There are plans already under consideration for the colonisation of Mars. Bases on the Moon, mining the asteroid fields, exploring Titan (Saturn’s moon) for life, all are on the horizon.
To be honest, it’s all quite exciting, both in real life and in terms of the sci-fi that can be written about such things. Scientific advancement, commercial gain and military advantage could all play a role in the near term exploration of the solar system.
On the scientific front, Mars and Titan present the most intriguing prospects. Mars is nearer, although getting there will still take months. Establishing a base will require substantial resources, but modern technology does offer some short-cuts that even a few years ago would have been impossible. For example, 3D printers mean that you don’t need every precise structure or tool to be carried with the human crew. Printing materials could be sent on ahead with unmanned or robotic expeditions, and future blueprints for improved structures could be sent from Earth and printed on Mars.
Any trip is believed to be one way, because of the lower gravity on Mars that would create health problems for anyone returning to Earth (not to mention prolonged exposure to zero-G on the way to Mars). For a long term settlement, a stable gene pool would be needed (which would also tie in neatly with the generally international approach towards space exploration). Of course, not everyone has to go at once. Farming would require internal agriculture (cultivating Mars would require it to be terraformed). Energy supply and other fuel sources is an interesting one. Solar panels could add some juice but I’m not sure if that’d be sufficient. Due to long flight times and the potential for mishaps, sustainability would have to be the goal. If the colony were reliant on fuel sent from Earth then it could easily find itself cut short.
There are diamonds the size of cars in Jupiter. Unfortunately, fishing them out is technically problematic. However, the delicious deposits contained within the asteroid belt are altogether more accessible.
In my short story Dead Weight (in Explorations: Through the Wormhole), I had to rework the early draft because I’d wrongly believed the Mars-Jupiter asteroid belt was some sort of Star Wars maelstrom. It’s not. There are big open spaces between the various rocks and, although you’d still need to be careful, mining them is eminently possible in the near(ish) future. The bigger problem is likely to be how you divvy up fairly, between either companies or nations, the resources of the asteroid belt.
An international company could be the way to go. So far, after the 1960s space race between superpowers, space exploration has generally been along rather friendlier lines than terrestrial politics. Whether that continues remains to be seen.
Mining could probably be done largely by robots, which would dramatically reduce the cost and complexity of operations. Humans are a pain in the arse to move through space. They need oxygen, food, water, psychological well-being (an increasingly important factor for longer flights), somewhere to get rid of the waste they produce daily, and if you land them too quickly they turn into meat paste (landing a robot too hard will break it, but they won’t leave behind upset relatives).
Titan is a moon of Saturn, and the only other place in the solar system where liquid water seems to exist. This presents the best possible chance of finding life in our near neighbourhood, which is very exciting until you remember that also means it makes an impending apocalypse a lot likelier. Leaving aside the Fermi Paradox and the Great Filter, life on Titan could also present a serious pathogen problem. It is, nevertheless, a fascinating prospect.
Any visit to Titan would be much harder than visiting Mars. For a start, it’s a lot further away. That means more time in zero-G and more time floating in a tin can, which will increase physical and psychological effects. Secondly, a mission would probably be about collecting samples and the like. Now, you could do this just with robots. That’s cheaper and safer. But humans are smarter than robots and more adaptable. The gravity, however, is less than half that of Mars. So, if you’re sending a human, that’s moving from prolonged zero-G to 0.14g. Very much a one way trip for something organic and squishy (it also raises the question of what happens if you actually found something advanced, say a space-donkey, and tried bringing it back to Earth. The affect would probably be the same as if you tried moving an Earth-donkey to a planet with 7g).
However, the Moon has surface gravity of 0.16g. That’s a seventh higher (akin to a human moving to a world with 1.14g). You’d notice, but it wouldn’t be horrendous. Species (or returning humans) could go to a lunar base for experimentation. No need to try and establish a permanent base on Titan, the gravity’s practically identical, and it’s miles (and then some) closer to Earth for fuel, communication, supplies and so on.
Most of the above assumes that we continue to have relatively friendly space adventures. However, the history of the human race is one riddled with conflict. Any nation that acquired dominance of space would have huge advantages. Asteroid-mining would give a resource and commercial advantage, access to the Moon, Mars and Titan would offer scientific progress denied to lesser nations, and the military aspect of near-Earth domination would be significant.
There are a number of existing or near-term weapons projects that operate from or in space. Tungsten rods operate by firing a rod of tungsten (as you may have guessed) at the Earth. The kinetic energy of it hitting the planet is immense, but also highly localised. It’ll annihilate a house, and the next door neighbour will be fine. (Sidenote, all ICBMs have nuclear warheads because a smaller payload would have less destructive potential than the kinetic energy of the missile itself).
Masers are also in development currently and would probably work in space. The problem with space warfare is that damage would commonly include explosive decompression and total destruction of the ‘enemy’. It’s hard to think of anything other than a war of annihilation (you might think of an EMP to knock out the electrics, but do that and how long will the oxygen and warmth last?).
Hopefully we won’t see military nonsense in space, but we’ll find out in the coming decades.