Explosive accident during or after bomb assembly (this would contaminate an area but would likely not result in detonation).
You can get rid of most or all of these problems by enriching uranium instead, or stealing bomb-grade materials (or finished weapons) from the ex-Soviet block nations. Given these avenues someone would have to be a fool to divert spent PWR fuel for bomb-making, and it appears that nobody with the money to make the attempt is that foolish.
Now and in the future, reactor grade plutonium appears to be the material most likely to be available to a terrorist group. Given the spontaneous fission rate, and the limited technology for rapid assembly, predetonation is a foregone conclusion....
Given that the system will disassemble well before compression is complete, an accurate symmetrical implosion is not really a necessity. Simply imploding the fissile material at a high rate even if imperfectly (that is, without a true plane or cylindrical shock wave), could produce the necessary rapid compression. For this to work, the fissile material would have to be fairly close to critical at the beginning of the implosion since an imperfect implosion would create unacceptable distortions if the compression factor were very large. As noted earlier in the discussion on nuclear testing, manufacturing a device that is close to critical is extremely hazardous and itself requires substantial sophistication. [emphasis added]
Sophistication which a terrorist group (as opposed to a cats-paw for a state actor, which would not require diverted PWR fuel) would simply not have. They would be at high risk of having an accident which reveals their plot, kills their essential skilled personnel, blows up friendly territory or all three. To be a threat to the US they have to avoid all of those failure scenarios and then get their bomb to the target undetected. This isn't trivial and is getting harder.
There's a common delusion, pushed by IFR fans among others, that there is a "safe" Plutonium output type which will not be a practical proliferation concern.
There's a common delusion among people world-wide that nuclear powerplants are more dangerous than chemical plants or oil refineries. Nothing could be further from the truth, yet the public misperception persists. If a terrorist wants to kill people, it would be much easier to put some sort of poison into municipal water supplies than to divert, process, and fabricate PWR fuel into a bomb; neither would such efforts tip off the civilized world beforehand and place the program at risk before it could yield results. It is easier
Slashdot Mirror
Here are more images of the destruction in Bam.
It looks like the CF saves about $80 on the first tube and, at a replacement cost of $9.00 per tube, $96 on each subsequent tube. Not bad, eh? Oh, these are 3-way ballasts, a simple one-way on/off would be about $10 cheaper these days.
- You're the one who made the questionable claims.
- You're the one who didn't check to see if the facts were straight.
- You're the one who didn't cite any source. ("Scientists" is not up to snuff.)
In casual conversation it's impractical to be so rigorous, but anyone posting toNow, I'd like you to tell me why it fell to me to take a look and correct what appear to be your misconceptions? Are you happy being ignorant and repeating inaccurate and misleading things?
What this will do is create a "bubble" of warm air inside the box that is vented when the fan is running and stable when it is off. This will keep your box temperature roughly even. If you are concerned about cold-starting hard disks after a period of off-time, make sure you have a power supply which remains off after a power loss and add a 100 W light bulb inside the box. When you want to power the system back on, switch the bulb on and leave it for an hour or two before you hit the power button, then turn the bulb off again. Do not bring cold hardware into a warm, humid house to warm up - you will get condensation.
As long as you have the bottom of the box screened against critters and otherwise isolated, you probably won't have to worry about static or other environmental nastiness.
Lifespan of a 150-watt incandescent is what, 200 hours or less? Figuring 10 bulbs at $1 each plus 300 KWH of electricity @ 8 cents, the same 2000 hours of light would cost $34. Looks like your approach is penny-wise, pound-foolish.
An educated layman can do this, but if you aren't up to passing the electronics portion of a ham test you should probably defer to people who know more than you do. This may mean as little as finding good designs on the web... but if you have little expertise you're going to have a lot of trouble telling the good from the bad. Especially don't go off based on vague suggestions like this:
If you wire a 5000 microfarad cap across the AC line, your life may get more interesting than you want - it will pull current (perhaps enough to overheat and blow the capacitor) and the high inductance of such a large capacitor will make it a poor bypass for RF emissions. You will want what are known as disc ceramic capacitors rated for several hundred volts (they have to endure line spikes) and with values chosen for the RF frequencies you are trying to get rid of.Last, the light itself may be radiating enough to bother you. There are probably ways to bypass radiated emissions from a circle tube, but I have not heard about them nor have I investigated the issue.
White light is a spectrum of frequencies; any one frequency is called "monochromatic".
See that "Engineer" in my moniker? It's not just for show.
Don't be silly. You can put power on the grid with a couple of solar panels and a synchronous inverter, back-feeding through a plug in your wall. Power goes right back through the pole-pig transformer at the end of the block, through the distribution lines and back to the substation transformer. There is nothing in the wiring that prefers one direction; that's all in the arrangement of generation and loads. Where's your reference or personal expertise that allows you to make this claim? You're fixated on capacitors as if they're magical devices. To me, they are reactive impedances at 1 / ( j omega c ). "Reactive power". There's another buzzword you learned without knowing its meaning. Let me tell you something else that you can use to impress rubes without really understanding it: synchronous alternators can either consume or make VARs depending how they are excited; it's induction generators which always consume VARs. I'll take that bet. (I love a sucker.) What do you want to make, a grand at even odds? A system like this is going to parallel the alternators on buses and run the power through transformers (probably a couple of stages, because 480 volts is mighty unweildy at at high power levels) and straight to the grid. No inverters, no fancy switching electronics, no capacitors except for power-factor correction. You want to take me up on it, get my e-mail from my blog.- The engine in these systems is mounted directly to the receiver at the focus point. There isn't room for much.
- The Stirling Energy Systems pages are very scarce on technical details such as drawings, but I did find a reference to "heat-pipe receivers". The amount of thermal mass in such a receiver is very small.
Rather than complicating the system with extra elements, it makes much more sense to manage it with the pieces that you already have for other purposes. It's going to be easier to point dishes off-sun to reduce excess production than it would be to store heat, and you can't beat the marginal cost: zero.Even if the production of AC was done with electronics, there would not be much storage in the system. Three-phase inverters have a flat power flow and require essentially none, and even single-phase sine wave inverters need but half a cycle or so. This is tiny compared to the time-scales we're talking about, and can be dismissed.
No, it's more of a "how much extra equipment do you need to manage it properly" issue. I suspect it won't be a huge amount, because the array will need dump loads to deal with the eventuality of transmission breaker trips (loss of load without removing motive power = overspeed and possible damage). You can use the same dump load to soak up the power while you are syncing to the grid. Given that you've got to have a dump load, it's not going to pay to have anything fancier - you are not going to use it enough for it to pay off. There are places like California where they can use every watt they can get many days. This is only going to increase if we get grid-chargeable hybrid vehicles. Fortunately, such vehicles are essentially rolling battery banks; if their chargers were synced to the generation coming on-line or going off, they could easily provide the balancing required by the grid. If only 1 million vehicles in California could provide such services, they could soak up a 200 MW change in generation by altering their flow by a mere 200 watts each.You could do the same with ice-storage air conditioners, varying the cycling of ordinary refrigerators on a second-by-second basis, etc. Appliances like that have enormous potential; how many refrigerators do you think there are among California's 30 million people? If it's as few as 10 million, they consume 250 watts each and half of them are controllable, that's 1.25 GIGAWATTS of potential demand-side balancing from refrigerators alone. If you added air conditioners the available DSM would be a large fraction of the total peak. With battery storage costing more than the power going into it, DSM is where the real potential is.
The Feds determine what is a car, a light truck or heavier vehicle for emissions and CAFE purposes. Yes, this means something can be classed as a truck by the Feds when determining its pollution limits and possible guzzler penalty, and as a car by your state government. Crazy, isn't it?
According to what I've read about grid regulation, it's not uncommon to have the slower-reacting plants ramping in one direction to follow the general trend while the fast-reacting plants go the opposite way to cover the short-term variations. Really rapid changes aren't managed at all, they are just allowed to change demand by altering the grid frequency slightly (lower frequency = less power demand from anything with a motor). Throwing large transients at this system is a certain way to break it; you want to design around this if you can, or even make the solar generator able to regulate faster than anything else (which gives it another revenue stream).
Even if you managed the system such that one dish started off the grid and further dishes started off the ones already running (exponential progression), you'd still have an issue with the grid balance. Typical grid demand fluctuates by a few megawatts on the time-scale of seconds; if you fired up a 100 MW dish farm over 5 seconds you'd have generation increasing by 20 MW/second for some time. Unless you also had demand, reactive power, transformer taps etc. scheduled in synchrony with this, it would make a lot more sense to leave dishes pointed off-sun until you could guarantee demand and had down-regulation capacity ready to handle any excess. It might make more sense to fire up big farms over 15 minutes or more (unless you can start generating with the weak morning sunlight and eliminate transient issues by following the curve of incoming sunlight).
I addressed pretty much the same issue in this essay on my blog.
The "think of the poor!" plea has been around since the 1970's. It has been an excuse for failing to give people any incentive to cut their fuel use, and it's gotten us exactly where we are today. Isn't it time to go back to what works? If your withholding taxes go down won't you be able to afford another quarter for that delivered pizza?
Ironically, many California cities restrict trucks over 6500 lbs GVW to truck routes; they wouldn't have to raise mileage standards to get those Hummers and Durangoes off the roads, all they'd have to do is enforce the truck restrictions they already have.
As you know (but others may not), high temperatures contribute to smog formation. Smog goes up by about 3% for each degree over 70 fahrenheit.
Why newspapers publish drivel like this, I'll never know. If it was hard to get right you wouldn't have amateurs fisking this stuff on Slashdot!
Smart-86, which will almost get to its destination but will wind up saying "Missed it by that much!"
Mars has all the elements required for life, including (if we can trust the evidence) water. It's difficult to get off Mars but you can do it with single-stage rockets. I don't know if you're going to be able to find an asteroid which yields everything you need for building materials, atmosphere, and the rest. Having to do a lot of scooting around to get those things from different rocks may increase your trouble and risk more than putting down on a little planet like Mars.
You can engineer rock into a weapon. Launch some sort of spacecraft capable of deploying a solar sail and cruising to a small asteroid. Hook on with a piton and a few km of line, then use the photon thrust to aim the rock at the desired target.
Too much effort, you say? Too hard to make sure it will all work? Takes too long? Other things pay off much more easily? Sure, no argument. Same thing with bombs from spent PWR fuel.
But orders of magnitude more threat of detection at any of these stages:
You can get rid of most or all of these problems by enriching uranium instead, or stealing bomb-grade materials (or finished weapons) from the ex-Soviet block nations. Given these avenues someone would have to be a fool to divert spent PWR fuel for bomb-making, and it appears that nobody with the money to make the attempt is that foolish.
Your own source agrees. I quote:
Sophistication which a terrorist group (as opposed to a cats-paw for a state actor, which would not require diverted PWR fuel) would simply not have. They would be at high risk of having an accident which reveals their plot, kills their essential skilled personnel, blows up friendly territory or all three. To be a threat to the US they have to avoid all of those failure scenarios and then get their bomb to the target undetected. This isn't trivial and is getting harder.
There's a common delusion among people world-wide that nuclear powerplants are more dangerous than chemical plants or oil refineries. Nothing could be further from the truth, yet the public misperception persists. If a terrorist wants to kill people, it would be much easier to put some sort of poison into municipal water supplies than to divert, process, and fabricate PWR fuel into a bomb; neither would such efforts tip off the civilized world beforehand and place the program at risk before it could yield results. It is easier
And not again, despite their shortage. There's a lesson, if you're open to learning it.