* 3. INSTALL THE SECONDARY MIRROR.

HST's Secondary Mirror is held in exact position (within 0.0025mm) by graphite-epoxy trusses in HST's Optical Telescope Assembly. In HST's Cassegrain optical system, the Secondary receives light gathered and reflected from the hyperbolic Primary Mirror. The Secondary's own precise curvature reflects and focuses the light down through the hole in the Primary, into the cameras and other scientific instruments in the Aft Shroud.

• From parts sheet B release the two halves of the SPIDER. Place them together slot into slot as shown, but turned at right angles to each other, to form a + when viewed from above. Secure with glue and let dry.

• From sheet A, release the small, circular, silver SECONDARY mirror. Place it silver side up onto the cross beams below the arrow in the illustration above. The edge of the mirror will snap into four small notches as it comes in contact with the crossbeam. It will be a tight fit, causing the SPIDER to deform slightly. Secure with a droplet of glue at each notch.

  

• From sheet A, release the BAFFLE. Wrap it around a pencil, curling it so its hashmarked end will be overlapped. Smear some glue over the hashmarked end. Wrap the other end around and overlap it so that the hashmarks are covered. This will create a cone-shape. Press the surfaces together, using a pencil inside, till the glue sets.

• Set the completed BAFFLE narrow end down, onto the silver SECONDARY MIRROR inside the SPIDER, as shown below. Secure with glue.

• Out at the ends of each of the four SPIDER legs there are 3 prongs. Bend the middle prong slightly one way, and the other two slightly the other way, on all 4 legs.

  

• Place the SPIDER inside the TELESCOPE TUBE with the silver SECONDARY MIRROR pointing aft toward the PRIMARY MIRROR. Adjust the bends in the SPIDER's prongs so that they brush against the inside of the tube enough to hold it in place.

• Work the SPIDER into the TELESCOPE TUBE with long-nose pliers, so that its top is 2-1/2 inches (65mm) down from the end of the tube. It will meet the truss printed inside. Turn the SPIDER so that one leg points in the same direction as the keel fitting. Secure with glue.