* 2. ASSEMBLE THE TELESCOPE TUBE.

HST's Telescope Tube is actually two parts: the Optical Telescope Assembly is a precision-engineered truss which holds the secondary mirror in exactly the right position. Forward of this is a shade called the Forward Light Shield which protects the optics from stray light.

• Select Parts Sheet D from the kit. Find the words OPTICAL TELESCOPE ASSEMBLY and FORWARD LIGHT SHIELD along one end of the silver side. Smear a small amount of glue, using a glue stick, along the whole end, covering the wording, and making the glue-smear exactly 1/2 (13mm) inch wide (measure first, and mark with pencil). The glue must cover all the way out to the edge.

• Bring the opposite edge around, forming a tube with the silver side out. Overlap exactly the measured and marked 1/2 inch (13mm) onto the glue. (If it overlaps less than 1/2 inch, other parts will not fit.) Adjust so that the overlap is straight. Press and hold the surfaces together until the glue sets. Insert a wooden ruler through the tube to press the seam against. Impart a curve to the seam to match the tube's curve. Be careful not to crease the tube anywhere, keeping it as evenly round as possible.

• Set your previously assembled AFT SHROUD down with the PRIMARY MIRROR ASSEMBLY facing up.

  

• Set the TELESCOPE TUBE down, centered on the PRIMARY MIRROR ASSEMBLY so that the seam is on the side across from the keel fitting. SCI's address should be at the bottom. Adjust the tube so that the Keel fitting, marked with an arrow, is centered below and between the two black circles on the tube. To be precise, the printed arrow should align midway between the letters P.O in SCI's address at the base of the tube.

  (The silver circle representing HST's Primary Mirror may not be exactly centered... sorry, this was due to a manufacturing error, which you can read more about if you want.) Apply glue to hold them together, and let dry.

  Anyway, make sure the TELESCOPE TUBE is centered atop the AFT SHROUD, even if the silver circle is not.