your code
shuttle(300,200)
mothership(50,50)
wall(200,150,200,300)
alien(100,300,350,300)
fuel(200,400)
wall(150,100,350,100)
asteroid(250,350)
asteroid(300,400)
wall(350,250,350,400)
planet(50,150,"earth")
planet(100,250,"mars")
alien(50,400,150,400)
wall(300,0,300,100)