The distance between Zoultan and Urelon was roughly 140 million kilometers at the time when City 3's rocket ship had taken flight. As a result, the ship had to push itself as fast as it could to cover such a massive distance in as short a time as it could.
Urelon was in fact moving toward them, and while one would assume it coming closer meant that the ship didn't have to travel at much, it turned out that the distance the moon covered before they reached it was negligible.
In fact, it had to be negligible. These humans could not afford to stay in the ship for more than a couple of days at best, and for that, they had to travel in space at the speed of nearly a thousand kilometers per second.
Compared to that, the measly 10-kilometer-per-second speed at which Urelon was traveling toward them in the vacuum of space was truly quite negligible.
