Short-term space travel, such as to the moon or a space station, is extremely expensive and dangerous. Sending a spacecraft to settle Mars or beyond would be vastly more difficult. But let's suppose that somehow, the money and technology were available. How would that play out? Life onboard the spacecraft would be similar to life on a nuclear submarine: cramped, dirty, noisy. Submarines at least come into port every few months so the sailors can get some fresh air and recreation. Space colonists would not have that luxury. Submarines also get periodic resupply, but that's not an option for travel beyond Mars.
This video is a good explanation of why colonizing Mars is a bad idea:
They made a similar one about a moon base:
For longer journeys, the need for strict nutrient recycling would mean no animals, so no meat or pets. People would live out their lives on the spaceship, and none of the original passengers would survive to the end of the journey, even to a planet in the closest star system. Once they finally arrive there, they won't be able to go outside for long or build anything new. It would be hard enough to keep the spaceship repaired. Whatever moon or planet they land on would just be a safe place to park. Life on board the ship would not change. The only viable power source is nuclear, and the reactor would run out of fuel eventually.
If by some incredible stroke of luck they land on an earthlike planet, they would be forced to be subsistence farmers for generations before building a rudimentary civilization. People would not volunteer for such a mission for the same reason they aren't lining up to settle Antarctica or even Wyoming. People, mostly young men, flocked to California and Alaska during the gold rushes because there was money to be made. There is nothing on the moon, Mars, or beyond worth mining. If the planet is inhabited by intelligent aliens, there is a good chance they would kill or enslave any humans they found. Alien germs could wipe out the colonists as well.
Space exploration (manned missions) is sort of like cave diving. It's unnecessary, unprofitable, dangerous, and the only reason to do it is to go where no one has been before. If we absolutely needed to know what was in an underwater cave, it would be much cheaper, easier, and safer to just send a probe. However, there is not much glamour in that.
The long-term survival of the human race depends on space colonization, but before we can do that, we need to survive on earth. Most species go extinct in 15 million years or less. We have about 600 million years before the earth can no longer support life.
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The luminosity of the Sun will steadily increase, causing a rise in the solar radiation reaching Earth and resulting in a higher rate of weathering of silicate minerals. This will affect the carbonate–silicate cycle, which will reduce the level of carbon dioxide in the atmosphere. About 600 million years from now, the level of carbon dioxide will fall below the level needed to sustain C3 carbon fixation photosynthesis used by trees. Some plants use the C4 carbon fixation method to persist at carbon dioxide concentrations as low as ten parts per million. However, in the long term, plants will likely die off altogether. The extinction of plants would cause the demise of almost all animal life since plants are the base of much of the animal food chain.
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Attempts to build closed artificial ecosystems like Biosphere 2 had many challenges. There is no point in proceeding with space colonization until that problem is solved.
The earth is basically a spaceship, so everyone is already an astronaut. There are plenty of exotic places to see here. It's odd that many of the people who fantasize about space travel won't go camping.
This excellent article by Charles Stross explains the situation well. If we let an astronomical unit be equal one inch, we get the following:
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Try to get a handle on this: it takes us 2-5 years to travel two inches. But the proponents of interstellar travel are talking about journeys of ten miles. That's the first point I want to get across: that if the distances involved in interplanetary travel are enormous, and the travel times fit to rival the first Australian settlers, then the distances and times involved in interstellar travel are mind-numbing.
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When we look at the rest of the solar system, the picture is even bleaker. Mars is ... well, the phrase "tourist resort" springs to mind, and is promptly filed in the same corner as "Gobi desert". As Bruce Sterling has puts it: "I'll believe in people settling Mars at about the same time I see people settling the Gobi Desert. The Gobi Desert is about a thousand times as hospitable as Mars and five hundred times cheaper and easier to reach. Nobody ever writes "Gobi Desert Opera" because, well, it's just kind of plonkingly obvious that there's no good reason to go there and live. It's ugly, it's inhospitable and there's no way to make it pay. Mars is just the same, really. We just romanticize it because it's so hard to reach." In other words, going there to explore is fine and dandy — our robots are all over it already. But as a desirable residential neighbourhood it has some shortcomings, starting with the slight lack of breathable air and the sub-Antarctic nighttime temperatures and the Mach 0.5 dust storms, and working down from there.
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In the comments, I found this gem:
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I will finish my post with quotes of Gregory Benford from his "Deep Time" and Bertrand Russell "The Value of Free Thought"
Bendord: "Still, we know that all our gestures at immortality - as individuals or even as a lordly species -- shall persist at best for centuries or, with luck, a few millennia. Ultimately they shall fail.
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Russell: "Our individual life is brief, and perhaps the whole life of mankind will be brief if measured on an astronomical scale. But that is no reason for not living as seems best to us. The things that seem to us good are none the less good for not being eternal, and we should not ask of the universe an external approval of our own ethical standards.
The free thinker's universe may seem bleak and cold to those who have been accustomed to the comfortable indoor warmth of the Christian cosmology. But to those who have grown accustomed to it, it has its own sublimity, and confers its own joys. In learning to think freely we have learnt to thrust fear out of our thoughts, and this lesson, once learnt, brings a kind of peace which is impossible to the slave of hesitant and uncertain credulity."
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