In ***Rogue One*** for the major assault that the rebels threw at the security planet, when the major rebel ships arrived, they started to try and shut down the security field.

When they did this, they pushed one enemy ship into another and by themselves they crashed into the gate-way ring that happens to be the **only** way onto the planet.

How did the destroyed ships sink down and collide with the gate-way from above, surely there is no gravity?
Surely if there was gravity the gate-way would also have been pulled in?