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.’
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.