December 7, 2021

I, Science

The science magazine of Imperial College

Alternative habitats in the solar system could provide us with opportunities to escape Earth

Somehow Surviving on the ISS

Space will kill you. The death list, in roughly chronological order, goes something like this: All the air explodes out of your body, causing massive trauma, and resulting in a lack of oxygen reaching your lungs and tissue. Heat escaping from your body will freeze you, whilst exposure to UV-rays will start to peel away your skin. Luckily, dehydration and malnutrition will probably kill you before a slow and agonizing death from the cellular mutations caused by high energy particles hitting your body. Space is a nasty assassin. So, it is somewhat surprising that humans have been living there permanently for the past 16 years, in the International Space Station (ISS).

On board, oxygen is generated from the electrolysis of water, whilst the temperature is regulated by pipes of ammonia, carrying waste heat to external radiator panels. Most of the incoming radiation is blocked, although higher energy particles and small meteors can still be problematic. Water is primarily provided by the Sabatier Cycle, which converts CO2 and hydrogen into H2O and methane. Food still comes from Earth, but methods for growing plants in space are currently in development.

Air, warmth, food, water and radiation protection; five things every space-farer needs if she wishes to survive. It’s not unreasonable to believe that during our lifetime we’ll start living, not just in space, but on other worlds within our celestial neighbourhood. Mars is often touted as the next step, but many other bodies in the solar system could feasibly become habitable. We may however have to abandon certain Earth based creature comforts, like a stable floor.

Cloud Cities on Venus

We humans have grown a firm affinity with the ground beneath our feet. However, if we were to plant our metaphorical flag on Venus, our celebrations would be fleeting. On Venus’s surface, 90 atmospheres of pressure, a sulphuric acid and CO2 atmosphere, and 400°C temperatures render it particularly hostile to humans. Nevertheless, there is hope. Around 50 km above the surface, temperatures range from 0°C to a balmy 50°C, the pressure matches that of Earth, and the atmosphere would shield us from cosmic rays. In fact, a 21:71 mix of oxygen: nitrogen in the air could be buoyant, allowing us to construct a literal cloud city inside a balloon. A 1km balloon of breathable air could conceivably suspend around 700,000 tonnes, enough to carry a fair few of us. Water could be provided by condensing sulphuric acid droplets, to produce CO2 and hydrogen, for use in the Sabatier Cycle.

Cloud City and space ships

A rendition of what a cloud city might look like. Image Czjuri

Food remains the biggest problem; travel time between Earth and Venus is around 3 months, so re-supply missions would be costly and devastating if lost. However, the ample room available in the balloon could provide space for us to grow crops.

Despite all this, the Venusian atmosphere outside the balloon would of course remain toxic and deadly, so no expedition could be undertaken without extreme peril. If one did desire to head outside, to mine rare metals for example, it would in fact be much easier to turn to the asteroid belt between Mars and Jupiter, or the dwarf planet Ceres.

Hobbit Holes on Ceres

Assuming Venus’s cloud city, with its gorgeous, pearly sulphur dioxide clouds, would be the artistic capital of the solar system, then Ceres, with its access to the asteroid belt and the abundance of resources that it offers would surely be the capitalist centre. At  945km in diameter Ceres may host no atmosphere, but is the largest body in the asteroid belt. Surviving on such a barren rock would certainly be difficult – but possible. A connected, inflatable, tent-like structure could provide living space, suitable pressure, and a limited supply of air, although may be vulnerable to small, pebble sized meteorites. However, by burying the habitat under surface material, much like the hobbit homes in Lord Of The Rings, we could protect the sensitive structure from impact strikes, UV, and cosmic rays. Furthermore, the conduction of heat through the material would regulate the temperature. In addition, preliminary studies suggest that Ceres has an icy mantle, which could provide us with water. This water could then be electrolyzed to produce hydrogen and oxygen. Again, the issue of nutrition is a troublesome one; large amounts of space would be required for food production, with estimates suggesting a minimum of around 700 m2 per person.

Such speculations are interesting, but unfortunately unrealistic. Most likely, the next step on our journey into space will be in our own backyard, the Moon. It’s gravity, 16% that of Earth’s, makes it an ideal site for launching missions and testing new technologies, helping us to discover the problems we might encounter further afield. Will we live to see and perhaps become some of these colonists? Maybe. We’ll probably have a Moon-base by the end of this century, and habitats on other planets another 100 years after that. If we survive long enough, then human beings will certainly make their first permanent steps out into the cosmos. But only if.

Josh Greenslade is studying for a PhD at Imperial’s Astrophysics Centre

Banner Image: Alien Planet, Rajesh Misra