your code
shuttle(100,400)
mothership(250,300)
wall(150,100,150,500)
fuel(450,250,400)
wall(150,100,500,100)
alien(350,150,350,400)
wall(450,300,550,300)
fuel(250,400,400)
wall(300,100,300,400)
alien(200,200,250,200)
asteroid(50,200)
fuel(100,100,300)