There is no single time of the turnaround, that is an idealization. In reality there are only velocities which are positive, zero, or negative. You are using the positive velocity to get one line of simultaneity, and then you fail to use the negative velocity to get a completely different line of simultaneity. You just claim it is "obvious" that you can do that, even though it is not obvious at all. No you haven't. All you've clearly done is make a mistake. No. I don't see any violation in the principle of causality in using the correct equations of SR or drawing correct Minkowski diagrams. If you want to show a violation of causality you need to show a "cause" occurring at a later time than its "effect". But first you need to assume the following is true, which you have not even done: STEP 1 ASSUME THIS IS TRUE: The calculation you show for the amount of her aging during pulse transit, 26.67 - 16.91 = 9.76, is only valid for the outbound leg of the trip, not the inbound leg. The reason is because the line of simultaneity you used to get 26.67 is not valid in the reference frame of the inbound leg. The line of simultaneity for the inbound leg would point to 53.33 and so your calculation for the amount of her aging during pulse transit for AFTER THE TURNAROUND should be 53.33 - 16.91 = 36.42. STEP 2 SHOW THAT IT RESULTS IN A CAUSE OCCURING AT A LATER TIME THAN ITS EFFECT: You fill in this part, please. If you can show a real violation of causality here, I will personally write to the Nobel Committee and recommend you. But you can't because the above (step 1) is standard SR and has stood for over 100 years.