Step 8: Engines
For the three Pratt & Whitney Rocketdyne RS-25 liquid fueled cryogenic rockets, take a round thing and and cut three little round pieces of black fleece from it. It's okay if they're not perfectly round, you can trim them up later.
Note: In retrospect, these would've probably looked better using a slightly different color, like dark grey, if you also have some extra grey scraps laying around after making a fleece Skyrim helm...
Sew them onto the triangle as shown, then you can trim around the circles to clean it up.
Sew the engine triangle onto the engine ledge. Be sure to have the seam on the inside of the shuttle, and the rockets on the outside!