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?

[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]

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: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."