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Good afternoon. We're going to be talking today about the plausibility of various events or concepts as they were presented in the book The Martian by Andy Weir and the movie based on that book, The Martian starring Matt Damon.

First, though, I want to introduce myself. My name is Loretta Hall, and I'm a space buff. I've been a freelance writer for over 30 years, and for the last 10 years or so, I've largely focused on researching and writing about humans preparing for and ultimately achieving spaceflight. I've written four books on space travel, including two on its history. I'm also a Certified Space Ambassador for the National Space Society, a great organization that works to promote manned space exploration and ultimately colonizaton. Its Space Ambassadors give presentations like this one to inform people about space exploration and hopefully generate interest in and enthusiasm for space missions. The NSS also develops education programs and sponsors competitions for students around the world to help them learn about space exploration. And they work to influence America's space policy. I left some information sheets about NSS in the back of the room, and I invite you to take one when you leave and learn more about the organization.

Now for The Martian. I’m going to compare the differences between how two topics were presented in the novel and the film: architecture and agriculture.

So, let’s consider architecture.

In the movie, the Hab appears to be structurally stronger than it is described in the book. They probably figured it had to look stronger to credibly withstand the windstorms. So when the airlock blew, the Hab lost pressure, but it didn’t collapse.

In the book, the Hab is an inflated “dome with flexible support poles maintaining the arch and rigid, folding floor material to keep its base flat. The internal pressure was a vital part of its support.” Somehow, it withstood the devastating windstorm that caused the mission abort. But when the airlock blew, the Hab collapsed.

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In the movie, Watley covered the opening left by loss of the airlock with transparent plastic secured with freight straps and duct tape. From what I’ve read, commercial-grade polyethylene can withstand temperatures down to -60̊C, which may not have survived the night. It’s also not strong enough to withstand the 14.7 psi atmosphere in the Hab, which would exert something like 70,000 pounds pressure against a 6.5-foot-diameter opening.In the book, Watley covered the opening with Hab canvas sealed with “unbelievably sticky resin.” Watley described how the Hab canvas was made this way: “Woven carbon thread ran slowly through the press, which sandwiched it between polymer sheets. The completed material was folded four times and glued together. The resulting thick sheet was then coated with soft resin and taken to the hot-room to set.” That type of patch material would be much more likely to be successful. It would have also been far more resistant to radiation than the clear plastic.

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Of the space habitats currently being developed, the one that most closely resembles the Martian’s Hab is made by Bigelow. A Bigelow Expandable Activity Module (BEAM) has been attached to the ISS for two years now. The walls are made of multiple layers of Kevlar-like material and flexible foam. The walls offer radiation protection and ballistic protection comparable to that of the ISS. Two earlier versions of Bigelow expandable space habitats have been in Earth orbit for a dozen years without loss of pressure.

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Mars One is planning to use inflatable habitat modules covered with Martian dirt. If this image is to scale, it looks like the cover would be about 7 feet thick. Sources I’ve found say that 16 feet of regolith cover would produce radiation protection similar to what we have on Earth.

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Many of the finalist designs in NASA’s 3D Printed Habitat competition for Mars use Martian regolith as a construction material or a cover for an inflatable structure. Some of them also recess the habitat into an artificial crater. Here are some examples:

[Top Image] The first runner-up in the competition would start by excavating a 5-foot-deep crater, fuse the surface with microwave-generating “Melter” robots, place inflatable modules in the crater, cover them with regolith, and fuse the surface with microwaves.

[Lower Image] Bubble Base earned Honorable Mention status. Its construction involves creating a small crater by a controlled explosion. An inflatable habitat placed in the crater has pillars and a shell that are then filled with fine-grain sand. The exterior is covered with bricks formed by sintering sand. This method might be less abrasive to the inflatable habitat’s surface than spreading raw regolith on it.

A somewhat simpler version of this concept would be to build habitats in Martian caves or lava tubes, which apparently can be quite large.

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The analogy for regolith shielding on our planet is earth-sheltered construction, which has many advantages including temperature stability. At a depth of about 10 feet, the constant temperature in Earth’s soil is equal to the average annual surface temperature at that location. Here in Los Angeles, that would be 64̊F. [Mars, -80°F] Besides that, an underground building generates a “thermal bubble” that partially equalizes the internal temperature with the surrounding soil. These combined effects significantly reduce summer cooling and winter heating loads.

We don’t know what the subsurface temperature conditions are on Mars or the structural stability of the subsurface materials. But regolith-sheltering seems to be a reasonable construction strategy. Radiation shielding might be a problem, as impacts of high-energy particles can generate secondary radiation in the regolith. Making the habitat material out of high-hydrogen-content plastic could help block that.

The second topic I’m addressing is agriculture. You remember that the stranded astronaut survived by growing potatoes on Mars.

In the movie, Watley places a dollop of "excrement" mixed with water into a trench, smooths a little Martian dirt over it, and screws part of a potato into that dirt, effectively pushing it into the "fertilizer." That would probably not promote growth or safe food.

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In the book, Watley mixes a small amount of compost ("leftovers" from his meals) along with water, poop, and a little Earth soil are gradually mixed with Martian dirt. The only poop containing pathogens comes from Mark himself.

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According to NASA's Johnson Space Center's website, “The soil on Mars actually does have the nutrients plants would need to survive on Mars. There may not be the right amount of nutrients depending on where astronauts land on the Red Planet.” But it doesn't contain any organic material (plant remnants, bacteria, worms) like Earth soil. It also contains perchlorates, which could be removed by washing the soil. And it contains heavy metals (e.g., cadmium, copper, lead, arsenic, and mercury), which are toxic.

NASA, ESA, and China have developed several Martian Regolith Simulants that researchers are using for various kinds of research, including growing plants.

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Dutch scientists have been growing plants in NASA's version of regolith simulant since 2013. They’ve determined that worms can live and reproduce in Martian soil simulant, and that radishes, peas, rye and cherry tomatoes grown it (with demineralized water) don't have dangerous levels of heavy metals and are safe to eat. They are still testing six other harvested crops, including potatoes, to evaluate their safety as food. Of course, this is only a simulation performed on Earth. Mars' lower gravity could affect some crops, and our regolith simulants are not exact matches for real Martian soil—they don’t contain perchlorates, for example. But the results seem to be encouraging.

From the standpoints of architecture and agriculture, I think The Martian presents generally plausible concepts, although the concepts can be developed more fully in the book than in the movie.

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I’d like to remind you to take a copy of the National Space Society handouts before you leave. Now, if you have any questions, I’ll be happy to answer them.

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