Knowing is half the battle. . . or something like that.

So, you're planning on starting a space colony.  Or, in my case, writing about one.  What kind of things should you take into consideration?
There are things that I'm going to take as a given.  The technology exists to create said colony.  The desire to establish said colony exists.  And we're not talking about a lot of handwavium to make the physics work.
So, we start with local (Sol System) colonies.  Where to colonize first?  The moon makes a lot of sense, even if she is a bit of a harsh mistress.  Upsides to colonizing the moon - its close.  There's a lot of aluminium in the lunar crust for construction.  And there's more helium 3 there than anywhere else close.  Helium 3 is important for fusion reactors, so if you're writing sci-fi its a good thing to have on hand.  Downsides - not a lot of water.  Water is key to earth based life.  So, you can either lift it out of the gravity well on earth (expensive given current technology, and probably not going to get cheaper anytime soon) or hand wave up a way to make it from the oxygen and hydrogen bound in the lunar crust.  But you've got to have it.

So if not the moon, how about Mars.  Mars has water, higher gravity levels and a slight atmosphere, all of which are advantages over the moon.  On the downside, rather than a trip of around 4 days give or take, you're looking at a minimum of seven months on a ship headed to Mars.  That's double (give or take) the time it took Columbus to get from Spain to the Caribbean.  Now, we have experience with long term missions in small metal tubes at this point - US Navy Submarines go out for six months at a time or longer on a regular basis.  One difference would be that you can't pull up to the Sub Tender at the half way point to Mars and say "Fill us up on beans and O2 please.  We've got another three months to go."  So, you've got to haul everything with you, including supplies for the return trip.  Even if you're going to colonize Mars, you're going to want the ship back - its cheaper to reuse what you've got rather than one shot the mission.  If, of course you can avoid the Paradox that was the Space Shuttle.  In my opinion, though, a lot of the cost issues with the shuttle and lack of missions was due to a lack of national will to move forward with the concept of moving people into space.  We lost the will when we reached the moon.

Next time we'll talk about why you want to take a large number of people to your proto colony.  And animals, and plants.