We Have Fed Our Sea

They named her Souther Cross and launched her on the road whose end they would never see. Months afterward shw was moving at half the speed of light; if there was to be enough reaction mass for deceleration and maneuver, the blast must be terminated. And so the long silence came. For four and half centuries the ship would fall. They manned her by turns, and dreamed other ships and launched them, and saw how a few of the shortest journeys ended. Then they died. After ten generations, the Souther Cross was not quite halfway to her own goal, though she was the farthest from Earth of any human work...