How is the air refilled on the ISS

Science in dialogue

How can a space station store enough oxygen to supply several people for months?

The first manned missions into space in the early 1960s actually started with a supply of oxygen in special tanks in their luggage. At that time, the missions did not last longer than a few days, so this supply did not take up much space. This would no longer be possible on the International Space Station ISS, which has been manned by astronauts almost continuously since November 2, 2000.

Oxygen is only one of several factors that are necessary for life and survival on board a spaceship. For light activity, a person needs around 800 grams of oxygen, two and a half liters of drinking water and 700 grams of food per day. These values ​​increase with exertion. Even frugal people use one to five liters of water a day for personal hygiene. A spaceship cannot simply be ventilated and the ambient temperatures often fluctuate extremely: in the sunshine up to 121 degrees Celsius are possible, in the shade up to minus 127 degrees Celsius. Therefore, air humidity, room temperature and air pressure must be artificially regulated.

Scientists have developed an internal treatment system for all of these processes, the so-called life support system, which recycles the air on a chemical basis. It ensures the correct composition of the breathing gas, ie the "air", filters out toxic substances such as the carbon dioxide we exhale or odors and regulates the room temperature.

These life support systems are constantly evolving. A team of scientists from the Ruhr University Bochum (RUB), the Karlsruhe Institute of Technology and the University of Bremen is currently researching whether the chemical treatment of the breathing gas could also be replaced by natural processes.

Green algae could turn out to be the perfect companion on space stations or during long space flights: “With the help of light energy, microalgae consume carbon dioxide and release oxygen. They can also supplement the astronauts' diet as a vitamin-rich and renewable diet, ”says the photobiotechnologist Prof. Dr. Thomas Happe.

Together with the other scientists, doctoral student Franziska Bleeke carried out various experiments during a so-called parabolic flight in September 2013. A parabolic flight is a special flight maneuver in which the aircraft first rises steeply into the air and then goes into free fall in a high arc - this creates weightlessness inside the aircraft for a period of approx. 20 seconds. “We use this phase for our series of tests,” explains the biologist, “for example, I examined the influence of weightlessness on green algae”. The results are optimistic, although many questions still need to be researched: for example, how to control the production of oxygen using certain nutrients or how to protect green algae from bacterial infestation.

It will take some time before such a biological life support system can be used in long-range missions. And all these further developments do not change anything in one thing: Spaceships and space stations will always have an emergency reserve of oxygen on board. And in bottles.

This is what a parabolic flight looks like: Video by Planet Wissen, published on June 4, 2012.

The biologist Franziska Bleeke from the University of Bremen supported us in answering the question.

WiD editorial team: wr