Astronauts seem to prefer tortillas to bread for making sandwiches in space. But some missions last months, and there weren't any tortillas that could last that long. That's where Taco Bell came to save the day, and it's why more and more foods are now capable of being consumed in space.

Taco Bell had produced a tortilla that could have a shelf life of up to nine months. And it's much easier to make sandwiches with tortillas than it is with bread.

Remarkably, the meat used in space doesn't float away from the tortillas. Instead, the special meat that had liquid added to it sticks to the tortilla.

Being able to create their own beef sandwiches with real beef and even condiments is a nice refresher to the old dried food and meals ready to eat (MREs) packets astronauts are accustomed to consuming.

"The freeze-dried stuff has a really nice taste, but not the right texture. It gets soft," says Jean Hunter, the Cornell University researcher who recently helped run a space-like experiment in Hawaii. "What they missed most was fresh fruits and vegetables," she told The Salt.

Astronauts get fresh food delivered sometimes during their missions. They especially appreciate these deliveries.

"They really like getting the fresh food," said Vickie Kloeris, manager of the International Space Station Food System. "That's what they miss. When they get it, it's pretty much gone right away."

NASA's next food challenge is the future missions to Mars, which will likely last a minimum of three years. Food would have to have a five-year shelf life for those missions.

Kloeris and her team are already working on getting food to last for those missions.

Even though many people have special dietary needs these days (no gluten, no dairy, vegetables only), Kloeris said she and her team haven't run into that yet. She says it's because astronauts have to be so healthy to be selected.

Kloeris added that an astronaut with dietary restrictions like a vegan would have trouble getting proper nutrients in space.