Once a crew has landed on Mars, they’ll need somewhere to live.

For short duration missions, perhaps a couple of weeks, they could live on the lander. For longer term, they’ll need more space.

A habitat will need to cater for a number of safety and mission requirements

1. Larger living accommodation

After 8 months cooped up with their fellow astronauts, the crew are going to need more space, ideally their own sleeping rooms, room for relaxation, entertainment and exercise. They’ll also need expanded workshops and equipment rooms for their exploration and experimentation operations now that they’ve reached Mars

2. Pressurised environment

Obviously, the base will need to be pressurised. Air locks will also need to be able to filter out the fine dust found on the Mars surface, and not let it get all around the base and into the crew’s lungs.

3. Radiation protection

Just because the crew have now landed, doesn’t mean they can now relax from radiation hazard. Mars does not have the thick atmosphere and magnetosphere that Earth does to protect from solar and cosmic radiation; the crew will be at as much risk on the surface as they were on their voyage to Mars. Any habitat will need to provide protection against this

Possible types of habitat include:

Linked up habitation units

Initially, the easiest way to expand accommodation will be to send extra landers to Mars and joining them together. These might be of the same configuration as the crewed lander or specialised configurations of floors, doors etc, for specific purposes, for workshop area for example.

These subsequent landers won’t be able to land right next to each other, there would be far too high a risk of them hitting each other. Instead, they might be maneuvered into position pulled by a tractor if the were given wheels on their landing legs, or potentially, if the landing legs were articulated, they might walk into position.

The different units could then be linked by pressurised tubes to walk or crawl through.

This might be the easiest initial solution to providing more room for the base, but it does have a few draw backs. The amount of extra room would be limited, and it wouldn’t exactly be more comfortable. Also, it wouldn’t afford much radiation protection. It definitely wouldn’t be a long term solution.

Brick buildings

One thing that Mars has a lot of is sand. With sand, you can make bricks. Brick habitat areas might be built on the surface, or used to line accommodation dug out of the Martian Regolith. Sand would have to be piled on top of any exposed areas by bulldozer, to seal the hab from the air pressure differential (or your brick building would blow apart) and to add further radiation protection. The inside could possibly be sprayed with plastic sealant to prevent air leaks. Window space might be limited, but this could be a straight forward solution for medium to long term habitation for ten to twenty people.

3D printed buildings

The advent of 3-printing will not only potentially allow the astronauts to make their own tools and spare parts from local resources, they may be able to print entire buildings. It’s been done on Earth already.

They’d still need to load them down to compensate for pressure difference and for radiation protection, though.

Lava Tubes

Lava tubes are hollow tubes embedded in the rock that are produced by volcanic activity. On Earth these usually measure a few feet in height.

There are indications that the same process may happen on the Moon and on Mars. However, since the gravity is lower, they may well be several meters tall.

Lava tubes could make excellent accommodation for explorers, being large, probably largely air tight, and deep enough underground to provide ready made radiation protection. All you’d have to do is dig down to one (or find one where is was already partly exposed to the open) and seal the open end off with a door. You might have to spray the inside with some sort plastic to make it absolutely airtight, or line it with a thermal insulator to stop heat leakage.

Of course, no natural light, but you can’t have everything.

Inflatables

Even to begin with, inflatable structures will be invaluable to the crew. Bigelow Aerospace are already developing inflatable habitation modules for attachment to the International Space Station. The same could potentially be used to extend living accommodation on Mars, and a larger, transparent version could be used as a greenhouse. In theory, a huge inflatable dome could be used to cober groups of buildings, allowing people to walk outside on streets and parks.

The trouble with anything inflatable is that it wants to stretch into a perfectly round shape, which isn’t useful when you want your tent or greenhouse to have a flat floor. Imagine trying to push an inflated balloon on the floor until it’s flat against the ground; it’s not easy!

One solution to this problem might be to anchor the sides of the tent down to stop them from “flipping upwards.” Another could be to excavate the Regolith under where the spherical tent is to be placed, then bring the dirt back in and bury the tent in place.

A greenhouse a few meters across might be comparatively easy to build by either method. A dome big enough to hold a city may be practically impossible, as the pressure on the tent to conform to a spherical share would be immense, possibly too big to just peg down the sides, and the amount of Regolith that would need to be excavated would be thousands, or millions, of tonnes.