How to Live on Other Planets: Mars

An old favourite for colonization, Mars, is now our focus.

Description

No planet in our Solar System has been the focus of as much attention as Mars. We've looked for water, for life, for a place to live on.

What we've found is a cold, dry planet. It is familiar on the surface: polar ice caps, tectonic features such as volcanoes and valleys, an atmosphere and a day barely longer than Earth's. 

However, it is different in every aspect. Atmospheric pressure is 1% of that on Earth. It is mostly unbreathable carbon dioxide, and does a poor job of spreading the warmth from half the sunlight we are accustomed to. Temperatures ranges from -135 degrees Celsius to an infrequent 35 degrees Celsius, averaging -55 degrees Celsius to Earth's 14 degrees. Dust storms sometimes fill the sky, but their main effect seems to be eroding the ancient geological features over a surface area equal to Earth's landmass. 

The planet is also long dead. Most of the core is no longer molten, meaning that it does not spin to generate a magnetic field. Being 15% of Earth's size, it cooled down to its present state much quicker.    

Habitability

Mars's thin atmosphere barely touches the surface features. 

Despite its downsides, Mars is pretty hospitable compared to other planets in the Solar System. It is cold, but no unmanageably so. It has a lot of solid, traversable ground. The polar caps contain billions of tons of water ice covered by a layer of solid carbon dioxide. The soil can be used for agriculture after some preparation. 

Martian gravity is 37.6% of that on Earth. It is doubtful whether this is enough to stave off the muscle atrophy and bone loss caused by prolonged living in low or micro-gravity. 

Atmospheric composition.

The low atmospheric pressure means that most architecture and equipment on Mars will have to be hermetically sealed and pressurized. This imposes structural constraints and a dangerous failure mode if the colony's walls are pierced. Obtaining breathable gasses might requires energy and time: oxygen can be removed from carbon dioxide by energy-hungry chemical reactions, of through the photosynthesis of plants. Nitrogen is present at a 1.0% concentration in the thin Martian air, so it can eventually be extracted for small colonies to use as fertilizer and breathing mix. Larger colonies would need to find it in the soil, either as NO3 or NO.  

The atmosphere actually helps with the cold, as it is so thin that lacks the ability to conduct heat away from the colony. It acts as an insulator. This makes dealing with Mars's low temperatures easier than on Earth, where a thick atmosphere steals heat away from buildings in Antarctica or Northern Canada much more quickly. 

Mars against the Solar Wind.

The lack of a protective magnetic field is problematic to hopeful colonists. It means that every living space must have radiation shielding. This can be in the form of a layer of Martian soil layered over colony habitats. Building the habitats and covering them in red dirt is faster and easier to do than digging them into the ground.  

The two best places to start a Martian colony are the poles or the equator. 

The poles are vast deposits of easily accessible water. While the lower latitudes experience violent outgassing and 400km/s storms, the center of the poles have stable temperatures and terrain. Sadly, that stable temperature is -25 50 -153 degrees Celsius. 

The equator receives much more sunlight, and has seasons that warm the surface to reasonable temperatures during the Martian Summer. However, equatorial colonies would be limited to where underground water deposits could be found.

Prospection

Mars is the perfect place to build a colony. Every material that could be required for building or farming can be taken from the environment without special precautions or techniques, such as on Venus or Mercury.

Mars's South Pole ices.

Compared to Venus, it trades convenient gravity, pressure, radiation protection and comfortable temperatures for greater security, ease of expansion and practical benefits such as over-land travel or surface landing.

The poles are vast sources of solid carbon dioxide and water. It is suspected that there is frozen methane too, rapidly destroyed by ultraviolet rays if they escape. 

Mars soil scooped up for analysis by the Phoenix probe. 

Martian soil only requires the removal of perchlorates and introduction of fertilizer to become farmable land. It can become literally dirt-cheap radiation shielding, and martian cement with an impermeable inner surface can be used to construct pressure vessels for habitation. 

Iron and most metals commonly found on earth are also present on Mars. Some require digging up from the yet unexplored bedrock or from ancient volcanic veins, but they can still be considered 'available'.

However, Mars is disadvantaged when it comes to exporting raw or manufactured products. 

This can be mitigated by the colonies' ability to become self-sufficient, but would hinder them if they tried to buy and import resources that cannot yet be manufactured on-site, such as processed nuclear fuel or phosphorus. This is especially important during the run-up to Mars's self-sufficiency, when more and more complex machinery is required.  

There are two main causes to this disadvantage: energy and gravity.

Mars is energy-poor. 

It lacks the atmosphere for reliable aerobraking. Attempting it requires specialized designs, incorporating large lifting bodies and heatshields. Earth and Venus, with their much thicker atmospheres, require less of such equipment. 

Mark Watney inspecting solar panels. An essential job. 

With half the sunlight, solar energy is less powerful. It is also vulnerable to dust storms that can cover the panels. While orbital solar power satellites can transmit power to the ground much more easily that on Earth (water vapor absorbs microwaves here), electricity will remain an expensive resource. Geothermal power is non-existent, and nuclear power requires advanced technology that is hard to replicate and fissionable fuel. 

Bedrock elements are easily mined, but require a lot of energy to extract from their chemical compounds. The same goes for the more reactive elements, such as oxygen from carbon dioxide or iron oxides.

The second cause is Mars's position with regards to deltaV. 

Liftoff, for example. Unlike Venus or Mars, it is hard to provide this deltaV cheaply through external power propulsion. Mass drivers on the ground are an option, considering that hypersonic flight is much less taxing on airframes than on Earth, but it just moves the problem around: lifting your products from Mars's surface costs 4.1km/s. If we are considering Earth is a destination, you would have to wait two years to attempt the lowest deltaV trajectory, while Venus and Mercury can attempt the same several times a year.

Rocket fuel from the surface of Mars is a good resource to export, either to missions departing from Mars, or to asteroid mining ventures exploiting the Asteroid belt. It can be made on the surface from carbon dioxide and water, producing methane and oxygen. This is what SpaceX intends to do to refuel its rockets, after they land on Mars. It is valuable if the only other source of rocket fuel is Earth, 225 million km and over 12km/s away. However, if there are colonies on other planets and asteroids, then lifting fuel up from the surface of Mars will not be competitive. 

Asteroids can also provide most of the minerals and metals found on Mars without the hassle of mining it from the bedrock or deeper. 

So what can Mars do?

Phobos and Deimos. 

Forget the surface. Mars's greatest asset is its two moons: Phobos and Deimos.

Phobos is about 22km wide and orbits at a mere 6000km altitude. Deimos is 12km wide and orbits at an altitude of 23460km. 

The two diminutive rocks have all the characteristics of asteroids captured from the depths of the Solar System. Properly used, they are Mars's key to a prolific position as the gateway of the inner Solar System.

Let's start with Phobos.
The closest description would be a floating pile of rubble, loosely held together by a layer of compacted dust. It is composed mainly of carbonaceous chondrite rock riddled with ices and crevasses that might take up to a third of its volume. What is it good for? Living and lifting.

View from Phobos. Mars fills a quarter of the sky.

Phobos has a surface gravity of about 0.0004g. Riding a bicycle on the Mars-facing side is enough to fall off the moon and start orbiting Mars instead. It also means that it is very easy to dig into Phobos and excavate large volumes. These volumes can be filled with orbital habitats. These will have access to large quantities of volatiles and minerals, and the surrounding rock will provide sufficient radiation protection. 

At 6000km, Phobos is also close enough to start considering orbital elevators. A cable can be dropped from the moon to an altitude of about 10km. In the simplest version, it passes over the surface at 2662 km/h. A mass-driver launched spacecraft or even a supersonic aircraft can catch up to the cable. The Martian end of the cable experiences nearly no drag, so it doesn't heat up. Structural requirements are so low that it can be built from existing materials such as Zylon. It only needs to be about 12 times heavier than the payloads it expects to receive. 

Once the aircraft or pod is attached, it simply climbs up to Phobos with no propellant required. This is a 'free' 4.1km/s of deltaV. 

A more advanced version has an equally long cable extending out from Phobos. The two cables rotate in opposite directions to the moon's orbit, allowing the lower end to nearly cancel its velocity, while the higher end travels at twice the orbital velocity.

A small tether on Phobos.

A cable system for interplanetary travel. From Hop's Blog.

The advanced version allows Phobos to 'pick up' payloads from the surface, then fling it outwards on the opposite end. At 4km/s, it can impart enough velocity to fling a payload all the way to Earth. In reverse, it can capture a spaceship entering the Martian system, and deposit it gently onto the surface at the other end. 

A cable system vastly cheapens travel to and from Mars's surface, Mars's moons and extramartian destinations. Mars might end up being an even easier destination than Venus with its aerocapture or Mercury with its beamed solar power. Thanks to low surface gravity and thin atmosphere, the cables can be made from conventional materials and do not require much protection.

Deimos is a more extreme version of Phobos.

It is even smaller and higher than Phobos, but nearly identical in every other way. With a cable system, it can capture interplanetary spacecraft and lower them to Mars's surface or Phobos's orbit even more cheaply in terms of deltaV saved, energy required and structural mass involved. 

So, by properly exploiting its moons instead of relying only on the surface, Mars becomes a very inviting destination for spacecraft. While it lacks the energy to produce or refine products cheaply, it can compensate by providing rocket fuel and sending off the products to other destinations at greatly reduced deltaV cost.

The Martian Colony

The Martian colony won't look like much from space. No open domes, no large exposed surfaces. Every building is covered by a dusty layer of martian soil to protect its contents from radiation. Early settlements would have a field of auto-wiping solar panels placed far away enough to prevent them being damaged. 

Since buildings are pressurized, they will have rounded, smooth shapes to prevent angled weakspots cracking under strain. They will also be relatively 'clean', as in little clutter marrs their exterior surfaces. Anything left outside, like an antenna or a door, will be subject to extreme temperature variations that if not causes them to fail, will reduce their useful lifespan. 

Most components are kept under a mound of Martian soil.

Thanks to the ease with which new buildings can be constructed, colonies might appear dis-organized. They are able to expand in steps without de-stabilizing the entire project. A floating colony on Venus must match its lifting capacity with the mass of the habitats, and a rotating space station must balance new weights with ballast on the opposing side. On Mars, it can be as simple as claiming new land and hooking the new building up to life support.

However, there will be notable differences. Breathable air takes energy to create from local resources, and energy on Mars is expensive. Every attempt will be made to conserve air. For example, vehicles will be docked directly with a building's airlock, instead of sitting outside. It would only involve a single airlock cycle that way, instead of two if colonists had to go outside then enter the vehicle. 

Vehicles might not be human-piloted near habitats, and driving in general would be tightly regulated. A collision with a habitat could mean the instant depressurisation of its interior.

The largest volumes of a Mars colony are dedicated to farming. They would resemble a sort of artificially-illuminated greenhouses, with rows of algae and vegetables growing in drip-fed batches. 

Tunnels between habitats are the safest way of travelling around the colony. They would replace the roads common to Earth's inner cities. Outdoors activity would be restricted due to radiation concerns. Overall, the colony would appear uninhabited from the outside.  

On the inside, the habitats would appear rather cramped. Due to pressurization reasons, rooms are small. The colony would appear to a colonist as a succession of 'bubble-rooms' separated by tunnels and airtight hatches. New arrivals would bump their heads constantly on the low ceilings, as they adjust to low gravity.

The longest distance to travel would be between the spaceport and the habitation spaces, for safety reasons. If the colony is of the industrial type, it might instead employ a mass driver or a landing strip for supersonic tether-to-orbit aircraft. 

Travel between colonies would require long road-trains, as air travel is no practical. The alternative would be some sort of suborbital hopper, probably reserved for transporting people instead of goods. Railroads would be possible, but the rails would have to survive the temperature extremes between night and day.

Dangers

Most dangers arising from living on Mars are caused by the fact that it is a cold, low-gravity desert. 

Rather familiar with the dangers of living on Mars.

Depressurisation is just as dangerous as in orbit. The thin atmosphere won't slow down micro-meteorites much, so an unexpected puncture of habitats has to be accounted for. A layer of sealing fluid might surround habitats. 

Radiation is greatly reduced through appropriate shielding, but colonists are expected to work outside in pressure suits. These will have much less effective radiation protection, so damage will accumulate and might lead to a much higher cancer rate than on Earth. 

The low gravity can cause long-term problems with bone less and muscle atrophy. These cannot be compensated for by short stays in a centrifuge. They require hormonal treatment and possibly genetics work to adapt colonists to being born and raised on Mars.

On Phobos or Deimos, the risks are a bit different. They are unstable, and it is likely that large pieces of rock will start moving if colonists remove the ice 'filler' in between them. Long-term stability of the moons has to be balanced against the growth of the colony. 

With a tether system, there's always the chance that the cable will be severed by a collision, and end up loose. They could whip around and strike the moon's surface, or detach and launch debris into Martian orbital space. The cables will not be as large or devastating as a terrestrial Space Elevator, but there will be less atmosphere in the way to slow the descent of debris to the surface. 

On Earth, debris from a space elevator will be slowed down and hit the ground at near the terminal velocity, which is just under Mach 1 for the largest pieces. On Mars, the same pieces can strike the ground at close to the orbital velocity, which is several kilometers per second. Even with smaller pieces, they can end up being more devastating. 

Evolution

In any colonization attempt, Mars is likely to be the first candidate, and the only option for a long time.

Early colonies will likely be research outposts, with the only commercial-industrial activity being the production of liquid methane and oxygen rocket fuels. The fuels can be used to return landers to orbit, or shipped to spacecraft going even further than Mars. 

An example of the latter will be asteroid mining operations. 

Colonization efforts will focus on the polar regions at first, as they offer vast quantities of volatiles. The reduced sunlight and consistently low temperatures will have to be compensated for by larger solar panels.

However, industrialization, both for supplying a self-propagating colonization effort and for supporting an interplanetary economy, is best done around the equator. The deltaV cost to reach orbit and leave Mars is significantly lower than from the poles, and greater sunlight means cheaper electricity. 

The transition from polar colonies to equatorial colonies depends on a reliable transport system. It will have to cross a 5500km stretch of land, about the distance from London to New York. Flight is unwieldy, and suborbital hops too expensive. 

The growth of martian colonies follows a snowballing model. As it develops, it can produce more and more rocket fuel and machinery. These will be cheaper to use than similar products shipped from Earth. Cheaper products means that investors can do more with the same investment, leading to growth and greater demand for martian products. These products can be metals from the asteroid belt, moved by martian rocket fuel, or more colonies on Mars.

Phobos and Deimos are the keys to Mars's maturity as an industrial power, as it will drastically reduce the deltaV cost of travelling to or from Mars. It will supplant Earth as the better investment for space-based industries. 

Ultimately, Mars will end up serving as the starting point of further colonization or resource exploitation efforts in the Outer Solar System. Leaving for Jupiter from Mars will be cheaper than doing the same from Earth. As colonization continues, the population on Mars will become a consumer base in its own right. Corporations might consider selling their produce directly to Martians, instead of shipping it to Earth. 

A permanent population on Mars will have to resort to more drastic measures against bone loss and muscle atrophy, and the increased radiation risk. Its colonies will develop into vast network-cities, where every point is accessible through shielded tunnels without ever having to step outside. This reduces exposure to radiation.

Land travel will start using railways instead of slower roads. Thanks to the near non-existent atmosphere, even conventional technology can push trains to supersonic speeds without the need for Hyperloop-style vacuum tunnels. It could end up being cheaper than flight.

A potential Martian space elevator.

Orbital space stations will flourish around Mars, with miniature cable systems to reduce the cost of reaching them. Their main function would be to tend to interplanetary spaceships so that they do not have to set down on the surface. A secondary function would be to create artificial gravity environments where colonists can compensate for bone loss and muscle atrophy.  

If Mars has to compete with colonies on other planets, such as Mercury or Venus, it would have to find ways to remain competitive despite its energy disadvantage. A historical perspective can help with worldbuilding this aspect of its colonization. Modern 'developed countries' were initially industrial, but transitioned in the past century to a services-based economy, where the wealth and infrastructure of their industrial past is optimized towards creating wealth without any physical products in play.