Imagine there are two space ships, Ship A and Ship B. Ship A sees Ship B travelling at 0.865c towards him. (And of course vice versa) From Ship A's FOR there is a marker 9,000,000 km away which is at rest wrt Ship A. The marker, Ship A and the path of Ship B therefore form a straight line. When Ship B reaches the marker, it will detach a shuttle that will accelerate to become at rest wrt Ship A, which should coincide with it reaching Ship A exactly, so it can dock safely. Once Ship B dispatches the shuttle, it will accelerate away in a different direction. So someone has to work out the acceleration the shuttle must go though so it can be at rest wrt Ship A after the it's travelled the distance from the marker to ship A. Without going into the actual calculations, my question are: 1) What distance is used to work out the rate of acceleration for the shuttle? (As from B's FOR, it will see the distance between the marker and Ship A length contracted by about half. So only 4,500,000 km. But from Ship A's FOR the marker is still 9,000,000 km away.) 2) If Ship B was travelling at the same speed relative to A but from left to right compared to line of the marker / Ship A, and still dispatched the shuttle when it reached the marker, what distance between the marker and Ship A would used to make the calculation? (I take it as the straight line the marker and Ship A make is no longer in the direction of travel of Ship B, then the distance between the marker and Ship A would not be length contracted?) Thanks in advance for any help on this.