your code
// shuttle
shuttle(50,50,400);
// mothership
mothership(350,350);
// planets
planet(100,300,"venus");
planet(300,100,"mars");
planet(200,200,"jupiter");
// fuel container
fuel(100,100,-200);
fuel(50,150,-50);
fuel(150,50,-100);
fuel(100,350,330);
fuel(350,100,430);
fuel(150,250,160);
fuel(250,150,120);
fuel(50,350,75);
fuel(350,50,50);
fuel(250,250,400);
// asteroids
asteroid(250,350);
asteroid(350,250);
// meteor walls
wall(150,80,150,130);
wall(80,150,130,150);
// aliens
alien(50,250,50,350);
alien(150,250,150,350);
alien(250,150,350,150);
alien(250,50,350,50);
// shuttle's flight