If you wanted to go to our nearest neighboring star, which is over 4 light-years away, and you wanted to do it with the kind of rockets that are on the space shuttle, and say you wanna do it in 50 years, you’re having to go 1/10 of the speed of light. Well, the amount of propellant you need for that journey is about the mass of our entire Sun.

Marc Millis
NASA Aerospace Engineer and Propulsion Physicist