What were the most inaccurate or accurate things in "The Martian"?

Question

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.

Answer 1

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.

Answer 2

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.

Answer 3

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.

Answer 4

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.

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?

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.

Answer 5

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.

Answer 6

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.

Answer 7

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.

Answer 8

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.

Answer 9

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.

Answer 10

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.