Take tip 5 and red buttercream. Pipe a small triangle at the top of the rocket. Make the base of the triangle curved. Tilt piping bag towards you at a slight angle so the buttercream flows out like a tube of toothpaste for thick and full lines. Pipe with a steady stream of pressure until its full of red at the nose of the rocket.
Next, use tip 5 with grey buttercream, pipe the center of the rocket by outlining the space and fill in horizontally back and forth with a steady stream of pressure until the center section is filled. Leave space for the bottom half of the cookie for the rest of the rocket.
Pipe the bottom half of the rocket with red and tip 5 again. Outline and fill in back and forth until its filled. Leave space open at the very bottom of cookie for the rocket flames.
Outline the fins on either side of the rocket with red and tip 5 and fill it in.
Use orange and tip 352. Have the beak of the tip facing down so the point is at the cookie as pictured. Hold piping bag at a 45-degree angle and start squeezing until you see the buttercream start to billow out and slowly pull down while squeezing. Stop squeezing when you want the flame to end. Repete this two more times so there are three flames total. Make a slight ripple with the buttercream to achieve a textured flowy look of the flames.
Use tip 5 and red buttercream and pipe red squiggly lines down the flames.
Take tip 12 and white buttercream, hold piping bag straight up and down. Hold bag about ¼ inch off the grey buttercream. Pipe and let the buttercream flow out and swirl it around to make a filled circle, stop squeezing and round off the end. Use a butterknife or an offset spatula to gently smooth the top of the white.
Attach tip 2 onto the red buttercream and pipe a small apple on the white rocket window. Place it off center. Outline and fill in.
Use tip 2 and green buttercream to pipe a small leaf.
Take yellow or white buttercream and tip 1 to pipe tiny dots all over the apple for the signature cosmic crisp dots.
Use grey and tip 5 to outline the small window so it stands out.
Use tip 2 and brown buttercream to pipe a small stem to complete the rocket ship cookie.