As time-dilation is stated in STR, 1.) it is an intrinsic decrease in rate of passing of time, with relative motion(radioactivity half-life change). 2.) it is non-directional, that is, time-dilation depends only on the magnitude of relative speed. Now, please consider the following scenario, Three spacecrafts A, B and C are parked in space in the sequence (A-B-C) with perfectly synchronized clocks on-board, where B always stays stationary in a particular observing reference frame while A and C starts moving away to left and right direction respectively and after some time they stop and return back to their original position. Now, considering that the spacecrafts A and C are programmed identically for their motion, that is, in the observers reference frame their motion is always equal and opposite. Now, my question is, How can one explain the time-dilation of the other two spacecrafts, 1.) from the rest frame of reference of B and 2.) from the frame of moving space crafts (be it A or C). Because in the rest frame the time-dilation of the two spacecrafts should be equal therefore time should also be equal, while in frame of any moving spacecraft the time-dilation of other moving spacecraft should be even bigger than that of in rest frame, that is, according to STR, time on moving spacecraft `A' w.r.t `C' should be different at the end of the journey. But at the end of the journey both the moving frame and the rest frame are one and the same. How can time be different at a particular instant in just one single reference frame ?