I don't think human spaceflight will ever be a significant factor in our history. We evolved for this planet, and there is little reason to send humans through

I don't think human spaceflight will ever be a significant factor in our history. We evolved for this planet, and there is little reason to send humans through space when we can send robots. When we discover another earth-like planet, we will send robots there that can replicate human life, and the two civilizations will communicate with each other but it's unlikely any person will ever travel between the two. As to how robotic interstellar travel is fuelled, we'll probably use converted asteroids with thrusters built into them.