Am I the only one here who, whenever they encounter this pre-teen version of profanity as in the above post, read it literally, as if the person was talking about bundles of wood, literal hats for asses, and donkeys going crazy next to bull shit?
But my analogy is this. Say that you're a pearl diver. You're browsing along a dive forum one day and see a picture from someone on their vacation to a remote tropical island holding a large, rare pearl that they found on a dive. You ask them where they found it, and they tell you they only did one dive and found it in waters of about 15 meter depth off the shore. Wanting to find many of these such pearls, you head out to the island. Now, you have two approaches you could take.
1. Spend a long time carefully doing a geological survey of the water depth around all of the shores of the island. Then do your dives in order of which are most precisely 15 meters deep, regardless of how convenient they are to access. Only move on to areas that are any more or any less than exactly 15 meters deep when you've exhausted all of the known 15-meter depth areas.
2. Go out and start diving wherever the water looks to be at least in the right ballpark of 15 meters depth. Start with the most convenient areas first. Don't obsess over the exact depth - exploring some 10 meter areas, some 20 meter areas, etc, just trying to keep it roughly in the ballpark of 15 meters. Because hey, for all you know, more than 15 meters or less than 15 meters might be an even better diving depth; you've only got one datapoint so far.
Which makes more sense? #2, obviously. Which is the same strategy we should be using with exoplanets in the search for life. We should be "favoring" Earthlike planets, but not obsessing over earthlike-ness in the search. We should be checking out a diverse range that is only "centered" on Earthlike bodies. And we should be focusing on those which lend themselves to easier, more detailed observation first, such as those closer to us and with a more favorable orbital alignment.
I have no clue where you're coming from. You rightly point out that life takes energy, but then proceed to consider internal sources of energy as worthless, when in reality in the universe far more things are exposed to internal energy than external. And radioactive decay-driven energy sources are only one. For example, Encelaldus's heat seems to be driven by the serpentization of rock, which also releases hydrogen, a potential food source to microorganisms. There are numerous chemical means which can release vast amounts of energy - yes, nuclear energy is many orders of magnitude more dense, but non-radioactive elements are also orders of magnitude more common.
Anywhere that there is heat and fluids (or solids that can undergo solid-state convection) can experience that heat being turned into harvestable forms of chemical energy, because chemical equilibriums are different at different temperatures. For example, at STP conditions, N2 + O2 is favorable, while at high temperatures NO2 is more favorable. N2 + O2 that goes to higher temperatures and forms NO2, which then comes back down to the lower atmosphere, is bringing a source of chemical energy with it.
Since heat differentials can and will be readily converted to chemical energy wherever it's associated with convection of any variety, then any source of heat is a fuel for life - and heat most definitely doesn't only come from nuclear decay - or chemical reactions. It comes also from the rebalancing of layers to a lower gravitational equipotential. It comes from impacts. It comes from tidal heating. It comes from thermal cycling in elongated orbits. It comes from mass loss due to solar wind exposure. There's a vast range of potential heating sources in the universe that can create heat differentials. And heat differentials make exploitable chemical reactions.
You make blind assertions that "these environments wouldn't be likely because of their composition". What do you know about this? You have a sample size of one of chemical processes that have created life. We can't even see deep into our own world to see what other alternatives might exist at higher pressures, let alone in other worlds. Heck, underground doesn't even mean particularly high pressures. Dwarf planets can have Earth-surface pressures at hundreds of meters or even kilometers depth. And life on Earth exists fine in the deep sea, wherever there's energy to support it, where pressures are at over 1000 atmospheres
Deep environments might prove even more prone to organic chemistry. In general, pressure is usually associated with faster reaction rates. You also often have more complex arrangements of possible chemical phases for each compound at higher pressures than with lower pressures. Water for example over its possible temperature range at a particular depth might have 3-5 potential ice phases, a liquid phase, a supercritical fluid phase, and a gas phase. This leads to a much greater range of possibilities for reactions to potentially exploit, because each chemical in each of its phases has the potential it interact with each other chemical in each of its other phases, or in the case of non-metastable forms, at least many of its other phases.
Common theories for the origin of life on Earth usually assume that it wasn't the sun that powered the first forms of life, even though that's the most convenient source of energy on our planet. Photosynthesis is much more complicated than most forms of chemosynthesis. Environments like black smokers, volcanic pools or acidic waters within deep iron-rich minerals seem like far more likely candidates.
Intelligence evolving within creatures that live in liquids? Oh, we've never seen that before!;) Except, of course, for the fact that the second-most intelligent category of mammals are aquatic (cetaceans), and the most intelligent invertebrates (mollusks) live there too. Rather, the oceans tend to be highly competitive environments, and thus good breeding grounds for intelligence.
I think it's silly in the regards that we have precisely one datapoint about the sort of environments in which life may exist, which is pretty terrible in terms of making any sort of definitive statement. I'd much rather they keep their options open, check out a wide range of environments, and just look for signs of "things that are hard to explain", whatever they may be. "Hmm, this body has both a strong oxidizer and a strong reducing agent in its atmosphere - how is that happening?"
I'm not saying "check planets in random order" or anything of that nature. Just that I don't think it's critical to obsess over being sure to examine them in order of "earthishness" from highest to lowest. We need to be looking at a diversity of worlds.
Heck, we don't even know whether the surface of a body is the best place to look, most life in the universe might be in sub-crustal layers for all we know. Certainly would partially help explain the Fermi paradox, if it were such that we rare "surface dwellers" have a far easier route to the cosmos than something that needs to be under gigapascals of pressure to survive and whose radiating transmissions, if any, would be blocked by their planet's crust.
Re:The movie was good because the book was short.
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Review: The Martian
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· Score: 0
If you want to keep "doing the math" and if you want to be called "hard sci fi", you need to do the math right. You can't say that because you've got 50 liters of oxygen that you're going to get 100 liters of water because O2 + 2 H2 = 2 H2O. Yet Weir does exactly that, over and over and over again, mixing up moles, liters, and kilograms. One of dozens of categories of huge fundamental science mistakes that he keeps repeating.
Re:The movie was good because the book was short.
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Review: The Martian
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· Score: 0
I'm sorry, I missed out where "accuracy" and "popularity" became interchangeable terms. I was responding to a post talking about the book's amazing scientific accuracy, when in reality it's a veritable MST3K of glaring science errors on almost every page. Or at least glaring to anyone who knows anything about the scientific fields involved.
At least with "soft" sci-fi where they don't try to explain how everything works you only get hit over the head with science problems whenever they describe a situation that's literally impossible. With bad pseudo-hard-sci-fi you get hit over the head with it again and again.
First, 1KW light output is if you want Earth's equatorial sunlight, which is far more than plants need - they saturate their input at far less than that.
Yes, one has to incorporate a "capacity factor" to account for angles, night and clouds. Something like 15% would be typical for potato-growing regions. But at the same time, when light is coming from LED lighting, you have to account for stray lighting (light that's not hitting your grow area) and efficiencies at generating PAR, which are 20-30% for proper grow lights, lower for normal room lights (as the phosphor wastes part of the light energy to make it a comfortable white rather than a painful pink). The two issues roughly cancel themselves out. You need in the ballpark of 1kW per square meter of electricity input to match normal potato growing conditions.
I arrived at 500W (input) of LEDs to produce the needed output for 1m^2
For 24-7 lighting, that's 50% of my above, but let's go with it.
, and about 2.5m^2 of solar panels to power them up.
Not even close. Your solar array too has a capacity factor - in the ballpark of 15% if fixed, maybe 35% or so if tracking. Then you have your panel efficiencies. The best large scale commercial panels are 22-23% efficiency. You might get 30%-ish if you used absurdly-crazy-expensive spectrolab cells. Then factor in dust constantly settling on the panels - say 25% loss even with regular cleaning. And Mars's solar constant is only 588W/m^2 *in space*. Earth's is about 1kW/m^2 *on the surface*, 1,4kW in space.
As in the book, 500W for lights per square meter would take 67 square meters of panels per square meter of crops. The best possible situation would take 10,5 square meters of panels per square meter of crops.
Note this is using your 500W figure, which is being kind to you. Double the required panel area to reach mine.
yep, 1m^2 per spotlight, 12 per rover (per movie)
Pure nonsense. 6kW of power consumption for LED lights on a rover? Um, no. Never. Period. That's patently absurd, you'd burn through your power supply in a heartbeat. That's the sort of power you'd use to run a drive motor on a rover on Mars - if you wanted it to drive at speeding-on-the-highway speeds at that. The Lunar Rover motor was only 0,1kW.
How the heck would you even cool a 500W LED spotlight (let alone 1kW, let alone 12 of them) in the near-vacuum atmosphere of Mars? The heat sinks would be massive. LEDs can't run hot, they have to be kept close to room temperature. I have some 600W grow lights. They have a 15kg heat sink and a half a dozen fans on each of them. And you can't practically just cool things with fans on Mars. And they're not like "spotlights", they're about half a meter by half a meter behind the glass panel, and have to be to keep the LEDs far enough apart. It's the reason why LED headlights for cars are a brand new thing, it's very hard to cram many LEDs into a small space without them overheating. A typical modern LED headlight is only about 15W; I was being generous and assuming bright 30W lights.
I wish you were here so I could show you what a 600W LED grow light looks like. It's blinding. The whole world looks pink for a while afterward. And they're massive, heavy things. To put it another way: 600W LED is equivalent to about 5000W incandescent.
I wonder how much could be saved by adapting growth density. Say, he could light up all the saplings with 2-3 lights, but as plants grow, they need more space. So instead of one massive harvest, to make it so that the grown plants take half the available light, grown in 3/4 half of the remainder, half-grown half of the remainder of that, and so on.
The optimal growth method is having 100% of your area lit up at all times, with leaves intercepting 100% of the light. Which can be approximated
Re:The movie was good because the book was short.
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Review: The Martian
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· Score: -1, Troll
Sort of. They still skipped out a lot of the description of what he's doing and why,
Thankfully. Almost every calculation in the book was wrong. The idiot author doesn't even know the difference between a mole and a liter. It's the sort of thing that fails you out of 10th grade chemistry.
I came up with a solution, but remember when I burned rocket fuel in the Hab? This’ll be more dangerous.
No, it would in no way, shape or form be. NASA technicians mess assembling probes and rovers do so without any special radiation precautions, just precautions against burning themselves. NASA technicians do not burn toxic hydrazine inside enclosed spaces that they're breathing that they can't ventilate.
I’m going to use the RTG.
The RTG (Radioisotope Thermoelectric Generator) is a big box of Plutonium. But not the kind used in nuclear bombs. No, no. This Plutonium is way more dangerous!
Completely false. It's far less dangerous.
Plutonium-238 is an incredibly unstable isotope.
It's an incredibly predictable isotope, with really only one meaningful decay branch, and that branch being to another element that decays in the same manner, just slower. The half life is certainly short compared to, say, U238, but there are countless isotopes with shorter half lives than it. Its rate of spontaneous fission are low, as are its fission cross section. This is hyperbole at best, completely false at worst.
It’s so radioactive that it will get red hot all by itself.
And? If he thinks something with an 88 year half life is terrible, he should see how elements with half-lives measured in days or hours are. Note that it only gets "red hot" when stored as a large enough lump inside an insulated container. The heat output on a typical RPG is similar to that of a blow drier or small portable space heater.
As you can imagine, a material that can literally fry an egg with radiation is kind of dangerous.
No, it is not, except for burning you. His freaking out about alpha radiation is totally ungrounded.
The RTG houses the Plutonium, catches the radiation in the form of heat
It "catches" it in the way your outer layer of dead skin, a sheet of tissue paper, or several inches of air would also catch it. Almost anything stops alpha.
, and turns it in to electricity. It’s not a reactor. The radiation can’t be increased or decreased. It’s a purely natural process happening at the atomic level.
As long ago as the 1960’s, NASA’s been using RTGs to power unmanned probes. It has lots of advantages over solar power. It’s not affected by storms; it works day or night; it’s entirely internal, so you don’t need delicate solar cells all over your probe.
No, but you need a giant cooling system and more complicated thermal management. And he seems to be talking about RTG-powered spacecraft, but then talks about "storms" and "day or night" which only applies to rovers, so I'm not sure exactly which he's thinking of.
But they never used large RTGs on manned missions until The Ares Program.
Why not?
Because 238Pu is produced in quantities of only a couple kg per year costing many tens of millions of dollars per kilogram. It is a manufactured product, not a waste product, and consequently incredibly expensive. If one wants more power than can be provided from an RTG, the next step up is a small nuclear reactor, not a larger RTG.
It should be pretty fucking obvious why not! They didn’t want to put astronauts next to a glowing hot ball of radioactive death!
No, you're a moron.
I'm exaggerating a little.
No, you're writing complete nonsense. External alpha radiation is completely harmless.
The Plutonium is inside a bunch of pellets, each one sealed and insulated to prevent radiation leakage even if the oute
EFTE is considered nonstick, as is common among fluorinated polymers - will ice even bond with it? Plus, "thin plastic membrane" and "unfiltered UV radiation", "ionizing radiation", "blowing perchlorate-rich dust", etc doesn't sound like a good combination. EFTE is considered resistant to UV degradation, but I have to question how long any thin film would last on an environment like Mars.
Not saying it's a bad concept, but it's definitely a concept that's not ready for prime-time as it stands.
A LED headlight is something like 30W. Times 2 for two of them. Times three for "super ultra powerful Mars headlights even though an actual Mars mission would be about saving power". Times 4 for "all of the other things you mentioned". That's still only 720W, what you might use to light up a single square meter.
Don't you get it yet? You simply don't "scrounge up" enough light bulbs to grow an entire person's diet worth of food. It's an impossibility - unless you happen to be trapped in a grow light warehouse or something of that nature. Nor do you just "scrounge up" 100kW of electricity. Plants take orders of magnitude more energy to grow from lights than Weir pictures, end of story.
Remember, individual care of individual plants, optimal temperature and humidity, exploiting the soil to the max,
Please don't make me get into why indoor growing in these situations, even with a person who knew what they were doing rather than Weir's countless things that would actually have killed his plants, is a recipe for terrible yields even if the light was ample. Because it'd be practically a book on greenhouse plant raising, and I really don't have time for that.
Great, now I'm picturing a Russian version of the "Monorail song", with the Lyle Lanley guy having a heavy Russian accent.
The Soyuz will not fit in there "The building's tall, like Russian bear!" What if perchance the roof should bend? "Not on your life, my Yakut friend!" What about us cleptocrats? "Your wallets will grow very fat!" My vodka's gone and now I'm sad. "Have another, dear comrade!" Were you sent here by the Kremlin? (displeased voice) ".... Next question please." (waves for undercover agents to take him out of the room) "You see it's Vostochny only choice. Now throw up hands and raise the voice." Cosmodrome! Cosmodrome! Cosmodrome!
The funny thing is that in 2013 they actually lost a Proton-M and $1.3B of technical equipment because a technician installed the angular velocity sensors upside down. There was one problem in doing so, in that they didn't even fit upside down - but no worries, he was able to hammer them into place;)
The Rada voted Yanukovich out - even including a majority of his own party. Russia claims that "proper parliamentary procedure" was not followed, but they're not the arbiter of that, the Ukrainian constitutional court is. And yeah, clearly the US is so into meddling in Ukraine that they won't even give them anti-tank missiles or counter-fire radar systems with a meaningful range. And it took a year of begging to even start go get anything more significant than blankets and sleeping bags. Yeah, the US is clearly so into helping Ukraine out! And look at all those US missiles in Ukraine, whooee! Meanwhile, Russia has been pouring some of its most advanced military hardware into Donbas, and when that wasn't enough, regular rotations of its army. But hey, Ukraine's got sleeping bags, so that's something, right?
There's long since been new elections in Ukraine. There were indeed two "nazi" candidates running. Combined they got barely more than 1% of the vote. The old "Ukraine is run by Nazis!" yarn is getting old.
... where all of the engineers have rounded up their buddies with trucks and backhoes and are trying to jam the rocket parts into place. "Come oooooon, it has to fiiiiit...."
I feel bad for whoever it is who will end up being declared a foreign agent embezzling money to support Ukrainian Nazis after this fiasco.
Nope - it decays to 234U, which has a 246k year half life and is also an alpha emitter. There's some minor spontaneous fission in 238Pu, which can produce basically whatever, but the spontaneous fission half life is 4,77e10 years, which is dwarfed by the alpha half life of 87,77 years. There's also the potential for the occasional alpha side reaction, but the cross sections are extremely low.
Yes, it is that bad. And he makes it even worse by boasting about how "incredible" the efficiency of the "super-efficient" panels and then giving it a terrible efficiency, something in the ballpark of 11% if I recall correctly. And then states that the panels are at a fixed tilt (with the "scientist" protagonist not understanding why they'd choose a particular angle... *snicker*) - so they're not sun tracking. Combine this with Mars's low solar constant. Combine this with the dust that he says he has to keep wiping off the panels. Combine this with the not-all-that-impressive panel area to begin with. Combine this with the maybe 20-30% efficiency you might get in producing PAR with a good LED grow light. Combine this with the fact that these are not grow lights, but rather the normal room lighting built into the habitat (white phosphor = loss of energy). Combine this with the fact that anyone who thinks you can grow caloric crops on normal room lighting is a moron, regardless of how much power you have available to you.
I can break it down with exact numbers for you if you want, but I'll just sum it up for you: it's 2-3 orders of magnitude off, and that's assuming that there's no bottleneck of how many lights the habitat was built with, which would actually probably bottleneck it to 3-4 orders of magnitude off. To people who've never grown caloric plants without sunlight, they can be forgiven for not understanding how vastly much energy it takes. Trust me: it takes a *ton*. The sun at Earth imparts about a kilowatt of light per square meter. Per *square meter* - and that's light, meaning to reproduce the sun, you have to use several kilowatts per square meter to account for the losses. Think of how much power an efficient light bulb consumes. Now think of how many of them you need to use to equal a kilowatt of power consumption. And how much of your light you lose to straying.
You have a few things going for you. The sun goes down at night. The sun isn't always high overhead, so you have cosine scaling. So you don't have to produce as much energy as the above implies. But it's still a mind-boggling vast amount of light to need to produce across a very large area. A very good yield of potatoes (which contrary to his claims, you absolutely will not get in his situation even if you had sufficient light - going into why would be a longer post than even this one) - is about 50 tonnes per hectare per year, or 5 kg per square meter per year, or 11000 calories per square meter per year, or about 3-4 days worth of calories for our anything-but-sedentary protagonist, meaning a farm area of about 100 square meters. If one assumes that the reduced solar output caused by sun angles and night to roughly compensate for the energy losses to convert electricity into light and the amount of light that strays, then you need about 1kW constantly per square meter, or 100kW, to match the energy input from the sun. That's the power consumed by 80 average houses in the US. Not like his hab would have 100kW of lights just built into it....
It's easy to forget how intense of an energy source the sun is, and how much energy it takes to keep a human going.
The thing is, had the author not been totally ignorant about plants (despite making his main character a botanist... a botanist that somehow nonetheless seems disgusted by manure;) ), there are ways one could have reasonably written in a doable scenario. But botany is one of the many, many things that Weir totally bungled in the book.
Clarification on radiation shielding: you generally don't use just a hydrogen rich layering, there may be metallic layers as well (such as the craft's outer skin, tankage, etc). But most of the high energy solar and GCR is charged particles, mainly protons. The lower end of the energy range will almost entirely impact whatever shielding you use, creating a small shower of secondaries. Some high energy particles will impact, some will pass right through. Those that pass through will most likely pass through everything, and those that do impact crew will mostly impart only a tiny fraction of their energy to them. Those that impact the shielding create an ever-growing shower of secondaries; where the secondaries aren't sufficiently blocked poses more of a risk to the crew than had the particle not impacted anything at all on the way in. Primaries at over 10MeV or so are particularly prone to kicking off secondaries, and once you get into hundreds of MeV spallation starts becoming a significant component.
All of this together means that the most important particles to block are the secondaries, in that they're more numerous, less likely to cause negative side effects by blocking them, etc. Heavier secondaries like alphas are easy to block, while it's unrealistic to block a significant fraction of high energy gammas on something as light as a spacecraft. This leaves the neutron secondaries as your prime target for elimination, which can generally be captured if moderated down first, but otherwise pose a risk to the crew. The lighter the element and the higher the cross section, the better the moderator; also, the lighter the element, the more you can carry on a spacecraft. Hydrogen fits all three bills well. Once moderated down, then the capture cross section becomes key. Hydrogen can manage thermal neutron capture over a sufficient distance, but far better is something like boron. In fact, metals can sometimes be counterproductive, especially on the inner side of the shielding. They increase the risk of spallation, bremmstrahlung, and your neutron captures are much more likely to produce short half life isotopes which will then undergo beta- decay.
There's no need for an unusual amount of metal in the shielding (over what would be needed to build the craft itself), and no need to make it a faraday cage. EM radiation and charged particles are very different beasts.
It is apart from solanine. Potato starch is indigestible raw. It passes all the way into the intestines intact, where it then begins to ferment under the influence of anaerobic bacteria. This yields significantly less caloric energy as well as indigestion and bloating.
Anyway, Weir wouldn't have had to worry about potatoes greening (solanine) because he had at least 2-3 orders of magnitude too little light to actually grow potatoes, thinks that the entire part of the plant above the soil is the "fruiting body", and thinks that potato mounding involves completely burying the plant and planting new potatoes directly on top of it. Not to mention the perchlorates, ethylene gas, or the 50 other things that would have actually killed his potatoes if grown as described. (Note to anyone who's ever owned a winter greenhouse or done significant indoor plant growing: expect to repeatedly hit your head against the wall if you read The Martian).
Oh, and try not to think too much about his plan of having humidity condense on the habitat and rain back down as a method for watering the plants (sensitive life-critical electrical systems and condensation: best friends 4everz!). It's bad enough when it happens in your apartment... I remember the day when my light fixture fell to the floor and broke because it had filled up with water and become too heavy to support itself - sure explained the reason why the breaker to that room kept throwing! At least in the movie they seem to have added a grow tent, judging from the trailer (haven't seen the movie yet). Although grow tents bring their own problems... and most clear plastic sheeting is polyethylene, which is a pain to bond.
At least the story is internally consistent: because the Hab is radiation-proof, radio waves don't go through it
Yet another Weir misunderstanding, confusing all forms of radiation as if they're the same thing. If you want to block radio waves with as little mass as possible, you use metals. If you want to block streams of charged particles with as little mass as possible (the actual goal), you use hydrogen-rich materials, ideally with a borated inner liner. Weir has a history of misunderstanding radiation and confusing all types as if they're the same thing - check out his rant about how horrificly dangerous the radiation from an RTG is;) Speaking of that...
I've also seen reviewers complaining that Mark Watney oversells the dangers of the radiation inside an RTG. In the book at least he is joking around a lot and using imprecise terms such as "box full of radiation"
He's not "joking around", the rant is like a page and a half long, describing it as vastly more dangerous than Pu-239, with a long line of superlatives for how to describe its incredible "danger". He talks about how it gets glowing hot with radiation and extends that logic to meaning that said radiation would be a lethal threat to his protagonist should the case crack. Which is of course absurd. Alpha doesn't even penetrate the outer layer of dead skin - alpha emitters are only dangerous if ingested or inhaled, and there's no realistic way to do that with an RTG, they're designed to even withstand unshielded reentry without burning up (and have done so - ex. Apollo 13). He'd be at far more risk of burning his suit - they're designed to operate at temperatures of 1000-1100C on the inner core and can still be very hot on the cooling fins (which, by the way, are often very large - on Curiosity, they're the giant angled section in the right near the guy in this picture. That's just to dissipate the heat used to produce a mere 125 watts of electrical power.)
My explanation of how the Hab is radiation-proof: a superconducting magnetic shield.
Microwave communications are based on photons, aka chargeless particles, aka no Lorentz force, aka no deflection.
Only protects against charged particles though...wouldn't stop gamma rays. How common is random gamma radiation on the surface of Mars?
Nor neutrons. Nor very high energy particles, such as in GCR, according to studies of realistically-implementable systems. But lower energy charged particles comprise the lion's share of the radiation exposure. Also, a lot of the neutrons and gamma that one would be exposed to with conventional shielding are secondaries.
There were far more major glaring errors than that. I managed to read about a quarter of the book, needing something to bang my head into on almost every page. No, I don't want to turn this thread into yet another "rip on the terrible 'science' in The Martian" thread, so I'm not going to start yet another "list" like I've done the last times the book came up on Slashdot.
Honestly, with how much he screwed up the science in general, I doubt Weir's "I did it for artistic license" excuse about the dust storm. It comes across as a post-facto to explain away one of his screwups that was getting the most complaints.
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Am I the only one here who, whenever they encounter this pre-teen version of profanity as in the above post, read it literally, as if the person was talking about bundles of wood, literal hats for asses, and donkeys going crazy next to bull shit?
But my analogy is this. Say that you're a pearl diver. You're browsing along a dive forum one day and see a picture from someone on their vacation to a remote tropical island holding a large, rare pearl that they found on a dive. You ask them where they found it, and they tell you they only did one dive and found it in waters of about 15 meter depth off the shore. Wanting to find many of these such pearls, you head out to the island. Now, you have two approaches you could take.
1. Spend a long time carefully doing a geological survey of the water depth around all of the shores of the island. Then do your dives in order of which are most precisely 15 meters deep, regardless of how convenient they are to access. Only move on to areas that are any more or any less than exactly 15 meters deep when you've exhausted all of the known 15-meter depth areas.
2. Go out and start diving wherever the water looks to be at least in the right ballpark of 15 meters depth. Start with the most convenient areas first. Don't obsess over the exact depth - exploring some 10 meter areas, some 20 meter areas, etc, just trying to keep it roughly in the ballpark of 15 meters. Because hey, for all you know, more than 15 meters or less than 15 meters might be an even better diving depth; you've only got one datapoint so far.
Which makes more sense? #2, obviously. Which is the same strategy we should be using with exoplanets in the search for life. We should be "favoring" Earthlike planets, but not obsessing over earthlike-ness in the search. We should be checking out a diverse range that is only "centered" on Earthlike bodies. And we should be focusing on those which lend themselves to easier, more detailed observation first, such as those closer to us and with a more favorable orbital alignment.
** I should clarify that when I say "mollusks", I mean like cephlapods, not like snails ;)
I have no clue where you're coming from. You rightly point out that life takes energy, but then proceed to consider internal sources of energy as worthless, when in reality in the universe far more things are exposed to internal energy than external. And radioactive decay-driven energy sources are only one. For example, Encelaldus's heat seems to be driven by the serpentization of rock, which also releases hydrogen, a potential food source to microorganisms. There are numerous chemical means which can release vast amounts of energy - yes, nuclear energy is many orders of magnitude more dense, but non-radioactive elements are also orders of magnitude more common.
Anywhere that there is heat and fluids (or solids that can undergo solid-state convection) can experience that heat being turned into harvestable forms of chemical energy, because chemical equilibriums are different at different temperatures. For example, at STP conditions, N2 + O2 is favorable, while at high temperatures NO2 is more favorable. N2 + O2 that goes to higher temperatures and forms NO2, which then comes back down to the lower atmosphere, is bringing a source of chemical energy with it.
Since heat differentials can and will be readily converted to chemical energy wherever it's associated with convection of any variety, then any source of heat is a fuel for life - and heat most definitely doesn't only come from nuclear decay - or chemical reactions. It comes also from the rebalancing of layers to a lower gravitational equipotential. It comes from impacts. It comes from tidal heating. It comes from thermal cycling in elongated orbits. It comes from mass loss due to solar wind exposure. There's a vast range of potential heating sources in the universe that can create heat differentials. And heat differentials make exploitable chemical reactions.
You make blind assertions that "these environments wouldn't be likely because of their composition". What do you know about this? You have a sample size of one of chemical processes that have created life. We can't even see deep into our own world to see what other alternatives might exist at higher pressures, let alone in other worlds. Heck, underground doesn't even mean particularly high pressures. Dwarf planets can have Earth-surface pressures at hundreds of meters or even kilometers depth. And life on Earth exists fine in the deep sea, wherever there's energy to support it, where pressures are at over 1000 atmospheres
Deep environments might prove even more prone to organic chemistry. In general, pressure is usually associated with faster reaction rates. You also often have more complex arrangements of possible chemical phases for each compound at higher pressures than with lower pressures. Water for example over its possible temperature range at a particular depth might have 3-5 potential ice phases, a liquid phase, a supercritical fluid phase, and a gas phase. This leads to a much greater range of possibilities for reactions to potentially exploit, because each chemical in each of its phases has the potential it interact with each other chemical in each of its other phases, or in the case of non-metastable forms, at least many of its other phases.
Common theories for the origin of life on Earth usually assume that it wasn't the sun that powered the first forms of life, even though that's the most convenient source of energy on our planet. Photosynthesis is much more complicated than most forms of chemosynthesis. Environments like black smokers, volcanic pools or acidic waters within deep iron-rich minerals seem like far more likely candidates.
Intelligence evolving within creatures that live in liquids? Oh, we've never seen that before! ;) Except, of course, for the fact that the second-most intelligent category of mammals are aquatic (cetaceans), and the most intelligent invertebrates (mollusks) live there too. Rather, the oceans tend to be highly competitive environments, and thus good breeding grounds for intelligence.
I think it's silly in the regards that we have precisely one datapoint about the sort of environments in which life may exist, which is pretty terrible in terms of making any sort of definitive statement. I'd much rather they keep their options open, check out a wide range of environments, and just look for signs of "things that are hard to explain", whatever they may be. "Hmm, this body has both a strong oxidizer and a strong reducing agent in its atmosphere - how is that happening?"
I'm not saying "check planets in random order" or anything of that nature. Just that I don't think it's critical to obsess over being sure to examine them in order of "earthishness" from highest to lowest. We need to be looking at a diversity of worlds.
Heck, we don't even know whether the surface of a body is the best place to look, most life in the universe might be in sub-crustal layers for all we know. Certainly would partially help explain the Fermi paradox, if it were such that we rare "surface dwellers" have a far easier route to the cosmos than something that needs to be under gigapascals of pressure to survive and whose radiating transmissions, if any, would be blocked by their planet's crust.
We can tell how habitable it is by how much it causes a start to warble
Chirp chirp chirp, triiiiiiiiiiiillll, triiiiiiiiiiiiiiiilllll! Chirp triiiiiiiiiiiiiiiiiiillll! Coooo-oooo! Cooooo-oooo! Chirp chirp chirp!!!
If you want to keep "doing the math" and if you want to be called "hard sci fi", you need to do the math right. You can't say that because you've got 50 liters of oxygen that you're going to get 100 liters of water because O2 + 2 H2 = 2 H2O. Yet Weir does exactly that, over and over and over again, mixing up moles, liters, and kilograms. One of dozens of categories of huge fundamental science mistakes that he keeps repeating.
I'm sorry, I missed out where "accuracy" and "popularity" became interchangeable terms. I was responding to a post talking about the book's amazing scientific accuracy, when in reality it's a veritable MST3K of glaring science errors on almost every page. Or at least glaring to anyone who knows anything about the scientific fields involved.
At least with "soft" sci-fi where they don't try to explain how everything works you only get hit over the head with science problems whenever they describe a situation that's literally impossible. With bad pseudo-hard-sci-fi you get hit over the head with it again and again.
Yes, one has to incorporate a "capacity factor" to account for angles, night and clouds. Something like 15% would be typical for potato-growing regions. But at the same time, when light is coming from LED lighting, you have to account for stray lighting (light that's not hitting your grow area) and efficiencies at generating PAR, which are 20-30% for proper grow lights, lower for normal room lights (as the phosphor wastes part of the light energy to make it a comfortable white rather than a painful pink). The two issues roughly cancel themselves out. You need in the ballpark of 1kW per square meter of electricity input to match normal potato growing conditions.
For 24-7 lighting, that's 50% of my above, but let's go with it.
Not even close. Your solar array too has a capacity factor - in the ballpark of 15% if fixed, maybe 35% or so if tracking. Then you have your panel efficiencies. The best large scale commercial panels are 22-23% efficiency. You might get 30%-ish if you used absurdly-crazy-expensive spectrolab cells. Then factor in dust constantly settling on the panels - say 25% loss even with regular cleaning. And Mars's solar constant is only 588W/m^2 *in space*. Earth's is about 1kW/m^2 *on the surface*, 1,4kW in space.
As in the book, 500W for lights per square meter would take 67 square meters of panels per square meter of crops. The best possible situation would take 10,5 square meters of panels per square meter of crops.
Note this is using your 500W figure, which is being kind to you. Double the required panel area to reach mine.
Pure nonsense. 6kW of power consumption for LED lights on a rover? Um, no. Never. Period. That's patently absurd, you'd burn through your power supply in a heartbeat. That's the sort of power you'd use to run a drive motor on a rover on Mars - if you wanted it to drive at speeding-on-the-highway speeds at that. The Lunar Rover motor was only 0,1kW.
How the heck would you even cool a 500W LED spotlight (let alone 1kW, let alone 12 of them) in the near-vacuum atmosphere of Mars? The heat sinks would be massive. LEDs can't run hot, they have to be kept close to room temperature. I have some 600W grow lights. They have a 15kg heat sink and a half a dozen fans on each of them. And you can't practically just cool things with fans on Mars. And they're not like "spotlights", they're about half a meter by half a meter behind the glass panel, and have to be to keep the LEDs far enough apart. It's the reason why LED headlights for cars are a brand new thing, it's very hard to cram many LEDs into a small space without them overheating. A typical modern LED headlight is only about 15W; I was being generous and assuming bright 30W lights.
I wish you were here so I could show you what a 600W LED grow light looks like. It's blinding. The whole world looks pink for a while afterward. And they're massive, heavy things. To put it another way: 600W LED is equivalent to about 5000W incandescent.
The optimal growth method is having 100% of your area lit up at all times, with leaves intercepting 100% of the light. Which can be approximated
Thankfully. Almost every calculation in the book was wrong. The idiot author doesn't even know the difference between a mole and a liter. It's the sort of thing that fails you out of 10th grade chemistry.
You cut short the rant. The full rant is:
No, it would in no way, shape or form be. NASA technicians mess assembling probes and rovers do so without any special radiation precautions, just precautions against burning themselves. NASA technicians do not burn toxic hydrazine inside enclosed spaces that they're breathing that they can't ventilate.
Completely false. It's far less dangerous.
It's an incredibly predictable isotope, with really only one meaningful decay branch, and that branch being to another element that decays in the same manner, just slower. The half life is certainly short compared to, say, U238, but there are countless isotopes with shorter half lives than it. Its rate of spontaneous fission are low, as are its fission cross section. This is hyperbole at best, completely false at worst.
And? If he thinks something with an 88 year half life is terrible, he should see how elements with half-lives measured in days or hours are. Note that it only gets "red hot" when stored as a large enough lump inside an insulated container. The heat output on a typical RPG is similar to that of a blow drier or small portable space heater.
No, it is not, except for burning you. His freaking out about alpha radiation is totally ungrounded.
It "catches" it in the way your outer layer of dead skin, a sheet of tissue paper, or several inches of air would also catch it. Almost anything stops alpha.
No, but you need a giant cooling system and more complicated thermal management. And he seems to be talking about RTG-powered spacecraft, but then talks about "storms" and "day or night" which only applies to rovers, so I'm not sure exactly which he's thinking of.
Because 238Pu is produced in quantities of only a couple kg per year costing many tens of millions of dollars per kilogram. It is a manufactured product, not a waste product, and consequently incredibly expensive. If one wants more power than can be provided from an RTG, the next step up is a small nuclear reactor, not a larger RTG.
No, you're a moron.
No, you're writing complete nonsense. External alpha radiation is completely harmless.
EFTE is considered nonstick, as is common among fluorinated polymers - will ice even bond with it? Plus, "thin plastic membrane" and "unfiltered UV radiation", "ionizing radiation", "blowing perchlorate-rich dust", etc doesn't sound like a good combination. EFTE is considered resistant to UV degradation, but I have to question how long any thin film would last on an environment like Mars.
Not saying it's a bad concept, but it's definitely a concept that's not ready for prime-time as it stands.
Are you really incapable of doing the math?
A LED headlight is something like 30W. Times 2 for two of them. Times three for "super ultra powerful Mars headlights even though an actual Mars mission would be about saving power". Times 4 for "all of the other things you mentioned". That's still only 720W, what you might use to light up a single square meter.
Don't you get it yet? You simply don't "scrounge up" enough light bulbs to grow an entire person's diet worth of food. It's an impossibility - unless you happen to be trapped in a grow light warehouse or something of that nature. Nor do you just "scrounge up" 100kW of electricity. Plants take orders of magnitude more energy to grow from lights than Weir pictures, end of story.
Please don't make me get into why indoor growing in these situations, even with a person who knew what they were doing rather than Weir's countless things that would actually have killed his plants, is a recipe for terrible yields even if the light was ample. Because it'd be practically a book on greenhouse plant raising, and I really don't have time for that.
Great, now I'm picturing a Russian version of the "Monorail song", with the Lyle Lanley guy having a heavy Russian accent.
The Soyuz will not fit in there
"The building's tall, like Russian bear!"
What if perchance the roof should bend?
"Not on your life, my Yakut friend!"
What about us cleptocrats?
"Your wallets will grow very fat!"
My vodka's gone and now I'm sad.
"Have another, dear comrade!"
Were you sent here by the Kremlin?
(displeased voice) ".... Next question please." (waves for undercover agents to take him out of the room)
"You see it's Vostochny only choice. Now throw up hands and raise the voice."
Cosmodrome! Cosmodrome! Cosmodrome!
The funny thing is that in 2013 they actually lost a Proton-M and $1.3B of technical equipment because a technician installed the angular velocity sensors upside down. There was one problem in doing so, in that they didn't even fit upside down - but no worries, he was able to hammer them into place ;)
The Rada voted Yanukovich out - even including a majority of his own party. Russia claims that "proper parliamentary procedure" was not followed, but they're not the arbiter of that, the Ukrainian constitutional court is. And yeah, clearly the US is so into meddling in Ukraine that they won't even give them anti-tank missiles or counter-fire radar systems with a meaningful range. And it took a year of begging to even start go get anything more significant than blankets and sleeping bags. Yeah, the US is clearly so into helping Ukraine out! And look at all those US missiles in Ukraine, whooee! Meanwhile, Russia has been pouring some of its most advanced military hardware into Donbas, and when that wasn't enough, regular rotations of its army. But hey, Ukraine's got sleeping bags, so that's something, right?
There's long since been new elections in Ukraine. There were indeed two "nazi" candidates running. Combined they got barely more than 1% of the vote. The old "Ukraine is run by Nazis!" yarn is getting old.
Lastly: might want to check where you get your information from.
... where all of the engineers have rounded up their buddies with trucks and backhoes and are trying to jam the rocket parts into place. "Come oooooon, it has to fiiiiit...."
I feel bad for whoever it is who will end up being declared a foreign agent embezzling money to support Ukrainian Nazis after this fiasco.
... who brought us the available-in-30-languages childrens' book "The Little Mole Who Wanted to Know Who Pooped on His Head"?
Nope - it decays to 234U, which has a 246k year half life and is also an alpha emitter. There's some minor spontaneous fission in 238Pu, which can produce basically whatever, but the spontaneous fission half life is 4,77e10 years, which is dwarfed by the alpha half life of 87,77 years. There's also the potential for the occasional alpha side reaction, but the cross sections are extremely low.
Yes, it is that bad. And he makes it even worse by boasting about how "incredible" the efficiency of the "super-efficient" panels and then giving it a terrible efficiency, something in the ballpark of 11% if I recall correctly. And then states that the panels are at a fixed tilt (with the "scientist" protagonist not understanding why they'd choose a particular angle... *snicker*) - so they're not sun tracking. Combine this with Mars's low solar constant. Combine this with the dust that he says he has to keep wiping off the panels. Combine this with the not-all-that-impressive panel area to begin with. Combine this with the maybe 20-30% efficiency you might get in producing PAR with a good LED grow light. Combine this with the fact that these are not grow lights, but rather the normal room lighting built into the habitat (white phosphor = loss of energy). Combine this with the fact that anyone who thinks you can grow caloric crops on normal room lighting is a moron, regardless of how much power you have available to you.
I can break it down with exact numbers for you if you want, but I'll just sum it up for you: it's 2-3 orders of magnitude off, and that's assuming that there's no bottleneck of how many lights the habitat was built with, which would actually probably bottleneck it to 3-4 orders of magnitude off. To people who've never grown caloric plants without sunlight, they can be forgiven for not understanding how vastly much energy it takes. Trust me: it takes a *ton*. The sun at Earth imparts about a kilowatt of light per square meter. Per *square meter* - and that's light, meaning to reproduce the sun, you have to use several kilowatts per square meter to account for the losses. Think of how much power an efficient light bulb consumes. Now think of how many of them you need to use to equal a kilowatt of power consumption. And how much of your light you lose to straying.
You have a few things going for you. The sun goes down at night. The sun isn't always high overhead, so you have cosine scaling. So you don't have to produce as much energy as the above implies. But it's still a mind-boggling vast amount of light to need to produce across a very large area. A very good yield of potatoes (which contrary to his claims, you absolutely will not get in his situation even if you had sufficient light - going into why would be a longer post than even this one) - is about 50 tonnes per hectare per year, or 5 kg per square meter per year, or 11000 calories per square meter per year, or about 3-4 days worth of calories for our anything-but-sedentary protagonist, meaning a farm area of about 100 square meters. If one assumes that the reduced solar output caused by sun angles and night to roughly compensate for the energy losses to convert electricity into light and the amount of light that strays, then you need about 1kW constantly per square meter, or 100kW, to match the energy input from the sun. That's the power consumed by 80 average houses in the US. Not like his hab would have 100kW of lights just built into it....
It's easy to forget how intense of an energy source the sun is, and how much energy it takes to keep a human going.
The thing is, had the author not been totally ignorant about plants (despite making his main character a botanist... a botanist that somehow nonetheless seems disgusted by manure ;) ), there are ways one could have reasonably written in a doable scenario. But botany is one of the many, many things that Weir totally bungled in the book.
Clarification on radiation shielding: you generally don't use just a hydrogen rich layering, there may be metallic layers as well (such as the craft's outer skin, tankage, etc). But most of the high energy solar and GCR is charged particles, mainly protons. The lower end of the energy range will almost entirely impact whatever shielding you use, creating a small shower of secondaries. Some high energy particles will impact, some will pass right through. Those that pass through will most likely pass through everything, and those that do impact crew will mostly impart only a tiny fraction of their energy to them. Those that impact the shielding create an ever-growing shower of secondaries; where the secondaries aren't sufficiently blocked poses more of a risk to the crew than had the particle not impacted anything at all on the way in. Primaries at over 10MeV or so are particularly prone to kicking off secondaries, and once you get into hundreds of MeV spallation starts becoming a significant component.
All of this together means that the most important particles to block are the secondaries, in that they're more numerous, less likely to cause negative side effects by blocking them, etc. Heavier secondaries like alphas are easy to block, while it's unrealistic to block a significant fraction of high energy gammas on something as light as a spacecraft. This leaves the neutron secondaries as your prime target for elimination, which can generally be captured if moderated down first, but otherwise pose a risk to the crew. The lighter the element and the higher the cross section, the better the moderator; also, the lighter the element, the more you can carry on a spacecraft. Hydrogen fits all three bills well. Once moderated down, then the capture cross section becomes key. Hydrogen can manage thermal neutron capture over a sufficient distance, but far better is something like boron. In fact, metals can sometimes be counterproductive, especially on the inner side of the shielding. They increase the risk of spallation, bremmstrahlung, and your neutron captures are much more likely to produce short half life isotopes which will then undergo beta- decay.
There's no need for an unusual amount of metal in the shielding (over what would be needed to build the craft itself), and no need to make it a faraday cage. EM radiation and charged particles are very different beasts.
It is apart from solanine. Potato starch is indigestible raw. It passes all the way into the intestines intact, where it then begins to ferment under the influence of anaerobic bacteria. This yields significantly less caloric energy as well as indigestion and bloating.
Anyway, Weir wouldn't have had to worry about potatoes greening (solanine) because he had at least 2-3 orders of magnitude too little light to actually grow potatoes, thinks that the entire part of the plant above the soil is the "fruiting body", and thinks that potato mounding involves completely burying the plant and planting new potatoes directly on top of it. Not to mention the perchlorates, ethylene gas, or the 50 other things that would have actually killed his potatoes if grown as described. (Note to anyone who's ever owned a winter greenhouse or done significant indoor plant growing: expect to repeatedly hit your head against the wall if you read The Martian).
Oh, and try not to think too much about his plan of having humidity condense on the habitat and rain back down as a method for watering the plants (sensitive life-critical electrical systems and condensation: best friends 4everz!). It's bad enough when it happens in your apartment... I remember the day when my light fixture fell to the floor and broke because it had filled up with water and become too heavy to support itself - sure explained the reason why the breaker to that room kept throwing! At least in the movie they seem to have added a grow tent, judging from the trailer (haven't seen the movie yet). Although grow tents bring their own problems... and most clear plastic sheeting is polyethylene, which is a pain to bond.
Aaargh... why do I always fall for the Rick Rolls? :P Well played...
Yet another Weir misunderstanding, confusing all forms of radiation as if they're the same thing. If you want to block radio waves with as little mass as possible, you use metals. If you want to block streams of charged particles with as little mass as possible (the actual goal), you use hydrogen-rich materials, ideally with a borated inner liner. Weir has a history of misunderstanding radiation and confusing all types as if they're the same thing - check out his rant about how horrificly dangerous the radiation from an RTG is ;) Speaking of that...
He's not "joking around", the rant is like a page and a half long, describing it as vastly more dangerous than Pu-239, with a long line of superlatives for how to describe its incredible "danger". He talks about how it gets glowing hot with radiation and extends that logic to meaning that said radiation would be a lethal threat to his protagonist should the case crack. Which is of course absurd. Alpha doesn't even penetrate the outer layer of dead skin - alpha emitters are only dangerous if ingested or inhaled, and there's no realistic way to do that with an RTG, they're designed to even withstand unshielded reentry without burning up (and have done so - ex. Apollo 13). He'd be at far more risk of burning his suit - they're designed to operate at temperatures of 1000-1100C on the inner core and can still be very hot on the cooling fins (which, by the way, are often very large - on Curiosity, they're the giant angled section in the right near the guy in this picture. That's just to dissipate the heat used to produce a mere 125 watts of electrical power.)
Microwave communications are based on photons, aka chargeless particles, aka no Lorentz force, aka no deflection.
Nor neutrons. Nor very high energy particles, such as in GCR, according to studies of realistically-implementable systems. But lower energy charged particles comprise the lion's share of the radiation exposure. Also, a lot of the neutrons and gamma that one would be exposed to with conventional shielding are secondaries.
There were far more major glaring errors than that. I managed to read about a quarter of the book, needing something to bang my head into on almost every page. No, I don't want to turn this thread into yet another "rip on the terrible 'science' in The Martian" thread, so I'm not going to start yet another "list" like I've done the last times the book came up on Slashdot.
Honestly, with how much he screwed up the science in general, I doubt Weir's "I did it for artistic license" excuse about the dust storm. It comes across as a post-facto to explain away one of his screwups that was getting the most complaints.