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I am curious what the most accurate, versus most inaccurate things that were depicted in the space movie, "The Martian"?

I thought the part where he punctures his suit and jets over to the rescue vehicle seemed implausible. Unless you had the hole directly jetting gas directly in line with your center of gravity, wouldn't you just spin around?

Also, the way the homemade "explosive" blasted a hole in the door seemed unbelievable to me, but I guess that would depend how tough the door is.

Also, I don't see how having a small hole in the habs tent would cause it to suddenly and violently blast apart the way it did.

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    $\begingroup$ Note that in the novel Mark also suggests the "iron man" but doesn't actually do it. $\endgroup$ – Roman Reiner Nov 10 '15 at 7:11
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    $\begingroup$ The novel/film assumed the existence of a well-funded human Mars program, but I'm guessing you're asking about scientific implausibilities... ;-) $\endgroup$ – Andrew Nov 10 '15 at 14:09
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    $\begingroup$ The thing that struck me as wrong while watching it was the crewmember waiting in an open airlock for the supply capsule to dock as they passed earth. He didn't have any role there except to die if things went south. $\endgroup$ – AShelly Nov 10 '15 at 19:27
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    $\begingroup$ @Adrian: Andy talked about the book, and how after the release a chemist contacted him, having calculated the Hab ambient temperature to be 400C after the hydrazine burning. Andy replied though that there's a plenty of heat-sinking capacity on Mars. (and he can get it done with the oxidator and air regulator, just by disabling their heaters: condense gasses outside the hab, dumping heat into Mars atmosphere, then dump them back into the Hab in liquid state.) $\endgroup$ – SF. Nov 12 '15 at 9:54
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    $\begingroup$ Asking for the most accurate thing is futile, because it's full of things that are 100% accurate. For example, the movie asserts that human beings can't survive for 500 days without food. It asserts that NASA management speak English in their meetings. And so on and so forth. $\endgroup$ – Mike Scott Nov 13 '15 at 7:16

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Watney did have trouble controlling himself with the "iron man" suit puncture trick; it's plausible that he could quickly get the hang of positioning his hand to thrust through his center of mass (though that all happened fast enough that I didn't see if it was so depicted). Mastering that technique in the few seconds he had available was pretty unlikely, though.

The least plausible thing about the story was the force of Martian winds -- at less than 1% of Earth atmospheric pressure, even a big storm on Mars wouldn't lift anything other than the finest grains of dust. Both the initial accident and the flapping of the makeshift hab repair job make no sense given that fact.

The next least plausible thing IMO is the decision by the Hermes crew to return to Mars to rescue Watney. Given that there was already a workable plan to keep him alive and get him back, it was criminally insane to divert a multi-billion dollar mission and risk five more lives in the process. If I remember correctly, the book devotes some attention to mechanical breakdowns aboard the Hermes during its extended mission; while it was designed to be reused as the interplanetary carrier for subsequent Ares missions, it was supposed to get some maintenance while parked in Earth orbit between trips. If Hermes had fallen apart en route, that would have been the end not only of the crew but the entire Ares program.

The convenient ability to electrically interface the hab solar panels to both Pathfinder's and the rover's electrical systems seems a bit unlikely, but not physically implausible per se.

Hydrazine and its decomposition products are pretty toxic, so his water source would have killed him.

The film doesn't address the problem of radiation exposure - with little atmosphere and magnetosphere, radiation shielding for human explorers is a necessity.

Pathfinder detached from its parachutes while still a ways up (it landed via airbag), but in real Martian weather I suppose it wouldn't have wandered too far, and Watney might have had access to this map to lead him from the chute to the lander.

There's a bunch of stuff that is barely physically plausible, but almost certainly wouldn't work out in practice, like improvising an orbital rendezvous using vented cabin air for thrust.

All that said, it's a fun movie, and the grossly plausible aspects of the science are interesting to see.

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    $\begingroup$ Thats true, I was kind of amazed that he just plugs the power cord from his base station right into the Pathfinder. I was like, wow good thing the Pathfinder uses exactly the same power interface as his power station. $\endgroup$ – Tyler Durden Nov 9 '15 at 22:28
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    $\begingroup$ At least some actual real life astronauts would very explictedly disagree with your second least plausible point: youtu.be/Wq3xtZ8AjPE $\endgroup$ – David Mulder Nov 9 '15 at 23:22
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    $\begingroup$ @DavidMulder: I found the decision of the other astronauts quite plausible. They had spent a year together getting there, so (could have) bonded well. They felt they had left a friend behind. Ask the military about "we leave no body behind". Here it was a live body. $\endgroup$ – Ross Millikan Nov 10 '15 at 4:33
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    $\begingroup$ @TylerDurden In the book he doesn't. He is an engineer and he builds an adaptor which he just plugs into the Pathfinder. Given the montage esque way everything is forced depicted, there isn't anything suggesting he plugged the power cord directly into the Pathfinder. Also thank God Nasa uses common connectors. They learnt that lesson on Apollo 13. $\endgroup$ – Aron Nov 10 '15 at 6:17
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    $\begingroup$ In the book, the common power system is explained well. $\endgroup$ – JDługosz Nov 10 '15 at 21:48
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The most inaccurate "artistic license" thing was the Martian storm - Andy Weir admitted that he misrepresented it for dramatic effect.

The most blatant error though was in growing the potatoes. In particular, the matter of lighting. For the depicted indoor growth, Mark would need 60 kilowatt worth of LED growth lights, and a proportionally sized solar farm. Potatoes are light-hungry. The sunlight levels on Mars are insufficient for direct sunlight growth, and for artificial light you'd need about 4m^2 of solar panels per m^2 of farmland.

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  • $\begingroup$ He could've tweaked that part. The only succesful, for 15 seconds, Russian soft landing om Mars, Mars 3 seems to have succumbed to the dust storm it landed in. The dramatic effect of the storm could've been preserved, but leading to suit malfunction, or something such, instead of tearing down anything. But that would be a bit abstract to the public, and in any case humans might very well have to evacuate from a dust storm on Mars. I give this a go. NASA crew leaving a body behind is what is most unrealistic. They'd rather leave all behind than just one. $\endgroup$ – LocalFluff Nov 10 '15 at 11:47
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    $\begingroup$ @LocalFluff The other astronauts thought he was dead. Additionally, if they didn't leave when they did, they would have stranded themselves on Mars. I think the unrealistic scenario would for a group of people to intentionally decide to maroon themselves on Mars to reclaim a dead body. $\endgroup$ – Dean MacGregor Nov 10 '15 at 16:04
  • $\begingroup$ @DeanMacGregor I think that it would have been psychologically and politically impossible to leave a body behind, even if it was thought to be dead. Even a found dead body would've been taken home to sacred ground. Or to stay with it. Most of Hollywood is on that theme. America hasn't changed that much yet, and I don't know of an example of an exception. $\endgroup$ – LocalFluff Nov 10 '15 at 21:17
  • $\begingroup$ @LocalFluff I'll certainly grant you that if they knew he was alive, they would have risked their life to rescue him before leaving him stranded. On the other hand, I reject the notion that much of Hollywood is on the theme of having multiple people risk their lives to recover a known corpse. For example, in Saving Private Ryan, they didn't know he was alive but still decided to risk people's lives to bring him home. In the beginning of the Martian, the other astronauts believed he was dead as opposed to just being unsure of his well-being. $\endgroup$ – Dean MacGregor Nov 10 '15 at 21:32
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    $\begingroup$ Note that there are plenty of frozen corpses on Mount Everest that are left alone because it is too dangerous and/or expensive to get them. Extrapolate that to Mars... $\endgroup$ – Brian Lynch Nov 12 '15 at 4:52
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The most obvious thing in my opinion was the orientation of Hermes in the scene right before they receive the hidden transmission with instructions for the Rich Purnell manoeuvre. They had just discussed the fact that Hermes is currently slowing down in its approach to Earth, which would mean the vehicle is pointing retrograde. However, when it cuts to Hermes you can clearly see it traveling towards Earth bow first with the engines brightly lit firing in the prograde direction. Either they intended that shot to be used after the manoeuvre was discussed and agreed upon by the crew but then edited it later, or the usual Hollywood lack of understanding is to always show a spacecraft pointing in the direction it is moving.

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With 2 mm/s^2 acceleration, Hermes' 124 day trip from Low Earth Orbit to Low Mars Orbit is impossible.

"Low earth orbit?" a Weir defender might object, "It's all hyperbolic fly bys."

Which is wrong, of course. The hyperbolic rendezvous were extraordinary maneuvers made under unusual circumstances (Watney needing rescue). The 124 day earth to Mars trip preceded the Sol 6 windstorm that stranded Watney. There aren't hyperbolic fly bys either at the beginning or end of this leg of the journey.

"The 124 day trip wasn't depicted in the movie". It was described in Weir's book as well as the movie's back story provided by Fox.

Also Neil DeGrasse Tyson's trailer for the movie. 1:15 of Neil Degrasse Tyson's trailer has Hermes departing from low earth orbit. 2:20 gives the trip at 124 days.

In addition here's a graphic from Inside Science (thank you Pearson Art Photo). I underlined the relevant phrase.

enter image description here

A Weir defender writes "The 124 day mission seems to not include LEO, but otherwise is fine."

This is like saying the 5 hour drive from Spokane Washington to Great Falls Montana seems to not include the Rocky Mountains but otherwise is fine.

The cities are 300 miles apart so a 5 hour drive seems plausible until you take into account that they're separated by the Rocky Mountains.

And so it is with the Hermes 124 day trip. When you're only accelerating 2 mm/s^2, getting out of LEO is huge. Here is an illustration from Mark Adler's answer to the Stack Exchange question General guidelines for modeling a low thrust ion spiral?

enter image description here

Mark Adler's description of above spiral:

Here is an example of a spiral from a circular orbit to escape (C3=0):

This is normalized to the starting circular orbit, where the distances are in units of the initial orbit radius, and the acceleration is constant at 10−3 of the gravitational acceleration of the body at the initial orbit radius. The total ΔV to escape is 0.856 of the initial orbit velocity, as compared to 1.0 for the rule of thumb. The total time to escape is 136 initial orbit periods. It goes around the body about 40 times before escaping.

In Hermes' case the 2 mm/s^2 constant acceleration would be about 2*10^-4 of the gravitational acceleration at the initial body radius, so the delta V would be more than .856 * 7.73 km/s. But I'll be kind and go with this under estimate.

.856 * 7.73 km/s is about 6.6 km/s. At 2 mm/s^2, it would take Hermes 3.3 million seconds to achieve this delta V. 3.3 million seconds is ~38 days. That leaves about 90 days to go from a 1 A.U. to a 1.52 heliocentric orbit. Which isn't doable at 2 mm/s^2 acceleration.

Most of that 38 days would be a slow spiral through the Van Allen Belts. Not only is the 124 day trip from LEO to LMO impossible, but it would also cook Watney and friends.

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    $\begingroup$ Andy Weir states he wrote a computer simulation to model the Hermes trajectory. The 124 day mission seems to not include LEO, but otherwise is fine. $\endgroup$ – PearsonArtPhoto Nov 9 '15 at 23:03
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    $\begingroup$ Which trajectory are you referring to? After the Hermes leaves Mars at the start of the movie, they never re-enter Earth orbit or Mars orbit; it's all fly-bys. $\endgroup$ – Russell Borogove Nov 9 '15 at 23:03
  • $\begingroup$ Hermes isn't in orbit, the time spent in orbit is irrelevant. $\endgroup$ – Loren Pechtel Nov 9 '15 at 23:06
  • $\begingroup$ insidescience.org/content/inside-spaceflight-martian/3251 shows the trajectory. $\endgroup$ – PearsonArtPhoto Nov 10 '15 at 0:16
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    $\begingroup$ That trajectory isn't really mentioned in the movie, which may account for some of the confusion you're getting in this comment thread, since OP didn't mention the book. $\endgroup$ – Russell Borogove Nov 10 '15 at 1:15
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I liked the film and found it quite realistic overall, but what I found very unrealistic was his repair of the hab using plastic foil and duct tape.

It has already been mentioned that the martian atmosphere is very thin. Inside the hab the air is breathable, so it's pressure must be substantially higher than that of the martian atmosphere.

If the pressure inside the hab was about the same as on earth, the force acting on the plastic foil would be very large:

F = p*A
F force in Newton [N]
p Pressure difference in Pascal [N/m^2]
A Area in square meters [m^2]

With p = 100'000 N/m^2, A = 4 m^2, the force would be

F = 400'000 N

about equivalent to the pull of 40'000 kg on earth!

Even if the pressure was lower and the area smaller, it's completely impossible that this repair would have worked.

Another unrealistic thing that was not mentioned yet was the "oxygenator", it was never explained how it was supposed to works.

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  • $\begingroup$ In English units, atmospheric air pressure is 14 PSI, so for a 40-inch portal (~ 1200 square inches) we would have 16,800 pounds of pressure on the portal or 8 long tons. Plastic and duct tape would not hold that. $\endgroup$ – Tyler Durden Nov 11 '15 at 16:22
  • $\begingroup$ 4 m^2 would be a portal with a diameter of ~2.2 m (88 inches). $\endgroup$ – alain Nov 11 '15 at 16:34
  • $\begingroup$ In that repair he also used two red compression tie-down straps - look for them in the first shot of the repair from outside the Hab. They would have been strong enough, if there was an entirely convex surface to strap it on to and he put them on correctly. I don't think he put them on in the best way - he ran the plastic under both of them, with the free edge pointing back toward the Hab. I would have run the plastic under one that was close to the Hab, then folded the plastic forward and put the other strap over the folded area - so it doubled back on itself. $\endgroup$ – Adam Nov 14 '15 at 16:29
  • $\begingroup$ We don't have to match earth atmosphere. However, in the movie, the foil is seen being moved in and out by the martian wind, which would not happened because of the pressure. $\endgroup$ – Antzi Aug 16 '16 at 16:21
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I find it improbable that earth would be making the call to abort the mission when it takes 12 minutes x 2 for them to get the Mars weather report and to relay their decision. Whether in the scenario portrayed in the movie or any potential scenario, the astronauts would need to be empowered to make their own decisions. This is relevant for the book and the movie.

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    $\begingroup$ In the movie, Earth-side mission control set the abort rules, but the mission commander on Mars made the call. $\endgroup$ – Russell Borogove Nov 11 '15 at 0:19
  • $\begingroup$ In the movie the time offset is ignored in the initial dust storm and in the live rescue of Watney. They mention that there's a delay but the filmakers don't implement it. $\endgroup$ – user12313 Nov 11 '15 at 17:59
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    $\begingroup$ The time delay is actually mentioned while the "live" rescue is happening. There's a conversation in Mission Control where the question is asked "what can we do?", and the answer given is "not a damn thing". It's then explained that Mars is 12 light-minutes away, and the rendezvous will take about 12 minutes, so it'll all be over by the time Earth finds out about it. They just interposed the shots of the rescue with the shots of Earth as they heard about it 12 minutes later, for dramatic effect - otherwise we'd have to watch them watching the screens when we already know the outcome. $\endgroup$ – anaximander Nov 13 '15 at 10:15
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One addition that I struggle with was the rapid way he was able to use poop and Martian regolith to create soil to grow the potatoes. In the book at least (didn't see the movie). I can't anywhere find data on how long it takes to make organic soil for plants; sure hydroponics are great, but that's not what Mr. Whatney did.

Soil takes a long time to create and it most certainly takes a long time if all you have is poop, bacteria, and the fine dust of Mars. Composting with worms can make some pretty good nutrition for plants, but that is a lot more ingredients than poop and sand. Once you've spent that time, you must then wait out the time to grow the potatoes.

That being said, I thoroughly enjoyed the quick read, and I hope to see the movie soon. Moreso, I hope it inspires people to believe more in the possibility of going to Mars sooner rather than later.

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Aside from the enormous pressure that would have torn the makeshift repair on the air lock apart, I think the hydrazine burning would have poisoned Watney.

The reaction happens in a more or less open setup, and hydrazine is toxic. Some would have evaporated or carried up as tiny droplets by the hydrogen and nitrogen, and escaped into the hab atmosphere.

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In the book (original epub version, anyway) the chemistry of making water had serious flaws. The narrative assumes that all materials have the same number of molecules per unit volume. I looked up density and molecular formulas in Wikipedia while I was reading, and found that the moles for the fuel was off by a factor of 2.

I also found that the name of the Chinese rocket translates as “The Titanic”, which I thought was inauspicious and would be remarked upon in the story.

As for the Big One: the air is so thin that even a hurricane air speed would not knock over the rocket or push the people around like that. It seems unlikely that the rockets stay there for years, for multiple missions in staging, and can't handle the weather that occurs just as the people show up! The worse wind to be expected would be a known factor. Now they could have made this more plausible by coming up with an unexpected factor, like the wind-bourne dust is giving an impact force amplified compared to the wind itself.

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  • $\begingroup$ "I also found that the name of the Chinese rocket translates as “The Titanic”, which I thought was inauspicious and would be remarked upon in the story." I don't see how this has to do with accuracy/inaccuracy. Red herrings are valid plot devices--and it really has nothing to do with the accuracy of the science. $\endgroup$ – called2voyage Nov 10 '15 at 22:23
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The hacking away at the rocket bothered me a lot. Thin atmosphere aside, I just can't stomach that you could hack that much off a a rocket and still have it work aerodynamically.

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    $\begingroup$ The entire point of "thin atmosphere" is that the means the rocket doesn't need to "work aerodynamically" because there is just not enough aero for it to matter. $\endgroup$ – Michael Borgwardt Nov 12 '15 at 13:57
  • $\begingroup$ I know that is what they were going for. I just don't think I buy it. The martian atmosphere is thin but it still exists. $\endgroup$ – chessofnerd Nov 12 '15 at 17:26
  • $\begingroup$ @MichaelBorgwardt: that's having it both ways, though. The atmosphere cannot be simultaneously thick enough to push you around the place, and thin enough that aerodynamics are irrelevant. That said, "neglecting air resistance" is, at a meta-level, extremely plausible in a fictional/modelled setting ;-) $\endgroup$ – Steve Jessop Nov 13 '15 at 11:33
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    $\begingroup$ My problem with hacking away at the rocket is why was that weight there in the first place? Yes, they can dump anything meant for cargo return but there shouldn't be anything else at all heavy on there that isn't essential. $\endgroup$ – Loren Pechtel Nov 21 '15 at 1:34
  • $\begingroup$ Loren, Thanks for agreeing! However, what I gathered from the book was that the aerodynamic stuff was for take off on earth. Then again, why not design it to be retrofitted once on mars. You raise an excellent point! $\endgroup$ – chessofnerd Nov 21 '15 at 8:13

protected by Deer Hunter Nov 12 '15 at 13:07

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