6. INSTALL THE APERTURE DOOR.

Normally wide open during scientific observations, the aperture door closes automatically if the HST reverts to its "safe" mode, and prevents bright sunlight, moonlight, or earthlight from inadvertantly flooding the instruments through the telescope.

• From sheet A, release the large APERTURE DOOR. With the silver side up, crease the two narrow side strips down 90 degrees. Turn it over, black side toward you, and fold the crosshatched panel down away from you. Fold the white panel back toward you. Fold the yellow tab back away from you.

  

• Hook the ends of the white panel into the ends of the folded side strips. Apply glue and let dry. Viewed from the side, the result should look like this:

• Bend the two halves of the yellow tab slightly toward each other, rounding the tab where it will glue to the TELESCOPE TUBE.

• Smear some glue on the yellow tab. Position it at the end of the TELESCOPE TUBE with the silver side up, right about on the seam, and the aperture door protruding out past the end of the tube. The joint between the yellow tab and the white panel should be right at the end of the TELESCOPE TUBE. Adjust the APERTURE DOOR slightly so that its center stands straight out from the tube, and the small tab at the bottom of the door is directly in line with the keel fitting. Press and hold until the glue sets.

  

• If you would like the door to remain open, bend it about 45 degrees up from the tube, and apply extra glue to the hinge to stiffen it there.

• From sheet A release the small DOOR LATCH. Holding it silver side up, bend the two side panels down 90 degrees. Apply glue to the crosshatched area, and press it onto the end of the TELESCOPE TUBE across from the APERTURE DOOR hinge. The slot in the DOOR LATCH should just protrude past the end of the tube. Let the glue dry.

• If you would like to close the door, bend it down and work its tab into the DOOR LATCH.