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Comment Re:seriously? (Score 1) 71

Are the other variants more dialectal? In addition to huoji ( / ) (fire chicken) what I read states that there's also qimianniao ( / ) (seven-faced bird), tujinji ( / ) (cough up a brocade chicken) and tushouji ( / ) (cough up a ribbon chicken)

(hope Slashdot doesn't mess up the characters)

Comment Re:seriously? (Score 1) 71

On the other hand I would want to talk to Archimedes

You speak ancient Greek and can communicate with the dead? Okay, I'm impressed. ;)

Thanksgiving trivia for the day: the word for "turkey" comes from extensive and long-running confusion about where the bird came from. For example, in English it's called Turkey. In Turkey it's called "hindi", referring to India. In India it's called Peru. In Peru it's called "pavo", referring to peacocks, which are native to south and southeast asia, such as India (cyclic there), Cambodia, Malaysia, etc. In Cambodia (Khmer) it's called "moan barang", meaning "French chicken", while in Malaysia it's referred to as "ayam belanda", meaning "Dutch chicken". Both of those in turn think it comes from India: in French it's called "dinde" (from "poulet d’Inde", aka "chicken of India"), while in Dutch it's "kalkoen", referring to a place in India. Greek has a number of local dialectal names, such as misírka, meaning "egyptian bird", while in Egypt it's called dk rm, meaning the Greek bird (even though the latter part of the name derives from Rome - the Italians, by the way, thinking it comes from India). One variant of Arabic even credits it to Ethiopia.

A couple languages deserve special credit for their words:

Best accuracy: Miami indian - nalaaohki pileewa, meaning "native fowl"
Worst accuracy: A tie between Albanian (gjel deti, "sea rooster"); Tamil (vaan kozhi, "sky chicken"); and Swahili (bata mzinga, "the great duck")
Most creative: Mandarin - many names with meanings such as "cough up a ribbon chicken" and "seven-faced bird"
Least creative: Blackfoot: ómahksipi'kssíí, meaning "big bird". Hmm...

Comment Re:The guy aint no Sagan... (Score 1) 294

Except that your cost examples are based around the price of rocks brought back as a "oh and we're going to do this too" mission add-on. It would be like as if I flew to America to visit my grandmother for Christmas via purchasing a $700 plane ticket and while I was there I bought a $15 sweater and brought it back, and you said, "See, she paid $715 to go to America and buy a sweater - American sweaters are unjustifiably expensive!" You simply cannot take the cost of the Apollo mission, divide by the mass of rocks returned, and pretend that that's anything even remotely close to the cost of retrieval per gram.

What's the actual cost of space mining? It's too early to say. But the mining of NEOs could be as little as *zero* dollars per gram (excluding capital costs and maintenance), insomuch as it would be possible to fire sintered minerals (using solar power) via a coilgun onto an aerocapture trajectory. You don't actually have to have a rocket to bring them back. What would the capital costs be like? That we don't know - again, it's too early to say. But it's normal for large mines on Earth to cost billions of dollars, and what one can do with a large mine on Earth one could do with a vastly smaller mine on a NEO due to the superb mineral concentrations on some of them. There are a number of peer-reviewed papers putting forth that it could work out to be economical (I was reading one from the USGS just the other day) as a result of this.

But time will tell. It's going to take a lot more basic research and engineering before we can get a good sense of just what it would cost to get what sort of throughput of what sort of minerals.

Comment Another useful vacuum tube: Thermionic converter. (Score 1) 94

Another vacuum tube technology with current applications and substantial advantages over semiconductor approaches to the same problems is the Thermionic Converter. This is a vacuum-tube technology heat engine that turns temperature differences into electric power - by boiling electrons off a hot electrode and collecting them, at a somewhat more negative voltage (like 0.5 to 1 volt), at a cooler electrode.

Semiconductor approaches such as the Peltier Cell tend to be limited in operating temperature due to the materials involved, and lose a major fraction of the available power to non-power-producing heat conduction from the hot to the cold side of the device. Thermionic converters, by contrast are vacuum devices, and inherently insulating (with the heat conducted almost entirely by the working electrons, where it is doing the generation, or parasitic infrared radiation, which can be reflected rater than absorbed at the cold side.) They work very well at temperatures of a couple thousand degrees, a good match to combustion, point-focused solar, and nuclear thermal sources.

Thermionic converters have been the subject to recent improvements, such as graphine electrodes. The power density limitation of space charge has been solved, by using a "control grid" to encourage to charge to move along from the emitter to the collector and magnetic fields to guide it (so it doesn't discharge the control grid and waste the power used to charge it).

Current thermionic technology can convert better than 30% of the available thermal energy to electrical power and achieves power densities in the ballpark of a kilowatt per 100 square cm (i.e. a disk about 4 1/2 inches in diameter). That's a reasonably respectable carnot engine. This makes it very useful for things like topping cycles in steam plants: You run it with the flame against the hot side so it is at the combustion temperature, and the "cold" side at the temperature of the superheated steam for your steam cycle. Rather than wasting the energy of that temperature drop (as you would with a pure steam cycle) you collect about a third of it as electricity.

It also beats the efficiency of currently available solar cell technology (and the 33.4% Shockleyâ"Queisser theoretical limit for single-junction cells), if you don't mind mounting it on a sun-tracker. Not only that, but you can capture the "waste heat" at a useful temperature without substantial impairment to the electrical generation or heat collection, and thus use the same surface area for both generation and solar heating. (Doing this with semiconductor solar cells doesn't work well, because they become far less efficient when running a couple tens of degrees above room temparature.)

Comment Re:Space-based Economy (Score 2) 294

As usual, "pop science" news overstated the case. We know that there's ppm quantities of water in most lunar regolith, but that's not what people usually talk about. There's also a good degree of confidence that there's a lot of *hydroxyl* group in a lot of places on the moon. But the connection between that and the group being specifically water is much weaker - and many missions sent to detect water in likely areas have failed. The best evidence for water have come from Chandrayaan and LRO, examining craters that were considered likely to find ice. They have both failed to find "slabs" of ice in the crater, but found evidence for ice grains in the regolith - about 5% according to LRO. On Earth that would be considered dry soil, but it's something at least.

Of course, if you're constraining yourself to such craters, you're really constraining where you can go. On the general lunar surface, the sun bakes water out of the regolith.

Iron, aluminum, and titanium are very useful for making things

They're all tightly locked up as oxides, without the raw materials that we use to refine them on Earth being available. There are however tiny grains of raw iron in the regolith, so there is some potential to comb it out magnetically. Still, asteroids present by far better resource options in much greater concentrations.

There really is just no reason to do your work in a gravity well as deep as the moon's, and then have to break out of it, when you can just mine NEOs. Yes, it's "half the gravity of Mars", but it's vastly more than asteroids. Rockets with a couple thousand spare m/s delta-V don't just grow on lunar trees.

Comment Re:Space-based Economy (Score 1) 294

The moon's surface is kind of boring, as far as geology goes. Aluminum oxide, titanium oxide, iron oxide, silicon dioxide... by and large it's stuff that's really common on Earth. And not much of the common stuff that's super-useful, like water. And really, it's way more of a gravity well than is ideal to have.

Comment Re:Cost of access is key. (Score 1) 294

No no, we can get much more than a 1-2% improvement in chemical rocket performance. The issue is that for our needs thusfar (large objects to LEO and GEO, small objects further out with long transit times and gravity assists or ion propulsion), H2/O2 has been fine and it's not been worth all of the headaches of more energy dense fuel mixtures, like Li-(LF2|FLOX|OF2)-LH2 triprop. But we can indeed get a 25% improvement in ISP if we're willing to work with very hazardous, toxic chemicals (at least the resultant LiF isn't as toxic as F2!). It was already done in a lab-scale development back in the late 1960s. And let's not kid ourself, NASA has indeed launched successful missions using toxic, corrosive and dangerous chemicals as propellants. But this would be a new upper bound in this regard. I doubt they'd ever use a propellant like that on a lower stage, but for an upper stage or a return stage... it's a possibility.

Without invoking significant toxicity we can improve the picture somewhat. Burning the lithium with O2 (and of course H2 for exhaust flow reasons) is also a very high energy propellant, but it still means working with metallic lithium in some form or another (liquid, hybrid, slurry, cryosolid, etc), which most people would really like to avoid. But it is possible to do.

A small boost to H2/O2 can be made with aluminum - it only boosts the Isp a few percent (I believe about 4%-ish, though I'd have to double check), but it also gives a nice secondary bonus of really increasing your propellant density. Aluminum is neither dangerous nor toxic, but burning it with the H2/O2, and in a reliable manner, hasn't been tackled yet.

Boron is another high-energy compound one can use. As is beryllium (Be-F2-H2 is even more powerful than Li-F2-H2 by a small margin), but it's hugely expensive and extremely toxic in dust form.

Beyond all of the "familiar" stuff there's a lot of research on more exotic compounds with strained chemical bonds which remain in a metastable state until burned; there's way too many such compounds to list here. But at present they all generally suffer from either production cost issues or problematic instabilities.

Oh, and you can also improve performance by increasing the chamber pressure. That said, it's rather modest - if I recall a doubling of chamber pressure is usually on the order of a 7% ISP boost. But it does mean that advances in material technologies can translate to advances in rocket ISP. And there's also a wide range of other modifications to engine design that could boost rocket ISP to lesser extents.

Comment Re:Cost of access is key. (Score 1) 294

Staging works pretty well to get around the energy density problem, at least early on.. though the rocket equation starts getting pretty tyrranical when it comes to returns from other planetary bodies. It's really hard to conceive of a manned Mars mission with return that doesn't involve at least the return ascent stage being fueled by one of the following:

1) In-situ propellant production
2) Extreme-ISP chemical propellant
3) Nuclear thermal

You can't rely on ion propulsion (even higher power variants like VASIMR) to get you off the ground. Nuclear thermal (1) should work (NERVA showed promise), but the development costs will be huge and it'd face massive public opposition, having that much nuclear fuel on a single craft. It also puts a rather large minimum size for your ascent stage - fission doesn't scale down well, and even as big as it was NERVA only had a thrust to weight ratio of 3 to 4. And the mass of that large, heavy ascent stage imposes significant mass penalties on your earlier stages, partially negating the benefit of that 800-1100 sec ISP.

For more advanced chemicals (2), there's lots of theoretical stuff, but with stuff that we could do today for a practical cost, it'd probably pretty much have to be some variant of lithium/fluorine/hydrogen triprop. The oxidizer could be LF, FLOX, OF2, or a couple other possibilities... but if you want an ISP(vac) from chemical propellants in 500-550 range and good density, that's pretty much what you have to do (yes, the LM and CSM used toxic, corrosive, dangerous propellants too, and NASA managed fine, but these are even worse). And even still, 500-550 sec is low enough that you'd probably still want some sort of ion "tug" cycler to move you between LEO and LMO, with your fuel only used for ascent.

If you don't want to or can't do either of those two options (#2 and #3), you're pretty much stuck with in-situ production (unless you want to have to launch a LOT of tonnage into orbit!) Which is why that's SpaceX's focus... it probably is the best option. Still, though, it's a challenge and a risk, no question.

Comment Re:Many a young engineer.... (Score 2) 94

... every schematic drawn by every semiconductor engineer got the arrow backwards.

As I heard it, The arrow is "backward" because Benjamin Franklin, when doing his work unifying "vitreous" and "resinous" electricity as surplus and deficit of a single charge carrier (and identifying the "electrical pressure" later named "voltage"), took a guess at which corresponded to a surplus of a movable charge carrier. He had a 50% chance to assign "positive" to the TYPICAL moving charge carrier in the situations being experimented with (charge transfer by friction between different substances, currents in metallic conductors, and high voltage discharges in air and water-in-air aerosols) and happened to guess "wrong".

Thus we say electrons have a negative charge, "classical current" corresponds to the sum of the flow of moving positive charge minus the flow of negative charge (i.e. the negative of the electron current, which is all there is in normal-matter metallic conductors), the arrowhead on diodes (and junction transistors) points in the direction of classical current across a junction, and so on.

But though it's the charge carrier in metallic conduction and (hard) vacuum tubes, the electron ISN'T the only charge carrier. Even in the above list of phenomena, positive ion flow is a substantial part of electrical discharge currents in air - static sparks and lightning. Positive moving charge carriers are substantial contributors to current as you get to other plasma phenomena and technologies - gas-filled "vacuum" tubes (such as thyratons), gas an LIQUID filled "vacuum" tubes (ignatrons), gas discharge lighting, arc lighting, arc welding, prototype nuclear fusion reactors, ...

Move on to electrochemistry and ALL the charge carriers are ions - atoms or molecular groups with an unequal electron and proton count, and thus a net charge - which may be either positive or negative (and you're usually working wit a mix of both).

And then there's semiconductors, where you have both electrons and "holes" participating in metallic conduction. Yes, you can argue that hole propagation is actually electron movement. But holes act like a coherent physical entity in SO many ways that it's easier to treat them as charge carriers in their own right, with their own properties, than to drill down to the electron hops that underlie them. For starters, they're the only entity in "hole current" that maintains a long-term association with the movement of a bit of charge - any given electron is only involved in a single hop, while the hole exists from its creation (by an electron being ejected from a place in the semiconductor that an electron should be, by doping or excitation, leaving a hole) to their destruction (by a free electron falling into them and releasing the energy of electron-hole-pair separation). They move around - like a charge carrier with a very short (like usually just to the next atom of the solid material) mean free path.

For me the big tell is that they participate in the Hall Effect just as if they were a positive charge carrier being deflected by a magnetic field. The hall voltage tells you the difference between the fraction of the current carried by electrons excited into a conduction band and that carried by holes - whether you think of them as actual moving positive charge carriers or a coordinated hopping phenomenon among electrons that are still in a lower energy state. Further, much of interesting semiconductor behavior is mediated by whether electrons or holes are the "majority carrier" in a given region - exactly what the hall effect tells you about it.

So, as with many engineering phenomena, the sign for charge and current is arbitrary, and there are both real and virtual current carriers with positive charge. Saying "they got it wrong" when classical current is the reverse of electron current is just metallic/thermionic conduction chauvinism. B

Comment Re:Affirmative Action won't take us to Mars. (Score 1) 294

I think his job is more "ticking large numbers of people off". For example, he was one of the leaders behind the "Pluto, Eris, Ceres, etc aren't planets" movement - he had references to Pluto being a planet removed from the Hayden Planetarium years before the IAU vote. He's not exactly popular among those who felt that hydrostatic equilibrium was the relevant constraint and that the "cleared the neighborhood" definition is fundamentally flawed.

Comment Re:The guy aint no Sagan... (Score 1) 294

Which is silly, because the Apollo mission was primarily oriented around the physics of getting a bunch of large mammals into space, keeping them alive on the way to the moon, landing them on the moon, keeping them alive down there while they explore, and then doing all of that in reverse. If they hadn't brought a single rock back the total change to the mission cost would have been almost unnoticeable.

Furthermore, who's focused on mining the moon? Most mining proposals focus on mining NEOs. It's way easier to get material from a NEO to Earth aerocapture. You could do it with a coilgun with no expenditure of consumables, again and again for years on end. They're also far more rich in interesting materials - much better than the best mines on Earth, and with no overburden.

Take your work seriously but never take yourself seriously; and do not take what happens either to yourself or your work seriously. -- Booth Tarkington