Let's say a ship is beyond Earth's meaningful gravity pull, and has solar panels. Assume that it can collect solar power and use it in a system which blasts propellant away from the ship to accelerate through space. The ship's goal is to leave the solar system and reach a new star, but to continue accelerating for half the distance, and decellerating the remainder, versus just drifting at a constant velocity. To me, this gives us two options: 1. The ship must leave our solar system with enough propellant to continue accelerating. This seems problematic because for every kg of propellant it takes with, the mass grows, negating the benefits of bringing the propellant with. 2. The ship must collect propellant along the way. This seems problematic because the ship is unlikely to encounter an appropriate amount of propellant along its linear path, or to solve the logistical problems associated with capturing them at high speed. This makes me think it's unlikely we could ever build a ship capable of propelling to another star. I hope my thinking is flawed?