your code
// shuttle
shuttle(300,200);
mothership(500,400);
fuel(100,100,571);
planet(300,100,"earth");
planet(500,50,"mars");
planet(500,300,"neptune");
planet(300,350,"mercury");
planet(100,300,"jupiter");
wall(200,150,400,150);
wall(200,250,400,250);
wall(200,140,200,280);
alien(500,100,500,250);
alien(200,300,450,300);