According to the dictionary, an astronaut is a person who is professionally trained to travel in a spacecraft. “Astronaut” is the term used by NASA since the start of their space programme. The Russian Federal Space Agency (or its Soviet predecessor) uses the term “cosmonaut”. These two became popularised during the 1960’s space race between the USA and the USSR. Other terms for people going to space include “taikonaut”, for Chinese astronauts, “parastronaut”, for astronauts with a physical disability, “vyomanaut” (from the Sanskrit word vyoman meaning ‘sky’ or ‘space’) or “gagannaut” (from the Sanskrit word gagan for ‘sky’) for Indian astronauts. In Finland, the word “sisunautti” has been used, where sisu means something like stoic, tenacious or determined. Some countries call their astronauts “space travellers”, like the German “Raumfahrer”, the Dutch “ruimtevaarder”, the Swedish “rymdfarare”, and the Norwegian “romfarer”. “Spaceflight participant” is the term for a space tourist or other non-professional travellers.
Science fiction, or not
Whichever term you pick, living outside the Earth is tricky. This is because our bodies and intuitions have evolved for hundreds of thousand of years to adapt to living subject to Earth’s gravity, under an atmosphere, on solid ground with access to liquid water, and benefitting from the biosphere. All this would change if we had to live in orbit, on the Moon, Mars or Europa, or in open space. The same applies to nearly all of our technology, which would require serious adaptations.
You may know science fiction movies or books that strive for scientific accuracy while exploring the theme of living beyond Earth. For instance, the movies “The Martian” (2015, Ridley Scott), “Interstellar” (2014, Christopher Nolan), “Moon” (2009, Duncan Jones) and “Ad Astra” (2019, James Gray), or the books “2312” or “Aurora” by Kim Stanley Robinson. These are always good to help us think of what we would need to live outside our cozy planet.
In orbit
The International Space Station (ISS) takes about 90 minutes to complete a full orbit around the Earth. This means that astronauts go over many timezones and see 16 sunrises and sunsets every 24 hours. Our bodies have adjusted to have a circadian rhythm of about 24 hours which optimises our functioning to the day-night cycle. When we travel to distant places on Earth, this rhythm gets perturbed in an effect we call jet-lag. At the ISS this becomes even weirder. There is no timezone, so UTC time is used. The windows are covered during “night hours” to help give astronauts a “normal” day-night cycle.
Then there is the absence of gravity, often called microgravity. Prolonged exposure to microgravity can lead to muscle atrophy, bone density loss, and other physiological changes. Even without noticing, many core muscles in our bodies are almost always working to keep us upright against gravity. Since muscles atrophy when they are not used, living in the absence of gravity is a problem. Astronauts follow a strict routine of physical exercise to keep their muscles toned. This takes a large percentage of their time, but is essential for musculoskeletal health. Related to this are the circulatory and respiratory systems. Exercise is needed to keep astronauts with a fit heart and lungs.
We need oxygen, water and food to keep our metabolism going. While oxygen is mostly generated through a combination of processes, including the electrolysis of water and the release of oxygen during the process of generating electricity, the station must be resupplied periodically by cargo missions from Earth, providing astronauts with fresh food and water.
Electrolysis of water is the primary method for producing oxygen on the ISS. It involves splitting water (H2O) into hydrogen (H2) and oxygen (O2) using an electric current. Water, brought to the station through resupply missions, is split into its component elements using electrolysis equipment. The released oxygen is then collected and supplied to the cabin for breathing. The crew has a backup option in the form of bottled oxygen and Solid Fuel Oxygen Generation (SFOG) canisters. In all cases, you see that lots of stuff (water, canisters, food, etc.) needs to come from Earth.
Moon, Mars and other “terrestrial” bodies
On the Moon or Mars there is gravity, but it is weaker. A 60 kg person would weigh only 10 kg on the Moon and 20 kg on Mars. On Jupiter’s moons Ganymede, Callisto and Europa, the same person would weigh even less: about 8 kg. Although Ganymede and Callisto are larger than the Moon, and Europa is not much smaller, gravity is weaker because these celestial bodies have a much larger proportion of ice in their composition, which is about 1/5 to 1/3 the density of rock. Such reduced gravity has similar negative effects on our bodies. Furthermore, it also impacts technology we have become used to on Earth.
A simple example is transportation on wheels. A car on the Moon, Mars or Ganymede would have less traction (which is proportional to the gravity pressing the wheels down to the ground). This would also imply less friction and hence larger stopping distances under braking. Vehicles would also be more prone to rolling over and have more difficulty turning and manoeuvring. Cruise velocities could not be very high because hitting a bump of small rock could send the vehicle into the air with no control. The dusty environment of the Moon and Mars could damage vehicles, although we have some experience with data on Earth from e.g. the Dakar rally. In any case, wheel materials design would need to take all these problems into consideration. Mobility in low gravity is challenging. and scientists are thinking of little rovers on even lower gravity.
Some positives would also result from using vehicles on those places. The reduced friction could result in vehicles being more energetically efficient. The same would apply to the lack of or much sparser atmospheres, which would lead to reduced air friction. Materials would suffer less wear and tear under reduced gravity. The same effect that makes a vehicle jump when hitting a bump could be explored to move around by hopping. You could hop over larger crevices making some “bridges” unnecessary.
To Infinity and Beyond
Anything beyond Jupiter will involve huge travel times. New Horizons was the spacecraft designed to be the fastest to move away from the Earth towards the outer solar system. It still took over 9 years to travel from the Earth to Pluto. Other probes like Voyager 1 and 2 and the Pioneers took decades to leave the solar system. Beyond our solar system, the nearest star is Proxima Centauri at 4.2 light-years distance from us. At the speed Voyager 1 is travelling, it would need more than 17 thousand years to travel a single light-year, or more than 71 thousand years to reach Proxima Centauri. Just to give you an idea, 70 thousand years ago humans were starting to make clothing.
When we are talking years or decades, maybe people could be made to hibernate. This has been explored in science fiction, but ESA is doing research on the topic. But with silly long travel times of tens of thousands of years it would take many generations of people between leaving the Earth and arriving at the destination. This means self-sustaining and reproducing crews that can bear to live together for that length of time in a spacecraft. Challenging.
Water
Based on our current understanding of biology and life on Earth, water is a vital and universal component of living systems.
Water is the universal solvent, meaning it can dissolve a wide range of substances. This property allows for the transport of nutrients and molecules within cells and organisms. Many biochemical reactions, including those involved in metabolism and energy production, take place in aqueous solutions. Water serves as the medium in which these reactions occur. Water has a high heat capacity, which means it can absorb and store a significant amount of heat energy. This property helps regulate temperature on Earth, making it suitable for life. Water is a key component of biological molecules like DNA, RNA, and proteins. It contributes to the three-dimensional structures of these molecules, which are essential for their functions.
Outside the Earth, we must find ways to get water. In “dry places” like the Moon and Mars, we can find water ice in craters that are never illuminated by sunlight, or in the subsurface. In icy moons like Ganymede, Callisto and Europa, there are plenty of ices on the surface, and we may be able to tap into subsurface oceans. We may even be able to live in those subsurface oceans (just think of the classic “20,000 Leagues Under the Sea” by Jules Verne). In outer space, we may have to rely on fully circular systems, where the same water is recycled and reused permanently.
In any case, extraction and reprocessing of water will certainly become a big business in the future.
Food and Energy
Back to the subject of food, living on the Moon, Mars or Ganymede gives us at least soil where we could potentially grow food. The Martian film explores growing potatoes on Mars. Could we do the same on the Moon or on an icy body like the moons of Jupiter?
MELiSSA (Micro-Ecological Life Support System Alternative) is an ESA project that has been running for 30 years to develop a fully circular life support system. It aims to fully recycle CO2 and human organic waste into food, oxygen and water. If you think of it, the Earth is a circular system. Nature already knows how to reuse the things it produces. Some human-made things take a long time, but will eventually be recycled. We need to learn how to make recycle times compatible with our lifetimes.
Energy is another issue. In space, the Sun is the go-to energy. Sunlight pervades the solar system, and can be captured and converted into electricity. But the further we get from the Sun, the weaker is sunlight. When living and travelling beyond Jupiter, clever ideas must come into play to collect enough sunlight for our needs.
Or we need to use other forms of energy. The water in the subsurface oceans in Jupiter’s moons is believed to remain liquid thanks to the heat from tidal forces. Could we learn to use that for our purposes?
Protection
Finally, outer space is a violent environment in terms of radiation and other forms of space weather. Some places, like the asteroid belt, are also dangerous in terms of collisions with debris. On Earth, our atmosphere is our shield against these risks. In orbit, on bodies with thin or absent atmospheres like the Moon, Mars or Jupiter’s moons, we need to develop protection without sacrificing mobility and general activity.
Could you think of business ideas to help us live outside the Earth?
Read more:
- Moon to Mars
- Mars in Fiction
- Humans in Space
- Astronaut Andreas Mogensen preparing for mission Huginn!
- International Space Station Environmental Control and Life Support System
- ESA Human and Robotic Exploration
- Moon Society
- MELiSSA Foundation
