your code
shuttle(50,0,1000);
mothership(700,700);
planet(200,200,"earth");
planet(250,500,"mars");
planet(100,500,"venus");
fuel(300,500,1000);
planet(100,700,"neptune");
planet(400,700,"mercury");
planet(400,400,"uranus");
planet(700,400,"jupiter");
fuel(500,500,1000);
asteroid(50,250);
wall(450,0,450,650);
alien(100,300,350,300);
alien(150,650,350,650);
wall(600,450,600,800);