1. The problem statement, all variables and given/known data A variation on the twin paradox, with uniform circular motion. The travelling sibling moves so that his acceleration is g at all times, pointing to the centre of his circular path, constant velocity. There is given that the trip takes twenty years in the frame of the traveller. Then how long will the astronaut be gone as seen by the inertial observer? 2. Relevant equations 3. The attempt at a solution I have an expression for the time elapsed (as seen by the inertial observer) in function of radius and velocity. And as I'm unable to calculate radius or velocity for this problem, I am stuck.