UFO Travel Calculator

Use the UFO travel calculator to design a fast-moving UFO and estimate its performance.

Earth time1,001.9356 yearsas measured at home. The difference of 988.4869 years is not an illusion: the traveller really does return younger

Ship time13.4486 yearsas experienced aboard — the crew ages this much

Time saved by travelling74.50098× compressionthe average Lorentz factor over the trip

Peak speed0.99999813creached at the midpoint turnaround

Peak Lorentz factor517.1476381 + a·d/c² for the burn — a strikingly simple result

Distance306.6014 pc1,000 light years, so light itself takes 1,000 years — no ship can beat that as seen from Earth

Contracted distance at peak speed1.9337 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 point6.7243 years ship timehalfway by distance, and by symmetry halfway by time as well

Mass ratio needed, with a PERFECT engine1,069,764.7:1for 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.