The cops stop firing at Arthur and friends and our heroes (well, you know, not really heroes) come out to see what's up.
Ford goes over to the now-dead cops and discovers that their life-support systems broke. Which is weird because there's usually a back-up computer on their ship.
So Arthur and friends (well, people he kind of knows and puts up with) rush out and discover that Slartibartfast has left them his aircar with a note telling them which button to press.