So feel free to dream on, but don't hold your breath that such things will ever actually come to be true.
The Moon is the only realistic goal, as it is rather close to Earth, only 240,000 miles (400,000 km) from the Earth. But look at what mankind has had to do to even send a total of twelve men to briefly walk on the Moon's surface. During the 1960s, we spent amazing amounts of money, tens of billions of dollars, to build the Saturn V rocket, which had to produce many millions of pounds of thrust in order to accelerate a sadly small Apollo spacecraft to get to the Moon. In order to keep the total weight of the Apollo as low as possible (in order to best accelerate it), the Apollo spacecraft was not even as sturdy as a beer can! Some of the astronauts who rode it it commented that they knew that they could easily have punctured the outer wall with their fingers, in a reminder of how flimsy and dangerous their environment always was.
And even with these economies of weight, the Apollo was a very cramped spacecraft for just three humans, and just for a few days. The Lunar Lander crafts were even smaller and lighter, only made to hold two humans. The dangerous Apollo 13 trip emphasized this fact, where all three Apollo astronauts had to survive within the smaller space for days, where they barely survived.
So the result of the six Apollo Moon landings was each to enable TWO men to have a few hours to walk around on the Moon. Not particularly impressive for an investment of ten years work of many tens of thousands of people, and of tens of billions of dollars of material wealth. Even if we did not consider providing any sturdy structures for humans to live on the Moon's surface, the practicality of ever having even a small community of a thousand humans living on the Moon, is really beyond the (fossil fuel) resources of the Earth.
We can also now consider the idea of providing a sturdy living structure for the Moon's surface. Many countries contributed hundreds of billions of dollars to build The International Space Station. This project also took many years and countless thousands of people's careers to create. We note here that only around seven or ten astronauts live in that structure. It IS solid and sturdy, and people HAVE proven that they can live for six-month periods in the ISS.
But the parts of the ISS had to be raised from the surface of the Earth in over a hundred huge rockets (mostly Space Shuttle launches), and it all had to be accelerated up to about 17,000 mph in order to stay in low earth orbit where it is. To send even a comparable sturdy structure up to the Moon would require that it all be accelerated far more, to get up to about 25,000 mph in order to get out to the distance of the Moon. Do you see the enormous extra amounts of rocket fuel that would be needed even to get the (tiny) existing ISS up to the Moon's distance? This would result in only providing living space for around seven humans, and the energy requirements to produce that much extra rocket fuel would again challenge the entire Earth's supplies of fossil fuels.
In order to provide the sturdy structure of living quarters on the Moon for even our tiny one-thousand-person community, would require astonishing amounts of rocket fuel to build everything there on the Moon. It is simply far beyond the capabilities of human civilization and Earth's resources.
Yes, we HAVE proven that we CAN build the ISS where around seven people can live. Note though that we regularly have to send up additional supply ships to provide them with the food they need to survive, and that is only even possible because the ISS is in such a low Earth orbit. The idea of regularly sending massively loaded supply ships to the Moon is not realistic, even if we concede that every hamburger would cost more than a million dollars! So, even though the ISS is a practical experiment in low Earth orbit, even trying to establish a stable group of even seven people on the Moon is not within what human society is now capable of. And the idea of Lunar farmers growing their own food is certainly many hundreds of years in the future, if at all.
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ANY time a spacecraft speeds up, it accelerates and a G effect occurs. Say that you COULD withstand 2 Gs of effective weight for an extended time. And you wanted to leave the Earth's surface to speed up to HALF the speed of light, which means about 150 million meters/second. How long would it take you to speed up to that speed, at a constant 2G acceleration? One G is 9.8 meters/second per second, so 2 Gs is about 20 meters/second per second. Therefore you would have to accelerate for 7.5 million seconds at that acceleration to get up to that speed. That is about 87 days. Your heart and body probably could not survive 2 Gs acceleration for that long!
More reasonably, your spaceship would probably have to accelerate at 1 G, which would result in your having to have your rocket engine firing constantly for about 174 days, about half a year! You would have a decent chance of surviving for such a trip! But notice that the result of such an extended rocket engine firing would ONLY be to get you up to HALF the speed of light! Star Trek and their instant acceleration up to Warp 7 is simply not remotely possible!
The oxygen supply that residents require for survival must always be provided by equipment and also maintained by the integrity of the structure of each spacecraft and each other living space. Since I was in Physics during the 1960s, I was regularly aware that MOST people involved with the US NASA Space Program were fearful that the Earth's atmosphere is hit every day by millions of small meteors (which we see burn up in our atmosphere as shooting stars). Even though most of those meteors were no larger than a grain of sand, they hit the atmosphere at such high speed that they (nearly) always burned up. Very few were large enough to survive passing through the atmosphere to land as meteorites.
It was an easy and simple calculation for any Physicist to know how likely it was (is) for a random meteor to crash into a spacecraft of any given area. And the result was justifiably terrifying! People in Japan are now fearful of the next earthquake and tsunami which they will have to try to survive. So far, in space, we have been very lucky, mostly because all of our spacecraft have been very small. But it is simply a matter of time before a sand-grain-sized meteor crashes into the ISS at 60,000 mph or more, and such an impact WILL puncture the wall if the ISS. If a person happened to be in the path, that person might be also punctured, as by a tiny bullet traveling 60 times faster than rifle bullets travel, so that person might easily be immediately killed. But if a puncture hole happens in the outer wall of the ISS, then the oxygen inside it will escape out into outer space. The size of the puncture hole will determine how quickly the oxygen escapes, and whether the residents have time to get into their spacesuits fast enough to survive. The possibility exists that all the residents of the ISS might die from lack of oxygen within seconds or minutes.
Again, all Physicists can easily and quickly calculate the statistical chances of such events, and so a MTBF (mean time before failure) has been known for each spacecraft since the 1960s. It is simply a matter of time before a terrible catastrophe occurs where a tiny meteor crashes into the ISS, or some other manned spacecraft.
It has been found that about a six-month interval in the ISS is about the longest that is safe for mankind. It turns out that the human body changes many behaviors when away from Earth's gravity. Astronauts are REQUIRED to do extensive physical exercise every day, to keep muscles from atrophying. It turns out that bones also become weaker and even the nervous system changes behaviors. When astronauts return to Earth, they must go through extensive procedures to try to recover muscle and bone strength and many more things.
There is another matter that seems to never be mentioned. We on the surface of the Earth are protected from very dangerous ultravolet radiation which the Sun creates, by a layer high in our atmosphere which contains sufficient ozone to protect us. If there were future people living on the Moon or elsewhere, or even in the ISS, the walls of craft or structures can provide some level of protection from ultraviolet (and also cosmic rays and gamma ray radiations), but not as well as we are protected here on Earth.
It figures to be very interesting to someday do a statistical analysis of all the people who stayed in the ISS or who were in the various spacecraft during the past 50 years, to see whether they developed more cancer than average people do, or whether they have more genetic mutations (due to such radiations). I suspect that will be a major news story of thirty or fifty years from now, where it might be found that (future) space tourists had twice as many deformed children, or something like that. But for now, absolutely no one seems to care! Only THIS WEEK matters to modern people, I guess! Sad!
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