This is a backup for the instrument spar for the Apollo Telescope Mount used on the Skylab manned space observatory. That assembly consisted of a 4-meter (14-foot) Sun shield, a scientific instrument canister, and an internal spar assembly that held the major instruments within the canister.
NASA's Marshall Space Flight Center designed and constructed the telescope mount and in 1982 transferred the backup instrument canister, Sun shield, and spar assembly to the Smithsonian. The sunward part of the canister and the Sun shield were reassembled and displayed in the National Air and Space Museum's Stars gallery.
Transferred from the National Aeronautics and Space Administration