Astronauts aboard the International Space Station are going to have a very special meal tomorrow. Red romaine lettuce is on the menu, and when they take a bite, it will mark the first time astronauts eat food that was grown on the ISS.

Casual observers may be surprised to hear that fresh vegetables haven't been growing on ISS for years. After all, if sci-fi movies have taught us anything, it's that every space ship needs a bountiful greenhouse to support its crew (the lush space garden from Sunshine is pictured above).

A greenhouse called Lada has been aboard the ISS since 2002 and has been used to study plant growth in microgravity for many years. But, until now, astronauts aboard the space station haven't been eating their science experiments.

Astronauts haven't eaten their experiments — until now

Scott Kelly planted the romaine on July 8th, according to NASA, and the plants were harvested 33 days later after consistent watering. But the whole experiment is a bit more complicated than just planting some seeds and eating them when they grow. Since there aren't just beds of soil on the space station, astronauts had to use a plant growth system called Veggie.

The collapsable system takes pre-made seed "pillows" and blasts them with light from red and blue LEDs to let them grow. The system successfully produced plants in 2014, but they had to be brought back to Earth for testing. In particular, NASA had to ensure that the plants were safe for consumption — the open air environment on the station could easily transfer contaminants to the plants.

Space veggies could have mental health benefits, too

Now that space plants have the go-ahead from NASA, all astronauts need to do before consuming the romaine is to give the leaves a wipe down with food sanitizing wipes. Then they can feast on their space bounty, though they do need to save half of the haul to send it back to Earth for further study.

Beyond offering a food source for long-term trips — NASA says packaged food can only last a maximum of two to three years — space gardens could be key to astronaut health. Fresh fruits and vegetables could help improve mental health by giving astronauts something to nurture. They also give astronauts a little piece of Earth to bring with them on long journeys. In addition, a good, fresh meal goes a long way after months of eating packaged food. NASA says it is monitoring the effects of fresh produce on the crew in preparation for any future trip to Mars. Until then, Scott Kelly and the ISS will have some fresh food to enjoy during their months aboard the station.