Space Travel Calculator

With the space travel calculator, you can plan your journey to another star system or even another galaxy.

Ship time3.5814 yearsas experienced aboard — the crew ages this much

Earth time5.9994 yearsas measured at home. The difference of 2.4179 years is not an illusion: the traveller really does return younger

Time saved by travelling1.67513× compressionthe average Lorentz factor over the trip

Peak speed0.951608654creached at the midpoint turnaround

Peak Lorentz factor3.2540171 + a·d/c² for the burn — a strikingly simple result

Distance4.367 light years4.367 light years, so light itself takes 4.367 years — no ship can beat that as seen from Earth

Contracted distance at peak speed1.342 light yearsthe crew do not see themselves going faster than light; they see a SHORTER journey. That is how ship time can fall below the light travel time

Acceleration9.8067 m/s² (1 g)1 g is comfortable and conveniently close to a light year per year squared

Turnaround point654.058 days ship timehalfway by distance, and by symmetry halfway by time as well

Mass ratio needed, with a PERFECT engine40.3:1for an ideal photon rocket converting mass entirely to light — the best physics allows. Any real fuel is enormously worse, which is why this is the hard part and the time dilation is not

Why you cannot exceed cyou never doconstant proper acceleration feels constant forever, yet the speed only approaches c. What grows without limit is the Lorentz factor, so the journey keeps getting shorter in the ship's frame rather than the ship getting faster in Earth's

The formula

T = 2√((d/2c)² + d/a); τ = (2c/a)arccosh(ad/2c² + 1)

The crew see a shorter trip, not a faster ship

Under a constant 1 g the acceleration feels constant forever, yet the speed only ever approaches the speed of light. What grows without bound is the Lorentz factor. From the ship, the journey does not take less time because the ship is going faster than light — it takes less time because the distance ahead is contracted. Alpha Centauri at 1 g with a turnaround takes about six years by Earth clocks and about 3.6 by the crew's.

Push the distance out and the ship time grows only logarithmically. The galactic centre, 26,000 light years away, is reachable in about twenty years of ship time; the Andromeda galaxy in about twenty-eight. Earth meanwhile waits 26,000 and 2.5 million years respectively, so these are one-way trips in every sense that matters.

Fuel is the real barrier

The time dilation is not the difficulty — it is the gift. The difficulty is the rocket equation. Even a perfect photon rocket, converting matter entirely into light with no waste at all, needs a mass ratio that climbs into the thousands for a nearby star and past anything imaginable for a galactic trip. Every real propellant is enormously worse. Relativity permits interstellar travel comfortably; engineering does not.