Inside the Spaceflight of 'The Martian'

benonemusic writes: Science writer Michael Greshko partnered with a team of scientists and engineers to explore the spacecraft and mission plans in The Martian (novel and movie), down to the rescue plan itself. Incorporating the help of Andy Weir, the novel's author, he comes up with a calendar of events for The Martian, explores the hazards of going back to save Mark Watney, and explains how a real world interplanetary spacecraft would pull off a rescue maneuver.

Comments

Are and storms that fierce on Mars?

[peter303]

I know they have sandstorms, sometimes dense enough to hide the surface. But with an atmosphere that never exceeds 2% the density of Earth's, can it blow people down and topple spaceships?

Re:Are and storms that fierce on Mars?

[ClickOnThis]

I know they have sandstorms, sometimes dense enough to hide the surface. But with an atmosphere that never exceeds 2% the density of Earth's, can it blow people down and topple spaceships?

The short answer is no.

Re:Are and storms that fierce on Mars?

[SharpFang]

Andy Weir explained in one of the interviews that it was the only point where he used his artistic license against hard science. "I wanted Mars to deliver the first punch". He said he could have done this differently, but he wanted this to be Nature's fault, not a human shortcoming.

He stayed true to science best to his ability the rest of the time. Not that he didn't make any mistakes - he made quite a few, but none of them were intentional violations, just his lack of universal knowledge - or developments that happened after he wrote the book.

To name a few:
- water content in soil, making Hydrazine burning moot.
- Chlorides content in soil, making it totally unsuitable for plants and harmful to health, unless purified.
- raw potatoes being merely "awful" while in reality they are quite poisonous.
- hydrazine reaction heat being neglected (someone calculated it would heat up the Hab to 400C).
- space radiation being handwaved away by "Hab is radiation-proof" while it's an inflatable structure.

Re:Are and storms that fierce on Mars?

[Irate Engineer]

- raw potatoes being merely "awful" while in reality they are quite poisonous.

Wow, they sell 5 lb bags of raw potatoes in the store! What a reckless thing to do! Amazing the personal injury lawyers haven't jumped on that!

Seriously, properly grown potatoes are harmless, raw or cooked. However, being nightshades, if potatoes are not hilled properly the ones near the soil surface that are exposed to sunlight will turn green and produce solanine, a glycoakaloid poison. I grow potatoes in my garden and just make sure to toss any potatoes that have any green on them.

Fresh young potatoes from the garden, sliced thin and sprinkled with a little sea salt are pretty darned tasty, but eating nothing but potatoes would start to suck ass pretty quickly.

Re:Are and storms that fierce on Mars?

[steveha]

- space radiation being handwaved away by "Hab is radiation-proof" while it's an inflatable structure.

At least the story is internally consistent: because the Hab is radiation-proof, radio waves don't go through it, which is why Mark Watney has to go outside the Hab just to check his email. (Actually, I think he ought to have strung a network cable; he cheerfully did more difficult tasks than that at various points in the book. But then the plot complication caused by going outside so often might not have occurred.)

When I like a book or movie I tend to try to come up with explanations of anything I wonder about. My explanation of how the Hab is radiation-proof: a superconducting magnetic shield. Only protects against charged particles though...wouldn't stop gamma rays. How common is random gamma radiation on the surface of Mars?

Here's an article about spacecraft using magnetic shields:

http://home.web.cern.ch/about/updates/2015/08/superconducting-shield-astronauts

P.S. 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" so I don't accept this as a valid complaint.

Re:Are and storms that fierce on Mars?

[Rei]

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.

Re:Are and storms that fierce on Mars?

[Rei]

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.

Re:Are and storms that fierce on Mars?

[Rei]

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.

Re:Are and storms that fierce on Mars?

[Rei]

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.

Re:Are and storms that fierce on Mars?

[Rei]

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.

Re:Fun Movie, Not Future Reality

[SharpFang]

Not entirely impossible, just unlikely. There was a lot that could go wrong, and very likely to go wrong. The deceleration through blowing the airlock would most likely send Hermes spinning instead of decelerating, the opening not being a precise nozzle but a random hole directing the air outside at a random angle. The rocket would most likely be unbalanced after such heavy strip-down, sending it spinning again.

OTOH everyone overestimates the "one chance" they had at the encounter.

You're moving 12m/s away from the target.
To reach 12m/s at 2mm/s^2 you need 6000s or 100 minutes. That puts the target at 72km distance.
Now give it a chase. Accelerate for half of that distance, decelerate the other half. 6m/s top speed, average 3m/s relative speed. That's another 6.6 hours.
Mark would need to spend about 8 hours waiting for Hermes to smoothly make a perfect rendez-vous after failing the initial encounter. There's no time pression of time like with suborbital trajectory - they are both on escape trajectory. Hermes would get a little off Purnell Maneuver trajectory, but 72km offset and 12m/s error is practically nothing for this kind of mission. The whole panic was simply unnecessary.

Re:Fun Movie, Not Future Reality

[Quarters]

Thanks for being the self-centered asshole who feels it's OK to fire up his phone screen in a darkened theater. Why should you have to bother to park your selfishness for 90-120 minutes and let the scores of other people see a movie in peace, right?

Re:Fun Movie, Not Future Reality

[RoccamOccam]

I just watched this tonight with a lady friend. I was bored enough to browse /. on my phone for a little while. Then she grabbed my hand and whispered that I'm supposed to be watching the movie.

Wow - you just casually admit to this? For the sake of others, please never do this again. There's a reason that theaters run the little public service announcements about turning off your phone before the movie. This should be a standard question on a test designed to identify sociopaths: "If you bored while watching a movie in a theater, do you a) suffer silently, b) leave the theater, or c) ignore the rest of the people in the theater that have paid to watch the movie and pull out your phone."

Re:Fun Movie, Not Future Reality

[AchilleTalon]

And just take this single fact the astronauts heading to Mars will be constantly and permanently striked by cosmic rays since Mars doesn't have a magnetic field and its atmosphere is much less dense than Earth's atmosphere. In case you don't know, when cosmic rays strikes you eye globe it produces flashes you can see. In short, these poor guys will have hard time to sleep. This is just one thing among a pile of others that would turn anyone unsane here after a couple of months.

Re:Fun Movie, Not Future Reality

[Quarters]

You realize that light bounces and people have peripheral vision. People shouldn't have to 'get over it'. If you are so self centered as to not care about other people, including the woman you were with, enjoying a movie then you are an asshole. If you are so attached to Slashdot that you can't go the length of a movie without checking it, get your ass up and go to the lobby.

Re:Fun Movie, Not Future Reality

[pepty]

No worse than the way people in zero-G in the Hermes flew in curves instead of straight lines.

Re:Fun Movie, Not Future Reality

[KGIII]

And yet that's never happened. Funny that. However, I certainly agree that I'm an asshole. On a more serious note, nobody noticed - it's not like I was anywhere that bugged people. Well, she noticed but it turns out she just wanted to hold hands. (She's still here, at any rate.) I was kind of surprised at how few people were in the theater - it was a Regal in Buffalo. They all went and watched the 3D version. If someone had even slightly indicated displeasure then I'd have certainly stopped - while I am an asshole I'm not that much of an asshole. I'm usually pretty perceptive too. I also wasn't holding it up and waving it about or anything. It was down between my knees and automatically dims in the darkness. You'd probably have had to work to notice as we had the entire row to ourselves and it was the furthest row back. Not even the usher complained - probably because it bothered nobody and was on silent.

It's tempting... Man is it tempting. I mean, hell, you're offering free life skills assistance, right? So far you've been willing to call me an asshole, without really knowing much, and that's certainly true. So you're willing to be brutally honest, perhaps perceptive, and you seem to be convinced you have all the answers to what is and isn't socially acceptable behavior. Boy have I got a wall of text and some questions for you. You have no idea how tempting that is... ;) Tempting indeed. I mean, you guys helped me pick my favorite Linux distro. You've given me advice on investing (albeit not intentionally). You, meaning Slashdot in general, are generally smart and insightful as a whole. In fact, I'm on my current adventure, in part, due to some advice from a person here on Slashdot.

Alas, I'll think I'll pass for now. I also need advice about buying a boat. I don't know anything about boats but I'm told I could invest a small amount and make a tidy sum on a resale assuming I'm willing to park some currency for a while. You don't know anything about boats, do you? It's a big boat, it has sails and a motor and stuff. It's in Barbados and has engine and cosmetic issues and the insurance had lapsed. It's huge, like 130' huge, and the price is pretty high as is the estimated repair cost but the resale value's pretty high too - a 200% profit would be reasonable but the turn-around could be a couple of years (or more - I don't know) as the market isn't that strong currently, or so I'm told.

I mean, yeah, if you're giving out free advice... *shrugs* It can't hurt to ask, right? I really should do a funny Ask Slashdot style journal post.