“Are they edible?” I ask, half expecting to be told to stay well clear.

“Sure,” says Hauslage, a plant physiologist, casually twisting one of the tomatoes from its stem and handing over the euro-sized fruit.

I put it in my mouth. To be brutally honest, it’s not the nicest tomato I have ever tried: the skin is a little tough and the taste is slightly bitter. But it is, nevertheless, a healthy, edible tomato.

Recycled sweat

It’s hardly surprising the tomatoes in Hauslage’s office aren’t the tastiest. The plants have been specially bred to be grown in space. This experimental tank of urine, pipes and plants is the original prototype for a satellite designed to prove that tomatoes could be cultivated successfully on the Moon or Mars.

Right now, almost all the food on the International Space Station (ISS) is ferried up in cargo ships from Earth. The only exception is a few lettuce and cabbage leaves astronauts have managed to grow in a hydroponics solution. Most of the water on board the ISS, however, comes from astronaut urine. Liquid waste from washing, sweat and the toilet is almost totally recycled using a complex processing system. Today’s urine is tomorrow’s coffee.

But what if you could use the useful salts in astronaut urine to grow food? If humans are ever to live for long periods on the Moon or Mars, they will need a self-sustaining food supply. “You will need more than protein bars,” says Hauslage.