One of these days an astronomer, somewhere, is going to discover a planet that might habitable. It probably won't happen this year. It may not happen for 100 years, but I am confident that, if our civilization doesn't collapse, someday such a planet will be located. When that happens, someone is going to want to go take a look at it. That will be a big undertaking.
More powerful telescopes are constantly under construction. Though not necessarily bigger than current telescopes, the technology that is going into them is making them more effective. Some Earth based scopes may soon challenge the Hubble for power and resolution. At the current rate of improvements we will soon be able to read license plates on Alpha-Centuri.
Given our current level of understanding of physics, traveling to another star would be an enormous undertaking. Before we actually try and send someone, we might want to send a probe to take a closer look. A probe would be smaller, cheaper, and perhaps faster. But eventually someone will want to go in person. And that will be a trick.
A trip to another star might take decades, so any expedition we mount should be prepared to survive indefinitely on their own resources. It would need to be a self-sufficient community, a colony even. A spaceship to carry such an expedition would need to be very large, and due to it's size, massive. Building such a ship on the surface of the Earth and then launching it into space would be difficult. Just launching all of the construction material from earth would be a major undertaking. It might be easier to build it in space, or on the moon. The largest part of the mass/material needed for this project would be the reaction mass needed for the propulsion system. Another large part would be the materials for the construction of the body of the ship itself. If automated factories could be built on the moon to deliver these two items, the most massive, and expensive part of the project would be taken care of. Building automated factories on the moon would not be an easy task, but it could be done.
Here's what we do. We build some semi-autonomous mining robots and send them to the moon. Start them digging an underground cavern. While they are trying to dig this first experimental cavern, we do a geological survey of the moon looking for useful minerals and ground conditions that are suitable for a large system of underground caverns. Why do we want caverns? Because of the radiation. Machines may not care about radiation, but for anyone living on the moon for more than a few days, radiation is going to be a big concern. Forget about domed cities on the surface. Any long term moon facility will need to be underground. When the survey is complete, and we have our second generation of mining robots, we can start on the real project of building a long term facility for human occupation.
After radiation, the second big problem with long term life on the moon is the weak gravity. To compensate for this, we build a circular tunnel a mile or two in diameter and put a train in it. The train would run some 200 kph, which would give it a time of about one minute to travel the length of the tunnel and would produce a full gravity of centrifugal force. The train would be running more on the wall than the floor of the tunnel due to these forces. If people stationed on the moon were able to spend half of their time on this train, the physiological problems that occur during prolonged periods of low gravity should be minimized.
At the speeds the train is running it would make sense to leave the tunnel open to vacuum. Since this project would need to last a long time with minimal maintenance, it might be better to use some sort of magnetic levitation/propulsion system, rather than wheels. However, wheels might be quicker and easier the first time. The tunnel could be circular in cross section. When at rest the train would sit upright. As it accelerated, centrifugal force would cause it to drift away from the center and so up the outside wall of the tunnel. At full speed, the train would be nearly horizontal. The tunnel would not need to be much larger in diameter that the train itself. If the train were running on wheels, the running surface of the tunnel would need to be very smooth. But robot mining machines should be able to do the job. It may take them a month of Sundays to do it, but they don't really have any appointments to keep, do they?
Now that we have a base on the moon, we can get down to the real job of building a power plant, a smelter and an orbital launcher. We have the mining machines to dig up the raw materials. We have the sun delivering power. All we need now is a large mirror, a steam generator, and a steam turbine driven electrical generator. The mirror could be constructed by digging a pit, smoothing the sides, and then spraying the sides with a reflective coating of some sort.
All this will take time, and will require a good deal of equipment to be shipped from Earth. Mining robots would not need to be very big. Maybe not any bigger than the Mars rover, and perhaps as small as a toy car. Shipping them to the moon would require a large rocket, but it wouldn't require a Saturn V.
Developing a rocket that could put 1,000 pounds into orbit reliably is all we really need. Launch one a week, every week for the next ten or twenty years. Design a second rocket to travel from LEO to the moon. Send it in pieces to LEO and then assemble it in orbit. Might take ten launches from Earth to put together a moon rocket with a mining robot or two. Turn them loose for awhile. In a year or so, we should have some idea of their capability. With more moon rocket and more mining robots we should be able to construct our underground tunnel in a decade or two, and it shouldn't cost that much, relatively speaking. Of course, as with any kind of mechanical equipment you are going to have breakdowns, in which case you will need repair robots. Big opportunity for robotic engineers.
Once we have our circular tunnel in place, we will need the train. I really don't see any alternative except to build it on Earth and ship it to the moon, in pieces presumably. We may be able to recover some fuel tanks used from previous moon rockets to use as bodies for our train, but they may not be large enough. Building the train and getting it operational will be a big task that will presumably require skilled, i.e. human, hands.
With the train operational, we have a real moon base. People can live there indefinitely and return to Earth without any ill effects, other than they may miss the moon and it's low gravity. Now we can start building a real space ship, one that can take us to other planets, and perhaps even to another star.
