When humans eventually go to Mars, or even further into the Solar System, one thing that will be essential to their survival is the ability to grow their own food and be self-sustainable on long-duration missions. And now a crucial step has been made toward that goal on the International Space Station (ISS).

Astronauts on the ISS are about to tuck into food grown in orbit for the first time. They will be eating red romaine lettuce from a plant growth system called Veggie. The lettuce leaves will be cleaned with sanitizing wipes containing citric acid before they are eaten. Half the bounty will be eaten by the crew on the ISS, and the other half sent back to Earth for analysis.

“The farther and longer humans go away from Earth, the greater the need to be able to grow plants for food, atmosphere recycling and psychological benefits,” said Gioia Massa, the NASA payload scientist for Veggie at the Kennedy Space Centre (KSC), in a statement. “I think that plant systems will become important components of any long-duration exploration scenario.”

The Veggie system uses colored LEDs to help the plants grow, a method first devised in the 1990s. Red and blue lights were used as they emit the most light, but green LEDs were also used so that the plants grew with a more appetizing color, rather than appearing purple. It took 33 days for this batch of lettuce to grow.

“Blue and red wavelengths are the minimum needed to get good plant growth,” said Ray Wheeler, lead for Advanced Life Support activities in the Exploration Research and Technology Programs Office at KSC, in a statement. “They are probably the most efficient in terms of electrical power conversion. The green LEDs help to enhance the human visual perception of the plants, but they don't put out as much light as the reds and blues.”

This is actually the second batch of lettuce grown on the ISS. The first was cultivated in May 2014 but was sent back for analysis on Earth in a SpaceX Dragon capsule to check that it was edible. With it confirmed safe to eat, the current crew – Expedition 44 – grew this second batch, and will now take one giant leaf for mankind (sorry).