From the article: > With graphene, the most suitable material, the cut-off speed for 1 g acceleration would be approached after an on-board flight time of thre

From the article: > With graphene, the most suitable material, the cut-off speed for 1 g acceleration would be approached after an on-board flight time of three years at a distance of about 10 light-years. After that, the acceleration would quickly drop to values that shatter the popular dream of reaching the galactic center in a lifetime. Note that this is already assuming you can build superconducting rings in space with a diameter of 2000 kilometer and with enough graphene to support them. If we assume for convenience that the acceleration will fall to zero after those three years, the relativistic speed calculator at https://www.omnicalculator.com/physics/space-travel https://www.omnicalculator.com/physics/space-travel (haven't checked it in depth, but I have no reason to doubt it) tells us we will have reached a speed of about 91% of c.