The extreme conditions during the polar night, with temperatures as low as minus 45 degrees Celsius, call for the technology of the EDEN ISS greenhouse and provide valuable insights for future plant cultivation on the Moon and Mars.

During the polar night the Sun does not rise above the skyline, so all that the researchers at the Neumayer Station III can see around noon is a bright glow on the horizon. After the winter solstice, this midday dawn gets longer by the day, until the Sun rises above the horizon again in late July.

The EDEN ISS greenhouse differs from past plant cultivation experiments in the Antarctic because of its completely closed circulation, in which all water not contained within the fruits and plants is recycled, analogous to eventual usage for space travel or in deserts on Earth.

Approximately 100 kilograms of fresh vegetables have been harvested so far to enrich the diet of the overwintering crew

Focus: Space, biosystems

The EDEN ISS greenhouse has been in the Antarctic for nearly six months, and for four of these, Paul Zabel from the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) has been operating the greenhouse on his own. It is now fully operational. Paul Zabel harvests an average of 740 grams of tomatoes, 1.8 kilograms of cucumbers, and 400 grams of kohlrabi every week, in addition to various herbs, lettuce and radish varieties. The extreme conditions of the polar night, with temperatures as low as minus 45 degrees Celsius, require this technology, and it provides valuable insights for future food production on the Moon and Mars as well as in harsh climates across the globe. Fresh vegetables enrich the diet of the 10 crewmembers overwintering at the Neumayer Station III, which is operated by the Alfred Wegener Institute. They were also a highlight of the midwinter festival.

"Work in and around the greenhouse is very intensive," says Zabel. "I spend about half my time sowing, caring for the plants and harvesting, and the other half of the time I care for the greenhouse technical systems and conduct the approximately 40 experiments and validation procedures." One special challenge for the researchers is always the weather, reports EDEN ISS Project Manager Daniel Schubert. "In mid-June we had a storm that lasted for days. During that time we had to control and monitor the greenhouse from Bremen for three days." The control centre for the Antarctic greenhouse is located at the DLR Institute of Space Systems in Bremen. From there, the researchers can speak with Zabel at the greenhouse via video conference, and receive images and technical data for all the plant populations in the greenhouse, including the previous yield of the pioneering supply experiment. To date, 35 kilograms of cucumbers, 39 kilograms of lettuce, 17 kilograms of tomatoes, seven kilograms of kohlrabi and four kilograms of radishes have been grown and harvested over a cultivation area of approximately 13 square metres. "Cucumbers thrive particularly well," explains Schubert. "Peppers, and particularly strawberries, are more difficult to care for."

Self-sufficient under extreme conditions

The EDEN ISS greenhouse differs from past plant cultivation experiments in the Antarctic due to its completely closed circulation system, in which all water not contained within the fruits and plants is recycled, analogous to eventual usage for space travel or in deserts on Earth. The researchers are also analysing the production of oxygen by the plants, which thrive without soil and sunlight through optimised artificial LED light and spray-on nutrient solutions (aeroponics). The only external supply is the power, which is provided by the Neumayer Station III.

Testing the greenhouse technology's durability throughout the Antarctic winter is also an essential part of the vegetable cultivation experiment. For example, in the past weeks Paul Zabel had to manage the outage of a regulation vent in the cooling system, the outage of an LED lamp, and inconsistencies in the complex control system. "I often had to address these at night or during the weekend, which made resolving the issues considerably more difficult. After all, the greenhouse is 400 metres away from the Neumayer Station III," he explains, and sees his efforts as a service to science. "A future greenhouse on another planet should also be in continuous operation, so technical failures and their repair provide us with valuable findings."

Polar night, halftime and the mid-winter festival

After all the work, the celebration of the mid-winter festival at the station was a welcome change for the winter crew. "The winter solstice, also called mid-winter, was a very special day for me in Antarctica," says Zabel. "This day marks the midpoint of the polar night and halftime for my stay in Antarctica." Station Leader Bernhard Gropp reports: "We celebrated mid-winter together at the Neumayer Station with a feast. That day, and every day, the fresh vegetables, lettuce and herbs from the greenhouse provide real dietary enrichment that we do not want to miss, so all crewmembers are happy to help. Our station chef and Paul Zabel work especially closely to optimise preparation of the freshly harvested vegetables."

During the polar night, the Sun does not rise above the skyline, so all that the researchers at the Neumayer Station III can see around noon is a bright glow on the horizon. After the winter solstice, this midday dawn gets longer by the day, until the Sun rises above the horizon again in late July. The weeks of constant darkness during the polar night are a great challenge for the researchers. "It feels like being on another planet, where you can no longer differentiate between day and night because of the lack of daylight," says Zabel. "In addition, during this season, the Antarctic is magical with its impressive natural phenomena. The sunsets that last for hours at the beginning of the polar night are unforgettable, as are the extraordinary starry skies and the aurora."

News about the project directly from Antarctica can be found on the EDEN ISS Facebook and Instagram channels, as well as through the #MadeInAntarctica hashtag on Twitter. Information compiled about the project is available at: www.DLR.de/EDEN-ISS.