InigoMontoya

One comment on flywheels... By the time you get one large/fast enough to store significant quantities of energy (like, for a 100 mile trip), you now have one hell of an interesting problem when it comes to the handling of your automobile. The gyroscopic forces are going to be significant. What's going to happen when you try to drive on an inclined/crowned/etc. road?

While there's always the possibility of serious injuries when you start playing with compressed gases, I've known several idiotic people who've managed to have 2 liter soda bottles explode in their hands. Bruising and very minor cuts are the only injuries I've heard reported.

I just wanna know how you get the raw egg in the 2 liter water bottle. edit: Oh, and what do you mean by "water powered"? The last time I checked, water is not a viable power source (although it can function as a power transmission medium).

And today I stumbled across a link the OP might appreciate.... http://www.planetsolar.org/

Within the bounds of your question, I've no idea. You're obviously interested in body armor and (I'm guessing) secondary fragments. Back when I played with armor I was interested in... Let's just say "larger systems and higher energy events" and leave it at that. The point being that my experience was far enough outside your parameters I simply have no gut feel for it. That said, you do have a well bounded problem at low energy levels. Things should scale pretty nicely. I've no idea what your table will look like but I believe such a table could be made. One thing to beware of... If I'm right about your interest being secondary fragments, you need to be aware that geometry will matter. By that I mean: Suppose you have a cube coming at you. Whether that cube hits face first, edge first, or corner first will matter. Extrapolate that statement as required.

And yet, there are a lot of folks out there with zero or one child. So... Those who are in that boat who also advocate population reduction are crazy? Huh. Who knew?

Only if somebody actually makes significant progress towards building them. A paper study isn't progress. It's just that: a paper study. If people can play in the freeway, why shouldn't they do so? Not to compare building such structures with playing in the freeway, but rather to point out the problem with that logic. There's nothing *wrong* with it, per se. I just don't see it happening. You're a family who's soon to be homeless due to the ocean rising. Do you spend your life's savings on getting a cabin on the Lilypad or do you spend half of that and simply move inland? Sure, a *few* people will opt for the Lilypad, but I'll wager that the numbers of people willing to do that will be small at best. Or if you prefer the big picture... You're a politician. Do you spend $100M building a Lilypad for 1,000 people to live on, or do you spend $100M building a land-based community for 2,000 people to live on? Are you prepared to explain to the 1,000 homeless people why you spent all the money on a boat? I already gave you my answer (that low-tech, simple migration is a better answer to the stated problem). Not that damned hard to determine. And heck, you really don't *have* to. In a word? Venice. Nobody's talking about oceans rising hundreds of feet in the foreseeable future. A quick wiki indicates that the worst case scenarios have the ocean rising less than 10'. 10 feet! Sure, some places (like Florida) will have a big problem, but the vast majority of the world? Not so much. The Santa Monica Pier goes away, but Los Angeles as a whole would be largely unaffected....

Is that a serious question? Very few ventures out there are set out upon with the goal of driving engineering progress. Or progress of any kind, really. Ventures tend to be started to accomplish a pragmatic goal. If that goal requires engineering progress, well then, so be it. But if it doesn't... Well, then it doesn't. That said... The goal of the lilypad structures as stated in the article is to provide a home for people displaced by rising oceans as a result of global warming. If that is the goal, I say that they're going to spend waaaaaay more money than is required to accomplish the goal. And I'm sure I'm not the only person to see this. Result? If that's the goal, it ain't gonna happen.

Prediction: For all the money spent on such a system you could just as easily create a city on some currently uninhabited chunk of shoreline that would house twice as many people....And with a lot fewer maintenance issues. Opinion: Looks cool and a scaled down version might make for a very cool resort... But as an honest to goodness city? No way.

[D'oh! Posted in wrong thread! Moderators, feel free to delete.]

It's not that easy. Hardness of the projectile matters. Mass of the projectile matters. Sectional density of the projectile matters. Velocity of the projectile matters. LOTS of variables here. And I don't just mean in the "mass and velocity determine energy" way. As one who used to play with armor for a living... I've seen light weight but very high energy projectiles fail to penetrate armor that was easily penetrated by much heaver but much lower energy projectiles. Energy is important. Yes. But so is momentum. Also note that differing velocities may yield different failure mechanics in your titanium plate which in turn affects deformation. Blah blah blah. The point is that you're going to need to narrow the scope of your question to get a meaningful answer.

I'll bite... What makes the tower awesome?

No, my frustration is based on your apparent complete lack of understanding regarding the concept of limiting factors of population and how that applies to the long term. Contrary to your belief, it is YOU who are looking at short term populations. You say, "Lets ignore natural resources" but that very assumption is utterly asinine. Without limitations there's no point in having a conversation regarding population growth. Might as well have a conversation about automobile gas mileage but then assume that all cars have Mr. Fusion as their power source; not gas. So... let me try this again.... POPULATION SANS EMIGRATION 1) Population grows at X%. 2) After LongTime years the population reaches BigNumber. 3) At BigNumber, the population stabilizes simply because you can't feed any more (any additional people starve to death). POPULATION WITH EMIGRATION 1) Population grows at (X-x)% 2) After LongTime+MoreTime years the population reaches BigNumber. Yes, the very same BigNumber mentioned previously. 3) At BigNumber, the population stabilizes simply because you can't feed any more people (any additional people starve to death). When you're say that I'm looking short term and you're looking term you're focusing in on step 2. What you're completely failing to realize is that BigNumber for BOTH processes is the same. Short term? Yeah, there's going to be some differences (very small, but yes, differences). Long term? Nope... The population will stabilize at BigNumber. Period.

[nevermind]

So the population of Africa has gone nuts since 1900. I'd wager that this is primarily due to the industrial revolution and modern medicine hitting the area rather than things returning back to normal. The slave trade (as an international trade) ended in 1853. What did the population of Africa due between 1850 and 1900? That would give you a better indicator of what effects emigration had on Africa's population. No, I can not. Can you? I would guess, however, that the population of Africa as a closed system would be LESS than it currently stands. After all, the other continents sure seem to ship an awful lot of food that direction. I don't even have the words to express my gut reaction to this statement.... I'm out.

Disagree. I think that even without the massive and forced emigration of the 1500-1800 timeframe (ie, the slave trade) that the population of Africa would be about... 1 billion give or take. Why? In a word: Malaria. Increased population would force more people into the "less desirable" areas of Africa. Result: Malaria, Sleeping Sickness, the Guinea Worm, and other diseases endemic to the area absolutely ravage these populations and... Voila, population remains largely unchanged. But you *can't* just leave out limiting factors. You can argue about the mechanisms or numbers of the limits, but you can't just assume that there are no limiting factors when discussing population growth. I mean, throw out limiting factors and the whole discussion of population growth and control becomes a moot point. Sure, but is it a meaningful delay? At the rates we're talking about, even with the "500 times current NASA" rate I was discussing earlier you're dealing with stuff like.... "The Earth will hit 8 billion people on Jan 1, 2020." vs. "The Earth will hit 8 billion people on Jan 2, 2020." Was there a delay? Yes. Was it meaningful? I would say not.

Fair enough, but I disagree with your premise. Just because 50 billion people are off-Earth doesn't mean that you're preventing an Earth-based population of 100 billion people. To do so assumes that food supply and such are sufficient for 100B people. Note: Whether Earth could or couldn't support any specific number is largely irrelevant here. Adjust the numbers up or down for your personal bias on what population the Earth will support. The point is that Earth's resources are finite and sooner or later you're going to run into a wall. At that point in time, it won't matter if there are 50B people living on Mars. You could birth 100B more people on Mars and it won't have an effect on Earth's - for lack of a better term - potential population because even if all those people were suddenly teleported to Earth they would all promptly starve to death and Earth's population would remain static. Hmmmm... Soilent Green, anyone?

No. There's this thing called the 2nd Law of Thermodynamics. However... Regenerative braking is a nice thing to have on electric vehicles....

You stated... "Similarly, if thousands of years from now humans are being born somewhere other than earth, I think it would be fair to say that space exploration contributed to a reduced population on earth." ...Emphasis is mine. I'm using the term "population control" as has been used since early in this thread. You're using the term "reduced population on Earth." Given the context of the greater thread, I view the two phrases in quotes as equivelent. If you don't, then I have no idea what you're trying to say.

OK... You're going to sit there and tell me that the removal of 1,000 people out of a global population of 6,000,000,000 people - not even 1 person in a million - fits any reasonable definition of population control? In my book that's the very definition of a distorted, and exaggerated position. You state that the death of insignificant numbers of people represent a "future population" and that's a valid point... to an extent. The problem with it is that it lacks context. Suppose that population of 1,000 people doubles every 20 years. In 100 year's you'll end up with 32,000 people. Wow, that's a lot, isn't it? No, not really... Because while those 1,000 people were doing their thing the rest of the 6,000,000,000 were doing theirs' as well. Double 6,000,000,000 every 20 years and you end up with 192,000,000,000 people. You can make similar comparisons for any length of time you like. The fact remains that those 32,000 people aren't even a drop in the bucket compared to 192,000,000,000 people. But let's put the ball back in your court. The discussion is whether or not space exploration would result in meaningful population control. Let's say that "meaningful" population control means nothing more than preventing 1% of the potential births out there. 1%. Mind you, that's not population control in the big picture; it's merely one tiny piece of a 100 piece puzzle. Surely that's not too difficult. All it takes is a national priority, right? OK... So you need to send 700,000 per year to somewhere out there.... Let's see your version of the numbers. How do you propose to do it? edit: Ooops, put 7,000,000 instead of 700,000. Mea culpa. Fixed.

Do you consider drunk driving effective population control? A quick google indicates that approximately 12,000 people per year die from DUI-related accidents in the US. That's on the order of 500X as many deaths in the US alone as the entire world sends up as astronauts each year. The point being that even if NASA turned around and sent up 500 TIMES AS MANY MANNED SPACE MISSIONS you still wouldn't be reducing the population in any meaningful way. Or put another way, you'd be sending up as many as 3 SPACE SHUTTLES EVERY SINGLE DAY and you still wouldn't be making any more of a dent than drunk drivers do. To put it in monetary perspective, NASA's 2010 budget (at least, according to wikipedia) was 18.7 billion dollars. Multiply that times 500? You're talking over 9 TRILLION DOLLARS and you're still not doing anything significant. It's not a matter of politics. It's a matter of sheer numbers. There are simply too many people in the world for the space program of any nation to keep up... Even if that nation were to declare the space program to be it's #1 priority! As for what *I* recommend for population control? Exactly that. Population control. Best example to date? China's "one child" policy. It's relatively inexpensive and effective. True, it won't fly in the US (at least, not for a long time) but I see it as the best option. What do I think will *actually* happen? A global famine. One year or another there will be a simultaneous drought that will hit multiple "bread basket" regions of the world. Whammo. A billion or two people will die of starvation, and the world's economy will be in ruins for a generation. The point was that if you want to call an activity that only removes statistically insignificant numbers of people from the Earth "population control" you're playing semantics games and being deliberately obtuse at best.

By that definition, the game of Football is a great population control tool. I mean, after all, from time to time people do die playing it. And I think that along those same lines, sandpaper is a great way to carve a tunnel through 2 miles of solid granite. After all, it does remove rock.

No, you really don't get it. Space exploration is - and always will be - such a fringe activity that it will have less of an impact on global population than the weather does. One heat wave or cold snap in Europe is responsible for removing more people from Earth than the space program has in 50 years (even assuming that those who went up never came down). Simply making drinking and driving totally legal would do MUCH MUCH MUCH more to curb population growth. Space exploration and population control simply shouldn't be mentioned in the same sentence.

It's relevant to my day job. Suffice to say that pic was taken in my office.

If you're not going to store the hydrogen, you'd be a fool to create it in the first place. Just feed that solar energy directly into an electric motor. One thing to keep in mind.... Sailing is quite possibly the oldest form of transportation still in common use(*). Over the *thousands* of years many, many people much smarter than you or I have done everything they could to improve upon the state of the art. Thus, I imagine sailing as one of the most mature arts out there. As such, making dramatic improvements is not likely to be easy. (*) The only form that I can imagine that compares is horseback riding, but how often is it still used as actual transportation rather than mere recreation anymore? A debatable point, I concede. Thus, this footnote.