Fuel

And MESSENGER, launched in 2004, orbited Mercury over 4,000 times in four years before exhausting its fuel and crashing into the planet's surface on April 30, 2015.

Due to the drastic fuel consumption that happens when flying the Boeing at this speed, it's rarely done.

Trains also use less fuel than planes or cars.

Rockets burn huge amounts of fuel to create this force.

Most of a rocket's weight at launch is fuel, not the spacecraft itself.

As the rocket burns fuel, it becomes lighter and can move faster.

When one stage runs out of fuel, it falls away and the next stage fires.