This small medallion designates the wearer as a recipient of the Congressional Space Medal of Honor. This particular medallion is a part of the set awarded to NASA astronaut Neil Armstrong in 1978.
The United States Congress authorized the creation of the Congressional Space Medal of Honor in 1969 to recognize “any astronaut who in the performance of his or her duties has distinguished himself or herself by exceptionally meritorious efforts and contributions to the welfare of the Nation and mankind.” The NASA Administrator nominates recipients for the Congressional award, which is then awarded by the sitting President. Armstrong, the first astronaut to set foot on the Moon during Apollo 11 in July 1969, was one of the first six recipients awarded the medal on October 1, 1978, by President Jimmy Carter. Like many other such awards, the medal comes with a small medallion, a lapel pin, and a ribbon bar in a special presentation case.
Following Armstrong's death in 2012, his sons Mark and Rick and their families donated the medal set to the Smithsonian Institution in 2019.
This object is not on display at the National Air and Space Museum. It is either on loan or in storage.