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Comment Re:Are and storms that fierce on Mars? (Score 1) 55

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.

Comment Re:Are and storms that fierce on Mars? (Score 1) 55

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.

Comment Re:Are and storms that fierce on Mars? (Score 2) 55

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.

Comment Re:Are and storms that fierce on Mars? (Score 1) 55

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.

Comment Re:Are and storms that fierce on Mars? (Score 1) 55

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.

Comment Re:Fun Movie, Not Future Reality (Score 1) 55

I've seen all but the A Class Divided and Tim's Vermeer. I'll take a look, thanks. We've watched a few now, it's pretty early in the morning but it has been a fun night.

This one was interesting:

It's about an escaped convict in Australia who lived among the aboriginal people back when white folk were new to the continent. His name was William Buckley.

Another that was interesting was:

That one was about the war in Afghanistan, right at the very beginning, when a bunch of Taliban were taken prisoner and revolted and caused a bunch of mayhem. It too was more interesting than I'd expected.

I only watch documentaries normally. If I had to average it out then I'd say I watch maybe a non-documentary once or twice a month, sometimes less than that. I don't watch them to learn anything, not anything deep. I don't even retain what I learn for very long but I do learn enough to be passingly familiar with a variety of subjects.

To me they're entertainment, I find them more entertaining than I do a thriller, an action movie, or something similar. I grew up watching many WWII and Korean War documentaries and longer expose-type news shows on the on-going Vietnam war. So, it's really been what I prefer for a long time - my whole life really. I think one of the greatest things in life is access to all these documentaries in an instant. 'Tis glorious. I usually watch one during the day and one at night as I sleep though I'll often leave some playing while I sleep.

Anyhow, thanks for the links and suggestions. I'll certainly look into them and likely watch them. I don't do the 'documentaries' you see on cable these days (Pawn Shop shows are not documentaries - nor is rummaging in somebody's attic) but I prefer stuff that is probably considered dry by most people's views. I'll take a gander and see.

Comment Re:Are and storms that fierce on Mars? (Score 1) 55

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.

Comment Re:How about that (Score 1) 72

Umm... Unless I am missing something, it appears that they did not misspell anything. They failed to include a word but they didn't misspell anything that I can see. My spelling isn't that good but those are pretty simple words and I think I'm spelling them properly. So, if spelling is the greatest accomplishment you've done then...

Comment Re:Again VOD release date? (Score 1) 55

As I posted up-thread, it's not worth seeing at home in my opinion unless you've a *very* good setup. There's little redeeming value other than the eye candy and good acting. It is marginally better than above average and that's only due to seeing it on the big screen. I don't expect it to do well once out of the theater unless they add some compelling content. (I do wonder if it would make an interesting video game, however.)

Comment Re:Decline of Soda?, Two words.. (Score 1) 326

*chuckles* Off-topic? Me? Ha! Surely you jest. That's my default state. I don't mind the moderation (not even a little) but it's unlikely to curb my behavior any. You're probably more likely to actually help people by reserving your moderation points for others (both positive and negative) as I am unlikely to be affected. It'd probably take some work to lower my karma rating from the 'excellent' status (which, considering how off-topic I am - constantly, is kind of surprising) or anything.

However, I think I'll use this as an opportunity to point out the futility of the system and I'll just post with my Karma Bonus. See? Now you have something new to mark as off-topic. That'll keep you amused for a few minutes.

The life of a repo man is always intense.