OK, I see some problems in flying a manned spacecraft to mars.

1. Exposure to cosmic rays and other forms of radiations.
2. Psychological stress - being away from Earth, living in such a tight room with other people
3. No advanced medical facilities.
4. Problem of being in the spacecraft for too long without gravity.

Sure, you could ignore all these and risk the lives of humans just to get someone to Mars. If that is the case, theoretically, it is possible to send a manned mission to mars. But practically, I don't see it happening in the near future.

1. This is an issue even if you fly to Moon and it can be solved.
2. That is a problem unless you put them asleep or select highly trained professionals, who has been for some time on ISS and send psychologist/therapeutist with them.
3. This one is shame, if something terrible happens out there.
4. Can be overcome either by daily excercises or by having emulated gravity by centrifugal force.

Thanks for making this thread.

EDIT:

Sorry for the book.

END EDIT:

The attempt would face many challenges. The first challenge would be getting someone to actually attempt it. There aren't many governments with the resources to fund a project like this, and it's possible that no one government could fund it. Convincing a nation or a group of nations to take on this project would be the first step.

But speaking purely of whether or not we're capable of colonizing another world, let's look at the possibilities.

Earth Colony:
Basically a second attempt at the Biosphere 2 project. After all, if we can't manage a closed system here on Earth, could we do it on another planet altogether?

Orbital Colony:
A space station would be a much better proof of our ability to maintain a closed system than anything here on Earth could. But an orbital platform is differs from an actual colony in several regards, such as lack of gravity, and still being close enough to Earth to receive help in an emergency.

Lunar Colony:
A colony on the moon would be the first step towards real colonization. Supplies and materials could still be ferried from Earth, but the cost of doing so would mean that building a self-supporting colony would be a priority for whoever was funding the project.

Martian Colony:
A Martian colony would need to be almost completely self-supporting. Current technology gives a minimum travel time from Earth to Mars of about six months, when the two planets are aligned just right. These trips would also be incredibly expensive, plus communications would have a long delay that would prohibit real-time discussion or anything close to it. A Martian colony would be effectively cut off from Earth.

Further Colonies:
Several moons of Jupiter and Saturn have been noted as possible colony sites in science fiction. But the cost and relative uselessness of these colonies will probably prevent anyone from building them unless humanity become active in the outer solar system.

Of course, selecting a site isn't the only thing. We must also build a ship to take the colonists and their supplies and materials to the site. For my purposes I will briefly discuss the needs for a colony that is at least as far as Mars.

The ship would have to carry enough colonists for a stable gene pool. I'm not sure how many people this would be, but it would probably be several hundred at least. The ship must carry enough supplies to keep them alive, and enough materials for them to build a colony on the site. It would basically need to be an Orbital Colony itself to sustain the population while the surface colony was built.

Before we can design the ship we need to know who is going to be on it, not specifically who but at lest how many people and what specific equipment and supplies they will need. Specialists such as doctors, engineers, technicians, farmers, ecologists, and even simple laborers will all be vital to the project. Their needs must all be accounted for.

All of this can be accomplished with the technology we have today, but the cost would be astronomical.

Now I will respond to all the pots that happened while I wrote this long-ass post.

This problem has in fact been solved already.

For an actual colony, and not just an exploration mission, there would need to be at least hundreds of people sent to create a stable gene pool. There wouldn't be much elbow room, though, so thorough psychological examinations of the participants would be necessary to weed out potential problems.

Can that be done currently? I think there are still issues with waking the people back up.

A colony would have to take fairly advanced medical equipment with them. Remember, we aren't going to be sending colonists on a space shuttle, more like a large, mobile space station.

Daily exercise can help with that. People have spent months in space and managed to recover, although they were weak when first returning to Earth. Also, Martian gravity is slightly lower, so the weakness would not effect them as much there. But that is a major problem.

The ship would have to be nearly a mile in diameter or the rotation would cause constant motion sickness. While the ship might end up being this large, rotating such a mass would be very cost-prohibitive.

For a while it would be dependent. And a truly self-sustaining colony is probably beyond our ability now. But we could make one that could last for several years on its own while waiting for the next supply ship from Earth.

I agree. It will be probably be much easier in the future. But having a colony out there, even if only as far as the moon, would provide an incentive to produce the technology that will make it easier, meaning we would reach that stage faster than if we simply sit on Earth and wait until it will be a piece of cake.

Financial viability is one of the major stumbling blocks for such a project, so it should be considered. But the main discussion is about whether we could do it, not whether we will, so for the purpose of discussing our ability to do it we should consider our budget nearly unlimited. The project would be impossible if the world economy collapsed halfway through because all our money was being sent to Mars, so our budget is limited to the maximum that all countries combined could commit to the project while still maintain their economies. A real world budget would be much lower, with probably just the U.S. and a few other nations contributing.

I think the discussion is whether we have the technology to build such a ship and the colony itself. The whole thread would be a moot point if we already had such things.

With a smaller craft the spin would have to be much faster to maintain a reasonable amount of pseudo-gravity. The speed of this spin would cause the disagreement between visually and kinesthetically perceived motion

Like Matthew said, this discussion is pointless without qualification. If for example the US decided to switch all military spending to colonization spending we could fast track the Ares V and start launching 150+ ton payloads into orbit on a monthly basis.

A year of that and you could put some significant hardware and infrastructure on Mars ready for the pathfinders (first explorers) to use.

Likewise, the Russians could start building and flying Energia's and do the same thing.

Using todays technology we could build a pusher-plate Orion type rocket and fly to Jupiter/Saturn in a couple of months, Mars in a couple of weeks.

Somebody just has to be willing to pay for it.

Getting to another planet is one thing. Sustaining ourselves there is another thing. I'm curious if we could actually recycle chemicals efficiently enough to provide ourselves with an unlimited amount of oxygen, food, water, and energy/fuel. With our current technology could we theoretically survive in space without Earth? With our current technology could be practically survive in space without Earth?

I remember watching a special on one of the discovery-like channels where they said that it wasn't practical yet. Theoretically, we are close, but in practical terms we still have a long way to go.

Oh, WOW! The first few posts in this thread reminded me of an old DOS game called Moonbase. I haven't played the game in probably over 15 years. It was about developing a base, searching for materials and becoming financially independent of Earth at some point (among other things).
http://www.allegro.cc/files/attachment/594837
http://www.allegro.cc/files/attachment/594838
http://www.allegro.cc/files/attachment/594839
http://www.allegro.cc/files/attachment/594840

I'm not sure how it works exactly, but i think it has something to do with the coriolis effect

From my knowledge, the Coriolis effect is weak enough that it will be overridden everywhere except very near the center by centrifugal force.