(Courtesy GlobalSecurity.org)

Before the Global Hawk and Gorgon Stare surveillance drones — in fact, way, way before — there was the Big Bird.

The Big Bird, formally known as the KH-9 Hexagon satellite, was first placed in orbit in 1971 after its development by the National Reconnaissance Office (NRO), making it one of the most advanced spy satellites of its time. It is believed to have produced images of the Soviet Union, China and other countries that held strategic importance for the U.S. government through the Cold War. But it was never seen outside the intelligence community.

This weekend, it will be available for all in the Washington area to see, but only for one day.

To celebrate its 50-year anniversary, the NRO, along with the Smithsonian Institution, is for the first time publicly displaying the newly declassified relic at the Steven F. Udvar-Hazy Center in Chantilly, Va. In doing so, the intelligence agency is prompting more than just a little bit of excitement among reconnaissance experts and technical hobbyists.

At roughly 60 feet in length and 10 feet in diameter, the Hexagon was the largest spy satellite the United States had ever placed into orbit at the time. It was kept operational through 1986, and it captured images that were used by the Defense Department and throughout the U.S. intelligence community. Among those images are believed to be pictures that documented elements of the Soviet space program.

“It constituted quite an advance in film-based imagery systems,” said Charles P. Vick, a senior technical and policy analyst at GlobalSecurity.org, a defense think tank. “We have to realize that these film-based systems were the highest technology at the time.”

The satellite allowed the intelligence community to capture the highest-quality imagery it had ever gotten with low-resolution camera, Vick said. It also allowed analysts to get a look at huge swathes of territory with fewer pictures — a single frame covered about 370 nautical miles, roughly the equivalent of the distance from Cincinnati to Washington.

In total there were 20 Hexagons put into orbit over the years. The one on display this weekend — which was not among them — has had portholes cut into the sides so that the internal camera machinery will be visible, according to Rick Oborn, an NRO spokesman.

After the event on Saturday, the Hexagon will be returned for a time to the headquarters of the highly secretive NRO, located south of Dulles, so employees and “alumni” of the agency will be able to see it.

“If you want to invite folks over here,” Oborn deadpanned, “they won’t get in.”

Plans call for the satellite to be moved later to the National Museum of the Air Force at Wright-Patterson Air Force Base near Dayton.