How much fuel do you need?

As you may have noticed, accelerating your spaceship to near-light speed requires a lot of energy.

Your spaceship (with you on board) has a mass of 1000 kilograms on Earth. If you wanted to accelerate to 0.866 times the speed of light (about 260 million meters per second), you’d need a hundred thousand trillion (100 000 000 000 000 000) joules of energy. That’s the equivalent of 2.5 billion (2 500 000 000) liters of gasoline.

As you go faster, your mass increases, and the required energy escalates quickly.

Suppose you wanted to increase your speed from 0.9 to 0.99 times the speed of light. You’d need almost five times as much fuel as you used to reach 0.9 times the speed of light in the first place!

By the way, so far we’ve only talked about the energy you need to accelerate your spaceship. Don’t forget that once you get to your destination, you’ll need the same amount of energy to slow it down!

 This graph shows how the fuel you need increases with your speed. As you approach the speed of light, the amount of fuel you need approaches infinity.