your code
mothership(100,400);
shuttle(500,50,2000);
fuel(100,200,1000);
planet(300,350,"mars");
asteroid(50,250);
wall(100,100,550,100);
wall(1,350,200,350);
wall(150,300,350,300);
asteroid(150,400);
alien(200,150,200,450);
alien(250,400,500,400);
planet(300,200,"uranus");
fuel(400,250,5000);