They're heavier than batteries for the same power out, but they last a LOT longer - many years in most cases, with the power output slowly decreaseing as the radioactive material decays. In Soviet Russia they used them to power remote automatic lighthouses.
They're also really damn expensive because you have to make the fuel in a nuclear reactor. Probably not suitable for home use. Also, there hasn't been much success making them really really tiny like you'd want for portable equipment.
Actually FYI RTGs are active from as soon as they're made... basically it's just a hunk of radioactive material that gets warm and a Peltier junction that turns the heat difference between that and the colder environment outside into electricity. All wrapped in some really hefty shielding of course.
This doesn't mean they're dangerous. They are all quite capable of surviving reentry and impact, and in one case (the NASA Nimbus B1 satellite in 1968) an RTG was recovered and actually reused in another spacecraft!
Furthermore even if one did break up in the atmosphere and somehow vapourise despite being made in a ceramic form that would stay in a few lumps, it would cause bugger all damage. Plutonium isn't especially radioactive, although it is moderately chemically toxic. The small amount in an RTG completely pales in comparison to the plutonium in the environment from all the nuclear tests, and those make up literally 0.5% of the radiation we receive each year. (The rest comes mostly from natural sources but a significant amount also from medical xrays.)
Nukes are very destructive, but most people have a conception of their destructive potential that is totally out of proportion to what they are actually capable of.
Actually I think the most common misconception is not of the destructive potential of nukes, but of just how damn big the world is!
If, 5 milliseconds after I die, I believe anything at all, then I will be surprised and change my opinions based on the new evidence. If a vengeful God chooses to damn me for not feeling the same way throughout my life despite lack of evidence, then screw Him.
Actually it's well accepted as by far the most likely candidate for what happened. By the way, other theories include the theory of gravity, relativity theory etc... all pretty much proven, ask Hiroshima about E=mc^2 if you don't believe that one:P
True enough - but I don't think that we'll be getting much He from fusion! Even if the whole world ran on it you'd only get a few tonnes/year He out, tops.
It couldn't possibly be omnidirectional. That would break the laws of physics. To get a boost in signal strength you must either make it more directional or increase the power itself with an amplifier.
It probably would help but as I explained, making it much lighter than normal helium won't end up making an awful lot of difference. Even if you could somehow "fill" it with vacuum while keeping the shape, it wouldn't lift more than 5% or so more.
Incorrect. The blimp expands until the pressure inside is the same as the pressure outside, so any change in air density will be reflected as a proportional change in helium/hydrogen density. See my other post for a longer explanation of that.
Actually I thought that, but when you run the numbers you find that helium is very close in terms of buoyancy for a couple of reasons.
Firstly, helium gas goes round as a single atom, He, because it's a noble gas. Hydrogen goes as pairs, H2. This means that in a given volume at fixed pressure, you would have twice as many hydrogen atoms as you would heliums, so that brings the difference in weight down to 1/2.
Secondly and more importantly, it's not actually the weight that counts. (Please if I've got this wrong, correct me, this is just from me thinking about it) The important thing is the difference in weight between e.g. a liter of air and a liter of helium/hydrogen.
Air is mostly nitrogen which has mass no. 14. This means that 1 mole of N2 molecules weighs 28g.
A mole of any gas occupies 24 liters at STP so air weighs about 1.17 g per liter. Running the numbers for He and H2 gives 0.16 and 0.08 respectively.
Now, looking at the difference in weight, which is what determines buoyancy, helium gives about 1.01 g per liter while hydrogen gives 1.09 g per liter. Not such a big difference after all! I think that the advantage of non-flammability probably outweighs this minor difference in buoyancy. On the other hand, it may very well be easier and cheaper to produce hydrogen in bulk than helium.
FWIW the sun is actually not a middling-bright star, but way above average in terms of brightness.
Of course it isn't creating a star, but it is using the same method and I think that's pretty cool, that we can produce energy from plain hydrogen rather than stored solar energy (fossil fuels) or supernova remnants (fission).
The plasma is VERY thin... and there's a reason why they have to try very hard to keep it away from the reactor walls. Not because the walls will melt but because the plasma will instantly cool down and stop doing its fusion thing.
As for the article, why bother designing the suits now? I'm sure that in 20 years there will be materials that will be much more advanced that we'll want to use instead.
Part of the problem is the need for a "feature freeze". At a certain point, probably around 10 years before launch, they have to stop adding new features and changing designs entirely, even when new and better technologies come out. This is vital so that all the systems can be integrated with each other and tests run to make sure everthing works together smoothly.
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And here's a list of 434 scientists named Steve who do believe in so-called "molecules to man" evolution. Your point?
Question - for what are Huggies damn useful? (apart from the obvious)
They're also really damn expensive because you have to make the fuel in a nuclear reactor. Probably not suitable for home use. Also, there hasn't been much success making them really really tiny like you'd want for portable equipment.
This doesn't mean they're dangerous. They are all quite capable of surviving reentry and impact, and in one case (the NASA Nimbus B1 satellite in 1968) an RTG was recovered and actually reused in another spacecraft!
Furthermore even if one did break up in the atmosphere and somehow vapourise despite being made in a ceramic form that would stay in a few lumps, it would cause bugger all damage. Plutonium isn't especially radioactive, although it is moderately chemically toxic. The small amount in an RTG completely pales in comparison to the plutonium in the environment from all the nuclear tests, and those make up literally 0.5% of the radiation we receive each year. (The rest comes mostly from natural sources but a significant amount also from medical xrays.)
Actually I think the most common misconception is not of the destructive potential of nukes, but of just how damn big the world is!
If, 5 milliseconds after I die, I believe anything at all, then I will be surprised and change my opinions based on the new evidence. If a vengeful God chooses to damn me for not feeling the same way throughout my life despite lack of evidence, then screw Him.
Not really intended to be.. I shouldn't have put that smily in there. War is bad.
Actually it's well accepted as by far the most likely candidate for what happened. By the way, other theories include the theory of gravity, relativity theory etc... all pretty much proven, ask Hiroshima about E=mc^2 if you don't believe that one :P
True enough - but I don't think that we'll be getting much He from fusion! Even if the whole world ran on it you'd only get a few tonnes/year He out, tops.
Fair enough. I don't know much about radio!
It couldn't possibly be omnidirectional. That would break the laws of physics. To get a boost in signal strength you must either make it more directional or increase the power itself with an amplifier.
SETI by name is a search for extraterrestrial intelligence.
It probably would help but as I explained, making it much lighter than normal helium won't end up making an awful lot of difference. Even if you could somehow "fill" it with vacuum while keeping the shape, it wouldn't lift more than 5% or so more.
Correction: a mole of any gas occupies 22.4 liters at STP. But this doesn't change the conclusion.
Incorrect. The blimp expands until the pressure inside is the same as the pressure outside, so any change in air density will be reflected as a proportional change in helium/hydrogen density. See my other post for a longer explanation of that.
Firstly, helium gas goes round as a single atom, He, because it's a noble gas. Hydrogen goes as pairs, H2. This means that in a given volume at fixed pressure, you would have twice as many hydrogen atoms as you would heliums, so that brings the difference in weight down to 1/2.
Secondly and more importantly, it's not actually the weight that counts. (Please if I've got this wrong, correct me, this is just from me thinking about it) The important thing is the difference in weight between e.g. a liter of air and a liter of helium/hydrogen.
Air is mostly nitrogen which has mass no. 14. This means that 1 mole of N2 molecules weighs 28g. A mole of any gas occupies 24 liters at STP so air weighs about 1.17 g per liter. Running the numbers for He and H2 gives 0.16 and 0.08 respectively.
Now, looking at the difference in weight, which is what determines buoyancy, helium gives about 1.01 g per liter while hydrogen gives 1.09 g per liter. Not such a big difference after all! I think that the advantage of non-flammability probably outweighs this minor difference in buoyancy. On the other hand, it may very well be easier and cheaper to produce hydrogen in bulk than helium.
Indeed... "chiropractic" is almost all complete bullshit. Anyone with real back or joint problems should see a qualified doctor.
Of course it isn't creating a star, but it is using the same method and I think that's pretty cool, that we can produce energy from plain hydrogen rather than stored solar energy (fossil fuels) or supernova remnants (fission).
The plasma is VERY thin... and there's a reason why they have to try very hard to keep it away from the reactor walls. Not because the walls will melt but because the plasma will instantly cool down and stop doing its fusion thing.
You say that, but just try putting one in a microwave and you might change your opinion! ;)
There's a BIG difference between an X-prize suborbital flight and doing a Martian mission, even with robots.
I'd imagine you can indeed save significant amounts of weight when you only have to insulate against -30 C rather than -230 on the Moon.
Part of the problem is the need for a "feature freeze". At a certain point, probably around 10 years before launch, they have to stop adding new features and changing designs entirely, even when new and better technologies come out. This is vital so that all the systems can be integrated with each other and tests run to make sure everthing works together smoothly.
Hey, don't say it like that. For food manufacturers to actually produce something that does what it claims really IS a discovery!
Check out this awesome photo of the Moon and Earth together, taken by Galileo more than a decade ago during its Earth flyby.