Humans have wanted to go to Mars for a long time. NASA says it wants to send people there by the 2030s, while private companies like SpaceX have proposed building colonies on the Red Planet.

There are, of course, a lot of kinks that have to be worked out for us to get there. One of them is living in an enclosed space with a few other people for months on end.

Another is the human need for food. Packing all the food and water for a Mars mission would take up a lot of room and would use lots of fuel. Trying to grow food would use up a lot of energy.

Now, scientists at Penn State think they've found a way for astronauts to create food with help from their own human waste.

Lisa Steinberg, a former postdoctoral astrobiology researcher at the school who now works as a science lab supervisor at Delaware County Community College, told NPR's Scott Simon about how the multistep process works.

"We collect the solid and liquid waste from the astronaut and we put it into a reactor where we have a mixed group of bacteria that break that waste down," she says. "And from that they produce methane, which is a gas. And then that methane can be fed to a second type of bacteria — that it grows up and then the cells themselves have a lot of protein, have a lot of fat."

Penn State News described the model they built:

"They created an enclosed, cylindrical system, four feet long by four inches in diameter, in which select microbes came into contact with the waste. The microbes broke down waste using anaerobic digestion, a process similar to the way humans digest food."

The process can grow a bacterium called Methylococcus capsulatus. It's already in use today as an animal feed.

In the case of the Penn State researchers, their end product looks like a type of "microbial goo," as Steinberg's co-author Christopher House describes it. He told Penn State News that it's similar to the Vegemite or Marmite spreads that people put on toast. The goo has a lot of protein and a lot of fat in it.

The substance "can serve as a supplement to the diet of the astronauts and the life support system," Steinberg says.

It's not quite operational yet.

"To put it in a life support system you would definitely need to have a lot of safety precautions in place," she says. "Astronaut protection would be first and foremost. You would need to make sure that there's no potential of pathogens from the waste getting into the food source."

The researchers didn't actually taste it, Steinberg says. She says people who have tasted the stuff in the past "described it as somewhat bland."

Steinberg has a solution for the good of the astronauts' taste buds, however.

"I recommended just bringing some Sriracha on board," she says, "and that'll make anything taste good."

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