> (and you WOULD NOT want to be there if a large, high-speed spinning > element broke off of its axis and started ricocheting about the room...)
John Logie Baird had exactly this problem with his invention, it consisted of lenses mounted in a spiral on a spinning wooden disc, people call it television these days.
While Baird's scanning device was extremely cumbersome, there was no instrinsic reason why it could not eventually be miniaturized, given sufficient progress in technology. 3D displays of the type under discussion here have to be able to disperse an incident light beam at arbitrary locations in a large 3D volume. How are you going to accomplish this without large pieces of matter whizzing around that volume at high speed?
Here's the best alternative I can think of: generate a continuous, fine mist of water droplets in your display area. Surround the display area with a ton of red, green, blue, and infrared lasers. Continuously track the position of each and every droplet in the infrared, then for each voxel you need to display, compute a free path to the nearest-floating droplet for a red, a green, and a blue laser, and fire. Repeat at insane speed to render a full 3D scene.
This looks doable in principle, but has the disadvantage that the scene will always appear enveloped in, well, mist. Also, there is no "hidden line removal" - since objects are rendered (literally) using smoke and mirrors, you can see right through them. (By the way, this also applies to the Hitachi device.)
If you have any better idea, I'm sure a lot of powerful people would like to talk with you.
Just the pendulum instability from the offset between CG and CL is going to drive you bats
But hey, if you just flip that damned thing upside down you almost have a semi-decent hangglider! You'd be flying it lying on your back though, good luck seeing the ground...
Seriously, a jet-powered hangglider would be infinitely cheaper, safer, and more fun to fly.
ObTroll for +5 informative: "Moeve" is German for "gull". Duh!
Hawking thinks that humanity needs to genetically engineer ourselves to pre-emptively keep machines from taking us over.
Well then, call me nuts, too, but I think this is actually a pretty inevitable conclusion once you start thinking of the big picture - say, developments over the next 1000 years or more. Hawkins may be disingenuous in going public with such long-range thoughts, but they are actually very well-founded.
> What NASA really needs is a tool to filter all superlatives from its press releases. Superlatives are why we are there.
Understood. My suggestion was tongue-in-cheek (though it might make a useful training tool for overexcitable NASA PR flacks). My objection is not to the superlatives per se, but to making trivial superlatives appear like the reason why we go out there. We're not on Mars *in order* to do U-turns there - it's incidental.
It is my opinion (and not necessarily that of NASA) that NASA PR should seek to provide a multi-tier service which caters not merely to the lowest common denominator, but also the the more scientifically inclinded citizens who seek more details.
Amen! This is exactly what I'm missing, thanks for articulating it so well.
My best wishes for the MERs - hope they'll both make it all the way to the bigger craters!
Lowest common denominator attention is better than no attention at all.
That's exactly what I would dispute. I've seen plenty of times how NASA's dumbed-down PR creates misperceptions in the many people who are more intelligent than NASA gives them credit for. These people (say, everyone with a college degree) may not have as many votes as the great unwashed masses, but they constitute the movers & shakers (engineers, politicians, what have you) of today and tomorrow. Their entirely understandable reaction to NASA playing up trivia such as the "first U-turn on another planet" is "WTF - I'm paying taxes for *this*?"
You and I may know that beneath the veneer of hyperbolic baseball stats pumped out by NASA's PR dpeartment lies real, exciting science worth every penny we put into it, but you sure wouldn't know from looking at NASA's press releases, and I'm afraid a great many people who control NASA's budget allocations have no clue of that either. To them the baseball stats *are* the real thing, and therein lies danger.
To give an example, during the live coverage on NASA TV of Spirit's landing, IIRC the airhead commentator was gushing about "the first *ever* pictures from the surface of Mars". Can't they get someone at least minimally knowledgeable as commentator? Such PR blunders are not only a public embarassment, they carry the real risk that some decisionmaker takes exaggerated NASA claims at face value, finds out that they are false, and gets *really* pissed off.
It would be quicker to *download* our existing knowlegde into the tike so that they don't have to re-discover the entire world, pausing and proding everything and everybody. But nature re-invents the OS almost from scratch for every birth so that they are too incompatable to do a direct transfer.
Good point, but... real geeks *like* to invent their own OSs! That would make God the Ubergeek. I've actually learned a lot by looking at the world through the eyes of a little kid, pausing and prodding everything. The mental equivalent of programming in assembler - takes more time, but gives you a much better understanding of how things work.
Anyone who has tried to go for a walk with a 2 or 3 year old kid knows what I'm talking about. You want to walk, but the annoying little brat will stop and examine very carefully every piece of litter, little stone, gravel or mark on the floor. Half way through the whole thing you'll get tired and just go home.
Exploring that piece of litter, stone, gravel, mark on the floor is the whole point of the walk for a little kid. Ditto for the Mars rovers. Our concepts of what a walk should be like do not apply - there is no predetermined itinerary that must be covered, only wide open eyes that want to understand all the marvels that they see.
What sort of over-hyped/overly-specific record is this?
NASA has the unfortunate habit of framing everything in terms of firsts and records, as if space exploration was some sort of spectator sport. I've lost count of how often I've seen the headline "Hubble spies oldest galaxy" - well duh, since Hubble is the only instrument in its class for imaging faint red-shifted objects, I'd be worried if it didn't find a new "oldest known galaxy" every month or so. The current "first sneeze/fart/ping/macarena/kernel panic on another planet" spate of Spirit/Opportunity PR is in the same vein.
Through a PR machinery that caters to the lowest common denominator, NASA systematically undermines the many good reasons we have for exploring space, and thus ends up shooting itself in the foot. If you reduce your own work to a mere set of pointless Guiness Book of Records entries, you shouldn't be surprised if people start to wonder whether it's worth paying billions of dollars for it. What NASA really needs is a tool to filter all superlatives from its press releases.
PS: a NASA TV channel that isn't dumbed down so much would also be nice.
I wonder whether they'll finally be able to (dis)prove the hypothesis that everybody knows everybody else within six (or however many) degrees of separation.
Yes, a great many. We are certain (well, as certain as those things ever are) that "cold" (i.e., non-lava) flows shaped those features on Mars. AFAIK the only alternative under consideration to liquid water being responsible for those flows is mixed gaseous/liquid CO2.
Such a gracious concession is quite a rarity around here! Apologies for my rather confrontational style - I do like hard (though fair) discussions, and poking fun at your post by mirroring it was just too hard to resist... thanks for taking it so well, looking forward to our next bout!:-)
But, as a member of the public, as a taxpayer, I would much rather that they pay for 50 select astronomers, geologists, physicists, engineers, chemists and biologists to come to a conference and ask them what kinds of space missions would be valuable from their perspective.
Good idea. But, as a politician with dropping approval ratings in an election year, I would much rather ask the public on any ideas how I might dazzle them by November...
I think the premise that Bush cares one whit about space science or exploration, whether manned or unmanned, is flawed.
Since you mentioned Aral sea, shall I mention Exxon Valdes and Alaska?
Or the Salton Sea and Laguna Salada, i.e. the Colorado River delta in the Southwestern U.S. Same problems as the Aral really in terms of upstream diversion of water for unsustainable agricultural use, except that here the most affected area is conveniently located south of the border.
you seem to imply that Electric fields are independent from Magnetic fields
I implied no such thing, I merely stated that they are different.
Magnetic fields are produced by charges in motion
Yes, and they also only affect charges in motion.
an "alternating electric field" would create an alternating magnetic field
True, but the proposed mechanisms by which EMF may constitute a health risk (heating, interference with ionic transport, etc.) all center on the electric component of the EMF, for good reason: in contrast to a magnetic field, an electric field can exert a force on stationary charges.
Unless you are habitually whirling around a high voltage line at high speed, the magnetic field component of its EMF is all but irrelevant to you. The very fact that an MRI with its magnetic field many million times stronger doesn't tear you apart illustrates this point. (A comparably strong electric field is called lightning, and that tends to have rather nastier effects on people.)
without empirical evidence, it cannot simply be deduced that they are "bound to be entirely different"
Yes it can. Note the use of "bound to be". It's Occam's Razor: there is no reason to suspect the connection that you postulate, precisely because of the different way in which electric and magnetic fields affect matter. You might as well postulate a connection with sunburn - after all sunlight is also "EM in nature".
An MRI exposes you to brief pulses of a strong, directed magnetic field. The EMF concerns center around continuous exposure to a weak, alternating electric field. On what basis do you expect one to have anything at all to do with the other? Even if both should turn out to have adverse biological effects, the mechanisms involved are bound to be entirely different.
Essentially, we don't guarantee our product works, but you should still pay us for it. Seems to be the philosophy of many software companies...
Indeed. I'm going to have a disclaimer printed on the back of my checks:
NOTE: While I endeavor to provide you with payment for your products and services, I cannot guarantee and do not warrant that any of my checks will clear promptly, or indeed at all. See my credit history for details of my limited ability to pay for purchases.
Is it just me, or didn't the decision to let the Hubble die early seem to come awefully quick after President Bush's policy directive?
Indeed, and I can understand O'Keefe very well. Say you're heading a space agency that's just been given the presidential directive to focus your efforts on his re-election, errr, a mission to Mars that has been estimated to cost on the order of 400B$. To accomplish this, you are given 1B$, and told to find the rest from within your existing budget of 13B$/year. Do you:
a) quietly cancel all those smaller, scientifically important, and already chronically underfunded science missions in order to scrape together a sum that you know just won't be enough anyway, or do you
b) rapidly, publicly, and shockingly cancel the one mission Joe Schmoe has heard of, and might care about enough to cry foul to his congressperson?
See, that wasn't so hard. NASA needs to stand up to undue interference from grandstanding politicians. Good work O'Keefe.
- nic
PS: The other thing he's achieved with this stunt is soliciting public statements to the effect that "it's worth risking lives for space exploration". This is just what NASA needs to get over its current obsession with total safety (which, of course, doesn't exist even here on Earth). Give this guy some credit, he's one smart operator.
Parent is incorrect on several counts, and severely overrated:
distorting effects of gravity on the mirror? dude, what the hell are you talking about? The big selling point of Hubble is not that it it's outside of Earth's gravity, which it is not but rather outside of it's atmosphere. ground based telescopes don't have to worry about being bent out of shape, they need to worry about all the air they have to look through.
They need to worry about *both*. Hubble, while certainly within Earth's gravity well, is in freefall, like anything in orbit, and therefore a zero-gravity environment. Hence there's no mirror sagging due to gravity, which *is* one of the major problems affecting large telescopes on Earth.
Regarding telescopes on the Moon: unlikely. There's no reason to put an optical telescope down a gravity well at all, except for the convenience of astronomers who are already sitting in the same gravity well.
If obsessed environmentalists don't like NASA sending up probes with any radioactive material ('it might blow up, ohh..'), then how did this little tidbit get by them?
Give us "obsessed" environmentalists some credit, 99% of us can differentiate quite well, thank you:
1) Each Mars rover's RTGs contain less than an ounce (8 LWRHUs with 2.67g each) of Pu-238; Pathfinder's a quarter-ounce (3 LWRHUs). nothing you'd like to swallow, indeed: lethal dose for Pu-238 is 30 micrograms inhaled. It's one of the most toxic, mutagenic, and carcinogenic substances known to man. While an ounce of such stuff is not trivial, it pales next to Cassini's load: 10.8 kg (24 pounds) of Pu-238. This should suffice to explain the different level of concern generated by these missions even to cyclopedian dunderheads.
2) As for blowing up, I have some news for you: Challenger. Columbia. NASA's own estimate for the probability of "catastrophic launch failure" of the rocket used to send up Cassini was 1 in 20. Sending things into orbit on top of the world's largest firecrackers is *inherently* unsafe. Might blow up, indeed. Even so, catastrophic launch failure was *not* a major concern: the Pu-238 is embedded in a ceramic matrix, and its container designed to withstand explosion of the launch vehicle. NASA worst-case scenarios were a contaminated launch pad.
3) What *was* cause for concern were the Earth gravity-assist flybys. A navigational error (metric/english conversion, anyone?) could have sent Cassini to burn up in the atmosphere. In the intervening years in space, its own alpha-rays weaken the ceramic matrix to the point where such an accident could release powdered Pu-238. Worst-case scenario for *that* was as much release of Pu-238 as all above-ground nuclear tests, ever, *combined*. Not Armageddon, but a Chernobyl-scale disaster in terms of the number of statistically attributable additional cancer deaths.
4) The concentration of so much lethal potential (300 million doses) in *any* one device of whatever nature raises certain concerns. Pu-238 is *the* material of choice for dirty bombs - 250 times as carcinogenic as the Pu-239 used in nuclear weapons. The RTG requirements of NASA and DoD are the only reason why Pu-238 is produced and stockpiled in the US. A single stolen 150g pellet of Pu-238 could be used to give up to a million people in a chosen location certain lung cancer. Nice terrorist potential there - 9/11 in slow mo. Cassini carried 72 such pellets. I sure hope security around these things is 100%. Wait a minute, there is no such thing as 100% security - doh!
Having said all that, I (environmentalist and all) still think that, for lack of better alternatives, the outer planet missions and the small Martian RTG heaters are worth the risk. IMO NASA actually does quite a good job evaluating these risks for each mission (thus no juiced-up Mars buggy, ever - sorry!), it's the DoD putting RTGs in LEO that worries me.
Finally, to the smartass trolls spewing baseless comments such as "more radioactivity in my backyard", "radiation is radiation", "we tested nukes in the atmosphere in the 50s with no ill effect": 1) you're utterly wrong, 2) think before you post. If thinking is too hard for you, at least google before you post. If googling is too hard for you, shut up and learn something.
Slashdot Mirror
> (and you WOULD NOT want to be there if a large, high-speed spinning
> element broke off of its axis and started ricocheting about the room...)
John Logie Baird had exactly this problem with his invention, it consisted of lenses mounted in a spiral on a spinning wooden disc, people call it television these days.
While Baird's scanning device was extremely cumbersome, there was no instrinsic reason why it could not eventually be miniaturized, given sufficient progress in technology. 3D displays of the type under discussion here have to be able to disperse an incident light beam at arbitrary locations in a large 3D volume. How are you going to accomplish this without large pieces of matter whizzing around that volume at high speed?
Here's the best alternative I can think of: generate a continuous, fine mist of water droplets in your display area. Surround the display area with a ton of red, green, blue, and infrared lasers. Continuously track the position of each and every droplet in the infrared, then for each voxel you need to display, compute a free path to the nearest-floating droplet for a red, a green, and a blue laser, and fire. Repeat at insane speed to render a full 3D scene.
This looks doable in principle, but has the disadvantage that the scene will always appear enveloped in, well, mist. Also, there is no "hidden line removal" - since objects are rendered (literally) using smoke and mirrors, you can see right through them. (By the way, this also applies to the Hitachi device.)
If you have any better idea, I'm sure a lot of powerful people would like to talk with you.
What if our Big Rip is the next universe's Big Bang? Or, to be more more precise, the next universe's inflationary period?
WowWee wants you to obtain the missing 's' by buying two of them.
You can program action sequences that are triggered by sensor events. Looks like just the thing to spook my cat :-)
Just the pendulum instability from the offset between CG and CL is going to drive you bats
But hey, if you just flip that damned thing upside down you almost have a semi-decent hangglider! You'd be flying it lying on your back though, good luck seeing the ground...
Seriously, a jet-powered hangglider would be infinitely cheaper, safer, and more fun to fly.
ObTroll for +5 informative: "Moeve" is German for "gull". Duh!
Hawking thinks that humanity needs to genetically engineer ourselves to pre-emptively keep machines from taking us over.
Well then, call me nuts, too, but I think this is actually a pretty inevitable conclusion once you start thinking of the big picture - say, developments over the next 1000 years or more. Hawkins may be disingenuous in going public with such long-range thoughts, but they are actually very well-founded.
> What NASA really needs is a tool to filter all superlatives from its press releases.
Superlatives are why we are there.
Understood. My suggestion was tongue-in-cheek (though it might make a useful training tool for overexcitable NASA PR flacks). My objection is not to the superlatives per se, but to making trivial superlatives appear like the reason why we go out there. We're not on Mars *in order* to do U-turns there - it's incidental.
It is my opinion (and not necessarily that of NASA) that NASA PR should seek to provide a multi-tier service which caters not merely to the lowest common denominator, but also the the more scientifically inclinded citizens who seek more details.
Amen! This is exactly what I'm missing, thanks for articulating it so well.
My best wishes for the MERs - hope they'll both make it all the way to the bigger craters!
Lowest common denominator attention is better than no attention at all.
That's exactly what I would dispute. I've seen plenty of times how NASA's dumbed-down PR creates misperceptions in the many people who are more intelligent than NASA gives them credit for. These people (say, everyone with a college degree) may not have as many votes as the great unwashed masses, but they constitute the movers & shakers (engineers, politicians, what have you) of today and tomorrow. Their entirely understandable reaction to NASA playing up trivia such as the "first U-turn on another planet" is "WTF - I'm paying taxes for *this*?"
You and I may know that beneath the veneer of hyperbolic baseball stats pumped out by NASA's PR dpeartment lies real, exciting science worth every penny we put into it, but you sure wouldn't know from looking at NASA's press releases, and I'm afraid a great many people who control NASA's budget allocations have no clue of that either. To them the baseball stats *are* the real thing, and therein lies danger.
To give an example, during the live coverage on NASA TV of Spirit's landing, IIRC the airhead commentator was gushing about "the first *ever* pictures from the surface of Mars". Can't they get someone at least minimally knowledgeable as commentator? Such PR blunders are not only a public embarassment, they carry the real risk that some decisionmaker takes exaggerated NASA claims at face value, finds out that they are false, and gets *really* pissed off.
It would be quicker to *download* our existing knowlegde into the tike so that they don't have to re-discover the entire world, pausing and proding everything and everybody. But nature re-invents the OS almost from scratch for every birth so that they are too incompatable to do a direct transfer.
:-)
Good point, but... real geeks *like* to invent their own OSs! That would make God the Ubergeek. I've actually learned a lot by looking at the world through the eyes of a little kid, pausing and prodding everything. The mental equivalent of programming in assembler - takes more time, but gives you a much better understanding of how things work.
PS: gorgeous sunshine here
Anyone who has tried to go for a walk with a 2 or 3 year old kid knows what I'm talking about. You want to walk, but the annoying little brat will stop and examine very carefully every piece of litter, little stone, gravel or mark on the floor. Half way through the whole thing you'll get tired and just go home.
Exploring that piece of litter, stone, gravel, mark on the floor is the whole point of the walk for a little kid. Ditto for the Mars rovers. Our concepts of what a walk should be like do not apply - there is no predetermined itinerary that must be covered, only wide open eyes that want to understand all the marvels that they see.
What sort of over-hyped/overly-specific record is this?
NASA has the unfortunate habit of framing everything in terms of firsts and records, as if space exploration was some sort of spectator sport. I've lost count of how often I've seen the headline "Hubble spies oldest galaxy" - well duh, since Hubble is the only instrument in its class for imaging faint red-shifted objects, I'd be worried if it didn't find a new "oldest known galaxy" every month or so. The current "first sneeze/fart/ping/macarena/kernel panic on another planet" spate of Spirit/Opportunity PR is in the same vein.
Through a PR machinery that caters to the lowest common denominator, NASA systematically undermines the many good reasons we have for exploring space, and thus ends up shooting itself in the foot. If you reduce your own work to a mere set of pointless Guiness Book of Records entries, you shouldn't be surprised if people start to wonder whether it's worth paying billions of dollars for it. What NASA really needs is a tool to filter all superlatives from its press releases.
PS: a NASA TV channel that isn't dumbed down so much would also be nice.
I wonder whether they'll finally be able to (dis)prove the hypothesis that everybody knows everybody else within six (or however many) degrees of separation.
This was first proposed in 1967 by social psychologist Stanley Milgram, (in)famous for his shocking experiments on human obedience, which inspired Peter Gabriel to create the subversive sing-along "We Do What We're Told", a.k.a. "Milgram's 37".
This paragraph brought you by a flock of hyperlinking free associators with Erds number 4.
Yes, a great many. We are certain (well, as certain as those things ever are) that "cold" (i.e., non-lava) flows shaped those features on Mars. AFAIK the only alternative under consideration to liquid water being responsible for those flows is mixed gaseous/liquid CO2.
Such a gracious concession is quite a rarity around here! Apologies for my rather confrontational style - I do like hard (though fair) discussions, and poking fun at your post by mirroring it was just too hard to resist... thanks for taking it so well, looking forward to our next bout! :-)
But, as a member of the public, as a taxpayer, I would much rather that they pay for 50 select astronomers, geologists, physicists, engineers, chemists and biologists to come to a conference and ask them what kinds of space missions would be valuable from their perspective.
Good idea. But, as a politician with dropping approval ratings in an election year, I would much rather ask the public on any ideas how I might dazzle them by November...
I think the premise that Bush cares one whit about space science or exploration, whether manned or unmanned, is flawed.
...blah blah blah COLOR CHART blah blah...
.
/.'s slipshod workings.)
So what do you call this?
Easy and low-tech, and there's only two possible excuses for this not being noticed by FL. .
1. Total incompetence, (which frankly, is entirely possible these days given
2. The convenience of being able to cover up inconvenient facts with bullshit.
Since you mentioned Aral sea, shall I mention Exxon Valdes and Alaska?
Or the Salton Sea and Laguna Salada, i.e. the Colorado River delta in the Southwestern U.S. Same problems as the Aral really in terms of upstream diversion of water for unsustainable agricultural use, except that here the most affected area is conveniently located south of the border.
you seem to imply that Electric fields are independent from Magnetic fields
I implied no such thing, I merely stated that they are different.
Magnetic fields are produced by charges in motion
Yes, and they also only affect charges in motion.
an "alternating electric field" would create an alternating magnetic field
True, but the proposed mechanisms by which EMF may constitute a health risk (heating, interference with ionic transport, etc.) all center on the electric component of the EMF, for good reason: in contrast to a magnetic field, an electric field can exert a force on stationary charges.
Unless you are habitually whirling around a high voltage line at high speed, the magnetic field component of its EMF is all but irrelevant to you. The very fact that an MRI with its magnetic field many million times stronger doesn't tear you apart illustrates this point. (A comparably strong electric field is called lightning, and that tends to have rather nastier effects on people.)
without empirical evidence, it cannot simply be deduced that they are "bound to be entirely different"
Yes it can. Note the use of "bound to be". It's Occam's Razor: there is no reason to suspect the connection that you postulate, precisely because of the different way in which electric and magnetic fields affect matter. You might as well postulate a connection with sunburn - after all sunlight is also "EM in nature".
Alright, once more in slow mo:
An MRI exposes you to brief pulses of a strong, directed magnetic field. The EMF concerns center around continuous exposure to a weak, alternating electric field. On what basis do you expect one to have anything at all to do with the other? Even if both should turn out to have adverse biological effects, the mechanisms involved are bound to be entirely different.
Clear enough for ya?
What about those machines where they put your head into a very strong magnetic field?
electric field != magnetic field
"It's not the bullet that kills you - it's the hole." (Laurie Anderson)
Indeed. I'm going to have a disclaimer printed on the back of my checks:
- nic
Is it just me, or didn't the decision to let the Hubble die early seem to come awefully quick after President Bush's policy directive?
Indeed, and I can understand O'Keefe very well. Say you're heading a space agency that's just been given the presidential directive to focus your efforts on his re-election, errr, a mission to Mars that has been estimated to cost on the order of 400B$. To accomplish this, you are given 1B$, and told to find the rest from within your existing budget of 13B$/year. Do you:
a) quietly cancel all those smaller, scientifically important, and already chronically underfunded science missions in order to scrape together a sum that you know just won't be enough anyway, or do you
b) rapidly, publicly, and shockingly cancel the one mission Joe Schmoe has heard of, and might care about enough to cry foul to his congressperson?
See, that wasn't so hard. NASA needs to stand up to undue interference from grandstanding politicians. Good work O'Keefe.
- nic
PS: The other thing he's achieved with this stunt is soliciting public statements to the effect that "it's worth risking lives for space exploration". This is just what NASA needs to get over its current obsession with total safety (which, of course, doesn't exist even here on Earth). Give this guy some credit, he's one smart operator.
Parent is incorrect on several counts, and severely overrated:
distorting effects of gravity on the mirror? dude, what the hell are you talking about? The big selling point of Hubble is not that it it's outside of Earth's gravity, which it is not but rather outside of it's atmosphere. ground based telescopes don't have to worry about being bent out of shape, they need to worry about all the air they have to look through.
They need to worry about *both*. Hubble, while certainly within Earth's gravity well, is in freefall, like anything in orbit, and therefore a zero-gravity environment. Hence there's no mirror sagging due to gravity, which *is* one of the major problems affecting large telescopes on Earth.
Regarding telescopes on the Moon: unlikely. There's no reason to put an optical telescope down a gravity well at all, except for the convenience of astronomers who are already sitting in the same gravity well.
- nic
If obsessed environmentalists don't like NASA sending up probes with any radioactive material ('it might blow up, ohh..'), then how did this little tidbit get by them?
Give us "obsessed" environmentalists some credit, 99% of us can differentiate quite well, thank you:
1) Each Mars rover's RTGs contain less than an ounce (8 LWRHUs with 2.67g each) of Pu-238; Pathfinder's a quarter-ounce (3 LWRHUs). nothing you'd like to swallow, indeed: lethal dose for Pu-238 is 30 micrograms inhaled. It's one of the most toxic, mutagenic, and carcinogenic substances known to man. While an ounce of such stuff is not trivial, it pales next to Cassini's load: 10.8 kg (24 pounds) of Pu-238. This should suffice to explain the different level of concern generated by these missions even to cyclopedian dunderheads.
2) As for blowing up, I have some news for you: Challenger. Columbia. NASA's own estimate for the probability of "catastrophic launch failure" of the rocket used to send up Cassini was 1 in 20. Sending things into orbit on top of the world's largest firecrackers is *inherently* unsafe. Might blow up, indeed. Even so, catastrophic launch failure was *not* a major concern: the Pu-238 is embedded in a ceramic matrix, and its container designed to withstand explosion of the launch vehicle. NASA worst-case scenarios were a contaminated launch pad.
3) What *was* cause for concern were the Earth gravity-assist flybys. A navigational error (metric/english conversion, anyone?) could have sent Cassini to burn up in the atmosphere. In the intervening years in space, its own alpha-rays weaken the ceramic matrix to the point where such an accident could release powdered Pu-238. Worst-case scenario for *that* was as much release of Pu-238 as all above-ground nuclear tests, ever, *combined*. Not Armageddon, but a Chernobyl-scale disaster in terms of the number of statistically attributable additional cancer deaths.
4) The concentration of so much lethal potential (300 million doses) in *any* one device of whatever nature raises certain concerns. Pu-238 is *the* material of choice for dirty bombs - 250 times as carcinogenic as the Pu-239 used in nuclear weapons. The RTG requirements of NASA and DoD are the only reason why Pu-238 is produced and stockpiled in the US. A single stolen 150g pellet of Pu-238 could be used to give up to a million people in a chosen location certain lung cancer. Nice terrorist potential there - 9/11 in slow mo. Cassini carried 72 such pellets. I sure hope security around these things is 100%. Wait a minute, there is no such thing as 100% security - doh!
Having said all that, I (environmentalist and all) still think that, for lack of better alternatives, the outer planet missions and the small Martian RTG heaters are worth the risk. IMO NASA actually does quite a good job evaluating these risks for each mission (thus no juiced-up Mars buggy, ever - sorry!), it's the DoD putting RTGs in LEO that worries me.
Finally, to the smartass trolls spewing baseless comments such as "more radioactivity in my backyard", "radiation is radiation", "we tested nukes in the atmosphere in the 50s with no ill effect": 1) you're utterly wrong, 2) think before you post. If thinking is too hard for you, at least google before you post. If googling is too hard for you, shut up and learn something.
- nic