Dehydrated and sealed away in a vacuum-packed plastic bag, a spaghetti and meat sauce dinner meant to be eaten in space is deceptively light. Lighter than the plate you’d use for it back on Earth. I got a feel of this space spaghetti when I visited the Johnson Space Center in Houston to learn about how astronauts eat. Sitting in the lab that makes the only food not consumed on Earth, it was clear that Mark Watney got a pretty raw deal in The Martian. Real astronauts will never have to live on potatoes alone.

No one expects to see “space chef” on a business card, but the scientists at the Johnson Space Center take cosmic cuisine very seriously. And astronauts didn’t always have an entirely custom menu. They once consumed food similar to the MREs (“meals ready-to-eat”) the military used, said Vickie Kloeris, manager of the Space Food Systems Laboratory. NASA even rented out the same facilities that produced the all-in-one meals. Once the Iraq War began, however, there weren’t enough facilities to accommodate our heroes above and below. That’s when the Space Food Systems Laboratory started making all the food dined on by astronauts aboard the International Space Station.

Production wasn’t the only problem with MRE-style meals. A soldier’s salt intake, for instance, is wildly different from what an astronaut should consume. “MREs are for 18-year-old kids, not 40-year-olds,” Kloeris said.

When you float in a micro-gravity environment, your body notices. Fluids aren’t tugged down to your legs in space, so a “fluid shift” occurs, pushing blood into the chest and head. This extra pressure in the head gives astronauts that puffy face, but it also impairs their vision. Kloeris calls it pressure on the optic nerve due to increased intracranial pressure. It is to some extent unavoidable. Still, when food scientists realized that reduced sodium content in meals could help with this pressure problem, steps were taken to minimize salt in all astronaut food (and sodium content is now prominently featured on each package).

A sampling of food available on the ISS. Velcro holds down utensils and food packets.

Growing your own food like Mark Watney will be crucial for astronauts embarking on longer missions—it’s just too expensive to pack all the food they would need. When we do send food in potentia along with space crews, however, it won’t be all potatoes and lettuce. Another lesson Kloeris and her team learned from military MREs was something called “menu fatigue.” According to military studies, soldiers got bored with the same food day-in, day-out, so much so that they would “survive but not thrive.” In other words, soldiers would eat enough to not starve, but not enough to be healthy.

“[Menu fatigue] will be a huge challenge for a Mars mission,” Kloeris told me in an email. “We want our crew to be at peak performance though out the Mars mission, so menu fatigue will be something we need to minimize/avoid.” That means sending around 50 different types of freeze-dried foods up to the ISS, along with powdered drinks and commercial cereal.

“Historically our freeze-dried shrimp cocktail has been very popular.”

A vacuum-packed spaghetti dinner meant for space. Try not to think about it looking like mealworms. Note the sodium label.

So what would Mark Watney eat on a Mars mission? (One that didn’t go horribly wrong, that is.) Many of the same foods that ISS astronauts eat now, but packaged differently. The time between production and consumption for ISS food is a few months; the time between packaging and eating on a mission to Mars could be five to seven years. “Although we can produce food that is microbiologically safe for that period of time,” Kloeris told me, “there are still chemical changes that occur in these foods over time that reduce the quality and nutritional content of the food.” These changes limit the variety of foods that could be sent with the first Martians.

“It is going to be a real challenge to have sufficient variety of foods that will still taste good and have enough nutritional content after that length of time.”

At least that food will be better than potatoes grown with your own feces.

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The Martian is available today for Blu-ray/DVD and digital download.

IMAGES: NASA Marshall Space Flight Center; NASA; Kyle Hill

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