Piscator
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Posts posted by Piscator
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Stage 1 of grief: Denial
Actually not a bad name for a first stage.
Goodbye, "Denial", we hardly knew ye.
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Hm, looks like the Martians made it here first ...
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I assume this is less about an attack on SpaceX itself and more about keeping the Starlink network operational in regions where someone might want to restrict access to it. Hard to tell from one tweet though.
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Iron particles in the blood would very likely kill you. The iron contained in your blood and the iron that's attracted by a magnet are two rather different things.
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A more fundamental problem might be that the whole concept of a warship in space is probably obsolete. As long as your most effective weapons are limited in range it makes a lot of sense to put a bunch of them on a vessel and drive them where they're needed. In space, range is not really an issue. There is little need to send a ship to Mars to launch a lot of warheads if you can just launch the warheads from Earth.
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16 hours ago, sevenperforce said:
Author Alan Bellows is a computer programmer but he is not, to my knowledge, a physicist or biologist, so I'm inclined to take this with a grain of salt.
That was the passage I was referring to and I came to the same conclusion pretty much. Which is why I didn't consider the source overly reliable.
16 hours ago, sevenperforce said:Boiling is what happens when the vapor pressure at the surface of a liquid is equal to the atmospheric pressure, and so you can't have "boiling" unless you have exposed liquids.
I was thinking about the topic quite a bit after my last post and I'm not sure that this is really how it works. Please correct me if you find a flaw with my line of argument, but as I see it, the essential part of boiling vs evaporation is that the pressure throughout the liquid needs to be lower than the current vapor pressure for boiling to occur. Only if this condition is met, cavities or instabilities that form inside the liquid for whatever reason would start accumulating gas from their surroundings instead of collapsing immediately. Or looking at it from a slightly different angle, a vapor bubble in a liquid wouldn't be stable unless its internal pressure (the vapor pressure) is greater than the pressure of the surrounding liquid.
If the total pressure is too high for bubbles to form inside the liquid, the only place where a phase change would occur is the surface of the liquid, where the vapor pressure of the substance might be able to overcome its partial pressure in the gas phase, or in other words evaporate.
Since bubbles form at the bottom of a pot of boiling water and would still form if you covered the surface with a layer of oil for example, this explanation seems to fit the observations rather better.
If my line of reasoning is correct so far, the question regarding vacuum exposure would be less whether a liquid is exposed or not, but rather whether it is enclosed by a membrane able to provide the necessary counterpressure. As mentioned, blood vessels are certainly able to do this but I have no idea how regular cell membranes would compare.
Since you would at least expect some readily findable results of animal experiments if bloating was a real concern, my guess is that it probably doesn't happen. I would still consider it imaginable though at this stage.
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Copper seems most likely. Raptors apparently use quite a lot of it. It's also far easier to vaporize than tungsten.
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19 hours ago, KerikBalm said:
You'd need more than a face mask, human flesh swelling to 2x volume doesn't sound great... (bodybuilder rather than overfilled balloon though...)
I was worrying about this point as well, but have a bit of a problem finding out why this would be the case. I'm of course aware of the Kittinger incident, but I'm not sure how much of the (apparently quite painful and debilitating) swelling was caused by the low pressure per se and how much was caused by the difference between the pressurized and unpressurized parts of the suit. After all, you can easily imagine body fluids accumulating in the only body part that's not pressurized.
Source link [2] in your quoted passage mentions water in your tissues beginning to boil as a cause, which sounds plausible enough. While your blood may be protected by vessels designed to withstand the pressure differences of a beating heart, other liquids in your body might be not so lucky. Then again, the descriptions of pressure chamber accidents don't seem to mention this effect. Does it take a while to develop? I'd really love to find a good source.
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On 1/12/2022 at 12:59 AM, sevenperforce said:
I wonder if you could lower the Armstrong limit using a high humidity breathing mix.
I'm a bit hazy on the subject, but doesn't "high humidity" just mean that the partial pressure of water vapor in the atmosphere is close to the vapor pressure of water for a given temperature? In other words, you'd have to have at least the Armstrong pressure in water vapor to achieve saturation, which means that below that pressure there's no such thing as "high humidity".
On the other side, we probably wouldn't have to worry about adding water vapor to our breathing mix (in the loose sense) since our lungs would autogenously pressurize. If my math checks out, you would need as little as 50mg of water per litre of internal cavity to reach Armstrong pressure, which seems quite manageable. I guess, that's where a mask does come in handy.
As has been established, all this would of course rely on finding another way to oxygenate your blood, since the oxygen partial pressure would be too low for your lungs to be much of a help.
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On 1/9/2022 at 4:26 AM, sevenperforce said:
Only if you're stupid enough to take your mask off.
The Armstrong limit only applies to exposed liquids. Skin is quite tough and can hold in pressure very well. If it couldn't then we'd all simultaneously explode; after all, our blood pressure is 16% higher than atmospheric pressure.
Why would a mask matter? Exposing your lungs to actual Martian atmosphere or to pure oxygen at Martian ambient pressure is - by definition - no difference pressure-wise. That said, I was less worried about your blood starting to boil and more about the drying-out of exposed lung tissues. I'm not quite sure how much this would actually impede the function of the lungs, but a complete evaporation of the water in your exposed mucous membranes would be very uncomfortable to say the least (especially if you take evaporation cooling into account).
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It's also an order of magnitude below the Armstrong limit/pressure, which would make prolonged survival a bit tricky.
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Walking and running in low gravity might be more problematic than you think, as it involves quite a lot of controlled falling. When we're making a step, we rely on gravity to pull us forward and downward. This means that in lunar gravity your usual walking cycle might actually be up to six times slower than on Earth. Even without a heavy spacesuit, hopping might be your most practical way to get around. It might also be some kind of power shuffle or ninja running. I will be very interested in seeing people getting actual experience in shirtsleeve low-g locomotion.
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4 hours ago, SunlitZelkova said:4 hours ago, tater said:
Nothing has been "sterilized."
Well, yes. Sterilized does not mean literally killing everything. It means doing the best you can.
Quick aside, but "literally killing everything" is exactly what "sterilize" means. See Wikipedia.
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On 12/28/2021 at 9:30 AM, Jacke said:
Most bacteria with enough food will reproduce every 20 minutes or so. One of the extremes in the other direction is Mycobacterium tuberculosis, which only divides once or twice per day. It's why antibiotics have to be taken for half a year or more to treat Tuberculosis, as most antibiotics tend to attack during cell division when the organism is more vulnerable.
This is certainly true for human pathogens and commensals which are optimized for warm, nutrient-rich environments (that is, humans) with a lot of competition. It doesn't need to be true for organisms adapted to less lush conditions though. For example, generation times of 2-6 days have been reported for various species of Syntrophobacter. Considering that this is close to the limits of what can be sensibly done in a lab (what would be an overnight culture for E.coli is now already a matter of months) and that we haven't been able to cultivate the vast majority of microorganisms at all, this is probably on the quicker end of the spectrum of microbial generation times.
I broadly agree with the points about radioresistance. While it would be in the realm of the biologically possible, I don't consider radioresistant Martian surface life very likely. In order to actively repair gene damage, you would need a fairly active metabolism, for which I don't see the margins in this kind of environment. More importantly though, the surface probably just isn't very attractive. Unless you require access to light or atmospheric carbon dioxide (which could as well be leached from carbonate rocks) there's little reason to expose yourself to a high-radiation environment. And - as a microorganism - you have to go where the water is anyway.
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Hm ... cover a large area with soon to be freeze-dried egg powder ... let it mix with perchlorate dust ... then land a rocket. I see you thought about the "killing with fire" part already.
In all seriousness though, I highly doubt we would be able to detect life on Mars by cultivation at all. And that's assuming we're employing a more sophisticated method than egging it.
I'm not sure about the exact numbers, but I think it has been estimated that for each Earth microbe we can cultivate there are ten which we can't. On the one hand, there's the problem of figuring out the exact growth condition, which is tricky but solvable. On the other hand, there is the more serious problem of generation time. It's quite easy to cultivate an E. coli that replicates every half an hour or so, but what do you do if you're dealing with a hardy little critter that's adapted to a rather Spartan lifestyle and replicates once a year? Assuming optimum conditions of course, which typically don't involve a lot of egg.
Considering the temperatures and the relative sparseness of nutrients, anything living close to the Martian surface would likely have a metabolism of the slow and steady kind, which would make any cultivation attempts very, very boring indeed.
PS I don't see radiation and perchlorates as huge problems. Microorganisms can be extremely radiation-hardy and perchlorate is actually a bonus, since it keeps water liquid at low temperatures and can be metabolized quite easily.
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Well, I think there was talk about using ground-based lasers (solar-powered in your scenario) to heat a rockets reaction mass to the necessary levels, but I don't know how seriously this can be taken. I guess heating the right parts and keeping the others cool might turn out rather difficult.
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Kerbiloid mentioned quite an important point there. It is actually quite difficult to sterilize anything and I highly doubt it has been achieved for a spacecraft yet. Or even can be achieved.
I remember from my university days that at one point planetary protection protocols involved rubbing down the spacecraft with alcohol soaked cotton swabs. Which kills some of the microorganisms but mostly just spreads them around. I assume, methods will have advanced from that quite a bit, but unless we build a spacecraft hardy enough to put into an autoclave, there's probably nothing we can do on Earth that's worse than exposing the stowaways to space/the Martian surface for a couple of months.
And even if we do manage to kill 100% of viable germs, we will probably leave enough organic debris to interfere with our attempts to detect native life, so killing them is actually only half the job.
Not sure what my conclusions are, but I guess there's very little we can do to avoid contamination entirely and we'll just have to design our experiments around this constraint.
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5 hours ago, SunlitZelkova said:
Any contamination is unacceptable. If it turns out there is extant life on Mars, they would potentially end up killing it all with Earth organisms before follow up studies can be conducted.
Is it really considered likely that some random Earth germ that evolved under Earth conditions would somehow be able to outcompete native Martian organisms that lived and evolved there for millions of years? It's not like introducing rats to some remote Pacific island, it's like introducing rats to the middle of Antarctica.
Contamination would certainly make the identification of native Martians a lot harder though.
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9 hours ago, FleshJeb said:
Hey, Louis Wu boiled a sea using high-temperature superconductors and "sunflowers" in the Ringworld series. It only took Puppeteer-level technology to do it! /s
Love the books, but I doubt that this particular scene would work as described even with Puppeteer tech. A thermal superconductor in contact with a liquid would ideed not get hotter than the boiling point of said liquid, but unfortunately it wouldn't remain in contact for very long due to the formation of a steam envelope. The superconductor would likely reach its thermal limits very soon and disintegrate, long before the steam has a chance to turn into something more spectacular like a rapidly expanding shell of plasma.
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Or put another spacecraft in orbit around it and measure the period.
Not practical? How dare you!?
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I guess it would be possible that they're thinking about switching to a less complicated engine cycle (respectively a less complicated engine in general). Having a very high engine efficiency is obviously nice, but being cheap, reliable and easy to maintain might be worth more when all is said and done. This would also seem in line with the "the less parts the better" design philosophy.
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I don't know if one seventh of a g instead of an eighth offers enough health benefits to counteract the effects of increased radiation exposure. Actually, since it's pretty much unknown whether lunar gravity levels offer that much of an advantage over no gravity at all, you might even choose one of the outer moons. After all, to reach Jupiter you'd likely have to spend a considerable time in microgravity anyway, so you'd probably be able to deal with it a bit longer. The ease of ferrying fuel, passengers and equipment from and to your base might very well be worth it.
If you're after harvesting, let's call it "geothermal" energy for simplicity's sake, you'd probably want to be as much inward as you can be (also if you're trying to utilize Jupiter's magnetic field in some way) but again, I don't know if it's worth the increased radiation exposure in the end.
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Wikipedia seems to support what I remembered:
https://en.wikipedia.org/wiki/Muscle_architecture#Force_generation
Muscle force is essentially proportional to the muscle's cross-section (an area) while the mass is of course proportional to the volume. A person twice as tall (yeah, yeah) would therefore have four times the muscular cross-section but weigh eight times as much. (Amusingly, the tall person would also have twice the body mass index, but that's a tangent.)
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2 hours ago, JoeSchmuckatelli said:
because muscle power tends to increase linearly, while mass increases exponentially.
As far as I know, both grow exponentially, but with different exponents. Power increases quadratically while mass increases cubically.
Don't try this anywhere
in Science & Spaceflight
Posted
Well, nitric acid is actually pretty friendly to the environment. The trouble is, it's rather less friendly to things running around in said evironment. At least in its concentrated form.