Ships That Move the Line

A ship moves, and its pull moves with it. So the right line changes from second to second.

A moving field

A moving mass makes the field change over time. The aim line flies its ghost rock through the field as it stands right now. Next frame it flies it again. So the line is exact for a still field, and live for a moving one.

In Traffic, two ships circle across the lane. Here is its aim line, solved and 7 s long, a second apart. Where the line ends depends on when you look:

big ship      3.85 units a second    a lap every 11.4 s
small ship    3.20 units a second    a lap every 7.9 s