The U.S. government agency in charge of intelligence satellites is displaying one of the largest spy satellites the United States has ever put into space Saturday.

The National Reconnaissance Office put the newly declassified Hexagon, or KH-9 satellite on display for one day only at a branch of the National Air and Space Museum located just outside Washington.

The satellite, nicknamed “Big Bird,” is 18 meters long and three meters in diameter.

While in orbit from 1971 to the early 1980s, the spacecraft took surveillance photos of the Soviet Union and other targets. The photos helped ensure the Soviet Union was complying with arms control treaties.

The satellite is on display to celebrate the 50th anniversary of the National Reconnaissance Office, which was itself a secret agency until it was declassified, or revealed to the public, in 1992.