Do you want to travel to another planet? Or perhaps even another star system?

Then you can use this calculator to work out how long it will take you, how much energy your spacecraft needs and what your maximum velocity will be. If you travel close to the speed of light, you can also see how much time it will take from your point of view and from the point of view of the people on earth. You can also see how the length of your spacecraft will shorten for observers watching it from earth, if only they had powerful enough telescopes.

This is the simplest way to use the space travel calculator:

1. Enter a distance to a planet or star. Don't know any? Then type Pr and press the down arrow. The distance to Proxima Centauri appears. Select it and the distance will be filled in. Try other places in space.
2. Click Calculate. The calculator determines the remaining unfilled values.
3. Click Run. Watch the space rocket travel from earth to your destination. Also watch the clocks of the observer and the traveler.

## Known problems

• The animation spacecraft is at a different scale to the distance between the observer and destination. Even for the shortest space travel distances, for example the earth to the moon, the spacecraft would occupy less than a pixel. This problem will not be fixed.

• As an object moves further into the distance it appears smaller to an observer. This change in perspective distance is not represented in the animation. The reduction in the spacecraft length from the observer's framework at velocities approaching the speed of light is an entirely different concept to perspective distance.

• If you set the iterations on the animation to a low number, e.g. less than 20, the animation's spaceship time will not be calculated accurately if the observer and traveler times diverge substantially.

A bug fix was made in June 2016. The calculation for the fuel needed for the trip did not take into account conservation of momentum. These two webpages helped me correct the error and I am grateful to the various people contributed the notes that helped me fix this (Physics Stack Exchange users user2096078, Qmechanic and udrv, Don Koks for the Relativistic Rocket, and John F who emailed me) :