your code
shuttle(450,400)
mothership(50,50)
asteroid(150,100)
asteroid(250,100)
wall(200,150,200,250)
asteroid(50,150)
wall(50,300,300,300)
planet(350,300,"uranus")
wall(400,250,400,400)
wall(400,150,450,150)
planet(450,100,"venus")
planet(350,50,"mars")
planet(250,250,"neptune")
wall(350,100,350,150)
fuel(300,100,1000)