Moon before Mars, but why?
Having a colony on the nearest celestial body to Earth would be beneficial, because we would be able to conduct research, extract resources, develop and use new technologies.
In general, colonizing the Moon is a huge stepping stone to expand to Mars, Venus and beyond. If there is an infrastructure on the surface of the Moon and in the orbit, it would be easier to refuel and repair spacecrafts heading farther out into the Solar System. We could also link space missions with the Moon infrastructure to reduce the costs of Space Exploration.
This is why NASA is planning on establishing a space station in orbit of the Moon – the Lunar Orbital Platform-Gateway. Also why ESA wants to build its Moon Village with international partners.
Profitable Benefits of Colonizing Moon
Lunar researches would be highly lucrative, too. By studying the effects of low-gravity on the human body, astronauts will be better prepared to deal with the effects of long-time space travel and missions to other celestial bodies.
The availability of resources on the Moon, such as helium-3 and various rare Earth metals, could also allow an export economy. Launching payloads into space would be way cheaper because the gravity on the moon is lower than the gravity on earth.
The amount of ice around the polar regions will provide settlers with a source of water for drinking, irrigation, and could even be processed to produce fuel and breathable oxygen.
Lunar water could also be used with electrolysis batteries as a source of power, also solar arrays could be a source of power.
Space-based solar power would also be able to provide abundant energy to settlements all over the lunar landscape. Nuclear reactors are another option, as are fusion reactors. The latter option is especially attractive because Helium-3, a power source for fusion reactors is more available on the lunar surface than on Earth.
The first problem are factors that damage the building materials. Damage can happen from huge temperature variations, micrometeorite impacts, high outward forces from pressurized habitats, material brittleness at very low temperatures and abrasion by high energy cosmic rays will all factor highly in the planning phase.
Also explosions in a vacuum would create countless high velocity missiles tearing through anything in their path, with no atmosphere to slow them down. The dust would obscure everything and settle, statically, on machinery and contaminate everything.
Decontamination via air locks will not be efficient enough to remove all the dust from spacesuits, Moon dust would be breathed in. This is a huge health risk which leads to death.
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