If we want to travel to the stars, we’re going to have to be creative. Conventional rockets aren’t nearly powerful enough to allow us to journey across light-years in a reasonable time. Even nuclear rockets might not be enough. So what’s humanity to do? The answer could be a light sail.

The challenge of any space journey comes down to delta-v. That is, how much you can change your speed relative to the speed of Earth. To gain delta-v, you need to have some kind of thrust. Rockets are a great way to get delta-v, but they have one big downside. Rocket fuel needs to be carried with you, and that means the faster you want to go the more fuel you need to carry. In other words, the greater the delta-v, the greater your mass to payload ratio.

You can reduce this ratio with an efficient rocket, and there are tricks such as fly-by maneuvers used by many of our space probes. But none of this will get you to a fraction of the speed of light, and that’s the kind of speed an interstellar spaceship would need. So if the problem is your need to carry fuel, why not get rid of the need for fuel altogether?

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