Being a techie I really enjoy science fiction movies. What ruins one for me is a technical inconsistency or failure to get a technology correct. This post is my second in a series on the subject where I go through popular movies, talk about what they got right and dissecting what they got wrong. I should mention that I have yet to see a science fiction movie I consider 100% technically correct. Numerous fiction films have done so, but creating the perfect science fiction film has so far eluded Hollywood. The allure big explosions, laser beams and warp drive is so much more appealing to the masses than the inner workings of an airlock.

In this post I discuss the recently released ‘The Martian.’

martianWinner: The Martian

When I read Andy Weir’s book shortly after it was published in hardcover, I was amazed at the technical detail and the accuracy portrayed in the story. As an ex-NASA Space Shuttle Experiment Engineer, I get very distracted by inaccuracies, especially those in near-term science fiction– I still can’t bring myself to write about Gravity. I can see why so many people like the movie, but it was all I could do to not walk out of the theater when I saw it. But I digress. Let’s call The Martian the Anti-Gravity. From a technical realism perspective, it is everything Gravity is not. Specifically: accurate.

Okay, so there is one error I’d like to get out of the way before I start talking about all the great stuff: the premise for the film in how the main character gets stranded.

In the film the Ares team is performing experiments on Mars when a sudden storm approaches, forcing them to evacuate their hab and make their way to the launch vehicle. The danger is that the wind is so strong that it’s pushing against said launch vehicle and threatening to tip it over. They have to leave or they could all be stranded. As they make their way to their escape craft, dust and debris swirl around and the strong wind rips an antenna off its mount which impales Mark Watney, the main character, and flings him away. The crew presumes he is lost and is forced to leave before their ship topples over in the hurricane force winds.

Hurricane force– that’s an interesting term. On Earth, ‘hurricane force’ typically is used to denote the speed of the wind. The strongest, non-tornadic, winds recorded on Earth were with tropical cyclone Olivia where a weather station on Barrow Island, Australia recorded a whopping 253 mph! In a tornado, winds have been recorded in excess of 300 mph. I don’t think that anyone would argue that in either of those cases if Mark Watney was placed within them he’d have been flung off and left for dead. But that’s on Earth. On Mars, it’s a little different. You see, what made Mark fly away is the force of the wind. Not the ‘hurricane force’ I mentioned above, but the actual force. The two are different. Force is NOT wind speed. Wind speed is used in determining the force, but, again, it is not the force.

So how does wind speed translate into force? Force is caused by pressure. Dynamic pressure is caused by wind (or something else like water, etc.) pushing against something. The formula is the pressure is one half the density times the velocity of the wind squared. In the case we are discussing, the density refers to the density of the atmosphere. And in the case of the movie, the density refers to the surface density of the Martian atmosphere — which is .02 kg/m3 — or .02 kilograms per cubic meter, according to the NASA-Goddard Mars fact sheet. Why is this important? Well Earth’s atmosphere is about 1.2 kg/m3 or 60 times that of Mars. That means on Mars to reach the force to equal what you’d experience inside a tornado (likely what it would take to fling Mr. Mark Watney away) the wind speed would have to be about 1800 miles per hour. And to put a large spacecraft in danger of tipping over? Maybe you could halve the wind speed to create a force equivalent to about gale-force. Still, 900 mph is out there. Additionally, all this is assuming similar temperature — and it’s colder on Mars, meaning the pressure is actually even lower (roughly 1/100th of Earth on average) and thus the discrepancy is even higher.

Okay, 1800 miles per hour (or even 900) seems extreme, but it’s Mars, an alien world. It’s possible, right? Maybe, but the highest recorded wind speed is in the 300 mph range, or the equivalent on Earth of a stiff spring breeze. So I think 1800 mph is quite possibly outside the realm of realism.

There are two other minor hiccups to bring up. The first has to do with the main mission ship. It has lots of big windows. Windows in a space ship are bad. They are, for the most part, unnecessary weak points and opportunities for structural failure. The first manned Mars mission will have very limited windows.

The second was at the end when Watney punctures his suit in the palm to give him propulsion to get to his rescuers. Sorry, but no. He wouldn’t be able to control it. I’ll forgive this Hollywoodism, but no.

Enough of the bad stuff, let’s talk about all the great things the book and movie got right.

First I’d like to speak a little about orbital mechanics. What are orbital mechanics? I won’t go into the depths, but basically it’s how different things move around each other in space — orbits. The book/movie did a pretty good job in depicting travel between Earth and Mars and I really liked the puzzle solving involved in figuring out how to rescue our hero. The book did a better job, of course, but the movie played it up pretty well. There was also Watney’s escape from Mars. Most cheesy Hollywood movies would have some escape spaceship and the hero makes it there, gets off the planet, then lives happily ever after. Not The Martian. In this one the whole orbital mechanics thing pops in and the escape ship doesn’t have enough umph to both get Watney off the planet and match the speed of the rescuing ship blasting through Mars’s orbit above. Watney has to take the whole thing apart and ditch weight. It reminded me of stories of bomber crews in WWII trying to make it home one one engine and throwing out everything that wasn’t bolted down. Very well done.

Another thing that was great was Mark Watney figuring out how to communicate with Earth by retrieving and using the Pathfinder probe and its transmitter/camera. Again, the book did a much better job of explaining the whole process and why it was dangerous to make it happen, but then the book has a few hundred pages and the movie just over a hundred minutes. Also, not many movies would go through the effort to explain communicating through hex-decimal. Very well done again.

Terminator 2 had one scene that really made me love the attention to detail. It was when Arnold is in the office building, spraying down cop cars with the mini-gun. He runs out of ammo then pulls out a grenade launcher and fires off a few rounds. One of those rounds is shot at a car. Most movies would simply show the car blowing up, but Cameron put in a split second of film showing the grenade penetrating the side window before exploding. I love that. In The Martian, one scene gave me a similar feeling. The hab’s airlock fails and decompresses the entire thing. The makeshift potato farm inside is destroyed. They could have just showed the dead plants and be done with it. But inside the potato farm, it was humid. Water vapor was being produced to condense and water the plants (another great solve). After the airlock blew and Watney was surveying the damage, there was a sheen of frost on the farm’s soil. Excellent attention to detail.

Lastly: the visuals. The depiction of the hardware, the vistas, everything on the surface of Mars was extraordinary. It was a great taste of what the first manned explorers will see. Additionally, while I didn’t like all the windows in the spacecraft, the zero-gee translating to one-gee (in the rotating section) scenes were outstanding.

The book was excellent, riveting in its technical detail. I was worried the movie wouldn’t do it justice. While it did fall light on certain areas, areas I hope the directors cut will partially address, overall it held true to the book’s technical realism. I highly recommend reading the book and watching the movie to help visualize what Andy Weir portrayed.

Photos courtesy of Twentieth Century Fox.

Posted by Darren Beyer

5 Comments

  1. […] ← Technology: Movies Getting it Right – And Wrong: The Martian Oct 5 2015 […]

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  2. The landscape on Mars resembled the American west, grand canyon and possibly Australia. Were any of the LANDSCAPE shots in the movie filmed in actual places on earth? Or was it all magically created by some process? I enjoyed the movie!

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  3. Evidently it was filmed in the Jordanian desert of Wadi Rum.

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  4. Are you, is anyone, bothered by the fact that spacecraft is jeopardized by strong winds in the first place – that a multi-year, millions (or billions) of dollars’ effort had to be abandoned because there was no contingency plan for what would seem to be a predictable event? Presuming enough was known about the Martian environment before undertaking the mission, wouldn’t the planners have thought of, and provided a means for, securing the spacecraft against such wind forces (regardless of what speed they might realistically be)? Granted, that would have meant “no movie” – or at least coming up with a different precipitating event – but still…… Or did I miss something?

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  5. I wrote David a reply via email – here is my response that also has some answers to questions he had about Gravity:

    Winds on Mars:

    The wind question is one that I have the most issue with in the movie. I spend a fair amount of words discussing the fact that the winds measured on Mars to date are in the 300 mph range. When you take into account that the pressure on Mars is much, much lower than on Earth, that equates to like 20 mph on Earth. So nowhere near what would be required to cause a spacecraft any sort of issue. But let’s say that they could get to the level required to cause problems. We would have seen the wind levels before and the spacecraft would have been designed to withstand them – OR – let’s say that those winds were measured and the mission planners said, “eh, it only happens once every 10 years – let’s take the chance.” In that case they would have seen the storm long before it hit and would have aborted the mission before it became an issue. In other words, you’re right. You didn’t miss anything.

    On to Gravity:

    Gravity was so filled with problems. On the reentry thing, a reentry path is defined by the retrograde burn – or the thruster burn that slows the spacecraft down. There really isn’t a whole lot to getting it right. You need to be oriented in the right direction and burn the thrusters for X seconds. Now – can you do that manually? The thruster burn, absolutely – there is some margin there that would allow you to get to the right orbital velocity – though hitting the right landing zone would be dicey. The orientation? Not so much. You have to know exactly how the spacecraft is oriented. If you’re off, then the burn wouldn’t slow it enough. Once you’ve done the burn, however, if it’s done right, there is really no control required after that. The capsule is like the payload of a ballistic missile at that point.

    So now the tether thing. It was incredibly poorly done – especially the part where Clooney gets ripped from Bullock’s grasp. There has to be force to do that. The only force would be centripetal force from some sort of spin exhibited on the space station – but that much force would require some pretty hefty spin and there was nothing to induce it. And you ask whether they dropped into an orbit that would have made gravity suddenly present. Orbits by their nature have no “felt” gravity because the centripetal force exhibited by zipping around the Earth (or whatever planet/moon/asteroid) are offset by the gravitational force of the Earth. If you slow down, you go into a lower orbit, but still feel no gravity. If you speed up, you go into a higher orbit, but still feel no gravity. Slow down enough and you start to drop out of orbit, but you won’t feel any gravity for a while since you’re effectively in freefall.

    A few of the many other things that were horrible in the movie:

    – At the beginning, when they are working outside the orbiter, one of the astronauts is zipping around, bouncing with his tether. No – just no. That wouldn’t happen. It’s just too dangerous. Everything in space happens slowly because one misstep and you’re dead.

    – The Marvin the Martian and other stuff was floating around the cockpit – and the wrenches, etc. outside. Everything outside is tethered. Everything. Inside, floating stuff is a hazard and kept to a minimum. Most things have velcro on them and there are velcro patches everywhere inside the orbiter.

    – The debris field from the Russian satellite might (unlikely) have posed a threat on the first pass, but then would have been way too dispersed – and the likelihood of a second, third, etc. threat would have been nil. Even the first pass would have been maybe a single piece of debris – and that would have been entirely plausible – not this whole shotgun blast of stuff. And the 90 minutes thing was way off. Technically orbits can intersect, but 90 minutes is the amount of time (mostly – totally depends on orbital altitude) that the orbiter takes to go around the Earth. Two things in same altitude, but different, intersecting orbits, would take much longer – if they ever even met again.

    – The Chinese space station burning up. OK – so for the record, it is entirely plausible that this would happen. Orbits decay and things can fall back into Earth’s atmosphere. However… if the station was that close to entering the atmosphere and burning up – anyone using a maneuvering unit to get there would be in the same boat. And please, using a maneuvering pack to go from space station to space station is completely implausible. First off, if you even had enough propellant to change your orbit by a meaningful amount so you could get to another station, it would take a long time to actually “catch” it. And the way it would work is backwards from what you saw in the movie. To “catch” something in the same orbit, you first need to slow down – yes, you don’t speed up to catch it, you slow down. Why? Because if you speed up, you go into a higher orbit, which actually slows you down in relation to the thing you’re trying to catch. You actually want to slow down to drop into a lower orbit, catch up, then speed up to go back to a higher orbit and intercept. This is not something you do manually when you can’t even see what you’re trying to catch.

    – The fire extinguisher thing – no. Just no. It’s the same issue I have with the Iron Man equivalent at the end of The Martian.

    There are many more issues with Gravity, but those are a few that are top of mind.

    Reply

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