Part of the fun of writing science fiction is imagining what other life forms might look like, how and why they may have evolved that way, and what impact space travel would have on humans. Homo Sapiens Sapiens has evolved to suit the conditions of our environment on this particular planet. We breath an atmosphere that is mostly Nitrogen, with around 20% Oxygen. We can't survive in an atmosphere where the Oxygen level is below around 12%, and if it goes much higher than around 23% we're in trouble as well. We've evolved to deal with the gravitational force exerted on our bodies by the Earth, and a lot of our physiognomy depends on our being in an environment where "up" is away from the direction of gravitational attraction. Our metabolism requires a certain amount of exposure to sunlight daily, we need water (60 to 80% of our bodies is water) to survive and we are adapted to a fairly narrow range of temperatures in which we can survive and live.
Once we leave the surface of our planet though, all of these essentials to our survival become scarcer and scarcer. In some senses space is like moving ourselves to an underwater habitation. We can't breath water, so, we need to create an air environment in which to live, work and eat. In space there is no atmosphere, so we would rapidly "decompress" if we stepped out of our capsule or space suit. As with being below the surface of the ocean, it is an environment we are not built for, but human ingenuity has provided us with the ability to create ways of dealing with these problems.
In many ways it seems logical to me that any space travel (and I firmly believe that humanity WILL one day venture beyond the solar system) will be somewhat similar to life in a submarine. In both cases you can't simply "go outside", because "outside" is an extremely hostile (to us) environment. Our ships, like a submarine, will need to be entirely self contained, self-sufficient and capable of carrying a crew and everything they may need for the journey. In all humanities earlier migrations, we could live off the land, one we venture into the space between planets, stars and out of our solar system, that will not be possible. So any long distance ship carrying humans is going to need a few features we are not yet able to provide.
Among these is some form of artificial gravity, necessary to keep our bones healthy and prevent muscle wastage. Then we also need some form of radiation screen, something to renew and refresh the atmosphere and some means of producing a supply of food. Some of these are easier than others to cope with. Gravitational effects can be created by creating a cylinder and spinning it at a suitable speed. One about 800 metres in diameter rotating at 50km/h would produce on it's inner surface the same effect as 1 G (Earths gravitational "pull" at the Equator) on Earth. You'd need to overcome the effect of the rotational torque on the lineal direction, probably by having two counter rotating cylinders. The biggest challenge in my view is going to be building these ships, since it will require a lot of effort to lift even small prefabricated sections in to orbit. But now we are into the realms of engineering.
As I said at the start of this, the fun for an author is to try to imagine what a future in which these major feats of engineering are "everyday". A hundred years ago, mankind had just started to learn to fly, and the century since then has seen enormous leaps in knowledge and technology. I remain confident that in the not very distant future mankind will find a way to venture beyond our planet and its satellite. It is just a question of how rapidly the means to do so are developed.