Economics is really what will drive space travel. Consider that launch costs are going down steadily, and worldwide GDP is going up considerably. Knowledge of t

Economics is really what will drive space travel. Consider that launch costs are going down steadily, and worldwide GDP is going up considerably. Knowledge of the solar system is going up at the same rate. Eventually a line will get crossed where transportation costs are lower than expected ROI. This is already the case for satellites. Eventually it will be the case for asteroid mining. Mining asteroids will further reduce the cost of getting raw materials into LEO, and yet more break even points will be crossed etc... I don't know if it will take 20 years or 200 years, but once there is serious money to be made you'll see humanity become a spacefaring species overnight.