Errors ever reduced by ever better measurements

Why do we need to know the distance to Saturn accurate to one mile? The story [link] refers to "calculating the correct trajectories for spacecraft" but we have been doing that for years without this measurement.

Errors ever reduced by ever better measurements is a hallmark of trustworthy science. Researchers passionately committed to trustworthy science are passionately committed to ever better measurements wether needed at the time or not. Those ever better measurements often uncover some new science.