your code
shuttle(200,150,1500)
mothership(300,700)
asteroid(300,300)
asteroid(100,200)
asteroid(300,50)
alien(100,300,250,300)
alien(300,100,300,250)
wall(500,50,500,300)
alien(400,300,600,300)
wall(200,450,500,450)
asteroid(100,350)
alien(550,425,551,425)
wall(50,600,400,600)
alien(250,450,250,600)
asteroid(520,320)
alien(300,450,300,600)
asteroid(475,375)
planet(250,370,"mars")
planet(50,500,"neptune")
fuel(450,500,200)
fuel(650,500,300)
fuel(650,200,1000000)