Many people think that in the future we will take our brain and nervous system out of our bodies and graft it unto metallic robot bodies. This is not my opinion of what will happen. Although it will be possible and some people will choose this path, the majority of people will choose the part that requires reengineering our bodies in place.
What will this re-engineering require? There is one fundamental technology that will make it possible, and that is full scale nanotechnology. Once we are able to fully control nanometer sized devices, we will use them re-engineer our DNA; clear out poisons from our bodies; activate stem cells and direct them to go to the right areas for repair; increase our respiratory capacity, optimize our cognition and ultimately defeat the steady deterioration of our bodies.
There will be three types of humans in the world, Nano-Enhanced, Unenhanced, and Robot-humans (Humans that have grafted their nervous systems and brains unto robotic frames).
Currently when I think of the human body, I see it like a large vessel that is mostly empty due to the chaotic way it has evolved from the past. I see humanity filling that vessel up with so much invention of our own making. With the advances in simulation systems of the future we will be able to test every new enhancement we add to the body to very high levels of details so we can foresee problems before hand and decide whether to go forward on a particular type of enhancement or not.
I don’t think we will be able to achieve interstellar travel without first being able to completely understand and modify our biology.